Unstabel post-infarction ischemia : Identification and risk statification with special emphasis on noninvasive methods

Abstract: The Karolinska Institute, Department of Cardiology, Karolinska Hospital, Stockholm, Sweden Unstable post-infarction ischemia Identification and risk stratification with special emphasis on noninvasive methods MIGUEL QUINTANAAlthough in-hospital mortality after acute myocardiat infarction has decreased, long-term mortality is still high.This study tested the prognostic value of detecting residual myocardial ischemia by different techniques in 74patients recovering from an acute myocardial infarction.The prevalence and prognostic significance of ST-segment depression detected by ambulatory electrocardiographywas studied. The prognosis in 22 (30%) patients with ST-segment depression was worse than in 52 (70%) without,regarding short-term cardiac events (defined as death or reinfarction or revascularization) (P<0.01), long-termmortality (P=0.01) and long-term cardiac events (P<0.001). Compared with clinical variables in a multivariateregression analysis, ST-segment depression was the strongest covariate assessing prognosis.Due to the high prevalence of prolonged or fixed ST-segment depression during ambulatory electrocardiography,new methods to detect ST-segment changes were assessed. ST-segment changes were analyzed from four referencelevels. ST-segment elevation was measured 0 to 5 ms after the J point. The presence of ST-segment elevationmeasured from a 24-hour median level was statistically associated with mortality (P=0.03). The sensitivity, specifi-city and accuracy of ST-depression/ST-elevation measured from the 24-hour median level in predicting mortalitywere 78%, 71% and 73%, respectively. These values are higher than those reported for ST-segment depressiondetected during exercise testing.The prognostic value of ST-segment depression detected by ambulatory electrocardiography was compared withthe outcome of exercise testing. Both tests were able to predict death, death or nonfatal infarction and cardiacevents. The sensitivity of both methods to assess death and death or nonfatal infarction was similar. The specificityof ambulatory electrocardiography was superior in predicting death (P=0.01) and death or nonfatal infarction(P=0.001). When both techniques were combined, the studied population could be classified in groups with low,medium and high risks. ST-segment depression detected by ambulatory electorcardiography was a stronger covariatein predicting mortality than exercise-induced ST-segment depression.The prognostic value of predischarge stress echocardiography was studied. The method was compared with exercisetesting and clinical variables. A positive stress echocardiography was associated with a poor prognosis (mortality:P=0.0002; cardiac events: P<0.0001). Even revascularization procedures, subsequently decided upon the results ofexercise testing and clinical symptoms, were predicted by the initial stress echocardiogram (P=0.02). A new-onsetwall motion abnormality during stress echocardiography was the strongest variable predicting death and death ornonfatal infarction.The cardiac sympatho-vagal regulation was studied immediately after the acute phase of AMI. Heart rate variabil-ity was evaluated in the time and frequency domains. Heart rate variability was compared in survivors, nonsurvivorsand a group of 24 healthy controls. Heart rate variability was higher in survivors than in nonsurvivors (P=0.005),higher in controls than in survivors (P=0.05), higher in controls than in nonsurvivors (P=0.0001) and higher inpatients without cardiac events and reinfarction (P=0.03 and P=0.03, respectively). In a multivariate regressionanalysis, including clinical variables and left ventricular ejection fraction in the model, heart rate variability retai-ned its independent and additive prognostic value.The prognostic value of several clinical variables and variables derived from diverse noninvasive methods wasinvestigated in a two-stage multivariate stepwise regression analysis. The following covariates were tested: clinicalvariables, ST-segment changes detected on ambulatory electrocardiography and exercise testing, heart rate varia-bility, ejection fraction, wall motion score index, worsened or new-onset wall motion abnormality on stressechocardiography and different physiological variables obtained during exercise testing. At the second stage of thismultivariate analysis only new-onset wall motion abnormality, ST-segment depression on ambulatoryelectrocardiography and decreased heart rate variability had additive and independent value to predict mortality,In conclusion, residual myocardial ischemia detected by different techniques was the strongest factor predictinglong-term mortality and should be studied in all patients recovering from an acute myocardial infarction.Key words: myocardial infarction, myocardial ischemia, prognosis, exercise test, stress echocardiogaphy. ambulatoryelectrocardiography, heart rate variability.Stockholm 1996 ISBN: 91-628-1906-2