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Post-myocardial infarction exercise testing. Non-Q wave versus Q wave correlation with coronary angiography and
C P Miranda1, W G Herbert, P Dubach
1Cardiology Department, Long Beach Veterans Affairs Medical Center, Long Beach, Calif 90822.
Insights
The presence or absence of Q waves does not affect exercise electrocardiography accuracy in identifying severe coronary artery disease post-myocardial infarction. Survival is linked to severe coronary disease, not Q wave presence.
Area of Science:
- Cardiology
- Diagnostic Imaging
- Clinical Medicine
Background:
- Exercise electrocardiography (ECG) is used to identify severe coronary artery disease (CAD).
- The diagnostic accuracy of exercise ECG may be affected by baseline Q waves in patients post-myocardial infarction (MI).
- Previous studies suggest Q waves might compromise exercise ECG's ability to detect three-vessel and/or left main disease.
Purpose of the Study:
- To evaluate if baseline Q waves impact the accuracy of exercise ECG in identifying severe CAD in post-MI patients.
- To assess the influence of Q waves and severe CAD on long-term survival after MI.
Main Methods:
- Retrospective analysis of 253 male post-MI patients undergoing exercise testing and coronary angiography.
- Patients were divided into Q wave (QMI) and non-Q wave (NQMI) groups based on baseline ECG.
- Exercise-induced ST segment depression was analyzed for correlation with severe CAD and long-term infarct-free survival.
Main Results:
- Exercise-induced ST segment depression reliably identified severe CAD in both QMI and NQMI groups.
- Receiver operating characteristic curve analysis confirmed the discriminating power of ST depression for severe CAD in both groups.
- Long-term infarct-free survival was significantly lower in patients with severe CAD (72%) compared to those without (86%).
Conclusions:
- Baseline Q waves do not significantly affect the accuracy of exercise ECG in identifying severe CAD in post-MI survivors.
- Long-term infarct-free survival after MI is primarily determined by the presence of severe CAD, not by whether the infarction was Q wave or non-Q wave.
Background:
The presence or absence of baseline diagnostic Q waves has been believed to compromise the accuracy of standard exercise electrocardiography in identifying severe coronary artery disease (three-vessel and/or left main disease); therefore, a retrospective analysis was performed using a personal computer data base of exercise test responses and cardiac catheterization results to evaluate this premise, and follow-up was performed to observe how Q waves and/or severe coronary disease impacted on survival.
Methods And Results:
Two hundred fifty-three male patients who had survived a myocardial infarction were studied. Patients on digitalis, those with left bundle branch block or left ventricular hypertrophy on their baseline electrocardiogram, those with previous revascularization procedures, and those with significant valvular or congenital heart disease were excluded. All patients performed either a low-level predischarge or a sign/symptom limited exercise test and underwent diagnostic coronary angiography within 32 days of each test (range, 0-90 days). Long-term follow-up on patients was performed for an average of 45 months (+/- 17 months). Group NQMI comprised 103 post-myocardial infarction patients lacking Q waves at the time of exercise testing and group QMI comprised 150 patients who developed Q waves with their myocardial infarction. The cut points of greater than or equal to 1 mm (chi 2 = 14.39, p less than 0.001) and greater than or equal to 2 mm (chi 2 = 26.11, p less than 0.001) of exercise-induced ST segment depression were reliable markers of severe coronary disease in Q wave infarct survivors. This was also true for non-Q wave infarct survivors as greater than or equal to 1 mm (chi 2 = 6.02, p = 0.01) and greater than or equal to 2 mm (chi 2 = 4.37, p = 0.04) of ST segment depression were reliable markers of severe coronary disease. Receiver operating characteristic curve analysis revealed that exercise-induced ST segment depression had discriminating power for the identification of severe coronary artery disease in both the Q wave myocardial infarction patients (area = 0.735, z = 4.47, p less than 0.001) and the non-Q wave infarct patients (area = 0.700, z = 3.20, p less than 0.001). After 4.4 years of cumulative follow-up, patients with severe coronary disease had an infarct-free survival rate of 72% (95%, CI, 50.0-86.0%), whereas those without severe disease had an 86% (95% CI, 76.5-91.5%) infarct-free survival rate (Cox chi 2 = 4.00, p = 0.045). Non-Q wave patients had an infarct-free survival rate of 81% (95% CI, 66.0-89.5%), whereas those with Q waves had an infarct-free survival rate of 85% (95% CI, 73.9-91.3%) (Cox chi 2 = 0.0005, p = NS).
Conclusions:
The presence or absence of diagnostic Q waves has no significant effect on the ability of the exercise electrocardiogram to identify severe coronary artery disease in survivors of myocardial infarction. Long-term infarct-free survival of patients with myocardial infarction is more related to the presence of severe coronary disease rather than if they suffered a non-Q wave or Q wave infarction.