By Eleanor McDermid, Senior medwireNews Reporter
Improved coupling of vascular and ventricular circulation during exercise appears to underlie the phenomenon known as warm-up angina, a UK study shows.
The researchers recruited patients undergoing percutaneous coronary intervention to undertake two consecutive bouts of exercise on a supine cycle ergometer. This allowed the team to invasively measure hemodynamic parameters, using dual sensor pressure/flow wires in the culprit coronary vessel and in the ascending aorta.
Patients exercised until they experienced ST-segment depression of at least 3 mm, or other endpoint such as maximal heart rate for age or physical exhaustion. They rested for 5 minutes between exercise periods, or until their measurements returned to near baseline values. Of the 16 patients (one female), 15 reached 1 mm ST-segment depression during both bouts of exercise, but the time to this point was a significant 53 seconds longer in the second than the first bout (313 vs 260 sec).
This pattern is consistent with warm-up angina, in which patients tolerate subsequent bouts of exercise better than the first one.
The mechanism underlying this is related to reduced central aortic pressure and myocardial microvascular resistance, report Michael Marber (King's College London) and team in Circulation.
The augmentation index, which reflects systemic arterial stiffness, was reduced by 33% throughout the second exercise period relative to the first in the current study. This reduces left ventricular work, says the team, as evidenced by a significant reduction in left ventricular ejection time.
Furthermore, the rate pressure product (central systolic blood pressure multiplied by heart rate) at the point of 1 mm ST-segment depression during the second exercise period rose in line with the reduction in the augmentation index.
Coronary microvascular resistance fell during the first bout of exercise, and was consistently reduced during the second period, resulting in an average 16% increase in coronary blood flow velocity relative to the first exercise period.
Also, the magnitude of the flow-accelerating backward expansion wave at the onset of diastole was increased 21% during the second versus first exercise period, which the team says "points to an improved myocardial relaxation in early diastole."
Marber et al note that recruitment of collaterals may also contribute to warm-up angina. But they conclude that "enhanced vascular-ventricular coupling, as well as persistent coronary vasodilation and improved cardiac-coronary interaction, play an important role in the improved performance seen on second exertion."
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