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
SUMMARY Sixteen patients with a non-invasively programmable pacemaker (Medtronic 2409) were examined with the unit in ventricular inhibited (WI) and atrial synchronous ventricular inhibited (VDT/I) mode, respectively. Maximal exercise capacity was determined by means of bicycle ergometry. Work load was increased in steps of 10 watts each minute. Atrial and ventricular rates, brachial artery pressure, and respiratory rate were studied at rest and during exercise while systolic time intervals were determined at rest. There was an important increase in maximal exercise capacity when changing from WI to VDT/I pacing. The extent of improvement was the same for patients above and below the age of 65 years. At comparable work loads VDT/I pacing resulted in significantly lower atrial rates than WI pacing. Systolic time intervals did not differ between WI and VDT/I pacing apart from an increase in left ventricular ejection time index with VDT/I pacing. Systolic time intervals and maximal exercise capacity with VVI pacing did not correlate with the increase in exercise capacity induced by VDT/I pacing. Physical performance can be significantly improved by VDT/I pacing in both young and old patients. Exercise capacity on VVI pacing cannot predict the possible benefit of change to VDT/I pacing.During recent years there have been many reports on the successful clinical use of electrodes for transvenous atrial pacing and sensing. '-3 Thus, one of the main obstacles to the more widespread use of physiological pacing has been overcome.4 For many patients with complete heart block and intact sinus node function, the most effective mode of pacing should be the atrial synchronous, and beneficial haemodynamic effects of this type of pacing have been described.56To our knowledge, systematic studies comparing the physical work capacity during ventricular inhibited (VVI) and atrial synchronous pacing (VAT; VDT/I) have not been published. One explanation may be that the use ofthe latter mode of pacing is, as yet, limited.48 Another comes from the difficulties that exist in comparing two different types of pacemakers when this either necessitates investigation with the pacemaker exteriorised or before and after the exchange of an implanted pacemaker. Recently, however, we described an atrial synchronous ventricular inhibited pacemaker offering unique investigational opportunities,
A consecutive series of 66 patients (males = 32; mean age +/- SD = 71 +/- 9 years) given atrial inhibited pacemakers for sick sinus nodes were followed to study the incidence of lead failures, chronic atrial tachyarrhythmias, and atrioventricular conduction disturbances. The need for rate responsive pacing was also assessed. Pre and postoperative investigation could include carotid sinus massage, Holter monitoring, exercise testing, and invasive electrophysiology. The mean follow-up time +/- SD was 32 +/- 29 months (median = 26 months). Three patients (5%) had their pacemakers replaced due to lead failures (loss of sensing = 2; exit block = 1). Two pacemakers (3%) were replaced after 5 and 22 months due to atrial fibrillation. Four patients (6%) received new pacemakers because of development of second-degree or complete atrioventricular block after 1, 6, 12, and 31 months, respectively. During exercise, most patients (76%) responded with an increase in sinus rate at least as marked as that achievable with the currently available rate responsive pacemakers. Assuming careful patient selection, atrial inhibited pacing is well suited for many patients with sinus node dysfunction and preserved atrioventricular conduction. There is a limited need for rate responsive pacemakers in these patients.
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