Disappearance of abnormal Q waves after aortocoronary bypass surgery

Assessment of residual myocardial viability in regions with chronic electrocardiographic Q-wave infarction

BACKGROUND

Q waves on the electrocardiogram are often considered to be reflective of irreversibly scarred myocardium due to antecedent transmural myocardial infarction. However, there are some indications that residual viable tissue may be present in Q-wave-infarcted regions. It is clinically relevant to know how many Q-wave regions contain viable tissue because these patients may benefit from revascularization in terms of improvement of function and long-term survival.

METHODS

Patients (n = 150) with chronic electrocardiographic Q-wave infarction, heart failure symptoms, and chronic coronary artery disease underwent dobutamine-atropine stress echocardiography to assess myocardial viability. Residual viability in regions with Q-wave infarction was considered present when the end-diastolic wall thickness (EDWT) was >6 mm and the response during dobutamine infusion indicated viable tissue.

RESULTS

Baseline echocardiography revealed 517 dysfunctional myocardial regions; 202 of the dysfunctional regions were related to Q waves on the electrocardiogram and the other 315 dysfunctional regions were not. EDWT was < or =6 mm in 13 regions with a Q wave on the electrocardiogram, with only 1 region exhibiting viable tissue during dobutamine stress echocardiography. EDWT was >6 mm in 189 regions with a Q wave, with 118 (62%) having viable tissue on dobutamine stress echocardiography. In 6 dysfunctional regions without a Q wave, EDWT was < or =6 mm, with all being nonviable on dobutamine stress echocardiography; of the 309 regions without a Q wave and EDWT >6 mm, 204 (66%) exhibited viability on dobutamine stress echocardiography.

CONCLUSIONS

Fifty-eight percent of dysfunctional regions related to chronic Q waves were viable according to the combined information of EDWT and dobutamine stress echocardiography. EDWT </=6 mm virtually excludes viability; regions with EDWT >6 mm need additional testing to detect or exclude viability.

Assessment of viable tissue in Q-wave regions by metabolic imaging using single-photon emission computed tomography in ischemic cardiomyopathy

Chronic electrocardiographic Q waves are often believed to reflect irreversibly scarred, transmurally infarcted myocardium. The aim of this study was to evaluate whether residual viable tissue persists in dysfunctional myocardial regions related to chronic Q waves on the surface electrocardiogram. A total of 148 patients with healed myocardial infarction and impaired left ventricular (LV) function with heart failure symptoms underwent electrocardiography and metabolic imaging using technetium (Tc-99m) tetrofosmin/F18-fluorodeoxyglucose (FDG) single-photon emission computed tomography (SPECT). The left ventricle was divided into 4 major regions to compare myocardial viability in regions with and without chronic Q waves on surface electrocardiography. According to FDG SPECT metabolic imaging, residual viable tissue persisted in a high proportion (61%) of dysfunctional myocardial regions with chronic Q waves. Regions with chronic Q waves were more often dysfunctional than regions without Q waves. Moreover, dysfunctional regions with chronic Q waves were less frequently viable compared with dysfunctional regions without Q waves on the electrocardiogram. This study demonstrates that chronic Q waves on electrocardiography do not necessarily imply irreversibly scarred myocardium. Residual viable tissue persists in a high proportion of dysfunctional ventricular regions according to FDG SPECT metabolic imaging.

Effects of surgery for postinfarction ventricular tachycardia on parameters of left ventricular function

Heart failure is the leading cause of death in patients after surgery for ventricular tachycardia. This study examines the effects of antiarrhythmic surgery on 4 parameters of left ventricular (LV) function. Global ejection fraction, segmental wall motion score, homogeneity of contraction, and diastolic function were measured in 32 patients by technetium-99m radionuclide ventriculography. Ejection fraction was measured from the left anterior oblique image. Wall motion score was assessed semiquantitatively for 11 LV segments from 3 projections. Homogeneity of contraction was expressed as the SD of the LV phase analysis curve during systole from the left anterior oblique image. Diastolic function was expressed in terms of peak and mean first time derivative of the action potential (dV/dt) of the LV function curve. Subgroup analyses were performed to distinguish the effects of aneurysmectomy, coronary artery bypass grafting, and changes in angiotensin converting enzyme inhibitor therapy. Mean systolic function improved after surgery (ejection fraction 22% vs 32%, p <0001; wall motion score 20 vs 13, p <0.0001; phase analysis 18 vs 12, p <0.03). Mean diastolic function also improved (peak dV/dt 0.83 +/- 0.32 vs 1.49 +/- 0.39, p = 0.006; mean dV/dt 0.41 +/- 0.15 vs 0.76 +/- 0.27, p = 0.006). Improvements were not confined to those who had aneurysmectomy or coronary bypass grafting and were not explained by changes in vasodilator therapy. Thus, antiarrhythmic surgery does not inherently damage LV function. Significant improvements were observed in most patients. Failure to improve indicated a poor longer term prognosis.

Regression of ECG signs of myocardial infarction related to infarct size and left ventricular function

Quantitative and qualitative analyses of Q waves and QRS scores were performed on 69 patients during the early phase of first myocardial infarction (MI) and 6 months subsequently. The regression of ECG signs of MI were compared with the enzymatically estimated size of MI, the location of MI, and with the changes of global ejection fraction (GEF) assessed by radionuclide ventriculography. Among 57 patients with Q wave MI a complete disappearance of ECG signs of MI was found in 9 (15.7%). Patients with MI of inferior location showed a significantly higher reduction of Q waves (p < 0.001) and QRS scores (p < 0.001) than the anterior MI group. In the group of 12 patients with non Q wave MI, 11 demonstrated complete regression of MI signs. Among all Q wave and non Q wave MIs, the authors found no significant difference in the size of MI between patients with and without complete regression of ECG signs of MI. The median of the percent of change of the QRS score was significantly higher (p = 0.04) in the group of patients with improved GEFs than in the group of patients with decreased or unchanged GEFs 6 months following acute MI. The sensitivity, specificity, and predictive values for improved left ventricular function according to the change of Q waves and ECG scores were 91%, 32%, and 62%; for changes of Q waves, 81%, 40%, and 63%; and for changes of ECG scores, 91%, 36%, and 64%, respectively. In the group of patients with non Q wave MI these values were 100%, 50%, and 91% as a result of ST-T disappearance.

Diagnosis of coronary artery disease using exercise echocardiography and positron emission tomography: comparison and analysis of discrepant results

Both exercise echocardiography and rubidium-82 positron emission tomography are used in the detection and characterization of coronary artery disease. This study compared results of both in 74 patients with known coronary anatomy, by use of exercise echocardiography before and after treadmill exercise and positron emission tomography with intravenous dipyridamole-handgrip stress. Significant (greater than 50%) coronary stenoses were present in 70 patients; exercise echocardiography and positron emission tomography each identified 63 patients (sensitivity 90%). Significant stenoses without previous myocardial infarction were present in 34 patients; 29 (85%) were identified by exercise echocardiography and 28 by positron emission tomography (82%, p = NS). Four patients had no significant coronary disease, and were all identified as normal by both methods. Segments were classified as either normal or showing stress or resting abnormalities, and the diagnoses were compared in the territories of the three major coronary arteries. Results were concordant with respect to the presence or absence of coronary disease in 185 of 222 territories (83%). The remaining 37 regions had abnormalities by exercise echocardiography or positron emission tomography but not both. Stress defects were identified by only one of the tests in 24 areas (in 12 [50%], angiographic findings correlated with positron emission tomography). Resting defects were diagnosed by only one modality in 13 regions (angiographic findings correlated with the results of positron emission tomography in 9 [69%] of these). Both exercise echocardiography and positron emission tomography are sensitive for the identification of coronary artery disease, although on a regional basis, positron emission tomography appears to be more specific for the diagnosis of resting perfusion defects.

Metabolic responses of hibernating and infarcted myocardium to revascularization. A follow-up study of regional perfusion, function, and metabolism

BACKGROUND

The presence of persistent myocardial uptake of 18F-deoxyglucose (FDG) within hypoperfused, dysfunctional segments has been shown to predict the recovery of regional contractile function after revascularization. The spectrum of metabolic responses of such hibernating tissue to revascularization is less clear.

METHODS AND RESULTS

Sixteen patients with previous infarction were studied before and after revascularization by myocardial perfusion imaging using 82Rb positron emission tomography, digitized two-dimensional echocardiography, and imaging of postexercise FDG uptake. Hibernation was identified in 35 of 85 segments showing perfusion and wall motion disturbances before intervention. At follow-up (4.9 +/- 2.6 months after revascularization), hibernating segments were characterized by reduction of wall motion score (p less than 0.001), improvement of perfusion (p less than 0.001), and reduction of FDG activity (p less than 0.001). Of the 35 hibernating segments, however, 10 still had abnormal elevation of FDG uptake (greater than 2 SD above normal) without differing from other hibernating segments with respect to postoperative perfusion or wall motion score. Segments with persistently abnormal metabolism were characterized before intervention by more severe malperfusion (p less than 0.01) and greater FDG activity (p less than 0.01).

CONCLUSIONS

Although wall motion and perfusion improve with revascularization of hibernating tissue, myocardial metabolism remains abnormal in a significant proportion of segments. These segments are characterized by more extensive perfusion and metabolic changes before revascularization.

Electrocardiography and postextrasystolic potentiation: utilization of the two methods to predict postrevascularization segmental myocardial function

We previously reported that postextrasystolic potentiation (PESP) is a useful predictor of changes in systolic wall function (SWF) following coronary revascularization. In the current study we analyzed ECG changes related to corresponding myocardial segments to determine their correlation with PESP and SWF. We found: (1) The PESP response in a jeopardized segment was a valid predictor of improved SWF even when Q waves, ST-segment changes, or T-wave changes were present. (2) However, when Q waves were present in two or more of the corresponding leads, positive PESP was less likely to be observed. (3) Thus Q waves in two leads predicted the least postrevascularization improvement. (4) Segments with no corresponding Q-wave postrevascularization usually improved SWF. (5) Furthermore, a continuum of responsiveness to PESP was found, ranging from T-wave changes, ST-segment changes to Q-wave changes, indicating dissociation between electrical and mechanical events. In conclusion, the ECG together with PESP provide good predictive information relative to the efficacy of revascularization. PESP is a more valuable predictive indicator. ECG alone may be of value in that the occurrence of Q waves in two or more corresponding leads predicts a low probability of improved SWF. Further studies are indicated to investigate the dissociation between electrical and mechanical events.

Significance of Q-wave regression after transmural acute myocardial infarction

A total of 313 consecutive patients was studied to assess the prevalence and prognostic implications of Q-wave loss after transmural acute myocardial infarction. Heart catheterization, including single-plane left ventriculography and selective coronary arteriography, was performed before hospital discharge. After a mean follow-up of 65 (1 to 100) months, 34 patients (11%) lost their Q waves. The time interval from the acute event to the first electrocardiogram showing Q-wave disappearance was 14 (1 to 32) months. Peak creatine kinase value was significantly higher in patients who retained their Q waves than in those who lost them (1,121 +/- 813 vs 779 +/- 464 IU, respectively, p less than 0.05). Severity of coronary artery disease, as judged by the number of diseased arteries and the number of arteries with total or subtotal occlusion, was similar in both groups. However, patients showing Q-wave regression had lower left ventricular end-diastolic pressure, higher ejection fraction and fewer abnormally contracting segments than their counterparts (12 +/- 6 vs 15 +/- 7 mm Hg, p less than 0.05; 53 +/- 11 vs 44 +/- 14%, p less than 0.001; 1 +/- 1 vs 2 +/- 1 segments, p less than 0.001, respectively). In addition, no patient with normalized electrocardiogram presented with left ventricular aneurysm. Although differences in mortality, nonfatal reinfarction and new onset of angina between the 2 groups were not significant, congestive heart failure was prevalent among patients with permanent Q waves (23 vs 6%, p less than 0.05). Our findings suggest that Q-wave loss after AMI may be related to a smaller infarct size.

Positron emission tomography. Diagnostic and therapeutic implications in human myocardial ischemia

Positron emission tomography and tracers of blood flow and of metabolism offer a most unique capability: The noninvasive study of regional myocardial metabolism and its derangements as a result of regional or global myocardial disease. Research with PET not only has confirmed the existence of metabolic fluxes and reactions as established previously through highly invasive or even destructive investigational techniques but has provided new insights into pathophysiologic processes, especially in ischemic and post-ischemic myocardium. From these investigations in both animal experiments and in humans, observations have emerged which indicate a place for PET in clinical cardiology. PET is likely to contribute to detection of disease, to characterizing its extent and severity as well as to decide upon the most appropriate therapeutic strategy and assessing its results. It is recognized that many of these observations with clinical implications await confirmation through larger clinical trials, follow-up studies as well as independent confirmation. Besides exploring ischemic heart disease, PET is equally suitable for examining substrate fluxes and interactions in other disorders as for example in intrinsic myocardial disease like primary and secondary cardiomyopathies. While derangements of metabolism in these disorders may be an expression of the consequences of the disease process or its underlying mechanisms itself, findings on PET will allow formulation of new hypotheses on disease mechanisms that conversely can then be tested. In addition to F-18 2-deoxyglucose and C-11 palmitate, the number of tracers for substrate metabolism is likely to increase. An example is C-11 acetate currently intensely investigated as a tool for measuring overall myocardial oxidative metabolism. Others as for example C-11 labeled short chain fatty acids are on the horizon. The study of cardiac receptors is similarly possible. Thus, a set of tools will soon be available for dissection of entire metabolic pathways and for determination of rate limiting steps in health and disease and to more clearly define specific defects in biochemical reaction steps that critically contribute to or even ae the specific cause of disease.

Regional perfusion, glucose metabolism, and wall motion in patients with chronic electrocardiographic Q wave infarctions: evidence for persistence of viable tissue in some infarct regions by positron emission tomography

Positron-emission tomography with 13N-ammonia and 18F-2-deoxyglucose was used to assess regional perfusion and glucose utilization in 31 chronic electrocardiographic Q wave regions in 20 patients. With previously published criteria, regions of infarction were identified by a concordant reduction in regional perfusion and glucose utilization, and regions of ischemia were identified by preservation of glucose utilization in regions of diminished perfusion. Only 10 of the 31 regions (32%) exhibited myocardial infarction tomographically. In contrast, positron tomography revealed ischemia in six regions (20%) and was normal in 15 regions (48%). Even when Q wave regions were reassigned and consolidated to enhance the specificity of the electrocardiogram, uptake of 18F-2-deoxyglucose was noted in the majority (54%) of the regions. Neither electrocardiographic ST-T changes nor severity of associated wall motion abnormality reliably distinguished tomographically identified regions of ischemia from infarction. Thus positron tomography reveals evidence of persistent tissue metabolism in a high proportion of chronic electrocardiographic Q wave regions, and commonly used clinical tests do not reliably distinguish hypoperfused but viable regions from tomographically defined regions of myocardial infarction.

Use of survival analysis to determine the clinical significance of new Q waves after coronary bypass surgery

There are few data on the long-term effects of new Q waves on survival and morbidity after coronary bypass graft surgery (CABG). We followed 1340 patients who underwent CABG in 1978 at 10 hospitals participating in the Coronary Artery Surgery Study (CASS). The incidence of perioperative Q-wave infarction was 4.76% (range 0.0-10.3% by hospital). The rate of infarction was higher in patients who had an increased left ventricular end-diastolic pressure or cardiomegaly on the preoperative chest radiograph. Patients who received more grafts or who had longer cardiopulmonary bypass time were also at higher risk of infarction. In a stepwise discriminant analysis of 44 clinical, angiographic and surgical variables, cardiopulmonary bypass time, topical cardiac hypothermia and cardiomegaly entered the stepwise selection of variables. Long-term survival was adversely affected by the appearance of new postoperative Q waves. The hospital mortality was 9.7% in the 62 patients who had new postoperative Q waves and 1.0% in the 1278 patients who did not (p less than 0.001); the 3-year cumulative survival rates were 85% and 95%, respectively (p less than 0.001). In patients who survived to hospital discharge, the presence of new postoperative Q waves did not adversely affect 3-year survival (94% and 96%, respectively). The survival rates were worse in patients who had a history of infarction or who had impaired left ventricular function preoperatively. The number of readmissions to hospital after CABG among the patients who had a transmural perioperative infarction was similar to to that among patients who did not. We conclude that the appearance of new Q waves after CABG adversely affects survival. The major impact on mortality occurs before hospital discharge. Patients who are destined to have a perioperative infarct cannot be predicted from commonly measured preoperative and angiographic variables.

Perioperative myocardial infarction and changes in left ventricular performance related to coronary artery bypass graft surgery

Recent advances in perioperative management and surgical technique have been associated with low operative mortality and a high incidence of symptomatic relief in patients undergoing coronary artery bypass graft (CABG) operations. The frequency and importance of perioperative myocardial infarction (MI) and immediate as well as long-term changes in left ventricular (LV) performance are factors of considerable current interest in any critical analysis of the effectiveness of CABG surgery. The present review describes the effects of patient selection, anesthetic techniques, and newer methods of myocardial protection as they relate to perioperative MI and LV performance. In addition, newer tests useful in the diagnosis of perioperative MI are discussed. The application of noninvasive techniques for the serial determination of LV performance and myocardial perfusion in CABG operations is also described.

Use of thallium-201 redistribution scintigraphy in the preoperative differentiation of reversible and nonreversible myocardial asynergy

Thallium-201 (201Tl) redistribution scintigraphy might differentiate reversibly from nonreversibly asynergic myocardial segments and thus predict the response of these segments to coronary artery bypass grafting (CABG). To test this hypothesis, 25 consecutive patients undergoing CABG, preoperative stress-redistribution 201Tl scintigraphy, and both pre- and postoperative resting equilibrium radionuclide ventriculography were evaluated. For both types of scintigraphic study, each patient was imaged in the same three views. Because of the effects of CABG on septal motion, this region was considered separately. Postoperative improvement was noted in 54% of 72 preoperative asynergic segments. Improvement was common not only in hypokinetic but also in akinetic and dyskinetic segments, and occurred in a similar proportion of studies performed early (less than 2 weeks) or late (3-6 months) after CABG. Thallium-201 redistribution scintigraphy was highly predictive of the pattern of postoperative asynergy: The redistribution pattern was normal in 90% of segments with reversible asynergy and abnormal in 76% of segments with nonreversible asynergy. The presence or absence of pathologic Q waves was less sensitive in this differentiation. Septal segments, however, frequently demonstrated abnormal wall motion postoperatively, despite normal 201Tl redistribution scintigraphy. Resting left ventricular ejection fraction (LVEF) was generally unchanged postoperatively, but in some patients with multiple areas of reversible asynergy it did improve. Thus, 201Tl redistribution scintigraphy appears to reliably distinguish viable from nonviable asynergic myocardial zones, and predicts the response of these segments to CABG.

Significance of new Q waves after bypass grafting: correlations between graft patency, ventriculogram, and surgical venting technique

New postoperative electrocardiographic Q waves have been described in eight of 40 per cent of patients undergoing bypass grafting for coronary artery disease. Various theories have been proposed to explain these new Q waves. Correlations of new Q waves to vein bypass occlusion, prolonged pump time or aortic cross-clamping time are controversial. Indeed, whether or not the appearance of new postoperative Q waves means real transmural myocardial infarction is not clear. We report herein our experience with postoperative Q waves in 56 patients with vein bypass grafts and the relationship of new Q waves to ventricular venting, graft patency, and the postoperative ventriculogram. Our observations indicate that: (1) Not all Q waves are due to occlusion of the saphenous bypass grafts (as noted by others). (2) A certain percentage of new Q waves may not reflect true transmural myocardial infarction, especially when all the vein grafts are patent and the postoperative ventriculograms show improvement. (3) Some new Q waves reflect true transmural infarction due to occlusion of grafts or of distal coronary arteries with deteriorated left ventriculograms. (4) The high incidence of new Q waves in patients with ventricular vents is probably due to direct myocardial trauma at the apex of the left ventricle.

Correlation of electrocardiogram and vectorcardiogram with coronary occlusion and myocardial contraction abnormality

Electrocardiograms and Frank vectorcardiograms were recorded in 156 consecutive patients with total occlusion of at least one coronary artery (on arteriography) and associated left ventricular contraction abnormality (on ventriculography). The angiograms and cardiograms were independently reviewed. In the presence of single vessel occlusion, appropriate vectorcardiographic diagnosis of myocardial infarction was determined in 118 of 156 cases (76 percent) compared with a lower electrocardiographic detection rate in 77 of 156 cases (49 percent). Findings diagnostic of two coexisting infarctions were observed in 71 percent of vectorcardiograms and 37 percent of electrocardiograms in 51 patients with double vessel occlusion and two areas of left ventricular dyskinesia. The vectorcardiographic detection rate was similarly superior to the electrocardiographic rate in the presence of subtotal coronary occlusion and myocardial asynergy in single (73 percent versus 53 percent) and double (53 percent versus 28 percent) vessel disease. The incidence rate of false positive diagnoses was 3 percent for electrocardiography and 4 percent for vectorcardiography. It is concluded that the vectorcardiogram is superior to the electrocardiogram in the diagnosis of obstructive coronary artery disease and left ventricular contraction abnormality.