Novel insights into the pathophysiology of different forms of stress testing

BACKGROUND: The impact of different forms of cardiac stress testing (exercise versus pharmacological stress testing) on cardiac wall stress and myocardial ischemia is incompletely understood.

METHODS: In a prospective study, 331 consecutive patients with suspected myocardial ischemia referred for nuclear perfusion imaging were enrolled: 266 underwent exercise (bicycle) stress testing and 65 adenosine stress testing. Levels of B-type natriuretic peptide (BNP) measured before and 1 min after stress testing, ischemic ECG changes, and typical angina symptoms were used to compare the 2 testing modalities.

RESULTS: Cardiac wall stress as quantified by changes in BNP levels significantly increased in the exercise stress group, but not in the adenosine group (increase in BNP levels 22 pg/ml (IQR 6-46) versus -3 pg/ml (IQR -3 to 28); p<0.001). In the bicycle exercise stress group, patients with reversible defects on nuclear perfusion imaging more often had angina symptoms (25% vs. 9%, p=0.0001) and ischemic ECG changes (33% vs. 12%, p=0.0001) during the stress test, and a greater increase in BNP levels (28 (IQR 11-58) versus 16 (IQR 3-34) pg/ml, p=0.001) compared to those without reversible defects. Those differences between patients with and without reversible defects were not observed with the adenosine protocol (p-values all >0.05).

CONCLUSION: Exercise stress testing but not adenosine stress results in an increase of cardiac wall stress, angina symptoms and ECG changes. The absence of these surrogates of myocardial ischemia suggests that adenosine stress does not induce acute myocardial ischemia, but rather displays relative perfusion differences.