We found the following characteristics predictive of CI in this pacemaker patient population: VO(2) max, existence of coronary artery disease or acquired valvular heart disease, previous cardiac surgery, as well as medication with digitalis, beta blockers, and amiodarone.

This study was undertaken to develop and test a morphology-based adaptive algorithm for real-time detection of P waves and far-field R waves (FFRWs) in pacemaker patient atrial electrograms. Cardiac event discrimination in right atrial electrograms has been a problem resulting in improper atrial sensing in implantable devices; potentially requiring clinical evaluation and device reprogramming. A morphology-based adaptive algorithm was first evaluated with electrograms recorded from 25 dual chamber pacemaker implant patients. A digital signal processing (DSP) system was designed to implement the algorithm and test real-time detection. In the second phase, the DSP implementation was evaluated in 13 patients. Atrial and ventricular electrograms were processed in real-time following algorithm training performed in the first few seconds for each patient. Electrograms were later manually annotated for comparative analysis. The sensitivity for FFRW detection in the atrial electrogram during off-line analysis was 92.5% (+/- 10.9) and the positive predictive value was 99.1% (+/- 1.8). Real-time P wave detection using a DSP system had a sensitivity of 98.9% (+/- 1.3) and a positive predictivity of 97.3% (+/- 3.5). FFRW detection had a sensitivity of 91.0% (+/- 12.4) and a positive predictivity of 97.1% (+/- 4.2) in atrial electrograms. DSP algorithm tested can accurately detect both P waves and FFRWs in right atrium real-time. Advanced signal processing techniques can be applied to arrhythmia detection and may eventually improve detection, reduce clinician interventions, and improve unipolar and bipolar lead sensing.

Chronotropic incompetence (CI), which has not been systematically examined in the ICD patient population, may have implications for device programming. A total of 123 ICD patients were classified into three groups: single-chamber ICD with sinus rhythm, dual-chamber ICD with sinus rhythm, and single-chamber ICD with permanent atrial fibrillation. Heart rate response, maximum oxygen uptake, and oxygen uptake at the anaerobic threshold were measured during treadmill exercise testing. In addition, clinical variables such as antiarrhythmic drug therapy, underlying heart disease, and left-ventricular (LV) ejection fraction were recorded. Of the patients studied, 38% were chronotropically incompetent (47/123). Significant predictors of CI were as follows: presence of a coronary disease (P = 0.036), prior cardiac surgery (P = 0.037), chronic drug therapy with beta-blockers (P = 0.032), administration of amiodarone (P = 0.025), and a combination of these two forms of treatment (P = 0.01). Spiroergometry revealed reduced exercise capacity (P = 0.041) and lessened VO2max (P = 0.034) among chronotropically incompetent patients. A large percentage of ICD patients demonstrates CI with subsequently reduced physical stress tolerance. In light of the DAVID study, we believe that a closer examination of rate-adaptive modes for ICD patients is warranted under enhanced conditions: (1) optimized AV interval programming; (2) utilization of new algorithms to reduce ventricular pacing in combination with rate-adaptive atrial pacing, with the goal of addressing CI while minimizing ventricular pacing; and (3) an optimized upper heart-rate limit.

Conventional Holter monitoring is of limited benefit in patients with infrequent symptoms suspected to be related to arrhythmia. A small recorder implanted subcutaneously might obviate many limitations of conventional monitoring. To determine the feasibility of obtaining adequate electrocardiographic signals from such a device, a prototype was temporarily implanted in 17 patients undergoing pacemaker implantation. The prototype contained four disc-shaped titanium electrodes, 0.21 inches in diameter embedded in epoxy. The four electrodes were in a square configuration spaced 0.72 inches center to center and were placed face down in a subcutaneous pocket in the left pectoral region. Bipolar recordings were made from a horizontal pair, a vertical pair, and both diagonal paris of electrodes (interelectrode distance 1.02 inches) and recorded on electromagnetic tape after filtering at 0.5-250 Hz. The mean peak-to-peak amplitude in each configuration was determined over a five-beat interval. Clear recordings were obtained from all 17 patients with recognizable P, QRS, and T waves. The amplitude of the signals obtained from the diagonal pairs of electrodes (175 +/- 51 and 170 +/- 54 microV) were greater than obtained from either the vertical pair (142 +/- 62 microV, P = 0.08 compared to diagonal electrodes) or the horizontal pair of electrodes (105 +/- 54 microV, P < 0.01). The maximum amplitude recorded from any configuration was 189 +/- 54 microV. In six patients the device was also tested with the electrodes face up in the subcutaneous pocket.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous studies with activity-based rate adaptive pacemakers have shown a somewhat paradoxical response when comparing ascending stairs to descending stairs. The objective of this investigation was to measure dual-sensor rate response provided by activity and minute ventilation (MV) compared with activity alone, and with a control group, during ascending and descending stairs. For dual sensor mode, measured mean peak pacing rate with 72 (92) steps per minute was 111 +/- 13 beats/min (124 +/- 14 beats/min) ascending stairs and 81 +/- 7 beats/min (97 +/- 13 beats/min) for descending. For activity mode alone, mean peak pacing rate was 90 +/- 12 beats/min (108 +/- 19 beats/min) ascending stairs and 97 +/- 12 beats/min (123 +/- 17 beats/min) descending. The mean peak control group heart rate ascending stairs for a step rate of 72 (92) steps/min were 116 +/- 11 beats/min (127 +/- 14 beats/min) ascending stairs and for descending 89 +/- 12 beats/min (95 +/- 11 beats/min). While for dual sensor controlled pacing there was a significant difference for ascending and descending stairs at both step rates, there was no difference between going upstairs and downstairs for activity mode alone. Rates with dual sensor did not significantly differ from respective rates of the control group. The mean correlation coefficient between MV and paced rate was 0.85. Pacing heart rates delivered by the dual sensor mode were appropriate for ascending and descending stairs. In contrast to activity mode alone, the peak heart rates for dual sensor mode are higher during ascending than during descending stairs.

Energy consumption and longevity of modern pacemakers are determined by the controlling electronic circuitry and by the stimulation energy. While with technological progress the electronics' energy consumption has been reduced significantly, clinical practice shows that many cardiac pacemakers are programmed to suboptimal settings with regard to minimization of pacing energy consumption. Several methods for optimizing pacemaker output settings have been proposed in the past. The most promising concept is an output parameter optimizing pacemaker with automatic capture detection. We examined whether it is possible to distinguish between effective and ineffective pacemaker stimulus capture by analyzing high pass filtered intracardiac impedance signals that are derived from standard bipolar pacing leads. In one series of 11 patients undergoing replacement or implantation of chronic bipolar pacemakers, four patients during electrophysiology studies, and eight volunteers undergoing invasive electrophysiology trials, we examined intracardiac impedance signals obtained with various stimulation rates and output parameter settings. Additionally we analyzed a series of five patients with implanted pacemakers that can measure and telemeter intracardiac impedance signals. Several evaluation concepts have been analyzed regarding their ability to discriminate between effective and ineffective stimuli. We developed an adequate algorithm that detects capture or loss of capture at different output parameter settings based on intracardiac impedance analysis. The sensitivity is 98.5% and specificity is 91% to loss of capture for the currently investigated algorithm and this can be used to determine the optimal setting of pulse width and amplitude with regard to energy consumption. This concept is currently under realization in the external programmer and in the future an implementation of these algorithms within the pacemaker itself is intended.

Background: Ritter's method is a tool used to optimize AV delay in DDD pacemaker patients with normal left ventricular function only. The goal of our study was to evaluate Ritter's method in AV delay-interval optimization in patients with reduced left ventricular function.

Investigation of dual chamber pacing and sensing interactions at high rates is becoming increasingly important with the advent of sensor driven dual chamber pacemakers. The present study was designed to investigate the pacemaker and lead interactions that will affect cross-talk during high rate atrial and ventricular pacing. The study was divided into two phases, phase one investigated the mechanisms of cross-talk using standard pacemaker circuitry and various electrode types in a canine model. In six dogs with complete heart block, dual chamber pacing was carried out with four lead types at increasing pacing rates, while output of the ventricular sense amplifier of a pacemaker breadboard was monitored. Ventricular sense amplifier output signals (n = 332) progressively increased from 31.5 +/- 18.3 mV at 100 ppm to 102 +/- 55 mV at 160 ppm. Smooth platinum-iridium and platinized leads were statistically different at higher pacing rates (P less than 0.05). This signal level is sufficient to lead to a ventricular sensing event. In a second phase of the study, the incidence of cross-talk at high pacing rates was studied in patients with implantable dual chamber bipolar pacemakers. In 166 clinical trials on 106 patients with the same pacemaker, there was evidence of cross-talk in 1/59 cases at 110 ppm and 3/47 at 130 ppm, but none at higher rates.(ABSTRACT TRUNCATED AT 250 WORDS)