Multilevel disease of the conduction system

Incidence of atrioventricular block and chronic atrial flutter/fibrillation after implantation of atrial pacemakers; follow-up of more than ten years

The incidence of atrioventricular (AV) block and chronic atrial flutter/fibrillation was determined in 41 patients, mean age 62.2 years (22 to 88 years) who received atrial pacemakers before October 1980. The mean follow-up period was 12.3 years, range 11-14.4 years. Twenty-five patients suffered from bradycardia-tachycardia syndrome, 13 symptomatic bradycardia, and 3 bradycardia related ventricular tachycardia. At follow-up: 18 patients (44%) had permanent I-AV block; 11 patients had II-AV block, 9 patients (22%) transient Wenckebach block and 2 patients (5%) transient Mobitz block, all asymptomatic. The cumulative incidence of III-AV block was 1 (2.5%). Chronic atrial flutter/fibrillation occurred in 6 patients (15%), 5 were not pacemaker-dependent; 1 received a ventricular pacemaker. Seventeen patients died after a mean of 7 years (0.6-12.2 years). Cumulative survival rate of 58% for 14.4 years, did not differ from a matched cohort of the normal population. There were no pacemaker related deaths. We conclude that long-term atrial pacing was safe and effective. The incidence of III-AV block and chronic atrial flutter/fibrillation was low.

Natural history of sinus node chronotropy in paced patients

The natural history of chronotropic incompetence is not clear. To assess this, we evaluated corrected sinus node recovery time (cSNRT) and sinus node chronotropy at rest and during exercise in two groups of syncopal patients with sinus node disease. Group A comprised patients with resting bradycardia but normal cSNRT and group B had resting bradycardia and prolonged cSNRT (greater than 1000 ms). An additional two groups (C and D) were studied. Group C comprised patients with complete AV (CAVB) and no evidence of sinus node disease and group D were asymptomatic controls of similar age. At diagnosis, patients with symptomatic bradycardia but normal cSNRT and no evidence of carotid sinus syndrome (group A) had resting bradycardia and impaired peak heart rate (PHR-I) on exercise compared to controls (P less than 0.001 and P less than 0.05, respectively), but no reduction in exercise duration. At follow-up group A patients demonstrated an increase in resting rate that was significantly slower than the controls (P less than 0.01). Peak heart rate (PHR-II) also remained significantly slower (P less than 0.05). There was no difference in exercise duration between groups A and D at follow-up. Group B was further subdivided according to follow-up findings of preservation of atrial activity in seven patients (group B-1) and junctional rhythm without any atrial activity in four patients (group B-2). Retrospective analysis showed no significant difference in resting heart rate at initial examination but group B-2 showed a significantly lower peak heart rate on exercise compared with B-1 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological evaluation of the sinus node in patients with atrioventricular and/or intraventricular conduction defects

The authors evaluated retrospectively sinoatrial conduction time (SACT), sinus node recovery time (SNRT), and corrected sinus node recovery time (CSNRT) in 272 patients with atrioventricular and/or intraventricular conduction defects without evidence of overt sinus node dysfunction. The study was designed to determine the prevalence of electrophysiologic sinus node abnormalities in patients with overt atrioventricular and/or intraventricular conduction defects. One or more sinus node electrophysiological abnormalities were observed in 133 cases (48.9%). There was a significant prevalence of electrophysiologic sinus node abnormalities only in patients older than 71 years of age. The data suggest that the involvement of the specialized conduction system is much more diffuse than one might expect simply observing the single recorded ECG defect and that the prevalence of associated defects of the conduction system increases with increasing age of patients.

Postexercise electrocardiographic and clinical changes in patients with sick sinus syndrome

Forty patients with sick sinus syndrome, 15 women and 25 men with a mean age of 53.83 +/- 13.34 years, were studied using a maximal graded bicycle stress test. None of the patients were using a pacemaker or being treated with drugs that would interfere with the sinus node function; one patient had family myocardiopathy and eight suffered from essential hypertension. All patients, including those suffering from very marked bradycardia (less than 40 beats/min) responded to the increased effort with increased heart rate. The exercise test was stopped in 22 patients (55%) after the appearance of clinical signs and in 4 (10%) after ST-segment depression greater than 1 mm. Eight (20%) finished the stress test after reaching the maximal heart rate according to age, due to an increase in sinus rate. The exercise produced or increased extrasystoles in five patients (12.5%), but only one was forced to suspend the test. The Q-T interval, corrected for heart rate according to Bazett's formula (QTc), was measured on the resting ECG before the start of the test and on the ECG recorded immediately following the end of the exercise in all patients, except one with atrial fibrillation. In 24 patients (60%), a QTc mean increase of 0.040 +/- 0.022 sec was observed at the end of the stress test. Fourteen (35%) had the usual shortening due to the increase in heart rate. One patient showed no variation of the QTc. A lengthening of the QTc at the end of the exercise in more than half of the patients was the most intriguing electrocardiographic change.(ABSTRACT TRUNCATED AT 250 WORDS)