SUMMARY Sixteen patients treated with a noninvasively programmable pacemaker were examiined after a prolonged period of ventricular inhibited (VVI) and atrial synchronous ventricular inhibited (VDD) pacing. Maximal working, capacity was determined by bicycle ergometry. Atrial and ventricular rates, brachial artery cuff pressure and breathing rate were determined at rest and during exercise. There was a mean increase in working capacity of 24% with VDD compared with VVI pacing (p < 0.001). Thirteen of the patients were catheterized. During VDD pacing, cardiac output was significantly higher, particularly during exercise (i 32%) due to the capability of heart rate increase and despite a substantial compensatory stroke volume increase during VVI pacing. Arteriovenous oxygen difference was much higher during VVI pacing, reaching 164 14 mi/I during the highest work load, while the corresponding level during VDD pacing was 140 ± 14 ml/l (p < 0.001). During exercise, arterial blood lactate was significantly higher during VVI than during VDD pacing. Heart size was significantly smaller, 568 ± 98 vs 530 96 ml/m2 BSA (p < 0.05), during VDD pacing. A questionnaire was completed by the patients to evaluate subjective symptoms and pacemaker preference. This part of the study favored the VDD mode of pacing. maker exchange. The VDD pacemaker we described' can be programmed noninvasively to either the VVI or the VDD mode, permitting comparisons of prolonged periods of pacing in either mode.The aim of the present study was to compare the acute and chronic hemodynamic performance at rest and during exercise with VVI and VDD pacing and to study the maximal exercise capacity after a prolonged period of VVI and VDD pacing.
Material and Methods PatientsSixteen patients treated with a VDD pacemaker gave informed consent to the study. Thirteen of the patients participated in the complete study and three agreed to the noninvasive part only (patients 9, 14 and 15). Selected data from the patients are presented in table 1.
The PacemakerThe pacemaker (Medtronic 2409) has been described in detail.9 Briefly, it is a VDD unit with a ventricular escape rate variable from 50-80 beats/min and a maximum atrial synchronous rate variable from 100-175 beats/min. These rates can be noninvasively programmed. When the backup rate is programmed, the mode is also programmed to VVI at the selected rate. Programming the upper rate limit simultaneously programs the mode to VDD without changing the previously programmed backup rate.
ProcedureThe study started with a period of pacing planned to last at least 3 months. During this period, patients 1-9 846 by guest on May 9, 2018 http://circ.ahajournals.org/ Downloaded from