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Myocardial ischemia caused by distal coronary-artery constriction in stable angina pectoris
G Pupita1, A Maseri, J C Kaski
1Cardiovascular Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
Insights
Constriction of distal or collateral coronary vessels, not just stenosis, can cause variable angina in stable coronary artery disease patients. This finding suggests new therapeutic targets for managing myocardial ischemia.
Area of Science:
- Cardiology
- Vascular Biology
- Ischemic Heart Disease
Background:
- The ischemic threshold for angina in stable coronary artery disease (CAD) is often variable.
- This variability is typically attributed to changes at the stenosis site, but distal or collateral vessel constriction is also a possibility.
Purpose of the Study:
- To investigate the role of distal and collateral coronary vessel constriction in causing myocardial ischemia in patients with stable angina.
- To test the hypothesis that factors beyond the primary coronary stenosis influence the ischemic threshold.
Main Methods:
- Studied 11 patients with stable angina, single coronary artery occlusion supplied by collaterals, normal ventricular function, and no vasospasm or other stenoses.
- Assessed ischemic threshold using heart rate-systolic blood pressure product during exercise testing, with and without nitroglycerin and ergonovine.
- Utilized ambulatory electrocardiographic monitoring and coronary angiography to evaluate ischemic episodes and collateral vessel function.
Main Results:
- Nitroglycerin increased the ischemic threshold by 19% (P<0.05), while ergonovine decreased it by 18% (P<0.01).
- Ambulatory monitoring revealed significant heart rate variations during ischemic episodes and instances of ischemia occurring at lower heart rates than exercise-induced thresholds.
- Angiography showed delayed and reduced collateral filling after ergonovine, correlating with ST-segment depression.
Conclusions:
- Distal coronary artery constriction, collateral vessel constriction, or both, can precipitate myocardial ischemia in patients with chronic stable angina.
- These findings challenge the traditional view focusing solely on epicardial stenosis and highlight the importance of microvascular and collateral function in stable CAD.
Background:
In patients with stable coronary artery disease, the ischemic threshold for the production of effort-related angina is often quite variable. Although this feature is commonly attributed to changes in the caliber of coronary arteries at the site of stenosis, it could also be caused by the constriction of distal vessels, collateral vessels, or both.
Methods:
In order to test this hypothesis, we studied 11 patients with stable angina, total occlusion of a single coronary artery that was supplied by collateral vessels, normal ventricular function, no evidence of coronary-artery spasm, and no other coronary stenoses. These conditions precluded the modulation of coronary flow by vasomotion at the site of the coronary stenosis.
Results:
The ischemic threshold--assessed by multiplying the heart rate by the systolic blood pressure at a 1-mm depression of the ST segment during exercise testing--increased by 19 percent after the administration of nitroglycerin (P less than 0.05) and decreased by 18 percent after the administration of ergonovine (P less than 0.01). Ambulatory electrocardiographic monitoring of the patients when not receiving treatment detected 73 ischemic episodes that, in keeping with the history, showed variations of 25 to 52 beats per minute in the heart rate at a 1-mm depression of the ST segment; 12 episodes of sinus tachycardia exceeded the lowest ischemic heart rate by a mean (+/- SD) of 22 +/- 13 beats per minute without ST-segment depression. Furthermore, 21 ischemic episodes occurred at a heart rate more than 25 beats per minute below that at a 1-mm depression of the ST segment during exercise testing. Delayed and reduced filling of collateral and collateralized vessels associated with depression of the ST segment similar to that observed during ambulatory monitoring was detected on angiographic evaluation after the intracoronary administration of ergonovine in three patients.
Conclusions:
We propose that the constriction of distal coronary arteries, collateral vessels, or both may cause myocardial ischemia in patients with chronic stable angina.