Clinical Observations with a Dual Sensor Rate Adaptive Single Chamber Pacemaker

The Topaz model 515 (Vitatron B.V.) is a dual sensor rate responsive pacemaker for single chamber stimulation. It can be driven by activity counts (ACT) and QT interval measurements. Inappropriate rate modulation due to one sensor can be corrected by "sensor cross-checking." It was implanted in ten patients (20-86 years) of whom seven had complete heart block and atrial arrhythmias. After implantation T-wave amplitude ranged from 0.9mV-3.5 mV. T-wave sensing ranged from 88%–99% in 9/10 patients at the follow-up of 3 weeks. Eight patients remained in default setting of the activity threshold, after evaluation with a short walking test. An exercise test was performed on all patients. In one test, QT sensing was marginal because of lead implantation in the right ventricular outflow tract. Therefore, this pacing rate was only modulated by ACT sensing. All others were tested with equal contribution of information from both sensors (ACT = QT). In 7/9, rate response was satisfactory. When the treadmill was repeated with ACT in five of these seven patients, rate generally accelerated too fast. In one patient the setting was adjusted to "QT > ACT," because of inappropriate acceleration due to activity sensing, in another it was adjusted to "QT < ACT" because of delayed response to activity. The pacing rate and the ACT during treadmill tests in "QT = ACT" mode were more closely correlated in the first 3 minutes, compared with the last 3 minutes. We feel that rate modulation with this new pacemaker is adequate. Sensor blending and sensor cross-checking are of clinical importance.     

Behavior of a Respiratory Driven Pacemaker and Direct Respiratory Measurements

In 10 patients with a mean age of 76 +/- 8 years, a rate responsive pacemaker (Meta-MV, Telectronics) was implanted in the left pectoral site. An exercise test was performed in SSI ("adaptive") mode, allowing the device to measure the changes in thoracic impedance. The "slope number" at maximal exercise was chosen to program the pacemaker for a second exercise test in rate responsive mode. Direct measurements of respiratory rate and minute volume were correlated with the pacing rate. After 1 minute of exercise, pacing rate increased by 6% and it decreased smoothly after maximal exercise. The programmed maximal rate was reached at the maximum exercise level in six patients. During 24-hour Holter recording, the mean maximal pacing rate was 103 +/- 18 beats/min. For individual patients, a good correlation of pacing rate with respiratory rate (r = 0.757), oxygen consumption (r = 0.731), and minute volume (r = 0.800) was observed. The data from the entire group showed a highly significant correlation of changes in pacing rate and in respiratory parameters for different levels of exercise and recovery. In a subgroup of five patients, the slope numbers at maximal exercise were reproducible after 10 months. It was concluded that minute volume and its changes were recognized in a reliable way by the Meta-MV pacemaker.     

Incidence of arrhythmias after atrial or dual-chamber pacemaker implantation

The incidence of sustained atrial, pacemaker-mediated and ventricularrhythm disturbances was studied retrospectively in a consecutiveseries of112 patients without a history of preexisting atrialtachy arrhythmias, receiving an atrial or dual-chamber pacemaker. Early atrial fibrillation (during the first week) was recordedtwice. Late atrial fibrillation was seen in seven patients,flutter in one, yielding a total incidence of 8.9% for 22 months.There were no significant differences with respect to age, aetiology,electrocardiographic diagnosis, pacing history, or the measuredintracardiac P wave between the group with and the group withoutatrial fibrillation. Treatment with digoxin reverted three patientsto sinus rhythm, association of digoxin and amiodarone, sixpatients. One patient with congestive heart failure remainedin atrial fibrillation. Pacemaker-mediated tachycardia was not a major problem. Onepatient of a subgroup with known ventricular arrhythmia hada non-sustained ventricular tachycardia during programming atfollow-up; sustained ventricular tachycardia was not recorded.Reprogramming to VDD, DVI or VVI was done in 6/100patients. The incidence of atrial fibrillation or flutter in highly selectedpatients with dual-chamber or atrial pacing is moderately low.It is not possible to identify patients with a high risk fordevelopment of atrial fibrillation; when it occurs, it is easilycontrolled with drugs. DDD pacing seems to be safe in patients with a history of seriousventricular arrhythmias, treated with appropriate drugs.     

An implantable antitachycardia pacemaker with back-up pacing and scanning burst mode

We used an automatically triggered antitachycardia device (PASAR4171) which is able to provide up to 7 stimuli in the atriumof three patients with AV-nodal tachycardia. A PASAR 4172 wasimplanted in a patient with WPW which gave two stimuli in theright ventricle. One revision was needed due to exit block. Temporary undersensingoccurred in one patient. Atrial fibrillation occurred for thefirst time postoperatively in the WPW patient, without majorside-effects. Treatment with low dosage amiodarone was initiatedto prevent recurrence. At follow-up, magnet application was useful to induce supraventriculartachycardia in the three 4171 patients with 4171 devices, provingeffective termination of tachycardia. Back-up pacing or concertinamode were used in 3 of 4 patients.     

Atrial Arrhythmias in Dual Chamber Pacing and Their Influence on Long-Term Mortality

A retrospective study of 252 patients who received a DDD pacemaker between October 1982 and December 1990 was performed. During a mean follow-up of 30 months, reprogramming to the VVI mode was necessary in 39 patients (15.5%). Technical problems causing downgrading occurred 15 times, of which 13 problems became permanent. A total number of 24 patients had sustained atrial arrhythmias, including 14 with atrial fibrillation and 10 with atrial flutter. In this group, conversion to sinus rhythm could be obtained in 38%. After 2 years, reliable DDD pacing was maintained in 86% of the surviving patients. The survival after 1 and 2 years was 94% and 89%, respectively, and was not influenced by arrhythmias or technical problems. We conclude that atrial arrhythmias including flutter are the most important reasons for reprogramming to the VVI mode, although in an important number of patients, predominantly those with flutter, restoration of AV synchrony can be obtained. The high number of patients with atrial flutter could imply some role for DDD devices offering the option of antitachycardia pacing. Reprogramming of the pacing mode did not influence mortality.