The short- and long-term prognosis of patients with transmural and nontransmural myocardial infarctio

To compare the long-term prognosis in patients surviving transmural with patients surviving nontransmural myocardial infarctions, the records of 188 consecutive patients with clinical histories and enzyme elevations consistent with acute infarction were reviewed. According to standard electrocardiographic criteria the patients were divided into two groups: 148 with transmural myocardial infarction (group 1) and 40 with nontransmural myocardial infarction (group 2). Of the patients who survived hospitalization, follow-up data were obtained on 119 of 124 patients in group 1 and 36 of 37 patients in group 2 at a mean follow-up period of 36 months. In group 2, the patients had a high incidence of sudden death after discharge (33 per cent in group 2 versus 15 per cent in group 1, p < 0.02) as well as a significantly higher incidence of death from all cardiac causes (41.6 per cent in group 2 versus 24.3 per cent in group 1, p < 0.05). Furthermore, the patients in group 2 still alive at the end of the follow-up period had an increased incidence of angina pectoris and of recurrent infarction. The data suggest that patients with nontransmural myocardial infarction carry a particularly guarded prognosis.     

Coronary angiography and left ventriculography in survivors of transmural and nontransmural myocardial infarction

Recent studies have suggested a similar prognosis for patients with transmural myocardial infarction and nontransmural myocardial infarction despite a smaller infarct size in the latter patients estimated by creatine phosphokinase (CPK). Thirty-one patients with transmural myocardial infarction and 17 patients with nontransmural myocardial infarction as defined by electrocardiographic criteria underwent coronary angiography and left ventriculography from 10 to 24 days after they had an acute myocardial infarction. Forty-three of these 48 patients were asymptomatic following their myocardial infarction. When compared to patients with nontransmural myocardial infarction, those with transmural myocardial infarction had greater peak CPK levels, 1,090 +/- 210 versus 290 +/- 60 IU (p less than 0.01). There was no difference in prevalence of single, double or triple vessel coronary artery disease, mean number of coronary arteries 50 per cent narrowed (2.0 +/- 0.2 versus 2.0 +/- 0.2), near total or total occlusions, coronary score (Friesinger) (7.9 +/- 0.6 versus 8.2 +/- 0.7), left ventricular ejection fraction (48 +/- 2 versus 53 +/- 4), or per cent of akinetic-dyskinetic myocardial segments (66 of 242 [27 per cent] versus 32 of 132 [24 per cent]) between two groups. The similar extent of coronary artery narrowing and degree of left ventricular dysfunction may explain the similar prognosis for patients with transmural myocardial infarction and those with nontransmural myocardial infarction despite differences in enzymatically estimated acute infarct size.     

The role of cardiac catheterization in patients after myocardial infarction

Cardiac catheterization is extremely important in defining prognosis and determining the approach to therapy in many subsets of patients with a recent myocardial infarction in addition to those undergoing early thrombolytic therapy or operation for potentially lethal complication of acute myocardial infarction. Such an approach seems prudent for most patients with nontransmural myocardial infarctions, patients under age 40 with a first infarction, and patients with post-infarction angina. In patients with uncomplicated myocardial infarction it is usually possible to separate relatively low-risk and high-risk patients, with risk stratification depending upon the results of low-level early post-infarction, symptom-limited electrocardiographic exercise testing and other noninvasive methods when indicated. Such an approach does not preclude the necessity of assessing each patient as an individual as well as within the subgroup in which he or she belongs.     

High mortality early reinfarction with first nontransmural myocardial infarction

Thirty-eight patients with first nontransmural myocardial infarction were studied to determine prognosis and clinical markers of a high-risk subgroup. We found a high incidence of reinfarction (18%) at a median time of 16 days post nontransmural infarction (seven patients). Reinfarction was uniformly associated with death within 24 hours. A total of 14 patients (37%) either died (eight patients) or required urgent revascularization (six patients). Predominant ST segment depression with presenting nontransmural infarction and a history of prior angina were associated with increased mortality (p less than 0.05 and p = 0.05, respectively). We conclude that patients with nontransmural infarction are at high risk for early recurrent infarction. Patients with history of prior angina and predominant ST segment depression may be at particularly high risk. Reinfarction in these patients is frequently extensive. We recommend that these patients be considered for early coronary angiography.     

Electrocardiographic, arteriographic and ventriculographic correlations in transmural myocardial infarction

To determine if significant interrelations exist between the electrocardiographic diagnosis of transmural myocardial infarction, sites of coronary arterial obstruction, and left ventricular asynergy, 235 patients with angiographically documented coronary artery disease were subdivided according to the electrocardiographic location of the myocardial infarction, the coronary arterial system involved and the site of ventricular asynergy. Of 82 instances of anterior myocardial infarction, the left anterior descending artery demonstrated significant disease in 79 (96 percent). Of 100 instances of inferior myocardial infarction, the right coronary artery was significantly diseased in 87 and the left circumflex in 55. When multiple infarctions were present, multivessel disease was found in 93 percent of patients. Left ventricular asynergy was present in 81 percent, including 84 percent of those with anterior infarction, 74 percent of those with inferior infarction, and 93 percent of those with multiple infarctions. The results of our study suggest that the electrocardiogram is often of value in indicating sites of coronary arterial obstruction and ventricular asynergy in patients with coronary artery disease and transmural myocardial infarction.     

Value and limitations of technetium-99m stannous pyrophosphate in the detection of acute myocardial infarction.

Technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial imaging was performed in 436 consecutive patients for the evaluation of chest pain and suspected acute myocardial infarction (AMI). Scintigrams were assessed independently by three observers with a 90% interobserver agreement. In 134 patients with documented AMI (97 TRANSMURAL, 37 NONTRANSMURAL), THE SENSITIVITY OF 99MTc-PYP imaging was significantly lower in patients with nontransmural AMI (41%) than in patients with transmural AMI (78%), 99mTc-PYP imaging correctly localized the site of transmural infarction in 53 patients (70%). A diffuse 99mTc-PYP uptake was found in nine (10%) of 91 patients with positive scintigrams: six of these had a transmural AMI and three nontransmural AMI. In 226 patients without AMI, the specificity of infarct imaging was 95%. A false-positive scintigram was found in 0%, 8%, 9%, and 2% of patients with unstable angina, progressive angina, stable angina, and noncardiac chest pain, respectively. A diffuse uptake was found in six (54%) of 11 patients with false-positive scintigrams. No patient with the clinical diagnosis of noncardiac chest pain showed discrete uptake. In 76 patients with uncertain diagnosis for AMI, 99Tc-PYP imaging was considered of value in 11 patients with ventricular conduction defects (two patients with WPW syndrome, nine patients with LBBB). These data suggest that: 1. 99mTc-PYP imaging is moderately sensitive in detecting and localizing transmural AMI and is insensitive in detecting nontransmural AMI; 2. A discrete 99mTc-PYP uptake is highly specific for AMI; 3. a diffuse uptake is neither sensitive to, nor specific for AMI. Myocardial imaging with 99m-Tc-PYP is of clinical value when the standard electrocardiographic and enzymatic techniques are inadequate for an accurate diagnosis of AMI.     

Nontransmural versus transmural myocardial infarction: A morphologic study

Although “nontransmural” and “transmural” are morphologic terms used widely to distinguish patients with myocardial infarction, controversy exists as to their meaning regarding clinical course. For this study, a transmural infarct was defined as one that involves essentially the full thickness of the ventricular wall, and nontransmural was defined as something less. The purpose of this study was to identify true morphologic nontransmural acute (less than 21 days old) infarcts at autopsy and compare them with transmural (full-thickness) infarcts in age-matched subjects, for clinical and pathologic similarities and differences. Among the autopsy subjects, comparing 35 nontransmural and 35 transmural infarcts, there was no significant difference with regard to subjects' race or sex, chest pain, arrhythmias, heart block, or cause of death; transmural myocardial infarctions did have a higher frequency of new Q waves (30 of 35 versus six of 35, p < 0.001) and presented more often with increasing dyspnea. At autopsy, there were no significant differences regarding heart weight, location of infarcts, severity of coronary disease, age of acute infarct, or total size of infarct (18 percent of left ventricle for nontransmural versus 22 percent for transmural). There was, however, a significantly greater tendency for those with nontransmural infarct to have evidence of prior infarction at autopsy (27 of 35 versus 19 of 35, p < 0.05). Acute coronary thrombi in the distribution of the infarct were significantly more common among transmural myocardial infarcts (32 of 35 versus 18 of 35, p < 0.001). Morphologically, the nontransmural infarcts showed mural involvement ranging from 20 to 90 percent of the left ventricle, and histologically showed more contraction band (i.e., reflow) injury (57 percent with more than 30 percent contraction band necrosis) compared with transmural infarcts (32 percent with more than 30 percent contraction band necrosis) (p < 0.05). Fatal nontransmural and transmural infarcts have major clinical and pathologic similarities, but differences in number of prior infarcts, type of necrosis, and occurrence of coronary thrombi suggest differing pathophysiology. The heterogeneity of both transmural and nontransmural infarcts likely accounts for existing differences among clinical studies regarding prognosis. Although this classification system has value in the clinical setting, that at times it represents an imprecise oversimplification of infarct type should be recognized in assessing individual patients.     

Contribution of Frank ECG measurements to the quantitative estimation of old anterior myocardial infarction

Twenty scalar and vector measurements of the Frank ECG were compared between men categorized as having suffered nontransmural (n = 47) and transmural anterior myocardial infarction (n = 124), on the basis of clinical and angiocardiographic findings. Variables which showed significant differences of group means between cases with anterior wall hypokinesis and anterior wall akinesis and/or dyskinesis were submitted to linear discriminant-function analysis. The stepwise selection procedure of Rao's method demonstrated the three most decisive variables for differentiation to be: (1) the angular sum of dorsal displacement of the 5 initial QRS vectors obtained at 0.01 sec intervals (sum of negative azimuth angles); (2) the Q duration in lead Z (anterior force); and (3) the Q duration in lead X (rightward force). The classification routine can identify correctly 81% of the nontransmural and 79% of the transmural anterior infarctions. The high percentages of correctly classified nontransmural and transmural infarctions show significant diagnostic potential for patient management. From the results of discriminant-function analysis, it is apparent that the sum of negative azimuth angles derived from the dorsally directed vectors during the first half of QRS exceeds substantially the scalar variables in their contribution to differentiation of the two conditions.     

The incidence and prognosis of unrecognized myocardial infarction in the Honolulu, Hawaii, Heart Program

The incidence of clinically unrecognized myocardial infarctions among 7331 Japanese-American men in Hawaii, aged 45 to 68 years and free of coronary heart disease at entry, was studied on the basis of electrocardiographic changes between successive examinations during 6 years of follow-up. The proportion of asymptomatic myocardial infarction accounted for 33% of transmural (Q-wave) myocardial infarctions identified by temporal changes on electrocardiogram and 22% of all nonfatal infarctions ascertained by either repeated examinations or hospital surveillance. The 10-year prognosis of unrecognized infarction, in terms of mortality from all causes, cardiovascular disease, and coronary heart disease, was worse (with risk ratios of 1.5 to 1.7) than that of recognized infarction, even after adjusting for age and other possible determinants, although the differences were not statistically significant. These findings suggest that regular health check-ups with an electrocardiogram would be important to detect asymptomatic myocardial infarction and to increase the opportunity of taking secondary preventive measures. However, the conclusion should await further studies based on intervention trials to determine the comparative effects of the secondary prevention on the prognosis of clinically recognized vs unrecognized infarction.     

Incidence and significance of the low-voltage electrocardiogram in acute myocardial infarction.

In a retrospective study of 304 patients with acute transmural myocardial infarction admitted to the coronary care unit, 22 percent (67 patients) exhibited low voltage on their electrocardiograms within 72 hours of admission. The course of hospitalization of these patients was compared with an equal number of consecutive patients with transmural infarctions and normal electrocardiographic voltages. Among the patients with low voltage, there was a significantly higher incidence of previous infarction or present extensive infarction, congestive heart failure, and cardiogenic shock. This group of patients also demonstrated a markedly higher mortality. This study substantiates the clinical impression that acute myocardial infarction complicated by a low-voltage ECG implies a poor prognosis. It is speculated that this electrocardiographic pattern may reflect decreased ventricular performance as a result of widespread myocardial damage.     

Nontransmural myocardial infarction: A comparison of hospital and late clinical course of patients with that of matched patients with transmural anterior and transmural inferior myocardial infarction

The hospital and long-term course of 67 patients with nontransmural myocardial infarction was compared with that of 66 patients with transmural anterior and 63 patients with transmural inferior infarction matched for age, sex, previous infarction and prior congestive heart failure. During their hospital stay, patients with nontransmural infarction had significantly less congestive heart failure and fewer intraventricular conduction defects than did patients with transmural anterior infarction; fewer atrial tachyarrhythmias and less sinus bradycardia and atrioventricular block than did patients with transmural inferior infarction; and an incidence of hypotension, pericarditis and ventricular irritability similar to that of patients in the other two groups. Patients with nontransmural infarction had a significantly lower coronary care unit mortality rate (9 percent) than that of patients with transmural anterior or transmural inferior infarction (20 and 19 percent, respectively). By 3 months, the mortality rate had risen to 14 percent in patients with nontransmural infarction, but was significantly higher (29 and 27 percent, respectively) in patients with transmural anterior or transmural inferior infarction. Angina was common in all three groups, occurring in more than 50 percent of patients during a mean follow-up period of 28.6 months after hospital discharge.In contrast, the incidence of subsequent myocardial infarction was significantly greater in patients with nontransmural myocardial infarction, occurring in 21 percent at 9 months compared with only 3 percent of patients with transmural anterior (p <0.01) and 2 percent of patients with transmural inferior (p <0.05) infarction. By 54 months, 57 percent of patients with nontransmural infarction had sustained a new infarction contrasted with only 12 percent of patients with transmural anterior (/p <0.001) and 22 percent of patients with transmural inferior (p <0.01) infarction. Late mortality increased in patients with nontransmural myocardial infarction and, although this group had a significantly better survival rate at 3 months, the overall late mortality of the three groups was comparable. The study suggests that nontransmural myocardial infarction is an unstable ischemic event associated with a great risk of later myocardial infarction and high late mortality rate. A more aggressive diagnostic and therapeutic approach may be warranted in patients with nontransmural myocardial infarction.     

Significance of the Q wave in acute myocardial infarction

Acute myocardial infarction may be associated with the development of Q waves on the electrocardiogram (ECG), or with changes limited to the ST segment or T wave. The ECG changes do not accurately differentiate transmural from nontransmural infarction. However, the presence or absence of a Q wave does correlate with some aspects of the clinical course of patients after myocardial infarction, and is therefore of prognostic value. Q-wave infarctions are more likely to be complicated by congestive heart failure during hospitalization. The in-hospital mortality is also higher after a Q-wave infarction than after a non-Q infarction. Both of these findings are probably due to the association of a Q wave with a larger mass of infarcted myocardium. The long-term mortality, however, is the same for Q-wave and non-Q-wave infarctions. This is probably due to an increased late mortality after non-Q infarctions, related in part to a higher rate of reinfarction. The differences between Q-wave and non-Q-wave infarctions are not due to obvious differences in extent and location of coronary artery obstructions. However, there may be differences in the collateral circulation, with more extensive collaterals associated with non-Q infarcts. Appreciation of the prognostic significance of the ECG changes in acute myocardial infarction may help direct the evaluation and management of the patient after myocardial infarction.     

Survival of patients with nontransmural myocardial infarction: A population-based study

A population-based study was conducted in metropolitan Baltimore in which the short- and long-term prognosis of 283 patients with nontransmural myocardial infarction was compared with that of 953 patients with transmural infarction. After simultaneous adjustment for several variables, the in-hospital case fatality rate was greater for patients with transmural (30.1 percent) than with nontransmural (18.3 percent) infarction (P < 0.01). However, for patients discharged alive from the hospital and followed up for as long as 10 years, no significant differences in survival were found between the groups with transmural and nontransmural infarction. A multiple adjustment procedure yielded 3 year case fatality rates of 27.1 percent and 28.3 percent, respectively, for patients with transmural and nontransmural myocardial infarction surviving the acute phase.These results suggest that the long-term prognosis of patients with nontransmural infarction is as guarded as that of patients with transmural infarction and that attempts to prevent subsequent mortality should be diligently pursued in both groups of patients.     

Submaximal exercise testing after acute myocardial infarction: myocardial scintigraphic and electrocardiographic observations.

The relation between global and regional left ventricular function and electrocardiographic signs of ischemia at rest and during submaximal supine exercise was studied in 27 patients 2 to 3 weeks after acute myocardial infarction. Dynamic myocardial scintigraphy was performed at rest and during submaximal exercise utilizing an in vivo method of labeling red blood cells with technetium-99m pertechnetate. Gated radionuclide blood pool scintigrams were obtained in a modified left anterior oblique, and in some patients also in the right anterior oblique projection, to measure left ventricular ejection fraction and segmental wall motion. Electrocardiographic monitoring of heart rate and rhythm was provided during the exercise. The submaximal exercise test was terminated when the patient's heart rate reached 125 beats/min or if angina, malignant ventricular ectopy or electrocardiographic evidence of myocardial ischemia developed before this rate was reached. The data demonstrate that patients with a recent anterior myocardial infarct, in contrast to patients with a recent inferior or nontransmural infarct, manifest a significant reduction in left ventricular ejection fraction with submaximal exercise. Of the eight patients with an anterior infarct, seven had segmental wall motion abnormalities at rest. Four of these eight manifested more severe abnormalities with submaximal exercise; three had abnormalities at rest that did not change with exercise. Four of the eight had a positive electrocardiographic response during exercise (two were taking digoxin). Of these four, only two had more marked wall motion abnormalities with effort. Of the 13 patients with an inferior infarct, 11 had apparently normal wall motion in the modified left anterior oblique projection at rest, including 2 who manifested segmental wall motion abnormalities with submaximal exercise; the 2 remaining patients had wall motion abnormalities at rest that, on exercise, became more marked in one and were unchanged in one. Four of the 13 had a positive electrocardiographic response with exercise (one was taking digoxin); only one of these had a detectably more severe wall motion abnormality with exercise. Of the six patients with a nontransmural infarct, four had no identifiable wall motion abnormalities at rest; in one of these, an abnormality developed with exercise. The remaining two patients had wall motion abnormalities at rest; in one, a positive electrocardiographic ischemic response developed with exercise. Patients with an anterior infarct appear to have a different functional ventricular response to submaximal exercise at the time of hospital discharge than patients with an inferior or nontransmural infarct. To identify ischemic responses with submaximal exercise in these patients one should ideally use both electrocardiographic monitoring and dynamic myocardial scintigraphy.     

Transient giant R waves in the early phase of acute myocardial infarction: Association with ventricular fibrillation

An unusual electrocardiographic (ECG) pattern was observed in five patients who suffered an acute anterior myocardial infarction. Early in their illness and following resuscitation from ventricular fibrillation (three patients), in the midst of recurrent ventricular irritability prior to development of ventricular fibrillation (one patient), and following a period of seizures (one patient), the ECG showed ST-segment elevation, marked increase in the R-wave amplitude, disappearance of S waves and merging of QRS complexes with the elevated ST segments. ECG patterns noted in these patients were similar to the ones recorded from dogs immediately after ligation of a large coronary artery, and from patients with severe episodes of variant angina. Although these early electrocardiographic changes probably reflect either marked regional transmural blood flow deprivation or its aftermath, they could not be taken as indices of eventual massive myocardial necrosis since in most of these patients the alterations were followed by development of nontransmural myocardial infarction. The possible mechanisms and the implications of such discrepancy between early and late electrocardiographic indicators of injury or necrosis is discussed.     

急性下壁合并后壁心肌梗死的心电图表现及其临床特点分析

目的探讨急性下壁合并后壁心肌梗死患者的心电图表现及其临床特点。方法对45例急性下壁合并后壁心肌梗死(A组)及60例单纯急性下壁心肌梗死(B组)患者的心电图进行对比分析。结果A组的平均RV1振幅、V1～V3导联ST段压低值及院内并发症发生率均显著高于乙组,两组比较差异有统计学意义(P<0.01,P<0.05)。结论急性下壁合并后壁心肌梗死患者的梗死面积大,院内并发症发生率高。后壁心梗的正确诊断对整个梗死面积的估计和预后判断有重要意义。     

Left ventricular functional alterations at rest and during submaximal exercise in patients with recent myocardial infarction

Submaximal exercise testing with radionuclide ventriculography was performed in 117 patients prior to hospital discharge 16.7 ± 6.7 days (SD) following acute myocardial infarction. The hypothesis tested in this study was that patients with different locations and types of infarction have different functional responses to submaximal exercise prior to discharge. The distribution of the myocardial infarctions were anterior transmural in 33, Inferior transmural in 39, anterior nontransmural in 23, inferior nontransmural in 19, and indeterminant in three. Patients with transmural infarction generally had significantly larger resting left ventricular volumes at enddiastole and end-systole and lower ejection fractions and systolic blood pressure/end-systolic volume Indexes than patients with nontransmural infarctions (p < 0.05). During submaximal exercise, the change in end-systolic volume was significantly different in these two groups. When patients were separated further into anterior and inferior transmural subgroups, the patients with anterior transmural infarction had significantly lower left ventricular ejection fractions and higher right ventricular ejection fractions than the group with inferior transmural Infarction (p < 0.05). In response to exercise, the group with anterior transmural infarction had a significant decrease in left ventricular ejection fraction and a blunted systolic blood pressure/left ventricular end-systolic volume index, in comparison to patients with inferior myocardial infarction (p < 0.05); this was the only group to have a significant increase in end-systolic volume. The group variance for the parameters studied was large, particularly during exercise when the individual responses were frequently directionally opposite from the group means. The group with anterior transmural infarction was the most homogenous, with 26 of 33 having a directionally abnormal response to submaximal exercise. It was concluded that the group with anterior transmural infarction generally displayed the most abnormal left ventricular function. However, despite significant group differences in resting ventricular function with different infarcts, the intragroup variability at rest and in response to exercise was too great to permit an accurate prediction of the subject's resting ventricular performance or to permit a prediction of exercise response based solely on location of the infarct.     

Clinical, electrocardiographic, and ventriculographic consequences of isolated occlusion of the right coronary artery

The effects of total occlusion of the right coronary artery, a sole lesion, were evaluated in an unselected series of 45 patients. Findings ranged from no detectable consequences to massive post-infarction left ventricular scars. Patients were divided into three groups: Group I, those without clinical or ventriculographic evidence of myocardial infarction (10 patients); Group II, those with clinical or angiographic evidence of nontransmural myocardial infarction (eight patients); Group III, those with electrocardiographic evidence of transmural myocardial infarction (27 patients). The critical compensatory importance of collateral vessels was demonstrated (1) by the difference between the presence of adequate collaterals in Groups I and II (89 percent), versus 44.5 percent in Group III (p less than 0.005), and (2) by the fact that the three patients without demonstrable collaterals showed the most extensive wall motion abnormalities. Four patients in Group I had no clinical evidence of ischemic disease, occlusion being an incidental finding. It is concluded that the natural history of total occlusion of the right coronary artery depends largely upon the function of collateral vessels.     

A Comparison of Nontransmural and Transmural MyocardiaI Infarction

Summary: A comparison of nontransmural and transmural myocardial infarction. J. Boxall and A. Saltups, Aust. N.Z. J. Med ., 1 980, 10 , pp. 176–179.
This report compares the past history, hospital course and follow-up of 70 patients with nontransmural myocardial infarction compared to 259 patients with transmural myocardial infarction
The pre-infarction history in the two groups is similar with respect to angina and infarction. The hospital course for non-transmural myocardial infarction is not a guide for future cardiac events and the post-hospital prognosis in the two groups is similar. Nontransmural myocardial infarction has a lower hospital mortality ( P <0.05). Patients in whom nontransmural myocardial infarction is a first coronary event have a lower incidence of subsequent angina ( P < 0.05).
The study demonstrates that myocardial infarction without development of q waves does not have an unfavourable long term outlook when compared to transmural infarction. This finding is contrary to reports which suggest a poor prognosis and recommend early coronary anteriography with a view to aorto-coronary bypass in patients with nontransmural infarction     

Myocardial imaging with thallium-201: a multicenter study in patients with angina pectoris or acute myocardial infarction

A multicenter study of rest and exercise thallium-201 myocardial imaging in 190 patients from five centers was performed. Exercise images were obtained after graded treadmill or bicycle stress with use of five different gamma camera models and were interpreted by the originating investigator without knowledge of other clinical data. Of 42 patients with less than 50 percent coronary stenosis, 4 (10 percent) had a resting image defect, 1 (2 percent) a new exercise defect and 5 (12 percent) either a resting or an exercise image defect, or both. Of 148 patients with coronary stenosis of 50 percent or greater, 64, (45 percent) had an image defect in the study at rest, 90 (61 percent) had new or increased defects after exercise, and 115 (78 percent) had resting or exercise defects, or both. New exercise image defects were more common than exercise S-T depression (90 of 148 [61 percent] versus 62 of 148[42 percent]; P less than 0.01). In a second group of 111 patients with acute myocardial infarction studied at three centers, 90 patients (81 percent) had image defects compared with 71 (64 percent) two had new electrocardiographic Q waves (P less than 0.01). Smaller infractions, as assessed with serum enzyme values, and diaphragmatic infarctions were less commonly detected than larger or anterior infarctions. These findings suggest that myocardial imaging complements the electrocardiographic identification of acute myocardial infarction of exericse-induced myocardial ischemia.