Overdrive suppression of implanted pacemakers in patients with AV block

Patients being permanently paced for symptomatic AV block were studied by overdrive suppression of the QRS-inhibited pacemaker, in order to observe the underlying heart rhythm. The chest wall stimulation method was used. In complete AV block the escape rhythm recovery time proved highly reproducible on repeated testing on the same day, and in many patients remained so over months or years. Occasionally, a doubling of the escape rhythm recovery time was seen, suggesting initial exit block of the escape focus. Resetting of the escape rhythm usually followed an exponential curve until stabilisation after about 3 minutes. An early escape rhythm with a recovery time of less than 4 seconds was found on every occasion in 21 of 58 patients with complete AV block, and inconstantly in 23 more; in 14 it was never observed. Accidental pacing failure was seen in 15 patients. The overdrive suppression test was helpful in selecting pacemaker dependent patients.

Diazepam in acute myocardial infarction. Clinical effects and effects on catecholamines, free fatty acids, and cortisol

Diazepam is a valuable drug in cases of acute myocardial infarction. The 10 mg intravenous loading dose and the subsequent 15 mg oral dose of diazepam administered three times daily produced safe, pleasant sedation, and reduced the need for analgesics. A much reduced excretion of catecholamines was recorded. It is presumed that diazepam causes a lower stress reaction, which is beneficial in diminishing the incidence of malignant arrhythmias and preventing the existing myocardial injury from spreading.

The effect of propranolol and verapamil on atrial and atrioventricular refractory periods in man

The atrial effective (ERP) and relative (RRP) refractory periods were examined at high atrial pacing rates in 12 patients before and after intravenous injection of propranolol, and in 5 patients before and after injection of verapamil, using the technique of paired pacing. Seven of the patients had A-V block grade II-III and 10 patients had sinus rhythm. The range of atrial ERP in all patients was found to be 200 to 270 msec. and the range of atrial RRP was 230 to 330 msec. The atrial ERP and RRP were longer at a pacing rate of 160 per minute than at a pacing rate of 240 per minute. The conduction delay between the second impulse and the atrial depolarization was found to be due to increased interval between the stimulus and the start of the depolarization wave. The atrial ERP increased after injection of propranolol in 8 of 12 patients, decreased in 3 patients and was unchanged in one patient. The atrial RRP increased in 7 patients, decreased in one patient and was unchanged in 4 patients. In all patients the changes were of moderate degree. The conduction delay between the stimulating impulse and the atrial response was shorter after propranolol in 7 patients, longer in one patient and unchanged in 4 patients. The ERP of the atrioventricular conducting tissue was 220 to more than 380 millisec. After injection of propranolol it increased in all of 3 patients in whom it could be measured. After injection of verapamil no significant effects on the atrial ERP and RRP were found. ERP of the atrioventricular conducting tissue was lengthened in 4 of 5 patients, and the degree of A-V block during rapid atrial pacing increased after injection of verapamil. It is suggested that the effect of propranolol on atrial arrhythmias is due to its effect on ectopic pacemaker activity rather than any effect on the refractory period of the atrium. The effects of verapamil on the atrioventricular conducting tissue may explain some of the antiarrhythmic effects of this drug.

Registration of sinus node recovery time in patients with sinus rhythm and in patients with dysrhythmias

Sinus node recovery time (SRT) after rapid atrial pacing has been recorded in 66 patients, 28 with coronary heart disease, 11 with advanced AV block, 10 with sick sinus syndrome and 17 with paroxysmal tachyarrhythmias. In patients with a normal functioning sinus node SRT was related to the basal heart rate. On an average SRT was 130% of the basal P-P interval with an upper limit of 160%. In patients with a presumed normal atrial function the mean SRT was found to be 1 080 msec, with an upper limit of 1 500 msec. This corresponds with previously published observations. In all 5 patients examined, beta-receptor blockade (propranolol 5 mg i.v.) prolonged SRT. The prolonged SRT was related to sinus bradycardia. Verapamil (Isoptin 5 mg i.v.) had no effect on SRT in the 7 patients examined. The observation of an SRT of more than 1 500 msec indicates a poor sinus node function. Recording of a normal SRT, however, cannot exclude a sinus node dysfunction, as normal SRT is occasionally found even in patients with a clinically proved dysfunction.