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The myocardial oxygen supply/demand ratio in patients with and without coronary artery disease
Insights
Patients with coronary artery disease show a reduced increase in coronary blood flow when myocardial oxygen demand rises, indicating an impaired blood supply. This contrasts with healthy individuals who exhibit an appropriate blood flow response.
Area of Science:
- Cardiology
- Physiology
Background:
- Assessing myocardial oxygen supply and demand is crucial in understanding coronary artery disease (CAD).
- Thermodilution and double product measurements offer insights into coronary sinus blood flow and myocardial oxygen demand, respectively.
Purpose of the Study:
- To investigate the relationship between coronary sinus blood flow and myocardial oxygen demand during atrial pacing.
- To compare this relationship in patients with and without coronary artery disease, particularly during induced ischemia.
Main Methods:
- Coronary sinus blood flow was measured using thermodilution.
- Myocardial oxygen demand was assessed via the heart rate-systolic arterial pressure double product.
- Atrial pacing was employed to increase myocardial oxygen demand in patients with and without CAD, with ischemia monitored by ECG and lactate.
Main Results:
- Coronary blood flow increase during pacing was significantly lower in patients with CAD (50 ml/min) compared to controls (79 ml/min).
- The ratio of coronary blood flow to double product decreased in CAD patients during pacing but remained stable in controls.
- No significant changes in aortic-coronary sinus oxygen content difference were observed in either group.
Conclusions:
- Patients without CAD demonstrate an appropriate increase in coronary blood flow to meet heightened myocardial oxygen demand.
- Individuals with CAD experiencing ischemia show an inappropriately low increment in myocardial blood flow, suggesting a compromised oxygen supply.
Abstract:
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 x 10(-3) controls, 11.6 +/- 2.7 x 10(-3) coronary artery disease; NS). At peak pacing, it was unchanged in the controls (10.4 +/- 2.0 x 10(-3)) but fell in those with coronary artery disease (9.0 +/- 2.5 x 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.