The hibernating myocardium

Delineation of myocardial stunning and hibernation by positron emission tomography in advanced coronary artery disease

With positron emission tomography, the resting flow abnormalities underlying reversible left ventricular dysfunction in 17 patients with chronic coronary artery disease were delineated. The level of flow in reversible dysfuncTional segments (i.e., those demonstrating improvement after revascularization) was markedly variable, ranging from 0.32 to 1.25 ml/gm/min. In 20 of these segments, flow was preserved, whereas in 12 segments, flow was reduced, when compared with that in, age-matched controls. Preservation of flow was associated with preservation of myocardial oxygen consumption and no alterations in myocardial substrate use. In contrast, a reduction in flow resulted in a decrease myocardial oxygen consumption and an increase in myocardial glucose use. Thus resting reversible left ventricular dysfunction in patients with chronic coronary artery disease can reflect a diversity of resting flow abnormalities. Moreover, myocardial perfusion at rest is frequently within normal limits, suggesting that the reversible mechanical dysfunction in these patients is attributable to intermittent myocardial stunning and not hibernation.

Comparison of dobutamine stress echocardiography with dipyridamole stress echocardiography for detection of viable myocardium after myocardial infarction treated with thrombolysis

OBJECTIVE

To compare the ability of dobutamine and dipyridamole stress echocardiography to detect functional recovery of stunned but viable myocardial regions early after acute myocardial infarction, and to predict late functional recovery of the reperfusion salvaged myocardium within the infarct area.

METHODS

Within 10 d of acute myocardial infarction, 51 patients--30 anterior and 21 inferior, 44 Q wave and seven non-Q-wave infarction--were submitted to a dobutamine echocardiography test at low dose (5-10 micrograms/kg/min over 5 min) and high dose (20-40 micrograms/kg/min over 3 min) and to dipyridamole echocardiography test (0.56 mg/kg over 4 min + 0.28 mg/kg over 2 min) on different days and in random order, after interruption of any vasoactive drug. Resting echocardiography was repeated at two months in 41 of 51 patients (80%). Regional wall motion of the left ventricle was analysed in a semiquantitative manner on a 14-segment model. Viability was defined as improvement of one grade or more of at least two basally asynergic segments in the infarcted area.

RESULTS

Regional functional recovery was detected by low dose dobutamine in 38/51 patients (75%) and in 147/308 (48%) of basally asynergic segments, compared to 25/51 patients (49%; P < 0.001) and 78/308 segments (25%; P < 0.001) only identified by dipyridamole. Late spontaneous functional recovery was detected in 24/41 patients (59%) and in 78/254 basally asynergic segments (31%). The sensitivity of dobutamine and dipyridamole echocardiography for predicting spontaneous functional recovery was 72% and 51% respectively (P < 0.001), specificity 68% and 82% (P < 0.001), positive predictive value 50% and 56%, and negative predictive value 85% and 79%.

CONCLUSIONS

In comparison with dipyridamole in patients with thrombolysed myocardial infarction, dobutamine induces regional functional recovery. This suggests that dobutamine is more sensitive in showing the presence of viable myocardium within the infarct zone, though it has a lower specificity in predicting delayed spontaneous functional recovery of non-contractile but still viable areas.

Analysis of microvascular integrity, contractile reserve, and myocardial viability after acute myocardial infarction by dobutamine echocardiography and myocardial contrast echocardiography

The purpose of this study was to evaluate, in postinfarction dysfunctioning myocardium, the relative potential of myocardial contrast and low-dose dobutamine echocardiography in detecting myocardial viability, and the relation between microvascular integrity, contractile reserve, and functional recovery at follow-up. Twenty-four patients with recent myocardial infarction were studied before hospital discharge with low-dose dobutamine and myocardial contrast echocardiography. In the dysfunctioning infarct area, wall motion score index was calculated at baseline, during low-dose dobutamine, and at 3-month follow-up. Revascularization of the infarct-related artery was performed if clinically indicated. Eighteen patients (group A) had myocardial enhancement of the dysfunctioning infarct area at myocardial contrast echocardiography of >50%, whereas the remaining patients (group B) had an increase of < or = 50%. Wall motion score index was similar at baseline in groups A and B (2.6 +/- 0.4 and 2.8 +/- 0.2; p = NS), but it improved during low-dose dobutamine and at follow-up only in group A (1.9 +/- 0.9 and 1.9 +/- 0.7, respectively; p <0.001 vs baseline). In group B, wall motion score index was 2.7 +/- 0.4 with low-dose dobutamine and 2.8 +/- 0.2 at follow-up (p = NS vs rest). In identifying viable myocardial segments, myocardial contrast echo had 100% sensitivity and 46% specificity, whereas low-dose dobutamine echo had 71% sensitivity and 88% specificity. Thus, microvascular integrity after acute myocardial infarction is a fundamental prerequisite for ensuring myocardial contractile reserve and regional functional recovery. Myocardial contrast and low-dose dobutamine echocardiography have different, but complementary, diagnostic characteristics in detecting myocardial viability.

Nuclear and echocardiographic imaging for prediction of reversible left ventricular ischemic dysfunction after coronary revascularization: current status and future directions

Modern therapy of coronary artery disease (CAD) increasingly involves interventional strategies aimed at restoring blood flow to the ischemic myocardium. The emergence of coronary artery bypass surgery, percutaneous transluminal coronary angioplasty, and more recently thrombolytic therapy, has helped to change the natural course of ischemic heart disease and contribute to the overall reduction in the mortality from both acute myocardial infarction and chronic CAD. Presumably, the beneficial effects of revascularization result from improving blood supply to dysfunctional but viable regions with subsequent improvement in regional and global left ventricular function. Over the past decade, several approaches have been proposed to predict the reversibility of left ventricular dysfunction after coronary revascularization. For the most part, these methods rely on assessment of basic cellular mechanisms that are known to play a central role in the recovery of systolic function after coronary revascularization. These include sufficient resting perfusion to provide metabolic fuels and to allow wash-out of toxic metabolites, maintain membrane integrity (which includes the ability to generate transmembrane ionic gradients and to transport energy providing substrates), preserve metabolic machinery (to allow glucose, fatty acid and oxygen consumption), and recruitable inotropic reserve. Among the available modalities, thallium imaging, positron emission tomography, and low-dose dobutamine echocardiography are currently the most frequently used in the clinical setting. All allow prediction of reversible dysfunction with a high degree of sensitivity (greater than 80%). They seem to vary, however, in terms of specificity, thallium imaging showing the lowest (50-55%) and dobutamine echocardiography the highest (80-85%) specificity. New promising modalities, such as FDG or MIBI SPECT imaging, contrast echocardiography and integrated backscatter imaging are just ahead and will likely strengthen further our ability to identify jeopardized but viable myocardium.

[Stunned myocardium or hibernating myocardium? Apropos of a case]

The authors relate a case report of unstable angina pectoris accompanied by a well-documented stunned myocardium phenomenon. Stunned and hibernating myocardium resulting from an acute or chronic coronary ischaemia on the myocardium are notions which widely govern revascularisation indications, especially after a myocardial infarction. At present, their detection is based on isotopic methods and stress echocardiography.

Exercise beta-methyl iodophenyl acid (BMIPP) and resting thalium delayed single photon emission computed tomography (SPECT) in the assessment of ischemia and viability

To clarify the significance of exercise BMIPP (beta-methyl iodophenyl pentadecanoic acid) and resting T1 delayed single photon emission computed tomography (SPECT) in the assessment of ischemia and viability, we studied maximal exercise-loading BMIPP SPECT following rest-injected T1 3 h SPECT in 11 control subjects, 20 patients with effort angina and 38 patients with old myocardial infarction. The left ventricular wall on ECT was divided into 9 segments. BMIPP and T1 uptake were scored as 0 = normal, 1 = reduced, 2 = severely reduced, or 3 = absent. Discordance was defined as when segments with a reduced BMIPP uptake had a better resting T1 uptake. Significant coronary artery stenosis was defined as stenosis of 75% or greater on coronary arteriogram. Left ventricular wall motion was assessed as either normokinesis, hypokinesis, severe hypokinesis, akinesis or dyskinesis on left ventriculogram. When discordance was considered to be a marker of ischemia, the sensitivity and specificity in effort angina and control subjects were 95.2% and 84.6% for patients and 83.9% and 94.4% for diseased vessels, respectively. There were no differences between the sensitivity and specificity in left anterior descending artery (LAD), left circumflex artery (LCx) and right coronary artery (RCA) lesions (83.3%, 95.5% in LAD, 83.3%, 95.5% in LCx, 85.7%, 92.6% in RCA, respectively). All of the patients with old myocardial infarction had reduced exercise BMIPP uptake in infarcted regions. In old myocardial infarction, 35 patients had segments with discordant uptake. Discordance was observed in 75 (91.5%) of 82 segments with hypokinesis, and in 24 (92.3%) of 26 segments with severe hypokinesis. Even among the 36 segments with akinesis or dyskinesis, 25 (69.0%) had discordant uptake. When discordance in the infarcted region was considered to be a marker of viability, regions with severe asynergy showed a high possibility of viability. Thus, discordant uptake on exercise BMIPP and resting T1 delayed SPECT may be a useful marker of ischemia in effort angina and of viability in old myocardial infarction.

Left ventricular dysfunction due to the new ischemic outcomes: stunning and hibernation

Several potential manifestations and outcomes are associated with myocardial ischemia and reperfusion. When ischemia is severe and prolonged, irreversible damage occurs and there is no recovery of contractile function. When ischemia is less severe or shorter in duration, recovery of contraction may occur instantaneously or more commonly, after considerable delay, which is the condition recognized as "stunned myocardium." Stunning is defined as a transient left ventricular dysfunction that persists after reperfusion despite the absence of irreversible damage and restoration of normal or near-normal coronary flow. Oxidative stress and alteration of calcium homeostasis during reperfusion are the probable causes of stunning. Clinically, stunning may occur after acute infarction, successful thrombolysis, unstable angina, angioplasty, resolution of coronary spasm, open-heart surgery, or transplantation. It can be treated with interventions aimed at prevention or reversal. When ischemia is prolonged but less severe, myocytes may remain viable but exhibit depressed contraction. Under these conditions, reperfusion restores normal contractile performance. This type of ischemia, leading to a reversible, chronic left ventricular dysfunction, has been termed "hibernating myocardium." The intrinsic mechanisms of this condition are unknown. Clinically, it is very important to diagnose hibernation because reperfusion of the hibernating myocardium by angioplasty or heart surgery restores contraction, and this correlates with long-term survival. A number of methods are available to access the hibernating myocardium. These include cardiac imaging techniques that evaluate myocardial viability, such as positron emission tomography and thallium myocardial imaging, or methods that evaluate contractile reserve, such as low-dose dobutamine echocardiography. Interestingly, reperfusion of patients with end-stage ischemic cardiomyopathy and hibernating myocardium can be considered an alternative to transplantation.

Paramagnetic metalloporphyrins: infarct avid contrast agents for diagnosis of acute myocardial infarction by MRI

In previous experiments in tumors we demonstrated that metalloporphyrins are particularly avid for nonviable tumor components. This study was performed to find out whether these agents can be used as MRI contrast agents for the visualization of acute myocardial infarction (MI). A total of 44 rats, 6 normal controls and 38 with occlusive MI (2-24 h old), were used. Gadolinium mesoporphyrin (Gd-MP) or manganese tetraphenylporphyrin (Mn-TPP) was intravenously injected at doses of 0.1, 0.05, and 0.01 mmol/kg. Three to 24 h after injection, axial and coronal T1-weighted (TR/TE 300/15 ms) spin-echo MR images were obtained before and after killing the animals and correlated with triphenyl tetrazolium chloride (TTC) histochemical preparations. The Gd-MP content in infarcted and noninfarcted myocardium was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES). MRI without contrast media could not discern the MI. However, 3-24 h after injection of either Gd-MP or Mn-TPP, the infarcted area was positively stained on MR images. This area matched well with the negatively TTC-stained area on the heart slices (r = 0.97). The contrast ratios between the infarcted necrotic myocardium and the noninfarcted regions varied from 150 to 300% depending on the type of agents and doses used. Neither false-positive nor false-negative findings were encountered. The metalloporphyrin concentration was more than 10 times higher in the infarcted than in the noninfarcted heart. Metalloporphyrins appear to be promising MRI contrast agents for detection and quantification of necrosis in MI. These preclinical results may open new perspectives in cardiac imaging.

Impairment of regional fatty acid uptake in relation to wall motion and thallium-201 uptake in ischaemic but viable myocardium: assessment with iodine-123-labelled beta-methyl-branched fatty acid

In coronary artery disease, discrepancy in the uptake of thallium-201 and of methyl-branched fatty acid at rest has been described. The purpose of this study was to evaluate iodine-123 labelled beta-methyl-branched fatty acid (BMIPP) myocardial uptake and wall motion at rest in segments with stress-induced ischaemia identified by stress 201Tl tomography in patients with chronic coronary artery disease. 123I-BMIPP myocardial tomography was performed at rest and was compared with the findings of exercise-reinjection 201Tl tomography in 45 patients with chronic coronary artery disease. Regional wall motion was evaluated by contrast left ventriculography in 36 patients. Among 237 segments with reversible 201Tl defects, equally decreased uptake on both reinjection 201Tl and BMIPP images was observed in 93 (39%), more severely decreased uptake of BMIPP in 118 (50%) and more severely decreased uptake of reinjection 201Tl in 26 (11%). On the other hand, among 90 segments with non-reversible 201Tl defects, each pattern was observed in 71 (79%), 6 (7%) and 13 (14%) segments, respectively. When comparing the ischaemic segments with and without more severely reduced uptake of BMIPP than of reinjection 201Tl, wall motion was impaired to a greater extent in the segments with more severely reduced uptake of BMIPP than of reinjection 201Tl [severe hypo- or dyskinesis was present in 64 (70%) of 91 segments and in 24 (22%) of 110 segments, respectively, P<0.005]. In patients with chronic coronary artery disease, resting fatty acid uptake was frequently more reduced than reinjection 201Tl in the segments with stress-induced ischaemia, while in most of the fixed perfusion defects BMIPP and reinjection 201Tl uptake decreased concordantly. In ischaemic myocardium, wall motion was impaired to a greater extent in those segments which showed more severely reduced uptake of BMIPP than of reinjection 201Tl. In ischaemic but viable myocardium, discordant BMIPP uptake less than reinjection 201Tl uptake may indicate metabolic alterations and wall motion abnormality at rest independent of perfusion abnormalities. In conclusion, the combination of resting BMIPP and stress-reinjection 201Tl imaging may provide information on metabolic alterations and wall motion abnormality at rest independent of perfusion abnormalities.

Salutary effects of myocardial ischemia in coronary artery disease

Although myocardial ischemia in patients with coronary artery disease should be eliminated with medical and surgical treatment, it paradoxically contributes to the preservation of compromised myocardium through various mechanisms. First, ischemic vasodilation of coronary and collateral vessels resulting from the activation of the ATP-sensitive K+ channel maximizes a blood supply to the area having imbalance between myocardial oxygen supply and demand. Second, myocardial ischemia secondary to severe coronary stenosis develops functionally significant collateral circulation, which alleviates the deleterious sequelae of coronary obstructive disease. Finally, myocardial preconditioning with ischemia attenuates the subsequent ischemic insult. Particularly if combined with early reperfusion of the infarct-related coronary artery, the infarct size is decreased to one fourth of the permanent occlusion in dogs. A thorough understanding of the mechanisms of self-protecting benefits of myocardial ischemia would be useful in the care of patients with coronary artery disease.

Comparison of myocardial contrast echocardiography and low-dose dobutamine stress echocardiography in predicting recovery of left ventricular function after coronary revascularization in chronic ischemic heart disease

BACKGROUND

Dobutamine stress echocardiography (DSE) and myocardial contrast echocardiography (MCE) can predict recovery of left ventricular function after myocardial infarction. DSE also has been shown to predict left ventricular functional recovery after revascularization in chronic ischemic heart disease, whereas MCE has not been evaluated in such patients. This study was performed to compare DSE and MCE in the prediction of left ventricular functional recovery after revascularization in patients with chronic ischemic heart disease.

METHODS AND RESULTS

MCE and DSE were performed in 35 patients with chronic coronary artery disease and significant wall motion abnormalities (mean ejection fraction, 0.36 +/- 0.09). Regional wall motion was scored by use of a 16-segment model wherein 1 = normal or hyperkinetic, 2 = hypokinetic, 3 = akinetic, and 4 = dyskinetic. Each segment was evaluated for contractile reserve by DSE and perfusion by MCE. Revascularization (coronary artery bypass graft [n = 13] and percutaneous transluminal coronary angioplasty [n = 10]) was successful in 23 patients. Follow-up echocardiograms were done to assess wall motion 30 to 60 days later. In 238 segments with resting wall motion abnormalities, perfusion was more likely to present than contractile reserve (97% versus 91%, P < .02). Revascularization resulted in functional recovery in 77 of 95 hypokinetic segments (81%) but only 18 of 57 akinetic segments (32%, P < .0001). DSE and MCE were not significantly different in predicting functional recovery of hypokinetic segments. In akinetic segments, DSE and MCE had similar sensitivities (89% versus 94%, respectively) and negative predictive values (93% and 97%, respectively) in predicting functional recovery. However, DSE had a higher specificity (92% versus 67%, P < .02) and positive predictive value (85% versus 55%, P < .02) than MCE in predicting functional recovery.

CONCLUSIONS

Both contractile reserve by DSE and perfusion by MCE are predictive of functional recovery in hypokinetic segments after coronary revascularization in patients with chronic coronary revascularization in patients with chronic coronary artery disease. In akinetic segments, myocardial perfusion by MCE may exist in segments that do not recover contractile function after revascularization. Thus, contractile reserve during low-dose dobutamine infusion is a better predictor of functional recovery after revascularization in akinetic segments than perfusion.

Regional myocardial blood flow, glucose utilization and contractile function before and after revascularization and ultrastructural findings in patients with chronic coronary artery disease

In patients with chronic coronary artery disease, follow-up measurements of myocardial blood flow, metabolism and function were correlated with histology. In 41 patients with chronic coronary artery disease and a severely stenosed left anterior descending coronary artery, a positron emission tomographic (PET) flow/metabolism study and nuclear angiography were performed immediately before and 3 months after bypass surgery. Biopsies were taken from the left ventricular anterior wall at the time of surgery. Control biopsies were taken from donor hearts for cardiac transplantation and from hearts of patients with a defect of the atrial septum. A significant improvement of flow (P<0.01) and regional contractile function (P<0.01) was observed in the mismatch group. Glucose utilization was significantly lower (P<0.001) as compared to preoperative values. The group with preserved flow and the PET match group revealed no significant changes in flow, metabolism or function. Control biopsies revealed significantly less myolytic cells as compared to biopsies taken from both match and mismatch groups (P<0.01) and less fibrosis as compared to biopsies taken from the match group (P<0.01). Postoperatively, linear relationships were found between flow and both % fibrosis (r = 0.71, P<0.001) and regional anterior ejection fraction (r = 0.7, P<0.001). Only mismatch areas revealed significant recovery of both flow and function after revascularization with a disappearance of enhanced glucose uptake. The better linear correlation between flow and % fibrosis after surgery as compared to preoperatively was probably due to improvement of flow values in the mismatch group.

Preoperative selection of patients with severely impaired left ventricular function for coronary revascularization. Role of low-dose dobutamine echocardiography and exercise-redistribution-reinjection thallium SPECT

BACKGROUND

Both thallium imaging and low-dose dobutamine echocardiography have been proposed to predict the reversibility of left ventricular (LV) dysfunction in patients with coronary disease. The present study was designed to evaluate whether the use of these techniques during the preoperative assessment of coronary patients with depressed LV function can improve our ability to identify those likely to have improved LV function after surgery.

METHODS AND RESULTS

Forty consecutive patients (age, 60 +/- 10 years) with coronary disease and an ejection fraction < or = 35% underwent dobutamine echocardiography (10 micrograms/kg per minute) and exercise-redistribution-reinjection thallium single photon emission computed tomography (SPECT) before coronary revascularization by bypass surgery (n = 33) or angioplasty (n = 7). Recovery of LV function was evaluated by echocardiography 5.3 +/- 2.4 months after revascularization. According to the changes in end-systolic volume and ejection fraction after revascularization, the patients were categorized into groups with (n = 19) and without (n = 21) postoperative functional improvement, defined as a > 5% increase in ejection fraction and > 10 mL decrease in end-systolic volume. Before revascularization, patients with improved postoperative function had smaller end-diastolic volume and less wall motion abnormalities than those with persistent dysfunction. They also showed greater improvement of wall motion score with dobutamine (6.1 +/- 2.4 versus 1.8 +/- 4.2 grades, P < .001) and smaller thallium defect score after exercise (38 +/- 12 versus 47 +/- 14 grades, P = .04). Discriminant analysis selected the improvement in wall motion score with dobutamine and baseline end-diastolic volume as independent predictors of postoperative recovery. Consideration of both parameters allowed prediction of functional outcome in 84% of the patients with and 81% of those without postoperative improvement.

CONCLUSIONS

Among the parameters commonly available before surgery in coronary patients with depressed LV function, the maintenance of significant inotropic reserve, the severity of LV remodeling, and the magnitude of the perfusion defect after exercise can predict the reversal of LV dysfunction after revascularization.

Dobutamine echocardiography in predicting improvement in global left ventricular systolic function after coronary bypass or angioplasty in patients with healed myocardial infarcts

The aim of this study was to determine whether low-dose dobutamine echocardiography (DE) could predict quantitative improvement in global left ventricular (LV) systolic function after coronary revascularization. Low-dose DE was performed in 71 consecutive patients with coronary artery disease and LV dysfunction. Successful coronary bypass surgery or angioplasty was performed in 44 patients, 37 of whom had a resting echocardiogram 1 to 3 months afterward. Group A consisted of 20 patients with contractile reserve during DE, and group B consisted of 17 patients without contractile reserve. As expected, regional wall motion score index (mean +/- SD) improved in group A (1.62 +/- 0.39 to 1.38 +/- 0.31, p < 0.01) but not group B (1.56 +/- 0.42 to 1.57 +/- 0.41, p = NS). In addition, LV ejection fraction (LVEF) improved after bypass surgery or angioplasty in group A (38 +/- 5% to 42 +/- 5%, p < 0.01), but not in group B (38 +/- 7% to 39 +/- 8%, p = NS). In group A, a significant linear correlation was observed between the number of segments with contractile reserve and the improvement in LVEF (r = 0.91, p < 0.0001). A good correlation also existed between the improvement in regional wall motion score index during dobutamine infusion and the improvement in LVEF after bypass surgery or angioplasty (r = 0.90, p < 0.0001). In conclusion, low-dose DE can be used to predict quantitative improvement in global LV systolic function after coronary bypass or angioplasty.

Detection of viability after myocardial infarction: available techniques and clinical relevance--a review

The differentiation of viable from nonviable myocardium in patients with myocardial infarction (MI) and left ventricular (LV) dysfunction is of important clinical relevance. It is now known that impaired LV function after infarction not always represents an irreversible process. LV ejection fraction is significantly reduced in many patients after infarction and, although abnormally contracting myocardial segments may result from irreversible scarring, numerous studies have shown that many asynergic zones have sustained metabolic activity. An accurate detection of myocardial viability aids in clinical decision making to select the appropriate therapy for patients with MI. Recently, cardiac imaging techniques that evaluate myocardial viability on the basis of myocardial perfusion, cell membrane integrity, metabolic activity and residual coronary reserve, have been developed with clinical success. These methods provide greater precision in the assessment of viable myocardium than can be achieved by analysis or coronary anatomy, regional function or the presence or absence of electrocardiographic Q waves, criteria that were used in the past. The clinical challenge is to predict which myocardial regions are viable and will improve systolic function after revascularization, thereby enhancing global LV function. In this review, the currently available imaging techniques for assessment of myocardial viability are discussed.

Changes in wall motion in patients treated for unstable angina. A suggestion of the stunned and hibernating myocardium in humans. UNASEM Collaborative Study Group. Unstable Angina Study Using Eminase

BACKGROUND

A double-blind, placebo-controlled study using anistreplase was performed in 159 patients with unstable angina. All patients had a history of unstable angina combined with typical ECG changes and without evidence of a previous, recent, or ongoing myocardial infarction. The purpose of the present study was to analyze the relationship between the patency of the culprit artery and the behavior of the ischemia-related regional left ventricular (LV) wall motion.

METHODS AND RESULTS

On entry to the study, all patients received conventional drug therapy: i.v. nitroglycerin therapy, an oral beta-blocking agent, and a calcium antagonist. Baseline angiography was carried out within 3 h after randomization, a mean of 4.2 +/- 3.0 h (range, 1 to 17 h) after the last attack of chest pain. Treatment with trial medication was withheld in 33 cases. Sixty-five patients with coronary artery disease received anistreplase (30 U/5 min)/heparin and 61 patients heparin-only therapy. Angiography was repeated 20.6 +/- 4.6 h (mean +/- SD; range, 12 to 39 h) after the baseline angiographic study. To assess changes in regional myocardial wall motion, the LV wall was divided into seven segments. The ischemia-related coronary artery stenosis was calculated quantitatively and related to the quantitatively assessed mean regional left ventricular ejection fraction (RLVEF) of the ischemia-related segments. In 118 of 126 patients who received trial medication, we found that anistreplase/heparin therapy leads to a significantly (p < 0.01) greater reduction in coronary artery diameter stenosis than heparin-only therapy (n = 63, mean +/- SD, 11 +/- 22, vs n = 55, mean +/- SD, 3 +/- 11%). Anistreplase/heparin therapy was related to a larger significant improvement of the ischemia-related RLVEF than heparin-only therapy, although the latter association was not statistically significant (n = 63, mean +/- SD, 7 +/- 15, vs n = 55, mean +/- SD, 5 +/- 14%). The effects of change of coronary artery stenosis on regional LV wall motion were also determined. A paradoxical finding was that a persistently occluded vessel or a vessel showing an increase in coronary artery stenosis was associated with a greater improvement of the ischemia-related RLVEF than a reopened vessel or a vessel with a reduction in coronary artery stenosis (n = 15, mean +/- SD, 7 +/- 11, vs n = 41, mean +/- SD, 8 +/- 13, vs n = 15, mean +/- SD, 1 +/- 12, vs n = 47, mean +/- SD, 5 +/- 16%, NS). One day after the last attack of chest pain, the regional LV wall motion was still abnormal in about 20% of patients.

CONCLUSION

In these patients with unstable angina, the LV wall motion improved both in the treated and the control group at follow-up angiography 1 day later. Improved coronary arterial anatomy was associated with a lesser improvement of the LV contractile function than when worsening of the coronary angiographic appearance occurred. There is no rational explanation of these results. This is a beginning of an effort to elucidate the clinical significance of the stunned and hibernating myocardium in humans.

Dobutamine stress echocardiography predicts early wall motion improvement after elective percutaneous transluminal coronary angioplasty

In 24 patients with chronic coronary artery disease, dobutamine stress echocardiography (DSE) was performed within 2 days before and after successful elective percutaneous transluminal coronary angioplasty (PTCA) in a blinded fashion. Patients with ischemic response on DSE before PTCA had significant improvement in the global peak-dose DSE score index after PTCA (1.62 +/- 0.35 to 1.40 +/- 0.29, p < 0.001), whereas patients without ischemic response had no improvement. The positive and negative predictive values of pre-PTCA DSE on early myocardial ischemia relief after angioplasty were 93% and 80%, respectively. In patients showing contractility recruitment during low-dose dobutamine infusion in the DSE before PTCA, there was significant improvement in the global resting wall motion score index in the DSE after PTCA (1.48 +/- 0.43 to 1.34 +/- 0.33, p = 0.004), while patients without contractility recruitment showed no improvement. Again, the positive and negative predictive values of pre-PTCA DSE on early hibernation recovery following angioplasty were 80% and 89%, respectively. In conclusion, DSE in patients with chronic, stable coronary artery disease accurately predicts wall motion improvement after successful angioplasty, and the expected improvement is safely demonstrated early after the procedure.

Incomplete, delayed functional recovery late after reperfusion following acute myocardial infarction: "maimed myocardium"

The objective of the current editorial is to introduce a new concept ("maimed myocardium") that we believe describes more accurately the incomplete, delayed recovery of LV function that may occur late after reperfusion after AMI. It has been demonstrated previously that myocardium remains viable for a prolonged period in many patients with nonsustained coronary occlusion, despite the occurrence of myocardial necrosis; late reperfusion may result in myocardial salvage in reversibly ischemic (stunned) segments (complete recovery) and in intensely injured (maimed) segments that display partial return of LV function over time (incomplete recovery). Clinically, the basis for maimed myocardium is the observation that delayed, LV functional recovery may occur in partially infarcted segments where there has been an antecedent ischemic insult of sufficient duration to result in some degree of myocardial necrosis. Certain acute coronary syndromes characterized by nonsustained coronary occlusion followed by spontaneous reperfusion (e.g., non-Q-wave AMI) or drug-induced reperfusion induced by the exogenous administration of thrombolytic therapy are associated with incomplete, delayed recovery of LV function as detected clinically by partial improvement in serial radionuclide-ejection measurement, enhanced metabolic integrity of cardiac tissue by F-18 deoxyglucose myocardial imaging, and scintigraphic findings of reverse thallium redistribution--findings that support the presence of partially viable myocardium that has been incompletely salvaged during reperfusion late after AMI. Experimentally, delayed LV functional recovery has been reported in animal models in which prolonged coronary occlusion (hours to days) followed by reperfusion is associated with late recovery of regional LV function in myocardial segments subtending border (stunned) zones and central infarct (maimed) zones. In studies in animals and human beings, postextrasystolic potentiation and pharmacologic inotropic interventions may augment maimed and stunned segments, although the magnitude of regional contractile reserve that can be unmasked with these interventions is quantitatively less in the maimed than in stunned segments. In summary, the propensity of intensely injured or partially infarcted LV segments to display intermediate functional recovery followed by reperfusion late after coronary occlusion suggests that even severely depressed but residually viable cardiac muscle can be salvaged incompletely over time.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of hibernating myocardium by dobutamine stress echocardiography: comparison with thallium-201 reinjection imaging

The aim of this study was to determine the diagnostic value of dobutamine stress echocardiography (DSE) in the identification of hibernating myocardium and to compare its predictive accuracy with that of thallium-201 reinjection (RI) imaging. The subjects were 26 patients with wall motion abnormalities related to stenosed coronary arteries. DSE predicted postrevascularization improvement in 31 of 33 segments that were considered to be hibernating and identified 8 of 10 nonhibernating segments. In contrast, thallium-201 scintigraphy predicted all 33 hibernating segments when a post-RI myocardial thallium uptake in ischemic areas of > or = 50% of the maximum count in normal segments was used as a positive marker of myocardial viability. However, thallium studies predicted only 30 of 33 hibernating segments when thallium redistribution (RD) was used as a marker of viability in delayed or RI images. Among the 10 nonhibernating segments, an uptake of < 50% was observed in 4 segments and negative thallium-201 RD was observed in 5 segments. The sensitivity, specificity, and predictive values (PV) of DSE were 94%, 80%, positive PV 94%, and negative PV 80%, respectively. In contrast, the sensitivity, specificity, and PV of thallium-201 RI imaging were 100%, 40%, 85%, and 100% with uptake > or = 50% and 91%, 50% 86%, and 63% with RD, respectively. These results suggest that DSE may be useful for identifying hibernating myocardium and could therefore be helpful in selecting candidates for coronary revascularization.

Incremental doses of dobutamine induce a biphasic response in dysfunctional left ventricular regions subtending coronary stenoses

BACKGROUND

Dobutamine stress echocardiography has been proposed as a diagnostic tool to identify viable myocardium. How regional wall thickening responds to dobutamine in the ischemic or short-term hibernating myocardium has not been adequately defined. We hypothesized that regional wall thickening would improve initially and subsequently deteriorate with incremental doses of dobutamine in viable myocardial regions supplied by a stenotic coronary artery. This study was undertaken to determine whether this biphasic pattern of regional function characterizes the response of ischemic or hibernating myocardium to dobutamine and to explore the factors and mechanisms that determine this response.

METHODS AND RESULTS

Twenty-six pigs in four groups were studied: a control group (n = 5) to assess the response of myocardium perfused by nonstenotic coronary artery to incremental doses of dobutamine, and three experimental groups with a left anterior descending coronary artery stenosis producing acute myocardial ischemia (n = 7), short-term myocardial hibernation for 90 minutes (n = 7), and short-term hibernation for 24 hours (n = 7) to determine the functional and metabolic response to dobutamine under these conditions. Regional coronary flow was reduced to 40% to 60% of baseline, with significant reductions of regional wall thickening as measured by two-dimensional echocardiography and sonomicrometers. An incremental dobutamine infusion from 2.5 to 25 micrograms.kg-1.min-1 increased wall thickening and coronary flow without lactate production in the control group. In the other three groups, during the incremental dobutamine infusion, regional wall thickening improved initially, from 11.4 +/- 7.5% to 19.8 +/- 11.4%, P < .01, at dobutamine doses of 2.5 to 10 (4.5 +/- 2.2) micrograms.min-1.kg-1 but deteriorated subsequently to 5.0 +/- 5.8% at the maximal dose of dobutamine of 12.6 +/- 4.1 micrograms.min-1.kg-1. The initial improvement of regional wall thickening was associated with a small increase in regional coronary flow (from 0.53 +/- 0.18 to 0.68 +/- 0.25 mL.min-1.g-1 myocardium, P < .05) and with regional lactate production. High doses of dobutamine did not further increase regional coronary flow but markedly increased lactate production and induced regional myocardial acidosis (pH 7.26 +/- 0.07). The biphasic pattern of response to dobutamine was observed in each of the three experimental groups. Both peak improvement and peak deterioration occurred earlier and at lower dobutamine dose levels in the group with acute ischemia compared with the group with short-term hibernation for 24 hours (P < .05).

CONCLUSIONS

A biphasic response of wall thickening to incremental dobutamine with initial improvement and subsequent deterioration is characteristic of ischemic or short-term hibernating myocardium. The initial low-dose dobutamine infusion improved wall thickening in the ischemic or hibernating myocardial region to a modest level. This initial modest improvement was transient and at the expense of metabolic deterioration of myocardial ischemia, so that at higher doses during prolonged dobutamine infusion, wall thickening deteriorated, lactate accumulated, and myocardial acidosis developed.

Is planar thallium-201/fluorine-18 fluorodeoxyglucose imaging a reasonable clinical alternative to positron emission tomographic myocardial viability scanning?

This comparative study was performed to determine whether a conventional planar gamma camera optimised for 511-keV imaging can reliably assess myocardial viability using the fluorine-18 fluorodeoxyglucose (FDG) metabolic tracer previously developed for positron emission tomography (PET). Twenty-seven patients with severe ischaemic cardiomyopathy (mean left ventricular ejection fraction: 20% +/- 9%) having clinically indicated nitrogen-13 ammonia/FDG PET myocardial viability studies consented to resting, four-view, planar myocardial thallium-201 perfusion and FDG metabolism imaging. The resultant PET and planar perfusion/metabolism images (PPI) were independently assessed for FDG defect size and perfusion/metabolism mismatch, using a four-point scale, in each of four vascular regions: apex, circumflex, left anterior and posterior descending coronary artery territories. Of 108 regions, 106 were evaluable (two not assessed by PET). There was complete agreement in 70% of coronary vascular territories, giving an unweighted kappa score of 0.56. Moreover, in 94% of segments agreement was within one grade. Interestingly, six of the seven differences of more than one grade occurred in the circumflex coronary territory, which was also the only region for which planar positron imaging underestimated FDG defect size. Three of four moderate areas of perfusion/metabolism mismatch seen with PET were also seen on PPI. PPI showed three small regions of mismatch not seen on PET, whilst the reverse occurred with one other small region of mismatch. Thus, for this PET protocol, PPI provides very similar information on the extent of regional FDG uptake and occurrence of mismatch.(ABSTRACT TRUNCATED AT 250 WORDS)

Ubiquity of myocardial stunning

The prolonged depression of myocardial function following episodes of myocardial ischemia now known as myocardial stunning, appears ubiquitous in both the experimental and clinical settings. With recent therapies designed to ameliorate ischemic myocardium, e.g., coronary artery bypass, coronary thrombolysis, coronary angioplasty, the inexorable progression from ischemia to necrosis has been averted more successfully and frequently, which permits appearance of myocardial stunning to become clearer. Myocardial stunning occurs in the presence of a multitude of inciting stimuli to myocardial ischemia, including a fixed stenosis, relief from stenosis or even in the presence of reduced coronary reserve, without a coronary stenosis. It will be potentially most interesting to determine if myocardial stunning also belies the hibernating myocardium and is, in fact, its actual mechanism.

Nitrate-augmented myocardial imaging for assessment of myocardial viability

201Tl myocardial perfusion imaging is presently done by several possible strategies. Stress/delayed redistribution, stress/redistribution/reinjection, and rest/redistribution imaging can be useful in the clinical assessment of myocardial viability. Unfortunately, the extent of myocardial viability may still be underestimated even by 201Tl reinjection imaging, compared with 18F-fluorodeoxyglucose positron emission tomography. 99mTc-labeled sestamibi imaging provides results similar to those of 201Tl imaging in the detection of coronary artery disease, but several previous studies suggest that stress/rest 99mTc-labeled sestamibi imaging significantly underestimates myocardial viability. Recently it has been reported that the administration of nitrates, before 201Tl reinjection, improves detection of defect reversibility. Several studies also suggested that administration of nitrates before the injection of 99mTc-labeled sestamibi significantly improved detection of reversibility with this agent, whereas additional studies showed further that this combination improves the predictive accuracy for recovery of left ventricular function and perfusion after coronary revascularization, compared with a standard rest 99mTc-labeled sestamibi study. Nitrate administration before the injection of 201Tl and 99mTc-labeled sestamibi may thus be a potentially attractive alternative for the evaluation of myocardial viability. Although the available results are encouraging, further studies are needed to evaluate the clinical value of 201Tl and 99mTc-labeled sestamibi imaging, in combination with nitrates, for predicting recovery of left ventricular dysfunction.

Intraischemic preconditioning. Increased tolerance to sustained low-flow ischemia by a brief episode of no-flow ischemia without intermittent reperfusion

Ischemic preconditioning (IP) and myocardial hibernation (MH) are both adaptive phenomena during acute myocardial ischemia, characterized by preserved myocardial viability and attenuated alterations of energy metabolism. Recent data from isolated buffer-perfused rabbit hearts pointed to a further link between IP and MH, in that an initial stimulus of no-flow ischemia was required to permit the development of MH during subsequent sustained low-flow ischemia. In the present study, we therefore investigated in the in situ pig heart whether a brief episode of no-flow ischemia enhances the myocardial tolerance to subsequent sustained low-flow ischemia. By blocking ATP-dependent potassium channels, we attempted to further determine whether such increased tolerance to ischemia is related to IP or MH, since blockade of ATP-dependent potassium channels abolishes the cardioprotection achieved by IP but not by MH. In 8 enflurane-anesthetized pigs serving as controls (group 1), the inflow into the cannulated left anterior descending coronary artery was reduced to achieve a 90% reduction in the anterior myocardial work index (sonomicrometry) for 90 minutes. In 15 pigs (group 2), a 10-minute no-flow ischemic episode preceded 80 minutes of sustained ischemia at a blood flow reduction identical to that in pigs of group 1. In 8 additional pigs (group 3), glibenclamide was administered before the 10-minute no-flow ischemic episode. In all pigs after 120 minutes of reperfusion, infarct size (IS, percentage of area at risk) was determined by triphenyltetrazolium chloride staining. In group 2, IS was reduced (6.8 +/- 6.0% [mean +/- SD], P < .05) when compared with groups 1 (13.2 +/- 9.8%) and 3 (16.7 +/- 8.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

Dobutamine echocardiography predicts improvement of hypoperfused dysfunctional myocardium after revascularization in patients with coronary artery disease

BACKGROUND

In patients with coronary artery disease, dysfunctional hypoperfused myocardium at rest may represent either necrotic or viable hibernating myocardium. The accuracy of inotropic stimulation in identifying hypoperfused, reversibly dysfunctional myocardium has not been extensively investigated.

METHODS AND RESULTS

Eighteen patients with stable chronic coronary artery disease underwent, while off drugs, quantitative 201Tl single-photon emission computed tomography after rest injection (2 to 3 mCi), two-dimensional echocardiography at rest and during dobutamine (5 to 10 micrograms/kg per minute i.v.), and radionuclide angiography. Single-photon emission computed tomography and echocardiography at rest were repeated 34 +/- 10 days after coronary revascularization, and radionuclide angiography was repeated 45 +/- 13 days after revascularization. Resting hypoperfusion was defined as 201Tl uptake < 80% of maximal activity. Systolic function was scored from 1 (normal) to 4 (dyskinesia), and functional improvement was defined as a score change > 1 grade. Of 79 dysfunctional hypoperfused segments, 48 (61%) improved function after revascularization. In 42 (88%) of these latter segments, function had improved during dobutamine. Conversely, systolic function after revascularization did not improve in 31 segments, and in 27 (87%), it had not improved during dobutamine. Functional improvement after revascularization was observed in 42 (91%) of 46 segments manifesting an improvement during dobutamine as opposed to 6 (18%) of 33 segments that did not improve during dobutamine. Resting 201Tl uptake (% of maximal activity) before revascularization (65 +/- 9%) significantly increased at follow-up in segments where function improved (70 +/- 12%, P < .005), whereas it did not change significantly in segments with unchanged systolic function after revascularization (from 57 +/- 13% to 60 +/- 17%, P = NS). In 10 patients with prerevascularization ejection fraction < 45%, left ventricular ejection fraction significantly increased from 36 +/- 7% before revascularization to 42 +/- 7% at follow-up (P < .05).

CONCLUSIONS

Inotropic stimulation using dobutamine echocardiography identifies hypoperfused reversibly dysfunctional myocardium. Functional improvement during dobutamine is highly predictive of improvement after revascularization.

Effects of nisoldipine in silent myocardial ischemia after healing of acute myocardial infarction

Silent myocardial ischemia occurring after acute myocardial infarction is classified as Cohn type II and has a frequency of 20-30% in all patients with acute myocardial infarction. Follow-up data of patients with either silent or anginal ischemia show a poor prognosis. Thus, all ischemic episodes occurring after myocardial infarction should be treated aggressively. Many multicenter studies have evaluated whether drug treatment can improve prognosis or protect from a nonfatal second attack. Calcium antagonists, especially those that increase heart rate, have not been considered as drugs of choice for this purpose, despite the many beneficial effects shown on myocardial tissue in experimental studies. In the study reported here, the effect of nisoldipine on postinfarction silent myocardial ischemia was evaluated by ambulatory left ventricular function monitoring. Ten patients were selected for study who showed silent myocardial ischemia after their first acute infarction. Blood pressure fell significantly (p < 0.05) after 4 weeks of treatment with nisoldipine (5-10 mg/day), but heart rate showed no change at rest. Exercise time improved (p < 0.05), with increased peak double products. During exercise, there was no significant change in end-diastolic volume but there was a marked improvement in end-systolic volume, and at the submaximal point the ejection fraction was significantly (p < 0.05) increased. Ejection fraction at rest also improved. The deterioration in ejection fraction due to dipyridamole was ameliorated by nisoldipine. Ejection fraction and blood pressure improved during the calculation test, and work performance also improved.(ABSTRACT TRUNCATED AT 250 WORDS)

From coronary artery disease to heart failure: role of the hibernating myocardium

Hibernating myocardium is defined as persistently impaired myocardial and left ventricular (LV) function at rest resulting from reduced myocardial blood flow. It may occur in unstable angina and chronic stable angina, acute myocardial infarction, and LV dysfunction and congestive heart failure. Recovery of the hibernating myocardium has clearly been shown to occur with the establishment of successful revascularization either by coronary bypass surgery or by percutaneous transluminal coronary angioplasty. It may be possible to show recovery of the viable myocardium by reducing myocardial oxygen demand and/or by increasing coronary blood flow with pharmaceutical agents.

Calcium antagonists and left ventricular dysfunction

Calcium antagonists are used in the management of a variety of cardiovascular disorders. Ischemia leads to left ventricular dysfunction, which is the clinical entity on which the calcium antagonists are expected to have their effect as a result of their anti-ischemic action. This article reviews the efficacy of calcium antagonists in several different settings of left ventricular dysfunction due to ischemia and reperfusion.

Angiotensin-converting enzyme inhibitors and calcium antagonists after acute myocardial infarction

This article examines trials of the use of two types of drugs in the treatment of myocardial infarction: angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists. ACE inhibitors are an established treatment for hypertension and heart failure and have been shown to reduce mortality from heart failure and after myocardial infarction. Six large studies have been carried out. In 1 in which an ACE inhibitor was given 3-16 days after infarction in patients with an ejection fraction < 40%, mortality was reduced by 17%. In a second study of patients who had evidence of heart failure and were followed up for 15 months, treatment with ACE inhibitors was given 3-10 days after myocardial infarction and mortality was reduced by 27%. Two other studies of 11,000 and 50,000 unselected patients with myocardial infarction showed only marginal clinical benefit. Calcium antagonists were introduced to treat hypertension and angina pectoris. In trials with patients with heart failure, the results have not been encouraging, and in some patients these agents seem to be harmful. Recently, long-acting calcium antagonists have become available, and these may avoid the deleterious effects of short-acting drugs. Since calcium antagonists act on smooth muscle, they may increase myocardial blood flow to improve function after "stunning" or "hibernation." This idea was investigated with a long-acting dihydroyridine calcium, antagonist in a randomized double-blind, placebo-controlled study (Doppler Flow, Echocardiography, and Functional Improvement Assessment of Nisoldipine Therapy-I--DEFIANT I), and a further study is being carried out. At present the widespread use of calcium antagonists after infarction is not recommended.

Clinical and therapeutic implications of chronic left ventricular dysfunction in coronary artery disease

In patients with myocardial ischemia, left ventricular dysfunction (LV) may arise from irreversible damage (cell death), myocardial stunning (postischemic dysfunction), or myocardial hibernation (persistent myocardial dysfunction at rest due to underperfusion). Chronic LV dysfunction usually refers to hibernating myocardium. However, stunning might also become chronic, producing persistent myocardial dysfunction. Clinical studies have demonstrated that many patients with coronary artery disease have subsequent recurring ischemic (symptomatic or silent) episodes at short intervals in the same area and that each episode may be followed by myocardial stunning. In these patients the myocardium may not recover fully between episodes and function may remain reversibly depressed for long periods or may even be clinically depressed. The recognition of both stunning and hibernation is very important clinically and therapeutically, since chronic LV dysfunction may have a negative effect on mortality and morbidity in patients with coronary artery disease. Moreover, both clinical states are potentially correctable. Pharmacologic intervention with beta blockers, angiotensin-converting enzyme inhibitors, or calcium antagonists might improve or protect hibernating myocardium. The acute hemodynamic effects of the dihydropyridine calcium antagonist nisoldipine have been investigated in patients with chronic LV dysfunction probably arising from hibernating myocardium. Nisoldipine was found to improve both left ventricular systolic and diastolic function without activating the adrenergic system. The improvement in systolic function may be due to a redistribution of coronary blood flow and to a slight reduction in afterload induced by nisoldipine. On the other hand, nisoldipine may improve diastolic function in these patients by an intrinsic mechanism, Reducing intracellular calcium overload or balancing intracellular calcium homeostasis in the ischemic areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Dobutamine-induced ST-segment elevation in patients with healed myocardial infarction. A marker of myocardial viability

The purpose of this study was to determine the significance of transient ST-segment elevation during dobutamine infusions in patients with healed Q wave myocardial infarction. Twenty-seven patients with previous Q wave myocardial infarction were studied prospectively with dobutamine-thallium-201 single-photon emission computed tomography. The presence of ST-segment elevation in leads with Q waves was related to thallium reversibility at 4-hour redistribution imaging or after reinjection, to residual flow, as well as to wall motion abnormalities in the infarcted zone. ST-segment elevation in infarct-related leads was observed in 15 patients; 11 (73%) showed viability by thallium-201 in the infarcted zone. In patients without ST-segment elevation, viability was shown less frequently (33%, P < .05). Hypokinesis in infarcted segments was present in 60% of patients with ST-segment elevation and in 25% of patients without ST-segment elevation (.05 < P < .1). Finally, infarct-related artery was patent and/or collaterals were present in 10 patients with ST-segment elevation (67%) and in 4 patients without (33%, .05 < P < .1). In conclusion, ST-segment elevation during dobutamine infusion is a marker of residual viability in infarcted segments.

Mechanism of impaired myocardial function during progressive coronary stenosis in conscious pigs. Hibernation versus stunning?

The major goal of this study was to determine whether impaired myocardial contractile function during the development of progressive coronary artery stenosis induced by ameroid constriction in conscious pigs reflected myocardial "hibernation" or "stunning." Minipigs were instrumented with a coronary ameroid constrictor and hydraulic occluder, regional wall thickness crystals, a left ventricular (LV) pressure gauge, and aortic and left atrial catheters. In the seven pigs in which it was measured, systolic wall thickening (WT) distal to the ameroid fell by a maximum of 56 +/- 6% at 20 +/- 3 days after ameroid implantation and then began to recover. At 1 day after ameroid implantation, brief complete coronary artery occlusion (CAO) resulted in wall thinning distal to the ameroid (-113 +/- 4%) and transmural decreases in myocardial blood flow in endocardial (from 0.82 +/- 0.08 to 0.02 +/- 0.01 mL/min per gram) and epicardial (from 0.73 +/- 0.13 to 0.03 +/- 0.02 mL/min per gram) layers. At 20 +/- 3 days, baseline myocardial blood flow was not altered either in endocardial (0.92 +/- 0.10 mL/min per gram) or epicardial (0.85 +/- 0.12 mL/min per gram) layers, whereas brief complete coronary artery occlusion still reduced WT (-83 +/- 12%) and myocardial blood flow in endocardial (to 0.21 +/- 0.03 mL/min per gram) and epicardial (to 0.43 +/- 0.12 mL/min per gram) layers, indicating that the coronary artery was not totally occluded. Pathology in four pigs demonstrated no gross necrotic myocardium shortly after this time point. Transient reductions in WT distal to the ameroid were observed during progressive coronary artery stenosis in response to spontaneous increases in activity. Beat-by-beat analysis of these episodes revealed that acute reductions in WT followed increases in LV dP/dt and heart rate and exhibited delayed recovery. These data suggest that the reduced function during ameroid-induced coronary stenosis reflected cumulative myocardial stunning rather than a primary deficit in coronary blood flow or "hibernating myocardium."

Relation between thallium uptake and contractile response to dobutamine. Implications regarding myocardial viability in patients with chronic coronary artery disease and left ventricular dysfunction

BACKGROUND

Both thallium scintigraphy and dobutamine echocardiography have been used to assess myocardial viability. However, thallium uptake and the inotropic response to dobutamine are expressions of different cellular phenomena. The present study was undertaken to investigate the relation between the two methods in patients with chronic coronary artery disease and left ventricular dysfunction to derive insights into the mechanisms related to myocyte viability.

METHODS AND RESULTS

Thirty patients (28 men and 2 women; age, 59 +/- 10 years) with chronic coronary artery disease and impaired left ventricular systolic function at rest (mean ejection fraction, 32 +/- 9%) were included in the study. Patients underwent transesophageal echocardiography during incremental doses of dobutamine from 2.5 to a maximum of 40 micrograms.kg-1.min-1 and single photon emission computed tomographic thallium scintigraphy using a stress-redistribution-reinjection protocol. The left ventricle was divided into 16 segments for analysis of echocardiographic and thallium images. Segmental myocardial contractile function was graded as normal, hypokinesis, akinesis, or dyskinesis at each incremental dose of dobutamine. Thallium uptake in each myocardial segment was graded on a 5-point scale from 0 (absent) to 2 (normal) for each of the stress, redistribution, and reinjection images. A segment was considered viable if the assigned thallium score was 1 or higher (normal uptake or only mild to moderate defect) in any of the stress, redistribution, or reinjection images. Among 472 myocardial segments available for analysis, 311 had resting wall motion abnormalities, of which 56% (173/311) showed contractile improvement with dobutamine (usually first observed at < or = 10 micrograms.kg-1.min-1) and 84% (262/311) were considered viable by thallium scintigraphy (P < .0001). Of the 262 segments considered viable by thallium, 167 (64%) had a contractile improvement with dobutamine; in contrast, only 6 of the 49 segments (12%) considered nonviable by thallium had a positive dobutamine response (P < .0001). Furthermore, a positive inotropic response to dobutamine was significantly related to the magnitude of thallium uptake: the proportion of segments with a positive dobutamine response rose with increasing magnitude of thallium uptake (P < .001). The disagreement between the two tests was related primarily to segments considered viable by thallium that did not show contractile improvement with dobutamine.

CONCLUSIONS

These findings demonstrate the existence of a relation between thallium uptake and the inotropic response to dobutamine in patients with chronic coronary artery disease and left ventricular dysfunction. However, the proportion of segments showing a positive response to dobutamine is significantly lower than those with thallium uptake, suggesting that the cellular mechanisms responsible for a positive inotropic response to adrenergic stimulation require a higher degree of myocyte functional integrity than those responsible for thallium uptake.

Dobutamine echocardiography in myocardial hibernation. Optimal dose and accuracy in predicting recovery of ventricular function after coronary angioplasty

BACKGROUND

Myocardial hibernation is a condition of chronic left ventricular dysfunction associated with severe coronary artery disease whereby significant recovery of function occurs after revascularization. Identification of hibernating myocardium has important prognostic and therapeutic implications. The presence of contractile reserve as assessed by dobutamine echocardiography may be promising in the detection of hibernation. We designed a prospective study to evaluate the accuracy and optimal dose of dobutamine echocardiography for predicting recovery of ventricular function after angioplasty in patients with stable coronary artery disease and ventricular dysfunction.

METHODS AND RESULTS

Twenty patients with stable coronary artery disease and segmental ventricular dysfunction scheduled for coronary angioplasty underwent dobutamine echocardiography before revascularization using incremental doses of 2.5, 5, 7.5, 10, 20, 30, and 40 micrograms/kg per minute every 3 minutes. Digital images of all eight stages were displayed simultaneously (two quad screens side by side) and interpreted using a 16-segment ventricular model and a 6-grade scoring system. Serial resting echocardiograms before, early (< 1 week), and late (> or = 6 weeks) after angioplasty were digitized and randomized in a quad-screen format for the assessment of recovery of function. Wall motion score index in the revascularized regions decreased from 2.86 +/- 0.76 before angioplasty to 2.12 +/- 1.03 late after angioplasty (P < .05). Of 320 ventricular segments, 148 had abnormal wall motion at baseline and 114 were revascularized. Recovery of function (> or = 2 grades) occurred in 25% of revascularized segments early and in 33% late after angioplasty. Of the 34 abnormal segments not revascularized, recovery of function occurred in only 1. During dobutamine echocardiography, abnormal segments exhibited one of four responses: biphasic (improvement at low dose and worsening at high dose) in 28% of segments, sustained improvement (persistent improvement till peak dose) in 18%, worsening in 15%, and no change in 39%. A biphasic response had the highest predictive value (72%) for recovery of function followed by worsening only (35%), while the lowest was seen with a "no-change" or sustained improvement response (13% and 15%). Combining biphasic and worsening responses resulted in a sensitivity of 74% and specificity of 73% for assessment of recovery of individual segments and 90% and 60%, respectively, for functional recovery of individual patients (n = 10). In segments with a biphasic response, the low dose at which improvement in wall motion was most prevalent (84%) was 7.5 micrograms/kg per minute and increased to 94% when the 5 and 7.5 micrograms/kg per minute doses were displayed. The reworsening phase of the biphasic response was usually seen with doses > or = 20 micrograms/kg per minute but was also observed as early as the 7.5 micrograms/kg per minute dose.

CONCLUSIONS

The wall motion response during dobutamine echocardiography is useful in the prediction of recovery of ventricular function after revascularization in patients with stable coronary artery disease and ventricular dysfunction. The administration of low as well as high doses of dobutamine is needed for optimal evaluation.

Imaging of the heart by MRI and PET

This review article describes the clinical usefulness and future potential of two new methods for the imaging of the heart, which have recently also become available outside research laboratories. These methods are magnetic resonance imaging (MRI) and positron emission tomography (PET). MRI is the most rapidly increasing imaging modality in medicine today. The moving heart forms a challenge to conventionally rather slow MRI-techniques. Techniques based on ECG-gating have been mandatory in making cardiac cine-MRI possible. Even though MRI provides accurate and quantitative information of the heart, conventional methods are time-consuming, confined to special laboratories, and rather expensive. Therefore, the clinical use of cardiac MRI is, in many laboratories, limited to cases in which echocardiography does not provide adequate information (e.g. pulmonary circulation) or when the patient is not willing to have transoesophageal echocardiography for better visibility. MRI is also used instead of or to complement invasive angiography to study large vessels, and it provides excellent information on paracardiac masses. Cardiac MRI is developing rapidly and within the next few years it is likely to have a profound impact on cardiac imaging. This is based on its noninvasive nature and on the comprehensive anatomic (including coronary arteries), functional, flow, perfusion and possibly also metabolic information it has the potential to provide in a manner not comparable to any other imaging method. PET is a nuclear medicine imaging modality that allows quantitative characterization of a variety of physiological and metabolic processes in vivo. Using positron-emitting flow tracers and analogues of metabolic substrates, regional myocardial blood flow, glucose and fatty acid metabolism and oxygen consumption can be studied noninvasively by PET in research as well as in clinical practice. For example, regional myocardial glucose utilization rates can be measured accurately by PET. This allows us to study the effects of nutritional interventions, hormonal and neural effects as well as disease processes on the glucose utilization of the human heart. PET is currently the only technique that permits noninvasive quantification of regional myocardial perfusion in absolute terms. Over the last decade, PET has also emerged as a clinically useful tool to study coronary artery disease and myocardial viability.

The hibernating myocardium: implications for management of congestive heart failure

Left ventricular (LV) function is one of the most important determinants of long-term outcome in patients with coronary artery disease (CAD). Patients with normal or near-normal LV function have an excellent prognosis, whereas patients with impaired LV function are at substantial risk of death during medical therapy. It is now apparent that LV dysfunction is not always an irreversible process and that LV function may improve considerably, and even normalize, after myocardial revascularization in a large subset of patients. The identification of such patients with "hibernating" myocardium that is underperfused and dysfunctional, yet viable, has important implications in the selection of patients with LV dysfunction for revascularization procedures. Both nuclear cardiology techniques and 2-D echocardiography can be used for this purpose. The radionuclide techniques include positron emission tomography to assess blood flow and metabolism (using agents such as [18F]fluorodeoxyglucose) and thallium-201 (and possibly technetium-99m sestamibi) to assess blood flow and cell membrane integrity. Alternatively, echocardiographic imaging during low-dose infusions of dobutamine can be used to assess inotropic reserve. The data available to date suggest that patients with CAD in whom hibernating myocardium is largely the cause of impaired LV function constitute a subgroup of patients who may achieve a substantial improvement in LV function and in outcome if identified and treated with revascularization.

Myocardial hibernation

From available results, the following schematic can be drawn: Reductions in perfusion pressure are not associated with impaired ventricular function as long as they take place within the autoregulatory range. Additional reductions in perfusion pressure that moderately diminish coronary blood flow will result in a particular ischemia with decreased but stable function: perfusion and contraction match, the myocardium hibernates. The process responsible for this new equilibrium could be termed down regulation of function. The trigger inducing hibernation is so far unknown. The strategy, however, is similar to that used by hibernating animals. Likewise, myocardial hibernation is a protective mechanism. As hibernators recover initial function after unfavourable periods are terminated, hibernating myocardium recovers after institution of physiologic perfusion. It is under debate, whether function quickly recovers or remains temporarily depressed. As hibernating animals might finally even die, if unfavourable periods last too long, myocardium might become irreversibly injured due to ischemia lasting too long. Additional reductions in perfusion pressure and oxygen supply below the hibernating range produce ischemia in the more classical sense, because oxygen supply and demand no longer match. Damage will become irreversible in case the situation persists longer than about 20 min. After onset of reperfusion, the myocardial function would remain depressed, however, for a considerable period: myocardial stunning. Considering the regional heterogeneities of myocardial blood flow, distinct differentiation between moderate and severe ischemia is difficult. Ischemia will induce more articulate damage in subendocardial than in subepicardial layers. Similarly, damage in the ischemic core will be more pronounced than in the border zone.(ABSTRACT TRUNCATED AT 250 WORDS)