Can exercise testing in patients with a history of myocardial infarction predict fatal and non-fatal reinfarction?

BACKGROUND AND OBJECTIVES

Exercise testing (ET) is the preferred initial strategy for risk stratification in patients who are able to exercise and have an interpretable electrocardiogram. However, although it is often suggested and widely applied, its usefulness years after myocardial infarction (MI) is questionable. Therefore, this study was designed to assess the value of exercise testing in predicting the risk of fatal or non-fatal reinfarction in patients with chronic stable coronary artery disease (CAD) due to old myocardial infarction.

METHODS

Our study involved 766 consecutive stable subjects [mean (SD) age 57 (8.6) years; male: 89%] with stable CAD due to old MI [mean time from MI: 2.8 (0.75) years], who underwent a Bruce treadmill test and whose data were prospectively entered into our institutional database. Patients were followed up for an average of 7 (0.6) years.

RESULTS

Reinfarction was observed in 62 patients; 54 non-fatal and 8 (13%) fatal. Relative risk (RR) of cardiac death for subjects with reinfarction was 4.02 [95% confidence interval (CI): 2.46 to 6.55]. Univariate predictors of fatal or non-fatal reinfarction were: multivessel disease (RR 7.99, CI 1.12 to 56.82), EF < 40% (RR 2.91, CI 1.64 to 7.17), ST depression on rest ECG (RR 2.4, CI 1.30 to 4.45), BP increase with exercise < 10 mmHg (RR 2.36, CI 1.41 to 3.93), BP/HR interaction < 10 mmHg + < 85% max (RR 2.16, CI 1.24 to 3.76). Markers of reduced risk of recurrence included low-risk Duke Treadmill Score (RR 0.55, CI 0.33 to 0.91) and EF > or = 40% (RR 0.34, CI 0.19 to 0.60). A Cox regression model with clinical and exercise parameters detected ST depression on rest ECG (RR 1.47, CI 1.07 to 2.02), BP increase with exercise < 10 mmHg (RR 1.41, CI 1.07 to 1.87), low-risk Duke Treadmill Score (RR 0.79, CI 0.60 to 1.02). A model with coronary anatomy and ejection fraction was also able to identify multivessel disease (RR 2.95, CI 1.43 to 6.09), EF < 40% (RR 1.62, CI 1.17 to 2.25) and BP increase with exercise < 10 mmHg (RR 2.53, CI 1.35 to 4.71).

CONCLUSIONS

Stable patients with a history of MI represent a very low-risk population in whom reinfarction continues to have a severe prognosis. ET is unable to identify subjects in whom there is a risk of recurrence, especially if only ischemic parameters are evaluated (in this setting, a clinical or anatomic risk stratification may be better). The application of the Duke Treadmill Score could help to identify a very low-risk group in which no additional testing is required. Therefore, routine ET in stable patients with a history of MI is better at identifying a very low-risk group than in predicting recurrence.