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 0.9 mV-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.

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.

Electrocardiographic determinants of efficacy of 8-Joule shocks for ablation of the atrioventricular node.

Factors determining the success of a single, low-energy, direct current-shock to achieve chronic complete heart block were studied in a consecutive group of 14 patients. A shock of 8 J was delivered by a modified device (Sirecust BS1, Siemens). If the first shock did not produce persistent complete block, multiple shocks were given. Standard 6 French U.S.C.I. catheters were used for all procedures. Chronic complete heart block was achieved with a single shock in six cases (43%; Group I); in eight others multiple shocks were needed (Group II). Neither polarity of the bipolar and of the distal His bundle recording nor the presence of sinus rhythm before the first shock were important factors to predict the outcome. The amplitude of the first recording of the bipolar His electrogram was 225 +/- 55 microV in Group I and 138 +/- 105 microV in Group II (P = 0.029). The duration of the HV interval before the first shock was 55 +/- 12 ms in Group I and 45 +/- 11 ms in Group II (NS). It is concluded that complete permanent heart block can be achieved with a single 8-J shock in 43% of the patients. The long-term success (follow-up at least 1 month, with a range of 1 to 8) of a single 8-J shock is predicted by a large amplitude of the bipolar and distal unipolar His bundle deflection, but not by its polarity or the HV interval.

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.

Ablation of ventricular tachycardia of right ventricular origin with low energy shocks.

Three shocks of 2 joules (2,000 volts within 0.3 msec) were given to a patient with ventricular tachycardia of right ventricular origin at the site of the earliest activation. A standard 6 Fr USCI mapping catheter was used. After the first shock the cycle length prolonged from 385 to 531 msec. After the second shock, the tachycardia was no longer inducible and it remained so after 1 week. No recurrences were seen during a follow-up period of 8 months. This is the first report demonstrating efficacy of modified low energy shocks for ventricular tachycardia.

Incidence of arrhythmias after atrial or dual-chamber pacemaker implantation.

The incidence of sustained atrial, pacemaker-mediated and ventricular rhythm disturbances was studied retrospectively in a consecutive series of 112 patients without a history of preexisting atrial tachyarrhythmias, receiving an atrial or dual-chamber pacemaker. Early atrial fibrillation (during the first week) was recorded twice. 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 measured intracardiac P wave between the group with and the group without atrial fibrillation. Treatment with digoxin reverted three patients to sinus rhythm, association of digoxin and amiodarone, six patients. One patient with congestive heart failure remained in atrial fibrillation. Pacemaker-mediated tachycardia was not a major problem. One patient of a subgroup with known ventricular arrhythmia had a non-sustained ventricular tachycardia during programming at follow-up; sustained ventricular tachycardia was not recorded. Reprogramming to VDD, DVI or VVI was done in 6/100 patients. The incidence of atrial fibrillation or flutter in highly selected patients with dual-chamber or atrial pacing is moderately low. It is not possible to identify patients with a high risk for development of atrial fibrillation; when it occurs, it is easily controlled with drugs. DDD pacing seems to be safe in patients with a history of serious ventricular arrhythmias, treated with appropriate drugs.

2:1 atrial capture as the cause of pacemaker alternans.

Two patients with sinus node disease and a physiologic pacemaker presented with 2:1 atrial capture. Both atrial leads were screw-in leads (6957 J, Medtronic), with normal position on X-rays. When atrial capture was absent, paced QRS complexes resulted in retrograde conduction to the atria. The next atrial spike was followed by a P wave and normal AV conduction. With atrial screw-in leads, alternating atrial capture may be caused by an altered ventricular and atrial contraction pattern, when retrograde conduction exists. Its presence may precede permanent exit block by several weeks.

Effect of DC-shocks of 400 Joules on the AV-node.

Ablation of the AV-node with direct current shocks and 6-French U.S.C.I. catheters was performed in 8 patients with disabling supraventricular arrhythmias. An initial shock of 400 Joules was chosen in most instances. In all patients transient or permanent complete AV-block was obtained. For one patient the procedure was considered a failure, after three sessions. Five patients remain in complete AV-block. Average escape rhythm at first ambulatory follow-up was 47 bpm. The block seems to be situated at the level of the bundle of His, or distal of this level. The other two patients are clinically improved with impaired AV-conduction. A pacemaker was implanted in all patients.