Hypertension-induced cardiac hypertrophy. Oxygen supply and consumption with pacing.

Abstract

The purpose of this study was to determine if hypertrophied myocardium was associated with diminished cardiac function, restricted oxygen supply, or oxygen consumption during tachycardia. Myocardial oxygen supply and oxygen consumption were determined during baseline and atrial pacing conditions 30 days after New Zealand White rabbits were prepared as one-kidney, one clip Goldblatt hypertensive or uninephrectomized sham control rabbits. Coronary blood flow and cardiac output, using radioactive microspheres, and small vessel oxygen saturations, using microspectrophotometry, were measured in hypertrophied and nonhypertrophied hearts. After 30 days, baseline blood pressure was significantly higher in the Goldblatt rabbits compared with sham controls, and hypertension was maintained during pacing. The myocardium was hypertrophied in the Goldblatt hypertensive rabbits compared with sham controls. Baseline heart rates were not different between animal groups (242 ±32 and 244±24 beats/min, respectively). Both groups were paced 35% above baseline heart rates; during pacing, cardiac output was similar to baseline values in the sham controls (304 ±99 versus 321±116 ml/min, respectively) but reduced in the hypertensive rabbits (248±43 versus 325±62 ml/min). Myocardial oxygen consumption increased twofold in both nonhypertrophied and hypertrophied ventricles during tachycardia. Oxygen extraction was significantly elevated, but coronary blood flow was not altered during pacing in either animal group. Therefore, at the pacing level chosen the diminished function in cardiac hypertrophy was not associated with reduced oxygen consumption. Conversely, reduced efficiency during pacing in the hypertrophied myocardium was suggested. (Hypertension 1990;16:35-42) S ystemic hypertension leads to myocardial hypertrophy, which is thought to be a beneficial, adaptive response. The oxygen supply in pressure-induced hypertrophied myocardium appears to be sufficient under baseline conditions. -2Resting myocardial oxygen consumption measured in hypertrophy may or may not be elevated. 12 However, coronary flow reserves are generally diminished in hypertension-induced cardiac hypertrophy compared with the nonhypertrophied myocardium, and minimal coronary vascular resistance is elevated.2 Clinical and experimental evidence suggest that the hypertension-induced hypertrophied myocardium is especially vulnerable to ischemia during stress.3 These observaFrom the Heart and Brain