SUMMARY Two hundred and 14 patients with chronic second degree heart block were seen and followed up in the Devon Heart Block and Bradycardia Survey between 1968 and 1982. The patients were divided into three groups according to the type of block. In group 1 there were 77 patients with Mobitz type I block (mean age 69 years), in group 2, 86 patients with Mobitz type II block (mean age 74 years), and in group 3, 51 with 2:1 or 3:1 block (mean age 75 years). The five year survival was similar in all groups, being 57%, 61%, and 53% in groups 1, 2, and 3 respectively. The presence or absence of bundle branch block did not appear to influence prognosis. In particular, patients in group 1 without bundle branch block did not fare any better than those in group 2 both with and without bundle branch block. One hundred and three of the patients were fitted with pacemakers, the proportion being greatest in group 2. In each group a significantly larger number of paced patients survived than unpaced. The five year survival for all the paced patients in the study was 78% compared with 41% for the unpaced. Since the paced patients were slightly younger than the unpaced two age matched groups of 74 patients each were selected from the paced and unpaced patients, but the five year survival of those paced was still significantly better.It is concluded that in the patients in the present study chronic Mobitz type I block has a similar prognosis to that of Mobitz type II block. Unpaced patients with both types did very badly, whereas those fitted with pacemakers had a five year survival similar to that expected for the normal population. These results refute the benign reputation of chronic Mobitz type I block and imply that patients with this condition should be considered for pacemaker implantation on similar criteria to those adopted for patients with higher degrees of block.The use of pacemakers has been a major advance in the treatment of different forms of bradycardia, and because of its dramatic effect in some groups of patients it has become the vogue. The reaction to this is the current reassessment of the place of the pacemaker in several conditions. Four years ago we produced evidence that the prognosis in chronic sinoatrial disorder (sick sinus syndrome) was not appreciably improved by pacing,' and recently the place of this form of treatment in high risk bundle branch block has been questioned.4 Second degree Mobitz type I (atrioventricular nodal) block is widely believed to be relatively benign.5-7 The corollary is that patients with this type of conduction disturbance do not require pacing in the absence of troublesome Requests for reprints to

Summary and conclusionsA total of 381 patients with established (156) or potential (225) sinoatrial dysfunction were included in a 10-year prospective survey to determine the course of the disease and the benefits of pacing. With the exclusion of nine patients who were lost to follow-up, 61 were fitted with pacemakers.The overall survival of patients with established and potential dysfunction was similar and apparently indistinguishable from that of the normal population. Pacemaker implantation had little discernible effect on mortality though it reduced some incapacitating symptoms.These findings suggest that sinoatrial dysfunction is a relatively benign condition. Hence pacing should probably not be adopted as a routine measure but be reserved for patients with troublesome symptoms.

Objective: To assess the need for pacing in adults with chronic Mobitz type I second degree atrioventricular block (Mobitz I). Design: Prospective study. Setting: District general hospital. Patients: 147 subjects aged > 20 years (age cohorts 20-44, 45-64, 65-79, and > 80) with chronic Mobitz I without second degree Mobitz II or third degree (higher degree) block on entry, seen from 1968 to 1993 and followed up to 30 June 1997. Sixty four had organic heart disease. The presence of symptomatic bradycardia was defined as highly likely in 47 patients (class 1); probable in 14 (class 2); and absent in 86 (class 3). Interventions: Pacemakers were implanted in 90 patients for the following indications: symptoms in 74 and prophylaxis in 16. Main outcome measures: The main outcome measure was death, with conduction deterioration to higher degree block or symptomatic bradycardia the alternative measure. Results: Five year survival to death was reduced in unpaced patients relative to that expected for the normal population (overall mean (SD) 53.5 (6.7)% v 68.6%, p , 0.001; class 3, 54.4 (7.3)% v 70.1%, p , 0.001). Paced patients fared better than unpaced (overall (mean (SD) five year survival 76.3 (4.5)% v 53.5 (6.7)%, p = 0.0014; class 3, 87.2 (5.4)% v 54.4 (7.3)%, p = 0.020; and organic heart disease, 68.2 (7.6)% v 44.0 (9.9)%, p ( 0.0014). There were no deaths in the , 45 cohort. Survival to first outcome (main or alternative) was further reduced to 31.7 (5.0)% in 102 patients unpaced initially and 34.2 (5.7)% in class 3. Only the 20-44 cohort and patients with sinus arrhythmia had . 50% survival. Conclusion: Mobitz I block is not usually benign in patients > 45 years of age. Pacemaker implantation should be considered, even in the absence of symptomatic bradycardia or organic heart disease.

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