Long-term responses of atrial rate and peripheral resistance to changes in ventricular pacing rate in awake dogs with atrioventricular block.

We wished to see if a maintained change in pressure at the baroreceptors leads to a maintained or a transient change in heart rate and total peripheral resistance, and if long-term changes in rate and resistance paralleled one another. In awake dogs with intact baroreceptors and complete atrioventricular block, ventricular rate was held alternately at high (90 beats/min) and low (50 beats/min) levels, each for 2 days. This cycle was repeated several times. Data were recorded for 1.5 hours each day. With this change in ventricular rate, there was a maintained change over 2 days in arterial (14.4 +/- 1.0 mm Hg) and central venous (3.0 +/- 1.2 mm Hg) pressures. These changes in pressure were accompanied by a maintained change in atrial rate of 41.1 +/- 9.4 beats/min; peripheral resistance, however, changed only transiently. In three animals, the half-cycle length was 1 week. Changes in heart rate also persisted for this period. It appears from these studies that there is long-term control of heart rate, but not of peripheral resistance. Hypotheses to explain these results are presented.