Effects of a rial pacing on regional myocardial gas tensions with critical coronary stenosis

O’RIORDAN, JOHN B., JOHN T. FLAHERTY, SHUKRI F. KHURI, ROBERT K. BRAWLEY, BERTRAM PITT, AND VINCENT L. GOTT. Effects of atrial pacing on regional myocardial gas tensions with critical coronary stenosis. Am. J. Physiol. 232(l): H49-H53, 1977 or Am. J. Physiol.: Heart Circ. Physiol. l(1): H49-H53, 1977. -Changes in myocardial carbon dioxide (Pm& and oxygen tension (Pm& measured by mass spectrometry have been shown to reflect quantitatively progressive degrees of regional myocardial ischemia associated with stepwise reduction in coronary blood flow. The present study utilized mass spectrometry to assess the severity of regional myocardial ischemia developing during atria1 pacing in the presence of a flow-limiting proximal critical coronary artery stenosis. Myocardial blood flow (MBF) to subepicardial and subendocardial layers was measured by the radioactive microsphere technique. Application of a “critical stenosis” resulted in a 6-mmHg decrease in PIQ,, and a 17-mmHg increase in Pm cos in the region of the myocardium supplied by the stenosed vessel. The addition of atria1 pacing resulted in a 3-mmHg further decrease in P~lrq,, and a 40mmHg further increase in Pmco,. In the region of myocardium supplied by the critically stenosed vessel MBF increased in the subepicardial layer, but decreased or remained unchanged in the subendocardial layer. The failure of myocardial blood flow to increase in deeper myocardial layers in response to the increased myocardial oxygen demand of atria1 pacing would provide a mechanism for the development of subendocardial ischemia in the presence of a critical coronary stenosis.