CONTRIBUTION TO HEART-RATE-VARIABILITY BY MECHANOELECTRIC FEEDBACK - STRETCH OF THE SINOATRIAL NODE REDUCES HEART-RATE-VARIABILITY

Background Heart rate variability is an important prognostic indicator for sudden death. An increased risk of sudden death and arrhythmia is associated with reduced heart rate variability in heart failure. In h eart failure, there is also dilatation of the atria, which raises the prospect that there could be some physiological basis to possibly link heart rate variability with atrial dilatation. We therefore investiga ted whether sustained atrial stretch could modulate heart rate variabi lity directly. Methods and Results Pigs were anesthetized and their he arts exposed. A specially built device stretched the sinoatrial node b efore and after vagal section and then after administration of propran olol. Stretch of the sinoatrial node decreases heart rate variability in the following ways: The standard deviation of the beat-to-beat inte rval decreases (4.2 to 2.6 ms; P=.004), and the high-frequency compone nts are reduced (control, 6.5+/-2.2 ms(2); during stretch, 1.4+/-0.3 m s(2); P=.003). After section of both vagi, the high-frequency componen ts are reduced by stretch of the sinoatrial node (2.8+/-0.9 ms(2) for control versus 1.2+/-0.3 ms(2) during stretch; P=.05). Similarly, afte r both vagal section and beta-blockade, stretch of the sinoatrial node reduces the high-frequency components (10.6+/-3.5 ms(2) for control v ersus 3.0+/-1.5 ms(2) during stretch; P=.01). Conclusions We conclude that stretch of the sinoatrial node reduces high-frequency heart rate variability. This may account in part for the reduced heart rate varia bility seen in clinical conditions in which the right atrium is dilate d, such as congestive cardiac failure.