The effect of hypertension and left ventricular hypertrophy on the lower range of coronary autoregulation.

Abstract

These studies were performed to test the hypothesis that left ventricular hypertrophy arising as a complication of chronic hypertension is associated with impaired coronary autoregulation. Twelve dogs with hypertension and left ventricular hypertrophy (one-kidney, one-clip model) and 11 normal dogs were instrumented and subsequently studied while conscious. Circumflex pressure, measured with an intracoronary catheter, was adjusted to 100, 75, and 40 mm Hg with a hydraulic occluder that was placed proximally. At each circumflex pressure, myocardial perfusion was measured with radioactive microspheres. Reduction of circumflex pressure over this range did not significantly alter heart rate, left atrial pressure, or arterial pressure. In normal dogs, reduction of circumflex pressure did not alter total myocardial perfusion or the transmural distribution of perfusion. In contrast, in dogs with hypertension and left ventricular hypertrophy, circumflex subendocardial perfusion decreased 46% when pressure was decreased from 100 to 40 mm Hg (p less than .05 compared with normal). Autoregulation was quantified for each third of myocardium with the use of autoregulatory gain values (1 = perfect autoregulation; 0 = the absence of autoregulation). For pressure changes of 100 to 75 mmHg, values for autoregulatory gain were near unity for all layers of myocardium in both groups of animals. When pressure was decreased from 75 to 40 mm Hg, values for autoregulatory gain among the normal and hypertensive groups were, respectively: for subepicardium 1 +/- 0.2 (mean +/- SE) vs 0.9 +/- 0.2 (p = NS), for the midwall 0.8 +/- 0.2 vs 0.5 +/- 0.2 (p = NS), and for the subendocardium 0.8 +/- 0.1 vs 0.1 +/- 0.2 (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)