AJP - Heart and Circulatory Physiology, Vol 246, Issue 2 232-H238, Copyright © 1984 by American Physiological Society
Transmural pH gradient in canine myocardial ischemia
R. M. Watson, D. R. Markle, Y. M. Ro, S. R. Goldstein, D. A. McGuire, J. I. Peterson and R. E. Patterson
The subendocardium is more susceptible to ischemia than the subepicardium.
Studies during critical coronary stenosis have demonstrated subendocardial
hypoperfusion relative to the subepicardium and transmural gradients in
certain tissue metabolites. Although ischemia causes acidosis, the
existence of a transmural pH gradient has never been demonstrated or
quantitated. Thus we reduced coronary blood flow to 20 +/- 5% of normal in
eight open chest anesthetized (morphine sulfate and pentobarbital) dogs and
to 45 +/- 5% in two dogs. We implanted specially designed miniature
fiber-optic pH probes in normal and ischemic subendocardium (depth 5.5-8
mm) and subepicardium (depth 3-4 mm). Separate experiments validated use of
the fiber-optic pH probe system to measure tissue pH. Although both probes
were located in the ischemic zone, there was a large transmural gradient,
i.e., from normal pH values (7.36) in the subepicardium to severely
acidotic (pH 6.94) 2 mm deeper in the subendocardium. This marked
difference in pH between nearby transmural layers may have important
implications regarding arrhythmogenesis in the setting of acute myocardial
ischemia.
