Exercise-induced ST-segment depression: imbalance between myocardial oxygen demand and myocardial blood flow.
OBJECTIVE
ST-segment depression is believed as a common electrocardiographic sign of myocardial ischemia during exercise testing. Ischemia is generally defined as oxygen deprivation due to reduced perfusion. However, the exact relationship of the ischemic definition to ST-segment depression remains unclear. This study was conducted to evaluate the correlation between myocardial oxygen demand and myocardial blood flow (MBF) when ischemic (horizontal or downsloping) ST-segment depression of > or = 0.1 mV 80 ms after the J point developed during low-level exercise.


RESULTS
Seventy-two patients with angiographically proven coronary artery disease (CAD) and 9 healthy volunteers underwent exercise positron emission tomography (PET). Myocardial oxygen demand was defined as a rate-pressure product (RPP, heart rate x systolic blood pressure) during exercise and MBF was quantified by nitrogen-13 ammonia perfusion PET. The myocardial demand-supply balance (MDSB) index was calculated from the MBF ratio (values during exercise/values at rest) against the RPP ratio (values during exercise/values at rest). The MDSB index was significantly lower in patients with ischemic ST-segment depression than in patients with non-ischemic ST depression and healthy volunteers (0.82 +/- 0.16 vs. 1.02 +/- 0.17, p < 0.0001 and vs. 0.99 +/- 0.14, p = 0.0109). Further, the presence of inadequate increase in MBF of < or = 10% (2 SD below the mean % value of healthy volunteers) during exercise in regional myocardium perfused by stenotic CAD significantly correlated with exercise-induced ischemic ST-segment depression (p = 0.0105).


CONCLUSIONS
Our study could demonstrate that exercise-induced ischemic ST-segment depression is associated with myocardial ischemia due to exercise-induced imbalance between myocardial oxygen demand and global and regional MBF supply in patients with proven CAD.
Watanabe
T
T
Third Department of Internal Medicine, Showa University School of Medicine, Japan.
Akutsu
Y
Y
Yamanaka
H
H
Michihata
T
T
Okazaki
O
O
Katagiri
T
T
Harumi
K
K
D000328:Adult; D000368:Aged; D000787:Angina Pectoris / Q000175:diagnosis / Q000503:physiopathology; D017023:Coronary Angiography / Q000379:methods / Q000706:statistics & numerical data; D003326:Coronary Circulation / Q000502:physiology*; D003327:Coronary Disease / Q000175:diagnosis / Q000503:physiopathology; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D012016:Reference Values; D014055:Tomography, Emission-Computed / Q000379:methods / Q000706:statistics & numerical data