The myocardial oxygen supply/demand ratio in patients with and without coronary artery disease

This study was performed to assess the relationship between coronary sinus blood flow (by thermodilution) and myocardial oxygen demand (heart rate‐systolic arterial pressure double product) during atrial pacing in patients with and without coronary artery disease. In 11 individuals with coronary artery disease, pacing was performed to ischemia, as reflected by electrocardiographic changes or lactate production; 8 patients without coronary artery disease served as controls. Coronary sinus blood flow (in ml/min) was similar for the two groups at rest. However, the increase in coronary blood flow from rest to peak pacing was less (P = 0.025) in those with coronary artery disease (50 ± 26 ml/min) than in controls (79 ± 26 ml/min). The ratio of coronary sinus blood flow to double product was the same at rest in both groups (11.1 ± 2.2 × 10⁻³ controls, 11.6 ± 2.7 × 10⁻³ coronary artery disease; NS). At peak pacing, it was unchanged in the controls (10.4 ± 2.0 × 10⁻³) but fell in those with coronary artery disease (9.0 ± 2.5 × 10⁻³; P = 0.002). The aortic‐coronary sinus oxygen content difference was similar at rest in both groups and did not change in response to pacing in either group. Thus, in response to augmented myocardial oxygen demand, patients without coronary artery disease have an appropriate increase in coronary blood flow and myocardial oxygen supply, while in those with coronary artery disease who develop ischemia the increment in myocardial blood flow (and oxygen supply) is inappropriately low.