Evidence of reduced resting blood flow in viable myocardial regions with chronic asynergy

Absolute Resting 13N-Ammonia PET Myocardial Blood Flow for Predicting Myocardial Viability and Recovery of Ventricular Function after Coronary Artery Bypass Grafting

OBJECTIVE

We aimed to evaluate the feasibility of resting myocardial blood flow (rMBF), quantified with dynamic 13 N-Ammonia (NH3) PET, for identifying myocardial viability and predicting improvement of left ventricular ejection fraction (LVEF) after coronary artery bypass grafting (CABG).

METHODS

Ninety-three patients with coronary artery disease (CAD) and chronic LVEF < 45%, scheduled for CABG, had dynamic 13NH3 PET and 18F-FDG PET imaging. The perfusion/metabolism polar maps were categorized in four patterns: normal (N), mismatch (M1), match (M2) and reverse mismatch (RM). The value of rMBF for identifying viable myocardium (M1, RM) and post CABG improvement of LVEF≥8% was analyzed by receiver operating characteristic (ROC) curves. Correlations of rMBF in segments to ΔLVEF post CABG were verified.

RESULTS

Mean rMBFs were significantly different (N=0.60±0.14; M1=0.44±0.07, M2=0.34±0.08, RM=0.53±0.09 ml/min/g, P<0.001). The optimal rMBF cutoff to identify viable myocardium was 0.42 ml/min/g (sensitivity=88.3%, specificity=82.0%) and 0.43 ml/min/g for predicting improvement of LVEF ≥8% (74.6%, 80.0%). The extent and rMBF of combined M1/RM demonstrated a moderate to high correlation to improved LVEF (r=0.78, 0.71, P<0.001).

CONCLUSION

Resting MBF, derived by dynamic 13NH3 PET, may be positioned as a supplement to 18F-FDG PET imaging for assessing the presence of viable myocardium and predicting potential improvement of LVEF after CABG.

The "fixed" SPECT MPI defect: Where are we and where should we be going?

This brief review focuses on reasons why myocardial perfusion imaging (MPI) SPECT defects may appear "fixed" (rest vs stress). A combination of technical and physiology factors are responsible in most cases and are discussed. Perhaps the major reason defects will appear fixed is that there is no absolute quantitative measurement of myocardial blood flow (MBF, rest and stress) with which to assess the magnitude and potential direction of change in the defect vs reference zone with stress. Cardiac PET MPI provides absolute measurements of MBF required to understand the clinical significance of the SPECT "fixed" defect and are highlighted. Emphasis is given to use of the actual MBF measurements though indexing stress MBF to that of truly normal subjects (RFR or FFRPET) will prove useful in recognition of multi-vessel CAD. The availability of 18F flurpiridaz for clinical use is likely to encourage more widespread adoption of cardiac PET MPI for evaluation of patients with known or suspected CAD.

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Myocardial responses to acute ischemia/reperfusion and to chronic ischemic conditions have been studied extensively at all levels of organization. These include subcellular (eg, mitochondria in vitro); intact, large animal models (eg, swine with chronic coronary stenosis); as well as human subjects. Investigations in humans have used positron emission tomographic metabolic and myocardial blood flow measurements, assessment of gene expression and anatomic description of myocardium obtained at the time of coronary artery revascularization, ventricular assist device placement, or heart transplantation. A multitude of genetic, molecular, and metabolic pathways have been identified, which may promote either myocyte survival or death or, most interestingly, both. Many of these potential mediators in both acute ischemia/reperfusion and adaptations to chronic ischemic conditions involve the mitochondria, which play a central role in cellular energy production and homeostasis. The present review is focused on operative survival mechanisms and potential myocardial viability molecular imaging targets in acute and chronic ischemia, especially those which impact mitochondrial function.

PET measurement of adenosine stimulated absolute myocardial blood flow for physiological assessment of the coronary circulation

Considerable awareness has been raised of late of the need to reduce radiation exposure and control costs of x-ray and radionuclide imaging procedures. PET/CT cameras are now widely available and in conjunction with appropriate radionuclides and commercially available software make quantitative measurement of absolute MBF feasible for routine clinical practice. Quantitative measurement of absolute MBF under condition of coronary vasodilation permits independent assessment of the functional status of each of the three major coronary perfusion zones and so obviates the need for rest MBF determination in the great majority of cases. Coronary microvascular function also may be assessed in this same way. Thus, the stress-only protocol with quantitative PET measurement of MBF provides essential information required for clinical decision making related to need for catheterization and intervention for patients with known or suspected ischemic heart disease. Moreover, the single PET determination of maximal MBF in contrast to the usual rest/stress procedure addresses both safety and cost concerns. The present review focuses on: (1) quantitative PET measurements of myocardial blood flow for physiological assessment of the coronary circulation and (2) the value and potential limitations of performing stress only imaging in the clinical context.

Left ventricular apical wall motion abnormality is associated with lack of response to cardiac resynchronization therapy in patients with ischemic cardiomyopathy

BACKGROUND

Many patients with appropriate indications fail to respond to cardiac resynchronization therapy (CRT).

OBJECTIVE

The purpose of our study was to determine the relationship between CRT response and preimplantation apical wall motion abnormality.

METHODS

We analyzed data from 83 patients with ischemic cardiomyopathy who underwent CRT. All patients had New York Heart Association class III or IV symptoms despite maximal medical therapy, left ventricular ejection fraction (LVEF) < or =35%, and QRS duration > or =130 ms or <130 ms with left ventricular dyssynchrony. CRT responders at 6 months were defined as surviving patients with: (1) no hospitalization for heart failure, and (2) improvement of New York Heart Association classification. Patients underwent echocardiography before and 6 months after implantation to assess changes in regional wall motion and LVEF.

RESULTS

At baseline, CRT responders (n = 39) and nonresponders (n = 44) had similar LVEF (22.9% +/- 6.9% vs 23.1% +/- 8.3%), QRS duration (159 +/- 43 ms vs 159 +/- 36 ms), and medical treatment. CRT nonresponders had a higher prevalence of preimplantation apical wall motion abnormality (68% vs 33%, P = .003). Patients with baseline apical wall motion abnormalities (n = 43) were less likely than others (n = 40) to show improvement in wall motion at 6 months (30% vs 81%, P < .001) or clinical response to CRT (31% vs 64%, P = .003).

CONCLUSION

The presence of a preimplantation apical wall motion abnormality was associated with a lower rate of CRT response in patients with ischemic cardiomyopathy.

Myocardial blood flow and oxygen consumption in patients with Friedreich's ataxia prior to the onset of cardiomyopathy

OBJECTIVES

We tested the hypothesis, in patients with Friedreich's ataxia and no overt structural heart disease, that impairment of cardiac oxidative metabolism may be compensated for either by increased rest myocardial blood flow or more efficient oxygen consumption in performance of external work.

BACKGROUND

Friedreich's ataxia is characterized by a mutant frataxin gene, which causes mitochondrial iron overload and impaired energy production. Further, it is frequently associated with cardiomyopathy. Studies using magnetic resonance spectroscopy, however, suggest impaired cardiac energetics even in the absence of structural heart disease.

METHODS

Positron emission tomography measured rest myocardial blood flow (N-13-ammonia method) and myocardial oxygen consumption (11-C-acetate, Kmono) in Friedreich's ataxia patients (n=8; 31+/-5 years, mean+/-SD, four women) and healthy controls (n=8; 30+/-7 years, five women) matched for stroke work index and age. Stroke work index and power were determined by electrocardiogram gated positron emission tomography N-13-ammonia using modified Simpson's rule to compute left ventricular volumes.

RESULTS

Neither stroke work index nor rest myocardial blood flow differed significantly between the groups. Although myocardial oxygen consumption was lower in Friedreich's ataxia (P<0.001), Kmono/rest myocardial blood flow, an index of myocardial oxygen extraction, did not differ between the groups. Power/Kmono, an index of the efficiency of myocardial oxygen consumption, was greater in Friedreich's ataxia (P<0.04). Rest myocardial blood flow normalized to rate pressure product was lower in Friedreich's ataxia (P<0.05).

CONCLUSIONS

Prior to the onset of cardiomyopathy, selected patients with Friedreich's ataxia may compensate for impaired cardiac energetics through more efficient oxygen consumption rather than increased rest myocardial blood flow. The data illustrate a more general mechanism pertaining to metabolic regulation of myocardial blood flow and myocardial oxygen consumption.

In vivo 18F-fluorodeoxyglucose positron emission tomography imaging provides a noninvasive measure of carotid plaque inflammation in patients

OBJECTIVES

Given the importance of inflammation in atherosclerosis, we sought to determine if atherosclerotic plaque inflammation could be measured noninvasively in humans using positron emission tomography (PET).

BACKGROUND

Earlier PET studies using fluorodeoxyglucose (FDG) demonstrated increased FDG uptake in atherosclerotic plaques. Here we tested the ability of FDG-PET to measure carotid plaque inflammation in patients who subsequently underwent carotid endarterectomy (CEA).

METHODS

Seventeen patients with severe carotid stenoses underwent FDG-PET imaging 3 h after FDG administration (13 to 25 mCi), after which carotid plaque FDG uptake was determined as the ratio of plaque to blood activity (target to background ratio, TBR). Less than 1 month after imaging, subjects underwent CEA, after which carotid specimens were processed to identify macrophages (staining with anti-CD68 antibodies).

RESULTS

There was a significant correlation between the PET signal from the carotid plaques and the macrophage staining from the corresponding histologic sections (r = 0.70; p < 0.0001). When mean FDG uptake (mean TBR) was compared with mean inflammation (mean percentage CD68 staining) for each of the 17 patients, the correlation was even stronger (r = 0.85; p < 0.0001). Fluorodeoxyglucose uptake did not correlate with plaque area, plaque thickness, or area of smooth muscle cell staining.

CONCLUSIONS

We established that FDG-PET imaging can be used to assess the severity of inflammation in carotid plaques in patients. If subsequent natural history studies link increased FDG-PET activity in carotid arteries with clinical events, this noninvasive measure could be used to identify a subset of patients with carotid atherosclerosis in need of intensified medical therapy or carotid artery intervention to prevent stroke.

Prediction of arrhythmic events with positron emission tomography: PAREPET study design and methods

BACKGROUND

In medically-treated patients with ischemic cardiomyopathy, myocardial viability is associated with a worse prognosis than scar. The risk is especially great with hibernating myocardium (chronic regional dysfunction with reduced resting flow), and the excess mortality appears to be due to sudden cardiac death (SCD). Hibernating myocardium also results in sympathetic nerve dysfunction, which has been independently associated with risk of SCD.

OBJECTIVES

PAREPET is a prospective, observational cohort study funded by NHLBI. It is designed to determine whether hibernating myocardium and/or inhomogeneity of sympathetic innervation by positron emission tomography imaging identifies patients with ischemic cardiomyopathy who are at high risk for SCD and cardiovascular mortality.

METHODS

Patients with documented ischemic cardiomyopathy, an ejection fraction of <or=35%, and with no plans for coronary revascularization will be recruited. Major exclusion criteria include: history of resuscitated SCD, sustained VT, ICD discharge, or unexplained syncope; recent myocardial infarction (30 days), percutaneous coronary intervention (3 months), coronary bypass surgery (1 year); or comorbidities that would be expected to reduce life expectancy to <2 years. All patients will undergo transthoracic echocardiography, and dynamic cardiac positron emission tomography to quantify resting perfusion (13N-ammonia), norepinephrine uptake as an index of sympathetic innervation (11C-meta-hydroxyephedrine), and metabolic viability (18F-2-deoxyglucose during glucose-insulin clamp). The development of SCD or cardiovascular mortality will be determined by telephone follow-up every three months. In patients with an implantable cardiac defibrillator, appropriate device discharge will be considered a surrogate for SCD.

CONCLUSION

The PAREPET study will prospectively determine whether the amount of viable dysfunction myocardium and/or cardiac sympathetic dysinnervation is associated with the risk of SCD. It is anticipated that the results of this trial will more specifically identify myocardial substrates of SCD. This will help target therapies intended to reduce arrhythmic death to those patients with the greatest likelihood of benefit.

Resting myocardial blood flow is impaired in hibernating myocardium: a magnetic resonance study of quantitative perfusion assessment

BACKGROUND

Although impairment in perfusion reserve is well recognized in hibernating myocardium, there is substantial controversy as to whether resting myocardial blood flow (MBF) is reduced in such circumstances. Quantitative first-pass cardiovascular magnetic resonance (CMR) perfusion imaging allows absolute quantification of MBF. We hypothesized that MBF assessed at rest by quantitative CMR perfusion imaging is reduced in hibernating myocardium.

METHODS AND RESULTS

Twenty-seven patients with 1 or 2-vessel coronary disease and at least 1 dysfunctional myocardial segment undergoing PCI were studied with preprocedure, early (24 hours), and late (9 months) postprocedure CMR imaging. First-pass perfusion images at rest were acquired in 3 short-axis planes by use of a T1-weighted turboFLASH sequence. In each slice, MBF was determined for 8 myocardial segments in mL . min(-1) . g(-1) by deconvolution of signal intensity curves with an arterial input function measured in the left ventricular blood pool. Cine MRI for assessment of global and segmental function and delayed enhancement MRI for detection of viability were also obtained. All coronary lesions were 80% to 95% stenosis in severity. Over all segments, mean MBF normalized by rate-pressure product ("corrected MBF") was 1.2+/-0.3 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) in segments without significant coronary stenosis and 0.7+/-0.2 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) in segments with coronary stenosis before PCI (mixed model controlling for slice and segment z=-23.9, P<0.001). Early after the procedure, the MBF was 1.2+/-0.2 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) in revascularized segments and 1.3+/-0.2 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) in nondiseased segments (z=-6.1, P<0.001). Late after PCI, the systolic wall thickening and end-diastolic wall thickness both increased significantly more (both P<0.001) in the myocardial segments subtended by severe coronary stenosis (8+/-17% to 40+/-19% and 6.5+/-1.1 to 9.3+/-2 mm, respectively) than in the myocardial segments supplied by nondiseased vessels. Mean MBF in dysfunctional segments with significantly improved contraction after revascularization was 0.8+/-0.2 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) before PCI and 1.2+/-0.2 mL . min(-1) . g(-1) . (mm Hg . bpm/10(4))(-1) after PCI (z=2.0, P=0.04).

CONCLUSIONS

CMR perfusion imaging detects impaired resting MBF in hibernating myocardial segments.

Regional Desensitization of β-Adrenergic Receptor Signaling in Swine With Chronic Hibernating Myocardium

Contractile reserve during submaximal beta-adrenergic stimulation is attenuated in patients and swine with hibernating myocardium. We tested the hypothesis that this arises as a regional adaptive response in beta-adrenergic adenylyl cyclase coupling. Pigs (n=8) were studied 3 months after instrumentation with a left anterior descending artery (LAD) stenosis when flow (LAD, 0.7+/-0.2 versus 1.2+/-0.1 mL/min per gram in normal remote; P<0.05) and wall thickening (LAD, 15.5 [corrected]+/-3.2% versus 40.0+/-5.5% in remote; P<0.05) were reduced in the absence of infarction. Whereas basal cAMP production was normal (LAD, 87+/-18 versus 91+/-19 pmol/mg per minute; P=NS), responses to isoproterenol were blunted (LAD, 83+/-6 versus 146+/-25 pmol/mg per minute in remote; P<0.05). beta-receptor density and subtype were unchanged, but there was a reduction in the number of high-affinity binding sites (LAD, 40+/-4% versus 53+/-7% in normal remote; P<0.05). The Gialpha2/Gsalpha ratio increased (LAD, 1.8+/-0.3 versus 0.99+/-0.3 in remote myocardium; P<0.05), although GppNHp-stimulated cAMP production was equivocally reduced. Forskolin responses were unchanged and similar to shams. These data indicate regional attenuation of beta-receptor adenylyl cyclase signaling in hibernating myocardium. This blunts the local contractile response to beta-adrenergic stimulation and may serve to protect against a myocardial supply/demand imbalance when external determinants of myocardial workload increase during sympathetic activation.

Effects of sildenafil on myocardial blood flow in humans with ischemic heart disease

BACKGROUND

We tested the hypothesis that sildenafil increases myocardial dilator reserve in humans with ischemic heart disease.

METHODS

Positron emission tomography measured myocardial blood flow in 14 patients with ischemic heart disease. Patients were studied twice, in double-blind, placebo-control, cross-over design with sildenafil (or placebo) given approximately 2-3 h before measurements of hemodynamics and myocardial blood flow: at rest, with cold pressor stress and with adenosine. All myocardial segments of each patient with myocardial blood flow <1.65 ml/min per g with adenosine under placebo conditions were combined into one abnormal zone for that patient. Segments with myocardial blood flow >1.65 ml/min per g were averaged and combined into a normal zone for that patient.

RESULTS

At rest, rate pressure product (heart rate x systolic arterial pressure, mmHg/min) was comparable, as was abnormal zone myocardial blood flow (ml/min per g; 0.76+/-0.48 placebo versus 0.64+/-0.20 sildenafil, both P=NS; mean+/-SD). Both rate pressure product and myocardial blood flow increased (P<0.01) with cold pressor stress (11+/-3 K and 1.14+/-0.59 placebo versus 10+/-3 K and 1.21+/-0.62 sildenafil). However, sildenafil failed to improve the myocardial blood flow response to cold pressor stress in abnormal or normal zones. In contrast, abnormal zone myocardial blood flow reserve with adenosine and sildenafil (2.6+/-0.7) exceeded that with adenosine and placebo (2.0+/-1.3, P<0.04, paired sign test).

CONCLUSION

Sildenafil improves myocardial blood flow dilator response to adenosine in abnormal zones, possibly by augmenting nitric oxide-mediated increases in cGMP because adenosine response in part is nitric oxide dependent. Failure to improve myocardial blood flow response to cold pressor stress suggests that alpha-adrenergic constriction may offset enhanced nitric oxide effects. Clinically, the data suggest sildenafil may exert an anti-ischemic effect in patients with coronary artery disease.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

Myocardial hibernation: a delicate balance

The pathophysiology of myocardial hibernation is characterized as a situation of reduced regional contractile function distal to a coronary artery stenosis that recovers after removal of the coronary stenosis. A subacute "downregulation" of contractile function in response to reduced regional myocardial blood flow exists, which normalizes regional energy and substrate metabolism but does not persist for more than 12-24 h. Chronic hibernation develops in response to one or more episodes of myocardial ischemia-reperfusion, possibly progressing from repetitive stunning with normal blood flow to hibernation with reduced blood flow. An upregulation of a protective gene program is seen in hibernating myocardium, putting it into the context of preconditioning. The morphology of hibernating myocardium is characterized by both adaptive and degenerative features.

Coronary blood flow, metabolism, and function in dysfunctional viable myocardium before and early after surgical revascularisation

OBJECTIVES

To assess the link between perfusion, metabolism, and function in viable myocardium before and early after surgical revascularisation.

DESIGN

Myocardial blood flow (MBF, thermodilution technique), metabolism (lactate, glucose, and free fatty acid extraction and fluxes), and function (transoesophageal echocardiography) were assessed in patients with critical stenosis of the left anterior descending coronary artery (LAD) before and 30 minutes after surgical revascularisation.

SETTING

Tertiary cardiac centre.

PATIENTS

23 patients (mean (SEM) age 57 (1.7) years with LAD stenosis: 17 had dysfunctional viable myocardium in the LAD territory, as shown by thallium-201 rest redistribution and dobutamine stress echocardiography (group 1), and six had normally contracting myocardium (group 2).

RESULTS

LAD MBF was lower in group 1 than in group 2 (58 (7) v 113 (21) ml/min, p < 0.001) before revascularisation and improved postoperatively in group 1 (129 (133) ml/min, p < 0.001) but not in group 2 (105 (20) ml/min, p = 0.26). Group 1 also had functional improvement in the LAD territory at intraoperative echocardiography (mean regional wall motion score from 2.6 (0.85) to 1.5 (0.98), p < 0.01). Oxidative metabolism, with lactate and free fatty acid extraction, was found preoperatively and postoperatively in both groups; however, lactate and free fatty acid uptake increased after revascularisation only in group 1.

CONCLUSIONS

MBF is reduced and oxidative metabolism is preserved at rest in dysfunctional but viable myocardium. Surgical revascularisation yields immediate perfusion and functional improvement, and increases the uptake of lactate and free fatty acids.

Assessment of clinical features in transient left ventricular apical ballooning

OBJECTIVES

We sought to assess the clinical features of transient left ventricular (LV) apical ballooning.

BACKGROUND

Although several cases regarding transient LV apical ballooning have been reported, the etiology remains unknown.

METHODS

We investigated 17 patients (14 women, median age 74 years old with a range of 54 to 91 years old) who fulfilled the following criteria: 1) transient LV apical ballooning; 2) ST-T segment change in several leads in electrocardiogram; and 3) no history of old myocardial infarction, valvular heart disease, subarachnoid hemorrhage, or pheochromocytoma.

RESULTS

Emotional and physical stress were observed in 16 patients (94%). Technetium-99m tetrofosmin tomographic imaging revealed decreased uptake at the apex of the left ventricle in 11 patients (85%) that later returned to uniform. No significant stenosis or angiographical slow flow in epicardial coronary arteries was observed (n = 9). Provocative focal vasospasm was induced in only one patient (14%) (n = 7). Moreover, no significant abnormality in the coronary microcirculation was detected by Doppler guidewire (n = 3) or contrast echocardiography (n = 1). No patients showed a rise in viral antibody titers. Biopsy specimens revealed interstitial fibrosis in six patients (100%) and slight cell infiltration in three others (50%) (n = 6).

CONCLUSIONS

These findings suggested that neither abnormalities in the coronary circulation nor acute myocarditis was related to the etiology. Although neurogenic stunned myocardium induced by emotional or physical stress was suggested as the etiology, further investigations are necessary.

Ischemic cardiomyopathy in pigs with two-vessel occlusion and viable, chronically dysfunctional myocardium

A chronic left anterior descending coronary artery (LAD) stenosis leads to the development of hibernating myocardium with severe regional hypokinesis but normal global ventricular function after 3 mo. We hypothesized that two-vessel occlusion would accelerate the progression to hibernating myocardium and lead to global left ventricular (LV) dysfunction and heart failure. Pigs were instrumented with a fixed 1.5-mm constrictor on the proximal LAD and circumflex arteries. After 2 mo, there were no overt signs of right-heart failure and triphenyl tetrazolium chloride infarction was trivial (1.4 +/- 0.1% of the LV). Compared with shams, regional function [myocardial systolic excursion (DeltaWT); 2.1 +/- 0.3 vs. 4.6 +/- 0.4 mm, P < 0.05] and resting perfusion (0.90 +/- 0.13 vs. 1.32 +/- 0.09 ml small middle dot min(-1) small middle dot g(-1), P < 0.05) were reduced, consistent with hibernating myocardium. Pulmonary systolic (45.9 +/- 3.3 vs. 36.5 +/- 2.2 mmHg, P < 0.05) and wedge pressures (19.1 +/- 1.6 vs. 11.2 +/- 0.9 mmHg, P < 0.05) were increased with global ventricular dysfunction (ejection fraction 43 +/- 2 vs. 50 +/- 2%, P < 0.05). Early LV remodeling was present with increased cavity size and mass. Reductions in sarcoplasmic reticulum Ca(2+)-ATPase and phospholamban were confined to the dysfunctional LAD region with no change in calsequestrin. Thus combined stenoses of the LAD and circumflex arteries accelerate the development of hibernating myocardium and result in compensated heart failure.

Clinical and angiographic correlates of dobutamine-induced wall motion patterns after myocardial infarction

The ability of different dobutamine-induced wall motion patterns to define the anatomic status of the infarct-related artery (IRA) was evaluated in 159 patients who underwent dobutamine stress echocardiography (DSE) and coronary angiography 10 +/- 2 and 18 +/- 3 days, respectively, after hospital admission. The DSE result was classified as: (1) biphasic: improvement with a low dose followed by deterioration with a high dose; (2) worsening: direct deterioration at low or high doses; (3) sustained improvement: improvement with a low dose that was maintained at high dose; and (4) no change: no change during the entire protocol. A diameter narrowing >70% (50% for the left main stem) of major coronary arteries indicated a severe lesion. Angiograms were classified according to the jeopardy score and collateral circulation graded according to Rentrop's classification. DSE was positive in 92 patients (22 had biphasic results and 70 had worsening results) and negative in 67 patients (14 had sustained improvement and 53 had no changes). Biphasic response was associated with more frequent anterior infarction (p <0.05) and higher resting (p <0.001) and peak (p <0.01) wall motion score indexes. The IRA was totally occluded in 4 of the 92 patients (4%) with positive (worsening pattern) and 12 of the 67 patients (18%) with negative (no change pattern) tests. The biphasic pattern was associated with the highest jeopardy score and was significantly (p <0.05) more specific (100%) compared with worsening (78%) in identifying a severe stenosis of the IRA. The combination of ischemic patterns provided a significantly superior sensitivity (p <0.0001). Logistic regression analysis identified the biphasic pattern as the only significant predictor. Conversely, the prediction of total occlusion of the IRA was poor. Sustained improvement was the most specific (100%) predictor of absence of severe stenosis of the IRA, whereas the combination with no change pattern provided a significantly superior sensitivity (p <0.0001). Thus, DSE effectively predicts the residual stenosis of the IRA. In particular, the biphasic response has an excellent specificity and positive predictive value and is the only significant predictor among clinical and echocardiographic variables.