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The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist II). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage I at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 +/- 4 vs 81 +/- 3 beats/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 +/- 14 vs -2 +/- 7%; Stage I: 36 +/- 6 vs 16 +/- 7%; Stage II: 25 +/- 15 vs 10 +/- 8%; recovery: 26 +/- 12 vs 4 +/- 9%; P less than 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 +/- 6 vs 23 +/- 6% at an AV interval of 150 msec, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of heart rate changes on the recovery of cardiac hemodynamics and lactate clearance after exercise was studied in nine patients with complete atrioventricular (AV) block treated with programmable pacemakers. A preliminary treadmill exercise test in which the pacing rate was externally increased stepwise from 70 to 130 bpm was performed to determine the maximum exercise duration. Two exercise tests involving an equal amount of exercise load were performed, the pacing rate was either programmed to the basic rate (abrupt decay) or gradually (modulated decay) immediately after exercise termination. Compared with abrupt decay, modulated decay resulted in a higher mean arterial pressure (100 +/- 4 mmHg vs 91 +/- 5 mmHg, P less than 0.05) and diastolic pressure (76 +/- 4 mmHg vs 59 +/- 4 mmHg, P less than 0.001) immediately on exercise termination. Immediately after exercise and during modulated decay, cardiac output (represented by Doppler derived minute distance) declined gradually and was determined mainly by a higher pacing rate without significant changes in stroke volume. On the other hand, minute distance fell abruptly during abrupt decay (996 +/- 107 m at peak exercise and 561 +/- 88 m immediately after a rate change at exercise termination, P less than 0.01) with a corresponding abrupt increase in systemic vascular resistance. This was later compensated by a gradual increase in stroke volume during the recovery period. The cumulative cardiac output between the two rate changes equalized at the 4th minute of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of an abrupt reduction in atrial pressures on atrial natriuretic peptide (ANP) secretion was studied in four patients with complete atrioventricular block with a dual-chamber pacemaker when the pacing mode was changed from the VVI to the DVI mode at an equal rate of 70/min. Simultaneous continuous hemodynamic monitoring was performed using a balloon-tipped thermodilution catheter. With DVI pacing, there was an immediate decrease of right atrial pressure from 4.5 +/- 0.9 to 1.8 +/- 1.1 mm Hg, and a reduction of pulmonary arterial wedge pressure from 7 +/- 0.8 to 4.5 +/- 0.9 mm Hg, together with a rise in cardiac output from 3.1 +/- 0.2 to 3.7 +/- 0.2 L/min. However, despite a constant hemodynamic status after dual-chamber pacing, the arterial ANP level steadily decreased from 151 +/- 26 pg/ml to a steady low level of 78 +/- 15 pg/ml after 20 minutes of dual-chamber pacing (percentage reduction- 48 +/- 8%, p less than 0.05). This persisted until the end of the study at 60 minutes. The time-dependent decay in ANP secretion after an abrupt and constant change in hemodynamic status should be considered when interpreting ANP levels.

A minute ventilation sensing rate responsive pacemaker was implanted in a 29-week pregnant woman with symptomatic complete atrioventricular (AV) block under echocardiographic and electrocardiographic (ECG) guidance. Satisfactory rate responses during a submaximal treadmill exercise test and daily activities were achieved. The course of pregnancy and cesarean section is discussed. During the cesarean section and after the delivery of the baby, changes in the ventilator settings confirmed that the pacing rate was closely correlated with both the tidal volume (r = 0.94, P less than 0.01) and the respiratory rate (r = 0.93, P less than 0.05).

A 67-year-old male patient with previous history of pulmonary tuberculosis presented with syncope due to complete heart block. Collapse of the right lung and deviation of the heart to the right chest had prevented visualization of the cardiac silhouette by fluoroscopy. Successful endocardial permanent pacing using a passive fixation electrode was achieved with the help of ultrasonic visualization of the cardiac chambers.

Most studies evaluating the rate response of adaptive-rate pacemakers have been based on treadmill or bicycle exercise. These studies disregard the fact that few pacemaker recipients voluntarily undertake such activities. The rate responses of nine patients (mean age 62 years, range 33-79 years) with implanted minute ventilation sensing (Meta) pacemakers were studied. The indications for pacing were complete heart block (seven patients), sick sinus syndrome (one patient), and five nodal disease (one patient). Significant improvement in maximum distance covered during a 12-minute walking test was observed in the rate adaptive compared to the VVI pacing mode (989 +/- 104 vs 921 +/- 90 m, P less than 0.02). The rate responses of this pacemaker during daily activities were recorded with telemetry during a variety of structured daily activities. The rate responses were also compared to those of an externally attached Activitrax pacemaker in each patient and to a group of ten age and sex matched volunteers. For less strenuous activities such as walking, descending stairs, washing, and bed making, both pacemakers achieved adequate rate responses compared to normal subjects. For more strenuous activities, the Activitrax pacemaker failed to achieve an adequate rate response. For example, the pacing rate achieved on ascending stairs was lower than that achieved on descending stairs (92 +/- 3 vs 102 +/- 3 bpm, P less than 0.02). The direction of rate responses was more appropriate for the Meta pacemaker. Similar to the normal subjects, the maximum rate was reached before the end of an activity with the Activitrax pacemaker.(ABSTRACT TRUNCATED AT 250 WORDS)