Joseph J. Florio

Comparative Evaluation of Rate Modulated Dual Chamber and VVIR Pacing

JUTZY, R.V., ET AL.: Comparative Evaluation of Rate Modulated Dual Chamber and VVIR Pacing. While dual chamber pacing is considered superior to VVI pacing at rest, there is a continuing debate as to the relative benefit of AV synchrony versus rate increase with exercise. To evaluate this question and to correlate different methods of evaluation, 14 patients with DDDR pacemakers were studied using serial treadmill exercise test with a CAEP protocol. Patients were exercised in DDD, DDDR, and VVIR modes. Echo‐Doppler cardiac outputs were determined and pulmonary gas exchange was measured during exercise. There was a significant improvement in cardiac output with exercise in the DDDR versus VVIR modes, and in DDDR versus DDD modes in patients with chronotropic incompetence. There were small increases in exercise duration in DDDR versus VVIR modes, and small but consistent increases in VO, at all levels of exercise, though not statistically significant. In this group of patients, DDDR pacing was superior to VVIR pacing, and superior to DDD pacing when chronotropic incompetence was present.

Comparison of intrinsic versus paced ventricular function.

There is increasing evidence supporting the benefits of providing optimum AV delay in cardiac pacing, though controversy exists regarding its value and the benefits of intrinsic versus paced ventricular activation. This study compared various AV delays at rest in patients whose native AV delays were 200 msec. Only patients with DDD pacemakers who had intact AV conduction and normal ventricular activation were included in the study. Nine patients were studied. Methods: Ten studies were performed. Evaluation was done in AAI and DDD modes at paced heart rates of 60/min or as close as possible to the intrinsic heart rate if this was > 60/min. Stroke volume (SV) and cardiac output (COJ were measured. Results: When AV sequential pacing in the DDD mode with an optimum AV delay was compared to AAI pacing with a prolonged AV interval, the average optimum AV delay in the DDD mode was 157 msec and ranged from 125 to 175 msec. The average AV interval in the AAI mode was 245 msec and ranged from 212 to 300 msec. In the DDD mode, there was an overall significant improvement in CO of 11% and SV of 9%. Patients with intrinsic AV conduction times of > 220 msec showed an overall significant improvement in CO of 13% and SV of 11%. In patients with intrinsic AV conduction times of < 220 msec, an improvement in CO of 6% and SV of 4% was seen. Conclusions: (1) An optimum AV delay is an important component of hemodynamic performance; and (2) AV sequential pacing at rest with an optimum AV delay may provide better hemodynamic performance than atrial pacing with intrinsic ventricular conduction when native AV conduction is prolonged > 220 msec.

A New Automode Switch Algorithm for Supraventricular Tachycardias

Patients with complete heart block on a spontaneous, or iatrogenic basis who also have recurrent supraventricular tachycardias, particularly atrial fibrillation and flutter, are often difficult to manage. Various techniques include: independently programmable maximum tracking and maximum sensor rates, limiting the maximum atrial tracking rate to the sensor response of the pacemaker, or automatically switching from DDDR to VVIR based upon the sensed atrial rate. This article will describe a mode switch algorithm that allows for an independently programmable atrial tachycardia detection rate (ATDR). This allows mode switching to occur only in response to the patients pathological tachyarrhythmia, and not during normal upper rate response. The ATDR is based upon a filtered atrial rate, which will prevent an isolated premature beat from initiating the algorithm. In addition, the unit can be programmed to switch to either DDI, DDIR, VVI, or VVIR. Extensive event counters in the pulse generator allows the system to record and store the number of algorithm activations, the average atrial rate which triggered each mode switch, and the duration of the mode switch. These reports are accessible at each follow‐up visit.

Physical Determinants of the Endocardial P Wave

SHANDLING, A.H., ET AL.: Physical Determinants of the Endocardial P Wave. Reliable atrial sensing of intrinsic P wave activity is important to ensure optimal atrial or dual chamber pacemaker function. Various physical factors (e.g., posture, respiration, exercise) may influence P wave characteristics and impair adequate sensing. To investigate this phenomenon, we measured the average of three P wave amplitudes (PWA) and calculated slew rates from telemetered printouts acquired from Pacesetter pacemakers in 32 patients. These measurements were performed in various body positions, with upright exercise and in varying stages of respiration. Results: the mean supine PWA increased on full inspiration (3.56 ± 1.3 mV versus 3.25 ± 1.2 mV during quiet respiration, p < 0.001), and also increased significantly with full expiration. The mean PWA increased on assuming the erect position (3.25 ± 1.2 mV increasing to 3.49 ± 2.3 mV, p < 0.001); in the upright position, the mean erect PWA during quiet respiration was not significantly influenced by the stage of respiration. The mean upright exercise PWA did not differ significantly from the preexercise erect PWA (3.50 f 1.2 with exercise, and 3.47 ± 1.5 before exercise; P = NS). Calculated slew rates were not different lying versus standing. Conclusions: the mean supine PWA increases significantly at the extremes of respiration and on assuming the erect body position; upright exercise results in no appreciable change in the erect PWA. Atrial sensitivity adjustments based on standard supine testing should be adequate for all body positions. (PACE, Vol. 13, December, Part I 1990)

Physiological Benefits of a Pacemaker with Dual Chamber Pacing at Low Heart Rates and Single Chamber Rate Responsive Pacing During Exercise

Dual chamber rate responsive pacing may be an ideal mode but may result in high current drain and premature battery depletion. To minimize battery drain during exercise, this study compared a combination pacing mode of IDDD and ventricular rate responsive pacing (WIR). Nine patients were studied who had complete heart block, sinus rhythm, DDD pacemakers, and a reduced mean left ventricular ejection fraction of 44%. Patients were exercised in DDD, WIR, and a combination of DDD at low heart rates and WIR at mean heart rates over 89 bpm. Blood pressure, heart rate, exercise duration, work rate, oxygen uptake, anaerobic threshold, and oxygen pulse were measured. There was no difference in symptoms or in mean cardiopulmonary function indices including exercise duration 10.7. 10.3. 10.3 minutes; heart rate 127. 133. 136 bpm; oxygen uptake 1.4. 1.5. 1.5 L/minute; or anaerobic threshold 5.6, 5.5, 5.7 minutes (p > 0.05) in any mode. A pacemaker that provides atrioventricular synchrony at low heart rates with ventricular rate responsiveness at high heart rates may be an alternative mode for some patients.

Limitations of testing methods for evaluation of dual chamber versus single chamber adaptive rate pacing.

Abstract As new modes of cardiac pacing are developed, it is important to determine if these modes offer additional benefits over already existing options. Comparisons between dual (DDDR) and single chamber ventricular (VVIR) rate-modulated pacing using standard exercise protocols have produced conflicting results. 1–4 Exercise duration alone does not appear to accurately reflect differences in cardiac efficiency and tissue perfusion. Similarly, maximal oxygen uptake tends to reflect exercise duration rather than cardiac performance. 5 This study was designed to compare the DDDR and VVIR pacing modes using measures of exercise duration and maximal oxygen uptake, as well as less frequently used parameters, including anaerobic threshold time, maximal carbon dioxide production, respiratory exchange ratio, cardiac output, and the ratio of cardiac output to oxygen uptake.