| Sumario: | Eighteen patients, jive women and 13 men, (mean age 70 ± S.E.M. 2 ears] treated with QT sensing rat responsive pacemakers due to symptomatic high degree AV block took art in a double-blind study, comparing the rate responsive (TX) mode with fixed rate ventricular inhibited (WI) pacing. The pacemaker was blindly programmed to either mode in a cross-over design. During the 1 month period a daily diary of symptoms (chest pain, vertigo, dyspnea, and palpitations) was kept. At the end of each period, a mental stress test and an exercise test were performed. The patient rated the general well-being and stated a preference for one of the modes. In the TX mode the heart rate was significantly higher at the end of exercise compared with WI (107 ± 4 vs 73 ± 3 bpm; P < 0.001} and the exercise tolerance was improved by 9% (104 ± 8 vs 96 ± 7 W; P < 0.01). The patients reported significantly less dyspnea and fatigue at comparable workloads with TX pacing. During the mental stress test the pacing rate increased by 10% in the TX mode (from 73 ± 2 to 82 ± 4 bpm; P < 0.001). There was a physiological rate variability on 24-hour Holter monitoring. Ten patients reported a significant improvement in feeling of general well-being in the TX mode. Eleven patients preferred the TX mode, five patients could not distinguish between the modes and two patients preferred the WI mode due to worsening of angina pectoris with TX pacing. This preference for the TX mode was significant (P < 0.05). The results of this controlled study indicate that TX is preferable to WI in most cases, but the worsening of angina pectoris in two of the patients and the occurrence of rapid rate oscillations in a third patient are factors that warrant some caution in selecting patients.
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