The hibernating myocardium

Prediction of improvement of contractile function in patients with ischemic ventricular dysfunction after revascularization by fluorine-18 fluorodeoxyglucose single-photon emission computed tomography

OBJECTIVES

We evaluated the use of fluorine-18 fluorodeoxyglucose (FDG) and single-photon emission computed tomography (SPECT) to predict improvement of left ventricular ejection fraction (LVEF) after revascularization.

BACKGROUND

FDG SPECT has recently been proposed for assessment of myocardial viability. However, FDG SPECT still awaits validation in terms of predicting improvement of contractile function after revascularization in patients with poor left ventricular (LV) function.

METHODS

Fifty-five patients with contractile dysfunction (including 22 with LVEF < 30%) underwent FDG SPECT during hyperinsulinemic glucose clamping and early thallium-201 SPECT (to assess perfusion). Improvement of LV function was evaluated 3 months after revascularization with echocardiography and radionuclide ventriculography.

RESULTS

The 55 patients were arbitrarily classified into two groups: 19 with three or more viable, dysfunctional segments on FDG SPECT and 36 with less than three viable, dysfunctional segments. LVEF increased significantly in the first group, from 28 +/- 8% (mean +/- SD) before to 35 +/- 9% (p < 0.01) after revascularization. In the second group, LVEF remained unchanged after revascularization (45 +/- 14% vs. 44 +/- 14%, p = NS). The 22 patients with severely depressed LV function were similarly classified into two groups: 14 with three or more viable segments on FDG SPECT in whom LVEF improved significantly (25 +/- 6% vs. 32 +/- 6%) and 8 with less than three viable segments in whom LVEF remained unchanged (24 +/- 6% vs. 25 +/- 6%).

CONCLUSIONS

This study shows that FDG SPECT can identify patients in whom LV function improves after revascularization. Because SPECT is widely available, this technique may contribute to more routine use of FDG for determination of viability.

Comparison of baseline-nitrate technetium-99m sestamibi with rest-redistribution thallium-201 tomography in detecting viable hibernating myocardium and predicting postrevascularization recovery

OBJECTIVES

This study aimed to define the optimal criteria for detecting viable myocardium with rest-redistribution thallium-201 (Tl-201) or baseline-nitrate technetium-99m (Tc-99m) sestamibi single-photon emission computed tomography (SPECT) using discriminant analysis and to compare the accuracy of the two tracers in predicting postrevascularization recovery.

BACKGROUND

Rest-redistribution Tl-201 imaging is currently used for detection of myocardial viability, but the optimal variables for territory classification have not yet been defined. Although Tc-99m sestamibi is reportedly less effective than Tl-201, its reliability can be increased by injecting it during nitrate infusion.

METHODS

In 35 patients with left ventricular (LV) dysfunction, tracer activity within asynergic coronary territories was quantified on rest and redistribution Tl-201 and baseline and nitrate Tc-99m sestamibi SPECT. Asynergic territory viability was evaluated on the basis of the postrevascularization functional outcome.

RESULTS

Percent activity within asynergic territories was significantly influenced by their viability (p < 0.005) and the type of acquisition (p < 0.0001) but not by the tracer used. Discriminant analysis identified redistribution Tl-201 activity and nitrate-induced Tc-99m sestamibi activity change as the two most significant predictors of postrevascularization recovery. The discriminant function defined for Tl-201, including redistribution activity and reversibility, correctly classified 38 of 56 asynergic territories, whereas that for Tc-99m sestamibi, including nitrate-induced activity change and activity in nitrate images, correctly classified 43 territories.

CONCLUSIONS

Redistribution activity is more important than reversibility when differentiating viable from nonviable territories using rest-redistribution Tl-201. In Tc-99m sestamibi SPECT, nitrate-induced activity changes are particularly useful in identifying myocardial viability. Baseline-nitrate Tc-99m sestamibi SPECT appears no less effective than rest-redistribution Tl-201 in predicting postrevascularization recovery.

Targeting of dobutamine to ischemic myocardium without systemic effects by selective suction and pressure-regulated retroinfusion

OBJECTIVE

To study the effects of low-dose dobutamine and/or glyceryl trinitrate in addition to selective suction and pressure-regulated retroinfusion with arterial blood on regional myocardial function of the ischemic myocardium and systemic hemodynamics.

METHODS

Using a pig model of repeated brief (90 s) occlusions of the left anterior descending artery, selective suction and pressure-regulated retroinfusion was carried out either with arterial blood alone (SSRalone) or with arterial blood and simultaneous application of low-dose dobutamine (0.1 microgram/kg/min (SSRDOB), glyceryl trinitrate (0.03 mg/kg/min) (SSRNIT) or the combination of both drugs (SSRDOB + NIT). Regional myocardial function of the ischemic and non-ischemic myocardium was determined by sonomicrometry (segment shortening).

RESULTS

Segment shortening in the ischemic area after 90 s of ischemia was preserved at 57.5 +/- 9.2% with SSRalone but at 78.0 +/- 22.3% of baseline with SSRDOB (P < 0.05). The addition of glyceryl trinitrate did not improve regional myocardial function further. No effects of locally applied dobutamine were observed with regard to non-ischemic myocardium or heart rate. Cardiac output and mean arterial blood pressures tended to be further stabilized with SSRDOB.

CONCLUSIONS

Local application of low-dose dobutamine together with arterial blood by selective suction and pressure-regulated retroinfusion during brief myocardial ischemia resulted in improved regional myocardial function without undesired effects on non-ischemic myocardium or systemic hemodynamics.

Influence of left ventricular function on survival after coronary artery bypass grafting

BACKGROUND

Preoperative left ventricular function is a most important predictor for survival in patients with ischemic heart disease. To elucidate the optimal timing of recommended coronary artery bypass grafting, we investigated the influence of different aspects of preoperative left ventricular function on relative survival.

METHODS

To calculate the relative survival and estimate the disease-specific survival, we compared 6,514 patients who survived the first month after primary coronary artery bypass grafting with the general Swedish population stratified by age, sex, and 5-year calendar period. In particular we studied the relation between relative survival and different aspects of left ventricular performance, namely left ventricular function at rest, New York Heart Association functional class, and number of previous myocardial infarctions.

RESULTS

The three variables (left ventricular function at rest, New York Heart Association functional class, and number of previous myocardial infarctions) as well as age and follow-up year gave independent information concerning relative survival. The results from this multivariate analysis were used to define a risk score for each patient. Patients were categorized into different risk groups. Patients in the low-risk group (30% of the total) showed a survival better than that of the population at large for 9 years after operation. The medium-risk group had no or low excess mortality for about 7 years, and the high-risk group (25%) showed increased excess mortality immediately after operation.

CONCLUSIONS

If primary coronary artery bypass grafting is performed before the left ventricular function and physical performance deteriorate, survival is excellent.

Stress echocardiography for assessing myocardial ischaemia and viable myocardium

Images

F18-fluorodeoxyglucose single-photon emission computed tomography predicts functional outcome of dyssynergic myocardium after surgical revascularization

BACKGROUND

Prediction of functional recovery after revascularization is possible with positron emission tomography and F18-fluorodeoxyglucose (FDG). Recently, the use of FDG in combination with single-photon emission computed tomography (SPECT), with 511 keV collimators, has been proposed to allow more widespread use of FDG. In the current study we aimed to predict improvement of regional left ventricular function after surgical revascularization with FDG and SPECT.

METHODS AND RESULTS

Twenty-seven patients with regional wall motion abnormalities (on echocardiography) underwent early thallium-201 (Tl-201) SPECT to assess perfusion and FDG SPECT to assess regional glucose uptake. The left ventricular myocardium was divided into 13 segments. For each segment, tracer uptake was evaluated visually (with the use of a 4-point scoring system) by consensus of two observers. Myocardial viability was determined in dyssynergic segments on echocardiography and defined as normal perfusion or increased FDG uptake in a perfusion defect (mismatch). Absence of viability was defined as a perfusion defect without increased FDG uptake (match). Improvement of regional wall motion was assessed 3 months after revascularization. In the group of segments that were viable on FDG/Tl-201 SPECT (n = 64), the segmental wall motion score decreased from 1.4 +/- 0.5 to 0.6 +/- 0.7 (p < 0.01), whereas the segmental wall motion score remained unchanged in nonviable segments (n = 72): 1.6 +/- 0.5 versus 1.5 +/- 0.6 (not significant). Forty-six (72%) of the 64 segments that were viable on FDG/Tl-201 SPECT demonstrated improved contractile function after coronary revascularization. In contrast, only 7 (10%) of 72 nonviable segments on FDG/Tl-201 SPECT showed improvement in function after revascularization (p < 0.01 versus viable segments). The sensitivity, specificity, and positive and negative predictive values were 87%, 78%, 72%, and 90%, respectively.

CONCLUSION

This study shows that FDG/Tl-201 SPECT can identify patients who improve in regional ventricular function after revascularization.

Nitrate administration to enhance the detection of myocardial viability by technetium-99m tetrofosmin single-photon emission tomography

A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with 99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent 201Tl rest-injection and 99mTc-tetrofosmin baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >/=50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of 99mTc-tetrofosmin at baseline correlated with that of 201Tl (r=0.82, P <0.001). On baseline 99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peak activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in 99mTc-tetrofosmin uptake from 40%+/-9% to 57%+/-9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on 201Tl studies, but 20 segments that were non-viable on 99mTc-tetrofosmin studies were viable on 201Tl studies. Using a threshold value of >/=40% of peak activity, only seven segments remained non-viable on 99mTc-tetrofosmin studies. Overall agreement between 99mTc-tetrofosmin with nitrates and 201Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with 99mTc-tetrofosmin was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.

Evaluation of myocardial viability using sequential dual-isotope single photon emission tomography imaging with rest TI-201/stress Tc-99m tetrofosmin in the prediction of wall motion recovery after revascularization

In patients with coronary artery disease (CAD), differentiation between severely ischemic but potentially viable myocardium and irreversibly infarcted tissue is clinically important, particularly when revascularization procedures are considered. Although thallium (TI) cardiac imaging has been shown to be a good tool for investigating myocardial viability in CAD, this tracer shows physical limitations, such as a low photon energy and long half-life. We assessed the results of a rest TI-201/stress Tc-99m tetrofosmin protocol in subjects with prior anterior myocardial infarction. All of the patients had an akinetic or dyskinetic area and more than 75% stenosis in the left anterior descending artery. All of the patients underwent revascularization after the examination. We evaluated the improvement in wall motion after revascularization using the centerline method with contrast left ventricular angiography. Fourteen patients showed reversible defects with the rest TI-201/stress Tc-99m tetrofosmin protocol or in additional TI-201 24 h redistribution images. All 14 patients showed a significant improvement in wall motion after revascularization. Dual-isotope rest TI-201/stress Tc-99m tetrofosmin single photon emission tomography data, acquired separately, may give fast and complete information about myocardial perfusion during stress and at rest, and on about myocardial viability.

Myocyte adaptation to chronic hypoxia and development of tolerance to subsequent acute severe hypoxia

Studies in animal models and humans suggest that myocardium may adapt to chronic or intermittent prolonged episodes of reduced coronary perfusion. Stable maintenance of partial flow reduction is difficult to achieve in experimental models; thus, in vitro cellular models may be useful for establishing the mechanisms of adaptation. Since moderate hypoxia is likely to be an important component of the low-flow state, isolated adult rat cardiac myocytes were exposed to 1% O2 for 48 hours to study chronic hypoxic adaptation. Hypoxic culture did not reduce cell viability relative to normoxic controls but did enhance glucose utilization and lactate production, which is consistent with an anaerobic pattern of metabolism. Lactate production remained transiently increased after restoration of normal O2 tension. Myocyte contractility was reduced (video-edge analysis), as was the amplitude of the intracellular Ca2+ transient (indo 1 fluorescence) in hypoxic cells. Relaxation was slowed and was accompanied by a slowed decay of the Ca2+ transient. These changes were not due to alterations in the action potential. Tolerance to subsequent acute severe hypoxia occurred in cells cultured in 1% O2 and was manifested as a delay in the time to full ATP-depletion rigor contracture during severe hypoxia and enhanced morphological recovery of myocytes at reoxygenation. The latter was still seen after normalization of the data for the prolonged time to rigor, suggesting a multifactorial basis for tolerance. An intervening period of normoxic exposure before subsequent acute severe hypoxia did not result in loss of tolerance but rather increased the delay to subsequent ATP depletion rigor. Cellular glycogen was preserved during chronic hypoxic exposure and increased after the restoration of normal O2 tension. As mitochondrial cytochromes should be fully oxygenated at levels well below 1% O2, hypoxic adaptation may be mediated by a low-affinity O2-sensing process. Thus, adaptations that occur during prolonged periods of moderate hypoxia are proposed to poise the myocyte in a better position to tolerate impending episodes of severe O2 deprivation.

[The significance of the elevation of basal and exercise segments on Q-leads after acute myocardial infarct]

INTRODUCTION

ST segment elevation on Q-leads has been related to a greater infarct size and to the existence of ventricular aneurysm. On the other hand, ST elevation during exercise testing has been related to the presence of myocardial viability.

OBJECTIVES

In the present study we investigated the relation between ST segment elevation on infarct-related electrocardiographic leads at rest and during exercise with: a) the extension and severity of the regional dysfunction; b) the presence of myocardial viability (response to dobutamine), and c) the residual stenosis in the culprit artery.

MATERIAL AND METHODS

The study group was composed of 51 patients; cardiac cathetherism (8 +/- 3 days) and exercise testing (8 +/- 2 days) were performed during the pre-discharge period. In contrast ventriculography (centerline method) we determined the circumferential extension (rads) and the severity (SD/rad) of the regional dysfunction at rest and after dobutamine (10 micrograms/kg/min). The minimal luminal diameter (MLD) in the culprit artery was also measured. Results are expressed as median [Q1-Q3] and the differences among the groups were assessed by Mann-Whitney U.

RESULTS

Patients with ST segment elevation in two or more leads at rest (n = 36) showed a greater (41 [30-51] rads vs 20 [14-41] rads; p = 0.007) and more severe regional dysfunction (1.9 [1.5-2.5] SD/rad vs 0.6 [0.5-2.4] SD/rad; p = 0.01), less response to dobutamine (% of reduction of the dysfunction extension after dobutamine) (17 [0-42]% vs 50 [24-100]%; p = 0.004) and smaller MLD (0.5 [0-0.9] mm vs 0.8 [0.6-1.1] mm; p = 0.03). Likewise, patients with exercise-induced ST segment elevation (n = 28) showed less response to dobutamine (15 [0-45]% vs 40 [21-57]%; p = 0.03) and smaller MLD (0.5 [0-0.7] mm vs 0.9 [0.5-1] mm; p = 0.02). There were non significant differences between patients with and without ST elevation during exercise in the extension or severity of the regional dysfunction. ST segment elevation both at rest (RR 0.2; CI 95% 0.04-0.85) and during exercise (RR 0.19; CI 95%: 0.05-0.69) decreased the probability of improvement with dobutamine.

CONCLUSIONS

We conclude that ST segment elevation on Q-leads at rest is related to a more extended and severe dysfunction. Patients with ST segment elevation (at rest or during exercise) show less response to dobutamine (myocardial viability less likely) and a more severe residual coronary stenosis.

Ischemic cardiomyopathy--revascularization vs. transplantation

Advanced coronary artery disease (CAD) and ischemic cardiomyopathy with elevated pulmonary artery pressures are criteria of a severe illness. In selected cases surgical revascularization has proved beneficial in terms of survival, reduction of morbidity and lowering the frequency of angina pectoris [6] in numerous studies over the past 25 years. But most of the earlier publications concentrated on patients with angina pectoris (AP) as a dominant symptom. Patients without AP but with predominant signs of congestive heart failure were largely excluded. This has changed recently [1-3,7,8,10,12,16,18] with the advent of the concept of hibernating myocardium. This term is defined as the presence of persistent myocardial and left ventricular dysfunction at rest due to reduced regional coronary blood flow that can be partially or completely restored to normal by myocardial revascularization [5,19]. Salvage of viable myocardium by successful revascularization improves left ventricular dysfunction. Diagnosis of hibernating myocardium is crucial because it does not leave the patient with chronic heart failure a candidate only for cardiac transplantation. Instead, these patients' left ventricular dysfunction is potentially reversible following revascularization by coronary bypass surgery. Furthermore we face a critical shortage of donor organs and extending waiting lists for possible transplant candidates. Following the start of the heart transplantation (HTX) program at our institution more than 690 operations were performed until September 1995. We screened more than 1600 patients for their eligibility as cardiac transplant recipients or for other forms of treatment. In this group of patients it has always been our policy to revascularize rather than transplant whenever possible.

Identification of hibernating myocardium: comparative accuracy of myocardial contrast echocardiography, rest-redistribution thallium-201 tomography and dobutamine echocardiography

OBJECTIVES

We sought to evaluate the comparative accuracy of myocardial contrast echocardiography (MCE), quantitative rest-redistribution thallium-201 (Tl-201) tomography and low and high dose (up to 40 microg/kg body weight per min) dobutamine echocardiography (DE) in identifying myocardial hibernation.

BACKGROUND

Myocardial contrast echocardiography can assess myocardial perfusion and may therefore be useful in predicting myocardial hibernation. However, its accuracy in comparison to myocardial perfusion scintigraphy and to that of high dose DE remains to be investigated.

METHODS

Eighteen patients (aged [+/- SD] 57 +/- 10 years) with stable coronary artery disease and ventricular dysfunction underwent the above three modalities before coronary revascularization. Myocardial contrast echocardiography was achieved with intracoronary Albunex. Rest echocardiographic and Tl-201 studies were repeated > or = 6 weeks after revascularization.

RESULTS

Of 109 revascularized segments with severe dysfunction, 46 (42%) improved. Left ventricular ejection fraction increased from 38 +/- 14% to 45 +/- 13% at follow-up (p = 0.003). Rest Tl-201 uptake and the ratio of peak contrast intensity of dysfunctional to normal segments with MCE were higher (p < 0.01) in segments that recovered function compared with those that did not. Myocardial contrast echocardiography, thallium scintigraphy and any contractile reserve during DE had a similar sensitivity (89% to 91%) with a lower specificity (43% to 66%) for recovery of function. A biphasic response during DE was the most specific (83%) and the least sensitive (68%) (p < 0.01). The best concordance with MCE was Tl-201 (80%, kappa 0.57). Changes in ejection fraction after revascularization related significantly to the number of viable dysfunctional segments by all modalities (r = 0.54 to 0.65).

CONCLUSIONS

In myocardial hibernation, methods evaluating rest perfusion (MCE, Tl-201) or any contractile reserve have a similar high sensitivity but a low specificity for predicting recovery of function. A limited contractile reserve (biphasic response) increases the specificity of DE. Importantly, the three techniques identified all patients who had significant improvement in global ventricular function.

Dobutamine echocardiography and quantitative rest-redistribution 201Tl tomography in myocardial hibernation. Relation of contractile reserve to 201Tl uptake and comparative prediction of recovery of function

BACKGROUND

The purposes of this study were to evaluate the comparative accuracy of dobutamine echocardiography and quantitative rest-redistribution 201Tl tomography in the prediction of recovery of function after revascularization and to assess the relation of contractile reserve to thallium uptake.

METHODS AND RESULTS

Thirty-four patients with stable coronary disease and regional dysfunction underwent dobutamine echocardiography (2.5 up to 40 micrograms.kg-1.min-1) and rest-redistribution 201Tl tomography 1 day before revascularization. Resting echocardiography and scintigraphy were repeated at > or = 6 weeks. Before revascularization, resting 201Tl uptake was similar in segments demonstrating biphasic or sustained improvement and was higher than in those exhibiting no change or worsening function during dobutamine. After revascularization, 201Tl uptake increased only in segments that showed a biphasic response (from 66 +/- 12% to 78 +/- 13%; P < .05). Biphasic response had a sensitivity of 74% and specificity of 89% for prediction of recovery. The use of biphasic or sustained improvement responses increased the sensitivity to 86% with a decrease in specificity to 68%. Qualitative thallium assessment provided a high sensitivity (98%) but poor specificity (27%). Quantification of thallium uptake, however, improved its accuracy: a maximal uptake (at rest or redistribution) of > or = 60% yielded a 90% sensitivity and a 56% specificity.

CONCLUSIONS

In patients with myocardial hibernation, biphasic response during dobutamine is less sensitive but more specific for recovery of function, whereas indexes of 201Tl scintigraphy are in general more sensitive and less specific, the least accurate being a qualitative assessment of thallium uptake. The sensitivity and specificity of both methods, however, can be altered depending on the quantitative criteria of thallium uptake or combination of responses of the myocardium to dobutamine.

Stress echocardiography using adenosine combined with nitroglycerin-dobutamine in the detection of viable myocardium in patients with previous myocardial infarction

The aim of this study was to assess the value of adenosine (A) and the combination of nitroglycerin (N) with dobutamine (D) stress echocardiography (SE) in the identification of viable myocardium. The clinical and electrocardiographic (ECG) effects of both tests were also evaluated. Fifty-two coronary artery disease patients, aged 56.4 +/- 8 years, with left ventricular dysfunction due to a previous myocardial infarction (mean ejection fraction: 49 +/- 8%) were included in the study. Cardiac catheterization was performed in all patients before A (140 micrograms/kg/minute for five minutes) and the combination of N with D (5-10 micrograms/kg/minute) stress echocardiography. On the echocardiogram, the left ventricle was divided into 16 segments and wall motion was graded semiquantitatively from 1 (normal) to 4 (dyskinesia). The echocardiographic index was also estimated. A segment was considered viable during A infusion when resting asynergy showed deterioration of one grade or more. In contrast, segmental viability was considered to be present during the combination of N with D infusion when resting asynergy showed improvement of one grade or more. A thallium 201 single photon emission computed tomography (SPECT) with reinjection was performed as reference standard for the identification of viable myocardium. Stress echocardiography during infusion of A was associated with short-duration angina attacks in 3 (5.8%) patients and transient complete atrioventricular (AV) block in 1 (1.9%), whereas during the combination of N with D infusion, 6 (11.5%) patients experienced ventricular bigeminy lasting for a short period. ST segment elevation greater than 1 mm was recorded in those leads having a Q wave, in 19 (36.5%) patients. In 10 of these 19 (52.6%), viable myocardium was present in SPECT, as it was in 33 patients (63.5%) having no ST segment elevation (P = NS). Of a total of 832 segments that were graded during A-SE, 276 exhibited resting asynergy and the remaining 556 had normal motion and thickening at rest. The echocardiographic index during A infusion increased from 1.52 +/- 0.22 to 1.71 +/- 0.24 (P < 0.001), whereas during D and N infusion it decreased from 1.53 +/- 0.31 to 1.30 +/- 0.42 (P < 0.001). With SPECT considered as the gold standard for the identification of viable myocardium, sensitivity, specificity, and positive and negative predictive values of A-SE in detecting viable myocardium were 54%, 86%, 65% and 80%, respectively. The respective values for the combination of nitroglycerin with D-SE were 91%, 89%, 78%, and 96%, respectively. Stress echocardiography during A, and the combination of N with D, constitute safe methods in the identification of viable myocardium. The detection of ST segment elevation in the ECG leads with a Q wave during the combined infusion of nitroglycerin and dobutamine is not related to the presence of viable myocardial tissue. The A-SE provide moderate diagnostic accuracy, while the combination of N with D during SE is much superior in detecting viable myocardium.

Correlation of functional recovery with myocardial blood flow, glucose uptake, and morphologic features in patients with chronic left ventricular ischemic dysfunction undergoing coronary artery bypass grafting

OBJECTIVE

Our objective was to investigate the influence of preoperative myocardial ultrastructure and metabolism on recovery of contractile function after coronary artery bypass grafting in patients with coronary artery disease and left ventricular dysfunction.

METHODS

Dynamic positron emission tomography with 13N-ammonia and 18F-deoxyglucose was used to assess myocardial perfusion and glucose uptake in 53 patients scheduled for coronary revascularization because of coronary artery disease and left ventricular dysfunction. The degree of tissue fibrosis and the presence of potentially reversible alterations of cardiomyocytes (loss of myofilaments and accumulation of glycogen) were quantified from transmural biopsy specimens. These were harvested from the center of the dysfunctional area during the operation and analyzed with a light microscope. The recovery of contractile performance was assessed from the changes in left ventricular function at contrast ventriculography or echocardiography before and 6 months after the operation.

RESULTS

According to postoperative changes in regional wall motion, left ventricular function was considered to have improved in 34 patients, whereas dysfunction persisted in 19 patients. In patients with improved wall motion, ejection fraction rose by 12% and end-systolic volume decreased by 28%. By contrast, in patients with persistent dysfunction, ejection fraction decreased by 6% and end-systolic volume increased by 25%. Before revascularization, myocardium with reversible dysfunction displayed higher levels of absolute myocardial blood flow, higher myocardial glucose uptake, less tissue fibrosis, and more altered cardiomyocytes than myocardium with persistent dysfunction. Significant correlations were found between regional blood flow and the surface of the biopsy specimen covered by fibrosis, as well as between glucose uptake and the density of altered cardiomyocytes.

CONCLUSION

In patients with left ventricular ischemic dysfunction, the recovery of regional and global left ventricular function after surgical revascularization is associated with higher preoperative blood flow and glucose uptake, with less tissue fibrosis and a higher amount of viable cardiomyocytes in the dysfunctional area. The current study thus confirms the value of noninvasive preoperative metabolic imaging for identification of residual viable myocardium and for prediction of the functional outcome after revascularization.

[Role of noninvasive examinations in the management of ischemic heart disease. III. Assessment of myocardial viability]

Assessment of myocardial viability is a field of growing interest. This article summarizes the pathophysiology of myocardial stunning and hibernation; both phenomena are associated with the presence of dysfunctional, viable myocardium. The techniques that are currently available for the assessment of viability, and the clinical situations in which these assessments may be more useful are discussed.

Assessment of viable myocardium and prediction of postoperative improvement in left ventricular function in patients with severe left ventricular dysfunction by quantitative planar stress-redistribution-reinjection 201-T1 imaging

A noninvasive approach to determine viable but asynergic myocardium will be clinically significant in identifying patients with coronary artery disease and severe left ventricular dysfunction who will benefit most from coronary bypass surgery. Accordingly, 12 patients (mean ejection fraction 0.32 +/- 0.03) underwent quantitative planar stress-redistribution-reinjection thallium scintigraphy and radionuclide ventriculography before and 8 weeks after revascularization for viability and segmental and global left ventricular function assessment, respectively. Reinjection scan showed new fill-in in 63% of segments without redistribution. Postoperative improvement in perfusion and function of asynergic segments were significantly better in viable compared to nonviable segments (P < 0.001, P < 0.01, respectively) with a strong correlation between improvement in 201-T1 uptake and function (P < 0.001). When adequacy of revascularization was considered, the predictive value of a positive preoperative viability test for functional improvement was 83%. Finally, mean ejection fraction and global wall motion score increased significantly after revascularization for the group as a whole (0.32 +/- 0.03 to 0.44 +/- 0.04, P < 0.001 and 24.08 +/- 2.90 to 33.16 +/- 3.32, P < 0.001, respectively). Thus, preoperative quantitative planar stress-redistribution-reinjection thallium imaging detects viable but asynergic segments which improve function postoperatively and may be valuable in selection of patients with severe left ventricular dysfunction for revascularization.

Elective stenting of the extracranial carotid arteries

BACKGROUND

Surgical endarterectomy has been shown to be superior to medical management in the management of severe carotid stenosis in both symptomatic and asymptomatic patients. Endarterectomy, although effective, does have limitations, and percutaneous techniques may offer an alternative method of treatment.

METHODS AND RESULTS

The feasibility and safety of percutaneous carotid angioplasty and elective (primary) stenting was evaluated prospectively in a consecutive series of 107 patients. One hundred twenty-six carotid arteries with significant stenosis were treated. This series represented a high-risk subset that included patients with previous ipsilateral endarterectomy and severe medical comorbidity. Forty-five percent of the patients were referred by surgeons. Patients had independent neurological examinations before and after the procedure and follow-up cerebral angiography at 6 months. The mean (+/- SD) stenosis was reduced from 78 +/- 14% to 2 +/- 5%. There were 7 minor strokes, 2 major strokes, and 1 death during the initial hospitalization and first 30 days after the procedure. For the combined end point of all strokes and death, the incidence was 7.9%. For ipsilateral major stroke and death, the incidence was 1.6%. There were no strokes during the follow-up period. Mean angiographic stenosis at 6 months in 81 patients was 18 +/- 16% (range, -21% to 57%). Four (4.9%) of these 81 patients had asymptomatic restenosis. Five asymptomatic patients had repeat intervention: 2 had angioplasty for restenosis, 2 had angioplasty for stent deformation, and 1 had endarterectomy for restenosis.

CONCLUSIONS

In a high-risk group of patients, percutaneous carotid angioplasty and stenting are feasible and can be performed with low restenosis and repeat intervention rates.

Hibernating myocardium has reduced blood flow at rest that increases with low-dose dobutamine

The study of Sun and coworkers is important because (1) it provides additional data that HM has an inotropic and an attenuated coronary vasodilator reserve. They also provided data that support the conclusion that with dobutamine, the improvement of abnormal LV wall motion is real in many patients. (2) It emphasizes the possibility of a deleterious effect (infarction) of dobutamine in HM and thus the need for appropriate caution during its use. (3) It provides additional data that confirm that areas of perfusion-metabolism mismatch on PET imaging (HM) are associated with a reduced MBF at rest. However, their conclusions about areas of LV dysfunction with "normal" MBF in coronary artery disease are problematic; therefore, one must be extremely cautious about these conclusions on the basis of the data that are presented.

Effects of dobutamine stimulation on myocardial blood flow, glucose metabolism, and wall motion in normal and dysfunctional myocardium

BACKGROUND

This investigation examines the effects of inotropic stimulation on myocardial blood flow (MBF) and glucose metabolism (MRGlc) in dysfunctional myocardium through the use of positron emission tomography (PET).

METHODS AND RESULTS

Nineteen patients with chronic coronary artery disease and 12 normal volunteers were studied with 13N-ammonia, 18F-deoxyglucose, and PET and with two-dimensional echocardiography at baseline and during intravenous dobutamine (5 to 10 micrograms/kg per minute). At rest, MBF in mismatch regions (n = 10) averaged 0.53 +/- 0.19 mL/g per minute and increased by 41.4 +/- 46.6% (P = .01) during dobutamine, whereas in match regions (n = 16) MBF was 0.28 +/- 0.09 mL/g per minute at rest without an increase during dobutamine (26.4 +/- 47.3%; NS). Myocardium with normal rest MBF was classified as normal remote (normal wall motion, n = 8) or abnormal remote (abnormal wall motion, n = 11). Dobutamine raised MBF similarly in normal subjects and in normal remote regions (by 82 +/- 85% and 84 +/- 42%, P < .01) but by only 33 +/- 34% in abnormal remote regions. MRGlc declined by 49 +/- 28% (P < .005) with dobutamine in the normal subjects, remained unchanged in normal and abnormal remote regions of the patients, but increased in mismatch and match regions (by 49 +/- 74% and 46 +/- 77%; P < .05). Wall motion improved with dobutamine only in mismatch and abnormal remote regions but not in match regions.

CONCLUSIONS

Blood flow-metabolism mismatch patterns are not consistently associated with a fixed downregulation of MBF; the increased contractile work in response to dobutamine stimulation is associated with an increase in MBF and a greater reliance on glucose utilization, possibly reflecting acute ischemia or alterations in substrate selection by chronically dysfunctional myocardium. Importantly, functionally impaired though normally perfused myocardium frequently exists in chronic coronary artery disease patients and may represent repetitively stunned or, more likely, remodeled left ventricular myocardium.

Course of impaired left ventricular function after acute myocardial infarction predicted with planar thallium-201 chloride and F18-fluorodeoxyglucose imaging

Planar reset myocardial thallium-201 chloride (201Tl)/F18-fluorodeoxyglucose (FDG) imaging has been shown to distinguish between viable and non-viable tissue. Twenty-five patients (60 +/- 9 years) with acute myocardial infarction were studied using this technique within 6 +/- 2 days (T1) after infarction and again after 42 +/- 4 days (T6). Serial assessment of wall motion with 2D-echocardiography was performed to determine the predictive value of radionuclide indices for the course of impaired regional left ventricular function. No revascularization procedure was performed. Segmental 201Tl and FDG uptake was evaluated using circumferential profiles. Echocardiographic wall motion was scored as normal, hypokinetic or akinetic. Myocardial segments were considered non-viable if a match between 201Tl and FDG uptake was present, which is a concordant reduction in 201 Tl and FDG uptake (Group A). Myocardial segments were considered viable if: a mismatch was present between 201Tl and FDG uptake which was defined as a segmental FDG uptake exceeding 201Tl uptake by > or = 20% in a segment with reduced 201Tl uptake (Group B); a normal FDG uptake (> or = 75%) was present without a mismatch pattern in a segment with reduced 201Tl uptake (201Tl < 75% of peak activity) (Group C); a normal 201Tl uptake was present in the area of wall motion abnormality (Group D). Corresponding scintigraphic images obtained at T1 and T6 were compared.

RESULTS

51 segments were normokinetic, 37 were hypokinetic and 6 were akinetic at T1. Of the 63 segments with wall motion abnormalities at T1, 18 regions showed a match (FDG-201Tl < 20%) (Group A). Regional function improved in only one (6%) of these segments. In 19 regions a mismatch was present (FDG-201Tl > 20%) (Group B) of which three (16%) showed spontaneous improvement in function (p = NS vs. matched segments), although recovery varied considerably among patients. Regional function in two segments deteriorated. In 14 regions with reduced 201Tl uptake, FDG uptake was normal (Group C) of which five (36%) were improved after 6 weeks (p < 0.05 vs. match; p = NS vs. mismatched segments). Of the 12 segments with normal 201Tl uptake (Group D), seven (58%) showed improvement in function, whereas five (42%) did not show improvement (p < 0.05 vs. match). In addition, all scintigraphically selected viable segments were grouped (Group B + C + D) and compared with the non-viable segments (Group A). The predictive value of a positive viability test for spontaneous functional improvement was 33%. The predictive value of a negative viability test for lack of functional improvement was 94%.

CONCLUSIONS

absence of residual FDG uptake shortly after infarction is associated with irreversible injury, while preservation of metabolic activity identifies segments with variable outcome. Wall motion alone is not a good indicator for the presence of viable tissue. Planar 201Tl/FDG imaging allows early identification of viable but jeopardized tissue and may help select patients who will benefit from aggressive therapy to salvage endangered myocardium.

Myocardial viability: methods of assessment and clinical relevance

Myocardial hibernation is hypoperfused dysfunctional myocardium that has the potential to recover function after coronary revascularization. Although recovery of regional function after revascularization is the gold standard for assessing the diagnostic accuracy of various techniques, improvements of EF, symptoms, and survival are fundamental end points. Despite important differences in the markers of viability by positron-emission tomography, single-photon emission tomography, two-dimensional echocardiography, and magnetic resonance imaging, their positive and negative predictive values in nonrandomized studies are fairly comparable. Assessment of myocardial viability may be clinically important in many patients but especially in those with EF < 30% and congestive heart failure. The degree of improvement in EF after coronary revascularization depends on the extent of hibernation, the suitability of coronary structure for revascularization, the lack of perioperative infarction, the completeness of revascularization, and the long-term patency of grafts.

Metabolic adaptation during a sequence of no-flow and low-flow ischemia. A possible trigger for hibernation

BACKGROUND

Myocardial hibernation is an adaptive phenomenon occurring in patients with a history of acute ischemia followed by prolonged hypoperfusion.

METHODS AND RESULTS

We investigated, in isolated rabbit heart, whether a brief episode of global ischemia followed by hypoperfusion maintains viability. Four groups were studied; group 1,300 minutes of aerobia; group 2,240 minutes of total ischemia and 60 minutes of reperfusion; group 3, 10 minutes of total ischemia, 230 minutes of hypoperfusion (90% coronary flow reduction), and 60 minutes of reperfusion; and group 4, 240 minutes of hypoperfusion followed by reperfusion. In group 3, viability was maintained. Ten minutes of ischemia caused quiescence, a fall in interstitial pH (from 7.2 +/- 0.01 to 6.1 +/- 0.8), creatine phosphate (CP), and ATP (from 54.5 +/- 5.0 and 25.0 +/- 1.9 to 5.0 +/- 1.1 and 15.3 +/- 2.5 mumol/g dry wt, P < .01). Subsequent hypoperfusion failed to restore contraction and pH but improved CP (from 5.0 +/- 1.1 to 20.1 +/- 3.4, P < .01). Reperfusion restored pH, developed pressure (to 92.3%), and NAD/NADH and caused a washout of lactate and creatine phosphokinase with no alterations of mitochondrial function or oxidative stress. In group 4, hypoperfusion resulted in progressive damage. pH fell to 6.2 +/- 0.7, diastolic pressure increased to 34 +/- 5.6 mm Hg, CP and ATP became depressed, and oxidative stress occurred. Reperfusion partially restored cardiac metabolism and function (47%).

CONCLUSIONS

A brief episode of total ischemia without intermittent reperfusion maintains viability despite prolonged hypoperfusion. This could be mediated by metabolic adaptation, preconditioning, or both.

Detection of myocardial viability in the prediction of improvement in left ventricular function after successful coronary revascularization by using the dobutamine stress echocardiography and quantitative SPECT rest-redistribution-reinjection 201TI imaging after dipyridamole infusion

The aim of this study was to assess the feasibility, safety, and respective diagnostic accuracy of low-dose dobutamine infusion and rest-redistribution-reinjection thallium 201 single photon emission computed tomography (SPECT) after dipyridamole infusion (Th-DIP), in the prediction of functional improvement of asynergic infarcted zones, after successful revascularization in patients with chronic ischemic heart disease. Thirty-one patients with a previous myocardial infarction and left ventricular dysfunction (mean ejection fraction: 41 +/- 5.8%) were studied. The regional wall motion of the left ventricle was evaluated by basic echocardiography before and 14 +/- 1.7 weeks after successful revascularization (19 by percutaneous transluminal coronary angioplasty and 12 by coronary artery bypass grafting). Dobutamine stress echocardiography (DSE) was performed in all patients with dobutamine infusion of 5 and 10 micrograms/kg/minute over five minutes. Within three days after DSE and prior to revascularization, all patients underwent Th-DIP for myocardial viability assessment. A 16-ventricular-segment model was used for basic, DSE, and Th-DIP images. Viability was assessed by applying the standard criteria for each technique. In the 31 patients, 496 segments were analyzed. By basic echocardiography, 164 (33%) of them were classified as asynergic. The DSE detected viable tissue in 69/496 (14%) segments, whereas Th-DIP identified viability in 95/496 (19%) segments. When the postrevascularization basic echocardiographic study was used as the gold standard in identifying myocardial viability, the sensitivity and specificity for the DSE and Th-DIP were 86.5%, 94.4% and 90.5%, 69%, respectively. No major side effects were observed with both techniques. In conclusion, DSE seems to be an accurate method for identifying viable but asynergic myocardium in patients with chronic ischemic heart disease, whereas Th-DIP overestimates the postrevascularization recovery. Detection of hibernating myocardium can be obtained by these two noninvasive methods. However, DSE seems to be more useful in determining the prospective selection of patients who are going to benefit from revascularization.

Inotropic reserve and histological appearance of hibernating myocardium in conscious pigs with ameroid-induced coronary stenosis

Inotropic reserve, demonstrated with administration of sympathomimetic amines, is characteristic of hibernating myocardium. The goal of this study was to determine whether inotropic reserve was present following chronic coronary artery constriction in the pig, which is one potential model of hibernating myocardium. The effects of isoproterenol were examined in five conscious pigs 21 +/- 2.1 days after ameroid implantation on the left circumflex coronary artery on measurements of left ventricular (LV) pressure, LV dP/dt, and regional wall thickening in the ameroid-dependent zone (posterior wall) and contralateral non-ischemic zone (anterior wall). Isoproterenol, 0.1 microgram/kg/min, increased LV dP/dt by 96 +/- 11%, heart rate by 43 +/- 13 beats/min, and normalized systolic wall thickening, slightly, but not significantly more in the ameroid-dependent zone (+1.57 +/- 0.31 mm) than in the contralateral non-ischemic zone (+1.04 +/- 0.31 mm), although the baseline wall thickening was reduced significantly in the ameroid-dependent zone. This occurred at a time when baseline myocardial blood flow was preserved and myocardial perfusion in the ameroid-dependent zone was derived in part from the native coronary circulation and also through collateral channels. Two weeks later histological evidence of lesions characteristic of hibernating myocardium, i.e., myofibrolysis and increased glycogen deposition, were observed. Thus, these histological changes and the confluence of chronically depressed regional function and residual inotropic reserve in the conscious pig with chronic ameroid-induced coronary constriction support this model for further study of hibernating myocardium.

The Contribution of the Left Atrioventricular Plane Displacement During Low Dose Dobutamine Stress Echocardiography in Predicting Recovery of Left Ventricular Dyssynergies

The aim of this study was to assess the significance of the left systolic atrioventricular (AV) plane displacement during low dose dobutamine stress echocardiography (DSE), in predicting the recovery of left ventricular dyssynergies after revascularization. In 30 infarctiers with left ventricular dysfunction scheduled for RE (14 percutaneous transluminal coronary angioplasty and 16 coronary artery bypass graft) and in 25 age- and sex-matched healthy subjects, a DSE, using a 16 ventricular segment model and a four-grade scoring system for the assessment of regional wall motion of the left ventricle was performed. Prior and during DSE, the left systolic AV plane displacement was recorded from the apical four- and two-chamber views, by M-mode echo, at four left ventricular sites, corresponding to the septal, lateral, anterior, and inferior walls, both in patients and controls. The study was repeated in all patients 101 +/- 14 days after successful revascularization. Healthy subjects showed a significant increase of left systolic AV plane displacement at all left ventricular sites during dobutamine infusion (DI) (P < 0.001). Patients also exhibited a significant maximum increase of left systolic AV plane displacement during DSE only in the dyssynergic sites with functional improvement in the postrevascularization echocardiogram (P < 0.001). In the remaining dyssynergic sites, without functional improvement after revascularization, the left systolic AV plane displacement did not change (P > 0.05). Selecting a maximum LAVPD increase of >2 mm at any site of the left ventricule to predict recovery of the regional ventricular dyssynergies, results in a sensitivity of 91%, specificity of 83%, positive predictive value of 88%, and negative predictive value of 87%. When two-dimensional DSE was used for the detection of reversible dysfunction, sensitivity and specificity were found to be 81.5% and 87.5%, respectively, while the positive and negative predictive values were 90% and 78%, respectively. When the two methods were in agreement the sensitivity was 90%, the specificity 100%, and the positive and negative predictive values were 100% and 84.2%, respectively. The assessment of left systolic AV plane displacement during DI constitutes a new, simple, and accurate method in the prediction of left ventricular dyssynergy recovery after revascularization. The combination of this method and two-dimensional DSE are basic predictor markers of viability of dysfunctional myocardium. (ECHOCARDIOGRAPHY, Volume 13, November 1996)

Effects of nitroglycerin infusion on segmental wall motion abnormalities after anesthetic induction

OBJECTIVES

To assess the effect of intravenous nitroglycerin (NTG) on segmental wall motion abnormalities (SWMAs) and global ventricular function after anesthetic induction in patients undergoing coronary artery bypass grafting (CABG).

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty patients scheduled for elective CABG.

INTERVENTIONS

Patients demonstrating SWMAs in at least two myocardial segments after induction received intravenous NTG at 2 micrograms/kg/min.

MEASUREMENT AND MAIN RESULTS

Transesophageal echocardiography (TEE) was performed before and after the NTG infusion for analysis of segmental wall motion abnormalities. Mean arterial pressure (MAP), central venous pressure, and pulmonary capillary wedge pressure decreased significantly after NTG infusion, whereas cardiac index and heart rate remained unchanged. End-diastolic area and end-systolic area decreased, and consequently fractional area change increased significantly. Two of 20 patients (10%) showed electrocardiogram evidence of ischemia after induction. After NTG infusion, 15 of 20 patients (75%) showed an increase in a wall motion score more than two points. In these 15 patients with NTG-responsive wall motion abnormalities, the mean ratio of peak early diastolic filling velocity (E) to peak late diastolic filling velocity (A) increased from 0.89 +/- 0.20 to 1.04 +/- 0.25 (p < 0.01) after NTG infusion despite a decrease in filling pressure. Systolic wall thickening improved in segments with poor preoperative function from a pre-NTG value (mean +/- SD) of -1.0% +/- 7.4% to a post-NTG value of 31.4% +/- 24.9% (p < 0.01).

CONCLUSIONS

Intravenous NTG improved postinduction SWMAs in 75% of patients with known coronary artery disease. TEE-guided NTG infusion after induction may provide an optimal baseline echocardiogram for monitoring intraoperative myocardial ischemia by improving the reversible portion of postinduction SWMAs.

Myocardial stunning, hibernation, and ischemic preconditioning

From the present review, it may be concluded that myocardial ischemia results in far more complicated syndromes than previously realized. Although not all aspects of the issues discussed in this review are currently a clinical reality in the daily practice of cardiovascular anesthesiologists, the understanding and application of these concepts are growing rapidly. Indications for revascularization procedures will be adjusted in patients with evidence of hibernating myocardium. In the future, postoperative myocardial dysfunction may be diminished by the prevention of myocardial stunning, for instance by altering the composition of the cardioplegic solution and other interventions. Finally, additional advances may involve reduction of the extent of perioperative myocardial infarctions by application of ischemic preconditioning.

Recovery of regional left ventricular dysfunction after coronary revascularization. Impact of myocardial viability assessed by nuclear imaging and vessel patency at follow-up angiography

OBJECTIVES

This study sought to evaluate an imaging approach using technetium-99m sestamibi scintigraphy and positron emission tomography with fluorine-18 fluorodeoxyglucose for assessment of myocardial viability proved by serial quantitative left ventricular angiography. Furthermore, the influence of successful long-term revascularization on functional recovery was studied.

BACKGROUND

Previous studies using positron emission tomography of myocardial perfusion and metabolism have demonstrated accurate identification of myocardial viability. However, most of these studies used a qualitative or semiquantitative wall motion analysis approach.

METHODS

Nuclear imaging with semiquantitative analysis of tracer uptake was performed in 193 patients with regional wall motion abnormalities. Regions were categorized as normal, viable with perfusion/metabolism mismatch, viable without mismatch (intermediate) and scar. Seventy-two of 103 patients with subsequent revascularization underwent follow-up angiography. In 52 of 72 patients, changes in regional wall motion were measured by the centerline method from serial angiography.

RESULTS

Wall motion improved in mismatch regions from -2.2 +/- 1.0 to -1.1 +/- 1.4 SD (p < 0.001). In contrast, regions with an intermediate pattern and those with scar did not improve. Restenosis or graft occlusion influenced functional outcome because regions with preoperative mismatch and successful long-term revascularization improved at follow-up (from -2.3 +/- 1.0 to -0.8 +/- 1.4 SD, p < 0.001), whereas wall motion did not change with recurrent hypoperfusion. Metabolic imaging added diagnostic information, particularly in regions with mild and moderate perfusion defects.

CONCLUSIONS

This imaging approach allows detection of viability in regions with myocardial dysfunction. Wall motion benefits most in myocardium with perfusion/metabolism mismatch and successful long-term revascularization.

Stress radionuclide studies after acute myocardial infarction: changes with revascularization

BACKGROUND

Successful revascularization of ischemic asynergic myocardium should be followed by improvement in contractile function. However, a clear improvement is not always observed. Assessment of contractile reserve may allow a better evaluation of procedural results.

METHODS AND RESULTS

To assess the changes in global and regional left ventricular ejection fraction (EF), as well as the contractile reserve after revascularization, equilibrium radionuclide angiography was performed in 16 patients with acute myocardial infarction who had periinfarct redistribution (observed in stress-rest-reinjection thallium single-photon emission computed tomography). Regional EF was defined in the asynergic region at rest, which corresponded to the infarct plus periinfarct areas. Both thallium single-photon emission computed tomography and equilibrium radionuclide angiography were performed at rest and during stress with dobutamine, up to a maximal dose of 40 micrograms/kg/min. The same studies were repeated 8 +/- 6 months after successful revascularization (nine coronary angioplasties and seven bypass procedures). After intervention, the thallium defect score decreased significantly at rest and during stress. Global EF changed from 45% +/- 10% to 47% +/- 11% (difference not significant) at rest and from 49% +/- 12% to 63% +/- 13% (p = 0.0001) at peak stress. Regional EF changed from 27% +/- 8% to 35% +/- 18% (p = 0.03) at rest and from 29% +/- 10% to 56% +/- 21% (p = 0.0001) at peak stress.

CONCLUSIONS

In patients with asynergy caused by periinfarct ischemia, there can be an increase in regional but not global EF at rest after revascularization. However, both parameters improve at peak dobutamine dose. This indicates an improvement in contractile reserve.

Assessment of myocardial viability with 99mTc sestamibi in patients undergoing cardiac transplantation. A scintigraphic/pathological study

BACKGROUND

99mTc sestamibi and 201 Tl are tracers that allow equivalent detection of myocardial infarction. However, because sestamibi does not undergo as much time-dependent redistribution as does 201Tl, it has been considered suboptimal for the detection of myocardial viability.

METHODS AND RESULTS

Fifteen consecutive patients with ischemic cardiomyopathy who underwent orthotopic cardiac transplantation received an intravenous injection of 99mTc sestamibi at 1 to 6 hours before transplantation. Rotational tomography of the excised, intact, native hearts was performed to quantify the extent of myocardial hypoperfusion. The hearts were then sliced and reimaged on a gamma camera, followed by pathological quantification of the extent and severity of scarred and normal myocardium. Samples of normally and abnormally perfused myocardium underwent gamma well counting to determine tissue radioactivity and were examined under light microscopy for delineation of myocardial structure after trichrome staining. The mean extent of scintigraphic scar quantified through the use of rotational tomography was 45 +/- 14% of the left ventricle and correlated closely with pathological scar size (r = .89), despite a slight overestimation. Scintigraphic scar size determined with planar imaging of the individual myocardial slices also correlated closely with pathological scar size (r = .88). A good correlation existed between tissue 99mTc sestamibi activity determined through well counting and histological evidence of myocardial viability (r = .89). Most hypokinetic and 40% of akinetic/dyskinetic myocardial segments contained scintigraphically and histologically normal myocardium.

CONCLUSIONS

99mTc sestamibi scintigraphy can be used to accurately quantify the extent of myocardial scarring. Furthermore, the relative sestamibi activity in perfusion defects, measured several hours after administration, is a good indicator of myocardial viability determined with microscopy.

Inotropic stimulation by dobutamine increases left ventricular regional function at the expense of metabolism in hibernating myocardium

The mechanism by which dobutamine increases the contraction of chronically dysfunctional myocardium and its effects on metabolism are still unknown. The aim of this study was to assess regional myocardial metabolism at rest and during an intracoronary dobutamine infusion in patients with hibernating myocardium. Eleven asymptomatic patients with single proximal stenosis of the left anterior descending coronary artery and persistent left ventricular dysfunction at rest (undergoing percutaneous transluminal coronary angioplasty [PTCA]) were studied prospectively. Regional left ventricular function was assessed by two-dimensional (2D) echocardiography and regional perfusion by thallium-201 single-proton-emission computed tomography. Great cardiac vein and aortic blood samples were obtained for measurements of lactate and plasma free fatty acid (FFA) concentrations. Inotropic challenge, obtained by using intracoronary dobutamine infusion, increases regional left ventricular function. However, the arteriovenous AV lactate difference was 0.206 = 0.070 mmol/L at rest, and it decreased to 0.018 = 0.069 mmol/L (p < 0.05 vs baseline) and 0.066 = 0.068 mmol/L (p < 0.05 vs baseline) at 4 and 10 minutes of dobutamine infusion, respectively. Thus the hibernating myocardium does not produce lactate at rest. However, when regional contraction is stimulated, dobutamine-induced inotropic challenge may cause a perfusion-contraction mismatch with an activation of anaerobic glycolysis.

Myocardial blood flow, glucose uptake, and recruitment of inotropic reserve in chronic left ventricular ischemic dysfunction. Implications for the pathophysiology of chronic myocardial hibernation

BACKGROUND

Previous work has documented that dysfunctional noninfarcted collateral-dependent myocardium, a condition typical of myocardial hibernation, exhibited almost normal resting perfusion. The present study was designed to test whether these observations could be extended to unselected patients with chronic dysfunction and a previous infarction.

METHODS AND RESULTS

Dynamic positron emission tomographic imaging with [13N]ammonia and [18F]fluorodeoxyglucose (FDG) to assess myocardial perfusion and glucose uptake was performed in 39 patients with chronic anterior wall dysfunction undergoing coronary revascularization. Left ventricular function was evaluated by echocardiography before (at rest and during low-dose dobutamine infusion) and 5 months after revascularization. At follow-up, wall motion was improved in 24 patients and unchanged in 15 patients. Before revascularization, absolute myocardial blood flow was higher (84 +/- 27 versus 60 +/- 26 mL.min-1 x 100 g-1, P = .007) in reversibly compared with persistently dysfunctional segments. In segments with reversible dysfunction, values of myocardial blood flow were similar to those in the remote segments of the same patients or in anterior segments of normal volunteers. During glucose clamp, FDG uptake was higher (69 +/- 17% versus 49 +/- 18%, P < .01) but myocardial glucose uptake was not different (38 +/- 20 versus 29 +/- 19 mumol.min-1.100 g-1, P = NS) in reversibly compared with persistently dysfunctional segments. A flow-metabolism mismatch was present in 18 of 24 reversibly injured but absent in 10 of 15 persistently dysfunctional segments. With dobutamine, wall motion improved in 17 of 24 reversibly dysfunctional segments and did not change in 13 of 15 segments with persistent dysfunction.

CONCLUSIONS

This study indicates that chronic but reversible ischemic dysfunction is associated with almost normal resting myocardial perfusion, with maintained FDG uptake, and with recruitable inotropic reserve. These data support the contention that chronic hibernation is not the consequence of a permanent reduction of transmural myocardial perfusion at rest.

Comparison of dobutamine transesophageal echocardiography and dobutamine magnetic resonance imaging for detection of residual myocardial viability

A dobutamine-induced contraction reserve in akinetic but viable myocardium, observed by echocardiography or magnetic resonance imaging (MRI), is a reliable indicator of myocardial viability. However, the comparative diagnostic accuracy of these 2 techniques is unknown. Therefore, 43 patients with myocardial infarction (infarct age > or = 4 months) and regional akinesia underwent dobutamine transesophageal echocardiography (TEE) and dobutamine MRI (10 microg dobutamine/ min/kg). Both imaging techniques were compared with the reference standard 18F-fluorodeoxyglucose positron emission tomography (FDG PET). An infarct region was considered viable if a dobutamine contraction reserve could be assessed visually by TEE or quantitatively by MRI in > or = 50% of segments graded "a" or dyskinetic at rest. Infarct regions were graded viable by PET if FDG uptake was > or = 50% of the maximal FDG uptake in a region with normal wall motion by left ventriculography. A dobutamine contraction reserve was found in 21 of 43 patients (49%) by TEE and MRI. A viable infarct region by FDG PET was diagnosed in 26 of 43 patients (60%). FDG uptake and dobutamine TEE were concordant in 36 of 43 patients (84%) and dobutamine MRI and FDG PET were concordant in 38 of 43 patients (88%). Sensitivity and specificity of dobutamine TEE and dobutamine MRI for FDG PET-defined myocardial viability were 77% versus 81% and 94% versus 100%, respectively. Both imaging techniques yielded similar results for the detection of myocardial viability as defined by FDG uptake, with a slightly higher sensitivity and specificity for the quantitatively evaluated dobutamine contraction reserve by MRI.

Factors influencing regional myocardial contractile response to inotropic stimulation. Analysis in humans with stable ischemic heart disease

BACKGROUND

We hypothesized that the response of a myocardial segment to maximal dobutamine reflects not only maximal blood flow but also tethering, metabolic, and beta-blocker status.

METHODS AND RESULTS

Patients with stable ischemic heart disease (n = 27) had positron emission tomographic measurement of blood flow at rest and with adenosine, and echocardiography at rest and with dobutamine. Positron emission tomographic measurement of [18F]fluorodeoxyglucose myocardial distribution also was made. Adenosine blood flow in segments that contracted normally at peak dobutamine was similar to that of segments that became hypokinetic (1.06 +/- 0.72 versus 1.02 +/- 0.77 mL.g-1.min-1). Segments that became akinetic failed to augment blood flow (0.68 +/- 0.30 mL.g-1.min-1). Fluorodeoxyglucose-blood flow mismatch was more common in segments with abnormal wall motion at peak dobutamine (24 of 59, 41%) versus those that contracted normally (63 of 269, 23%; chi 2, 7.40; P < .01). In patients off beta-blockers, segments that contracted normally at peak dobutamine increased blood flow with adenosine (0.70 +/- 0.31 to 0.86 +/- 0.46 mL.g-1.min-1; P < .05), whereas those that became abnormal did not (0.63 +/- 0.24 to 0.65 +/- 0.19 mL.g-1.min-1; P = NS). Segments of patients on beta-blockers that contracted normally at peak dobutamine increased blood flow with adenosine (0.78 +/- 0.31 to 1.10 +/- 0.70 mL.g-1.min-1; P < .05), as did segments that became abnormal (0.74 +/- 0.34 to 1.06 +/- 0.82 mL.g-1.min-1; P = NS). However, segments adjacent to ones with abnormal wall motion at rest had higher frequency of abnormal response at peak dobutamine in groups on (48% versus 16%; chi 2, 14.1; P < .001) and off (51% versus 21%; chi 2, 10.9; P < .01) beta-blockers.

CONCLUSIONS

Augmented contraction at maximal dobutamine depends not only on increased myocardial blood flow but also on tethering, metabolic, and beta-blocker status. Furthermore, impaired flow reserve does not preclude a normal response to maximal dobutamine, since blood flow need not increase greatly to meet demand.

Regional cardiac sympathetic nerve dysfunction and the diagnostic efficacy of metaiodobenzylguanidine tomography in stable coronary artery disease

The present study endeavors to correlate regional myocardial sympathetic nerve dysfunction with reversible and persistent perfusion abnormalities and depressed regional wall motion, and to determine the diagnostic efficacy of radio-iodinated metaiodobenzylguanidine (MIBG) tomography for detecting coronary artery disease. In 28 consecutive patients with stable coronary artery disease and 7 patients with atypical chest pain but no coronary stenosis, regional MIBG uptake was semiquantitatively evaluated in 13 left ventricular segments early (30 minutes) and late (4 hours) after injection. Regional MIBG uptake was reduced in 68 of 90 segments (76%) showing reversible perfusion abnormality and 72 of 81 segments (89%) showing persistent abnormality 4 hours after injection. Although the sensitivity and negative predictive values of late MIBG scanning for detecting myocardial perfusion abnormalities were relatively high (82% and 85%, respectively), the specificity, positive predictive value, and kappa value were low (63%, 57%, and 0.41, respectively). Right coronary lesions were detected by late MIBG scanning with a high sensitivity (85%) but a low specificity (41%). Conversely, the sensitivities for detecting lesions in the other 2 major left coronary arteries were low (55%). The overall diagnostic accuracy of late MIBG scanning was 66% and the positive and negative predictive values and kappa value were low; 60%, 70%, and 0.31, respectively. Similarly, regional sympathetic dysfunction was observed in 42 of 49 asynergic segments (86%) on late MIBG scans, of which 32 segments were viable and 10 nonviable; but the low specificity (73%) and positive predictive value (44%) reduced the kappa value (0.43). Thus, regional cardiac sympathetic innervation is impaired in ischemic, asynergic but noninfarcted myocardium as well as in myocardium which is infarcted or has a persistent perfusion abnormality. The diagnostic efficacy of MIBG tomography to detect coronary artery disease, however, is limited probably because of nonspecific reductions of MIBG uptake in the inferior and posterolateral regions.

The use of dobutamine stress echocardiography for the determination of myocardial viability

Determining the presence of viable myocardium has prognostic and therapeutic implications in the treatment of ischemic heart disease. Dobutamine stress echocardiography (DSE) is one possible technique to help identify both hibernating and stunned but viable myocardium. Low-dose dobutamine infusion has an increased inotropic effect, while higher doses cause both inotropic and chronotropic effects. Thus, at lower doses cardiac augmentation occurs, and at higher doses regions of ischemia may be produced in the presence of significant coronary artery disease. This is manifested echocardiographically as changes in segmental wall motion. In theory, therefore, areas of viable myocardium should show improved wall motion at low doses, and areas of irreversible myocardial damage will remain akinetic. Five studies have investigated DSE for determining viability in the setting of acute myocardial infarction, thus looking for stunned but viable myocardium. DSE was shown to compare favorably with positron emission tomography and was highly sensitive and specific for predicting functional myocardial recovery. Five additional studies examined DSE for determining the presence of hibernating myocardium. The sensitivity and specificity of DSE were found to range from 71 to 92% and from 73 to 93%, respectively. The benefits of DSE include lower cost, convenience to both patient and physician, additional ancillary information, and determination of the possible need for urgent revascularization. Limitations of DSE include occasional technical difficulty in obtaining and interpreting studies and the need for larger volumes of viable myocardium to detect changes predictive of functional recovery. Larger trials are currently underway to confirm DSE as a reliable technique for determining myocardial viability.

Functional and structural alterations with 24-hour myocardial hibernation and recovery after reperfusion. A pig model of myocardial hibernation

BACKGROUND

Short-term myocardial hibernation of 3 hours resulting from a moderate resting coronary flow reduction has been reproduced in pigs. This study was designed to determine whether any structural changes accompany short-term hibernation caused by a moderate flow reduction maintained for 24 hours and whether any such structural alterations are reversible after reperfusion.

METHODS AND RESULTS

A severe left anterior descending coronary artery (LAD) stenosis was created with a reduction of resting flow to approximately 60% of baseline and maintained for 24 hours. Regional coronary flow was measured by a flowmeter; wall thickening was determined by echocardiography, and local metabolic changes were measured. Of 17 pigs, 11 completed the study protocol of 24 hours. The LAD flow was reduced from 0.91 +/- 0.11 to 0.52 +/- 0.13 mL.min-1.g-1, a 43% mean decrease, at 15 minutes after the LAD stenosis and was maintained at 0.56 +/- 0.11 mL.min-1.g-1 at 24 hours. The reduction of regional coronary flow initially produced acute myocardial ischemia, as evidenced by reduced regional wall thickening (from 37.2 +/- 6.9% at baseline to 11.5 +/- 6.8%), regional lactate production (-0.34 +/- 0.28 mumol.g-1.min-1), and a decrease in regional coronary venous pH (from 7.41 +/- 0.035 at baseline to 7.30 +/- 0.030). At 24 hours, the reductions in coronary flow and wall thickening were maintained relatively constant and the rate-pressure product was relatively unchanged, but lactate production ceased and regional H+ concentration normalized, with a tendency toward a further reduction in regional oxygen consumption, from 3.10 +/- 0.90 mL.min-1.100 g-1 at 15 minutes after stenosis to 2.52 +/- 0.95 mL.min-1.100 g-1 at 24 hours (P = .06), indicating metabolic adaptation of the hypoperfused regions. Of 11 pigs, 6 were free of myocardial infarction; 3 had patchy necrosis involving 4%, 5%, and 6% of the area at risk; and 2 other pigs had a few scattered myocytes with necrosis, detected only by light and electron microscopy. Ultrastructural changes consisted of a partial loss of myofibrils and an increase in mitochondria and glycogen deposition. Regional wall thickening recovered 1 week after reperfusion in most pigs, and the ultrastructural changes reverted to normal.

CONCLUSIONS

In this pig model, moderately ischemic myocardium undergoes metabolic and structural adaptations but preserves the capacity to recover both functionally and ultrastructurally after reperfusion.

Only hibernating myocardium invariably shows early recovery after coronary revascularization

BACKGROUND

The aims of this study were to identify hibernating myocardium (hypocontractile, hypoperfused viable myocardium that regains contractility after revascularization) in the clinical setting and to predict functional outcome in patients with coronary artery disease after coronary revascularization.

METHODS AND RESULTS

Preoperative data related to the anterior free wall of the left ventricle were collected in 50 coronary bypass surgery candidates (positron emission tomography [PET], [13N]NH3 for flow, and [18F]FDG for metabolism [MET]; equilibrium-gated nuclear angiography [EGNA] for regional ejection fraction [REF]; and histological data from myocardial biopsies for percentage fibrosis and viable myocytes). Three months after surgery, the patients had follow-up PET and EGNA investigations. A principal-components analysis identified four patient clusters. Cluster 1 (n = 9) had normal viable myocardium. Cluster 2 (n = 18) had viable hypocontractile myocardium (REF, 39 +/- 12%) showing a PET mismatch pattern. Cluster 3 (n = 16) had viable hypocontractile myocardium associated with morphological myocyte injury showing a matched moderate decrease in flow (66 +/- 11%) and MET (70 +/- 11%). Cluster 4 (n = 7) had hypocontractile myocardium with mainly scar tissue (fibrosis, 74 +/- 12%). After surgery, only cluster 2, with hibernating myocardium, showed significant improvement in REF (from 39 +/- 12% to 50 +/- 13%, P < .05). Cluster 3, with sites of morphological myocyte injury, showed no recovery. The stepwise logistic regression showed a combination of low preoperative REF and high MET to be the best predictor of functional recovery (P < .008).

CONCLUSIONS

Multivariate analysis identifies hibernating myocardium showing early postrevascularization recovery, as opposed to viable but myolytic myocardium with no early recovery. Postrevascularization recovery can be predicted (combination of low REF and high MET) by noninvasive techniques.

"Hibernating" myocardium: asleep or part dead?

Chronic ischemic dysfunction of the left ventricle is commonly presumed to represent "hibernating" myocardium. The implication of this assumption is that with successful reperfusion, systolic function will improve. Several diagnostic techniques including dobutamine stress echocardiography have been used to detect "viable" myocardium in the setting of chronic left ventricular dysfunction. Predictive accuracies of 70% to 85% have been reported for identifying myocardium that recovers function. Recovery of function has been variable and often dependent on the severity of dysfunction. All current models have presumed that chronically dysfunctioning myocardium is "hibernating." Obviously, in the chronic setting, dysfunction may have many causes and include components of transmural and nontransmural infarction as well as hibernating myocardium. This review focuses on the independent role that nontransmural infarction may play in chronic dysfunction and suggests its impact on diagnostic techniques used to identify hibernating myocardium.

Myocyte degeneration and cell death in hibernating human myocardium

OBJECTIVES

The aim of this study was to analyze the morphologic characteristics of myocyte degeneration leading to replacement fibrosis in hibernating myocardium by use of electron microscopy and immunohistochemical techniques.

BACKGROUND

Data on the ultrastructure and the cytoskeleton of cardiomyocytes in myocardial hibernation are scarce. Incomplete or delayed functional recovery might be due to variable degree of cardiomyocyte degeneration in hibernating myocardium.

METHODS

In 24 patients, regional wall motion abnormalities were analyzed by use of the centerline method before and 6 +/- 1 months after coronary artery bypass surgery. Preoperative technetium-99m sestamibi uptake was measured by single-photon emission computed tomography for assessing regional perfusion. Fluorine-18 fluorodeoxyglucose uptake was measured by positron emission tomography to assess glucose metabolism. Transmural biopsy specimens were taken during coronary artery bypass surgery from the center of the hypocontractile area of the anterior wall.

RESULTS

The myocytes showed varying signs of mild-to-severe degenerative changes and an increased degree of fibrosis. Immunohistochemical analysis demonstrated disruption of the cytoskeletal proteins titin and alpha-actinin. Electron microscopy of the cell organelles and immunohistochemical analysis of the cytoskeleton showed a similarity in the degree of degenerative alterations. Group 1 (n = 11) represented patients with only minor structural alterations, whereas group 2 (n = 13) showed severe morphologic degenerative changes. Wall motion abnormalities showed postoperative improvements, and nuclear imaging revealed a perfusion-metabolism mismatch without significant differences between the groups.

CONCLUSIONS

Long-term hypoperfusion causes different degrees of morphologic alterations leading to degeneration. Preoperative analysis of regional contractility and perfusion-metabolism imaging does not distinguish the severity of morphologic alterations nor the functional outcome after revascularization. The insufficient act of self-preservation in hibernating myocardium may lead to a progressive structural degeneration with an incomplete and delayed recovery of function after restoration of blood flow.

Clinical importance of viability assessment in chronic ischemic heart failure

BACKGROUND AND HYPOTHESIS

Revascularization has provided an effective treatment of depressed left ventricular function in patients with chronically ischemic or "viable" myocardium. Assessment of viable myocardium can be achieved by several noninvasive techniques including dobutamine stress echo or radionuclides such as flurodeoxyglucose (F18DG). F18DG uptake studies are based on the assumption that enhanced glucose uptake in areas of diminished blood flow provides evidence of viable myocardium. To determine the clinical utility of viability assessment in the management of chronic ischemic left ventricular dysfunction, we reviewed the findings and short-term treatment of a series of patients referred for heart failure evaluation who had subsequent F18DG uptake scans.

METHODS

We retrospectively reviewed 59 consecutive F18DG viability studies in a series of patients who had documented coronary artery disease and depressed left ventricular function. Single photon emission computerized tomography (SPECT) with F18DG was performed in the patients and these images were compared to SPECT images of resting myocardial perfusion using thallium, sestamibi, or teboroxime. Clinical decisions based on the results of these scans were obtained from chart review. Thirty-day mortality was determined from chart review or contact with the patient's physician. The patients were divided into those without and with F18DG uptake consistent with viable ischemic myocardium. Further analysis included subgroups of patients who were advised to undergo transplantation, revascularization, or to continue medical therapy.

RESULTS

Of 34 patients referred for cardiac transplantation, 18 had viable myocardium and 13 underwent revascularization. In the entire study group, 34 of 59 (58%) had evidence of viable myocardium and 29 had subsequent revascularization procedures. Thirty-day survival for all revascularization patients was 86%.

CONCLUSION

Assessment of myocardial viability with F18DG SPECT imaging in patients with ischemic left ventricular dysfunction led to a clinical decision for revascularization in approximately half the patients with severe coronary disease and left ventricular dysfunction who were evaluated for myocardial viability in our institution.

The clinical impact of thallium-201 reinjection for the detection of myocardial hibernation

Thallium-201 reinjection improves detection of hibernating myocardium in about 30%-50% of persisting defects. The main goal of cardiac revascularization techniques is amelioration of clinical symptoms such as angina and dyspnoea; however, improvement in regional and global pump function is an additional and important target. The aim of this study was to investigate whether fill-in in the reinjection study is correlated with improved contractile function after treatment (percutaneous transluminal coronary angioplasty/aortocoronary bypass surgery). We studied 32 patients with coronary heart disease and impaired regional wall motion (RWM). RWM and ejection fraction (EF) were assessed by analysing ventriculographic images using the centreline method (values in standard deviations from mean values found in a healthy control group). Three 201Tl single-photon emission tomographic studies (stress, redistribution and reinjection) were performed prior to revascularization and analysed using a bull s-eye scheme. Patients were divided into two groups (group FI-=no fill-in, n=16; group FI+=fill-in, n=16). Fifty-six percent of all patients showed persisting defects, and 56% of these defects showed fill-in after reinjection. Fill-in in our patient group was independent of the size of the persisting defects. After revascularization RWM increased significantly in group FI+ (from -1.9 to 0.0 SD, P<0.001) whereas group FI- showed no significant change (from -1.6 to -1.8 SD). EF increased from -4.3 preoperatively to -2.1 SD postoperatively in group FI+ and did not change significantly in group FI- (-2.5 to -3.2 SD). The predictive value of reinjection for improvement of RWM was 88%. It is concluded that fill-in in the 201Tl reinjection image can predict recovery of RWM and EF after revascularization and should be used in all patients with impaired RWM and persisting defects independent of their extent.