The effects of DDD (fully automatic) and VVI (ventricular demand) pacing modes on exercise tolerance, symptom diary cards, and Holter monitoring were investigated in a randomised double blind crossover study of 16 patients who had had DDD pacemakers implanted because of frequent syncope. Eight patients presented with sick sinus syndrome and, with one exception, retrograde atrioventricular conduction and eight age and sex matched patients presented with 2:1 or complete atrioventricular block. Maximal symptom limited exercise in those with atrioventricular block was significantly higher after one month of DDD pacing than after VVI pacing. In those with sick sinus syndrome, however, maximal effort tolerance was not significantly different for the two pacing modes. In all but one patient with sick sinus syndrome sinus rhythm developed during exercise in VVI pacing. For both VVI and DDD modes maximal atrial rates were significantly lower in those with sick sinus syndrome. Palpitation and general wellbeing were significantly improved during DDD pacing in the eight patients with sick sinus syndrome. Shortness of breath was improved by DDD pacing in the eight patients with atrioventricular block but not in those with sick sinus syndrome. Holter monitoring showed that sick sinus syndrome patients remained in paced rhythm, either DDD or VVI, for most of the 24 hour period. DDD pacing was better than VVI pacing in sick sinus syndrome with retrograde atrioventricular conduction. Despite their ability to show sinus rhythm and inhibit their pacemakers on exercise patients with sick sinus syndrome are just as likely to have symptomatic benefit from DDD pacing as patients with atrioventricular block.

Baroreflex sensitivity was measured by the heart rate response to the transient rise in blood pressure induced by phenylephrine, in 11 patients with carotid sinus syndrome, 6 patients with sick sinus syndrome and nine age and blood pressure matched controls. Patients with carotid sinus syndrome were divided into those with a hypersensitive carotid sinus reflex manifest as sinus arrest (n = 9) and those with a reflex manifest as atrioventricular block (n = 2). The mean gain of the baroreflex sensitivity was significantly increased (p less than 0.001) in patients with carotid syndrome manifest as sinus arrest (12.7 +/- 5.1 ms . mmg-1) compared to that in patients with sick sinus syndrome (3.8 +/- 2.6 ms . mmHg-1) and controls (4.2 +/- 2.1 ms . mmHg-1). Patients with carotid sinus syndrome manifest as atrioventricular block did not have increased baroreflex sensitivity measured by their sinus node response (2.1 +/- 0.5 ms . mmHg-1). There was significant correlation (p less than 0.001) between the corrected carotid sinus inhibitory response to carotid sinus massage and the measurement of baroreflex sensitivity in the carotid sinus syndrome patients. Patients with carotid sinus syndrome manifest as reflex sinus arrest have an increased gain in baroreflex sensitivity for their age, which is not seen in patients with symptomatic sinoatrial disease. This study provides further evidence of a different mechanism of bradycardiac symptoms in patients with carotid sinus and sick sinus syndromes.

Au cours ?une période de cinq ans, nous avons comparé la stimulation ventriculaire et la stimulation. “physiologique” chez 50 malades. Dans 17 eas de stimulation de type DVI, le débit systolique était plus éevé que dans la stimulation VVI, (P < 0.005), de même la pression télédiastolque du ventricule gauche était plus basse (P < 0.05). Chez 44 maJades la performance au cours de ľexercice était meilleure avec la stimulation VDDJDDD (P < 0.01). Ces effets se sont confirmés à long terme. La dyspnée était moindre (P < 0.01) et ľimpression de “bien‐être”était confirmée (P < 0.01) avec la stimulation physiologique. Nous concluons que la stimulation cardiaque synchrone àľoreillette est le mode de choix en ľabsence de contre‐indications.Over a five‐year period, hemodynamic exercise capacity studies and a randomized controlled trial have been performed in a total of 50 patients. DVI vs. VVI pacing showed an increase in stroke work index (P < 0.005) and a fall in left ventricular filling pressure (P < 0.05) in 17 patients. VDDJDDD pacing vs. VVI showed an exercise capacity benefit in 44 patients (P < 0.01) including 8 patients with sinus node disease and a lower peak heart rate (P < 0.02). Maintenance of benefit was also shown of VDDJDDD pacing in the longer term (13 months) vs. acute (P ‐ NS). The controled trial VDDJDDD vs. VVI showed benefit in shortness of breath (P < 0.01) and general well being (P < 0.01). It is concluded that atrial synchronous ventricular pacing (VDDJDDD) is the mode of choice in suitable patients.

The ability of rate hysteresis programming with the escape interval longer than the automatic interval lo reduce the hypotensive response to carotid sinus massage at the onset of ventricular pacing was studied in six patients paced for carotid sinus syndrome. Rate hysteresis significantly reduced this hypotensive response and abolished spontaneous symptoms in two patients and symptoms reproduced by carotid sinus massage in four patients.

Twenty-one patients treated with DVIM pacemakers for carotid sinus syndrome were entered into a double blind randomised trial of DVI versus VVI pacing. Daily symptoms were recorded on a diary card and overall preference for either treatment period reported blindly at the end of the trial. Six patients could not tolerate the change from DVI to VVI mode and were withdrawn from the trial. All had pacemaker syndrome related to ventriculo-atrial conduction. Of the fifteen patients who completed the trial, seven reported a preference for DVI pacing. There was no significant difference for symptom scores for dizziness with either pacing mode. DVI preference related to presence of V A conduction, but it did not correlate with the magnitude of the vasodepressor response or pacemaker induced hypotension. The high incidence of pacemaker syndrome makes DVIM pacing superior to VVI pacing in carotid sinus syndrome.

Thirteen patients have completed a randomised double blind cross over study to compare the effects of chronic ventricular and atrial synchronous pacing on exercise capacity and symptoms. Maximal symptom limited exercise was significantly increased after one month of atrial synchronous pacing compared with ventricular pacing. Symptomatic assessment (by diary card and monthly symptom scores) of "shortness of breath", "palpitation", and "general well-being" was significantly improved during the physiological pacing mode. Atrial synchronous pacing has been shown to be superior to ventricular pacing.

Fifty-three patients have received 'physiological' pacemakers, 37 with atrioventricular (AV) block having atrial synchronous units (VAT or VDD) implanted and the remaining 16 patients with both AV block and sick sinus syndrome having 'universal' (DDD) pacemakers. Effort tolerance was assessed by serial bicycle ergometry and in 16 patients direct comparisons between ventricular pacing and atrial synchronous pacing could be made acutely. Physiological pacemakers were found to increase maximum effort tolerance by 43% compared to pre-pacing values (P less than 0.01). The increase was sustained over a mean of 33 months post pacing. The atrial synchronous mode increased maximum effort tolerance by 34% acutely compared to ventricular inhibited pacing. Dual chambered 'physiological' pacemakers represent a significant therapeutic advance over standard ventricular inhibited pacemakers.

Seventy patients have been paced for carotid sinus syndrome over four years. Twelve patients had persistent symptoms despite adequate ventricular pacing. Patients with persistent symptoms were found to have a significant vasodepressor response, a significant hypotensive response to ventricular pacing (pacemaker effect), and a severe hypotensive response to carotid sinus massage with introduction of ventricular pacing, which reproduced symptoms in all patients. A group of 14 asymptomatic paced carotid sinus patients was found to have a significantly lower vasodepressor response, pacemaker effect, and combined vasodepressor response plus pacemaker effect than the group with persistent symptoms. Atrioventricular sequential pacing was shown to eliminate the hypotensive effect of ventricular pacing and is considered to be the treatment of choice for patients with carotid sinus syndrome who have both cardioinhibitory and significant vasodepressor responses.