© 2002 The Medicine Publishing Company Ltd 137 DISORDERS OF CARDIAC RHYTHM MEDICINE Bradycardia and Permanent Pacemakers Mark J Mason Vince Paul The investigation and management of bradycardia is an in- creasingly complex topic, but with the development of pace- makers there are few areas of medicine that offer such sub- stantial improvements in patients’ quality of life. About 400,000 pacemakers are implanted worldwide per year; about 270 are implanted per million population in the UK, 370 per million in Europe as a whole and 434 per million in the USA. The use of pacing varies, however, depending on the avail- ability of expertise to recognize the potential benefits of pacing, to select an appropriate type and to implant the device. This contribution focuses on the investigation of patients with bradycardia and the subsequent indications for pacing. The indications are based on the recommendations of the American College of Cardiology/American Heart Association. Bradycardia The pathophysiology of bradycardia may be divided into: • failure to initiate a cardiac impulse – sinus node disease • failure to conduct the cardiac impulse – atrioventricular (AV) node disease • ‘neurocardiogenic’ syncope. Sinus node disease is also known as sino-atrial node dis- ease, ‘sick sinus syndrome’ and tachy/brady syndrome. The aetiology is most commonly idiopathic, probably related to conduction tissue fibrosis, though the condition may occur in association with myocardial infarction (MI), cardiomyopathy or infiltrative conditions such as amyloidosis. It is most likely to occur in the seventh or eighth decade, but may occur at any age. Sinus node disease is the most common indication for pacing in young individuals. Subsequent development of AV node disease is reported in 10–20% of those with sinus node disease; the incidence increases with age. AV node disease – the aetiology of AV node disease can be: • idiopathic (most common – likely to result from conduction tissue fibrosis) • acute MI • congenital (in isolation or with other congenital defects) • post-cardiac surgery (particularly aortic and less commonly mitral valve replacement) • deposition diseases (amyloidosis, sarcoidosis) • infections (e.g. Lyme disease, chronic brucellosis) • drug toxicity (e.g. digoxin, β-blockers, verapamil). The classification of AV block is shown in Figure 1. Neurocardiogenic syncope – the most widely recognized forms of neurocardiogenic syncope are as follows. Mark J Mason is a Locum Consultant Cardiologist at Harefield Hospital, Harefield, UK. Vince Paul is Consultant Cardiologist at St Peter’s Hospital, Chertsey, UK. Classication of atrioventricular block First-degree AV block is identified by prolongation of the PR interval to > 200 milliseconds. Second-degree AV block may be classified as: • Mobitz type 1 (‘Wenckebach’) block – progressive lengthening of the PR interval with each successive complex until a P wave is not conducted and a QRS complex is ‘dropped’ • Mobitz type II block – PR interval is constant, but QRS complexes are dropped either intermittently or in a fixed ratio to the P wave rate (e.g. 2:1, 3:1, 4:1) Third-degree ʻcompleteʼ AV block: there is complete dissociation of atrial and ventricular electrical activity. P waves remain regular at a rate determined by the sinus node and QRS complexes ‘march through’ independently in an idioventricular ‘escape’ rhythm. The rate is typically 30–50 per minute (higher levels of block lead to faster rates and narrower QRS complexes). 1 North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group recommendations on general indications for pacing Class 1  acceptable and necessary • Acquired symptomatic complete AV block (unpaced 1-year mortality is 30–35%, compared with 5% if paced) • Symptomatic congenital complete heart block (decisions regarding timing may be difficult in children and teenagers who are still growing – seek expert advice) • Symptomatic second-degree AV block (Mobitz I or II) • Symptomatic sinus bradycardia • When accompanied by significant symptoms, sinus bradycardia that is the consequence of long-term drug treatment for which there is no acceptable alternative • Sinus node dysfunction ± tachyarrhythmia or AV block • Sinus node dysfunction ± symptoms in patients with potentially life-threatening ventricular arrhythmia or tachycardia secondary to bradycardia • Bradycardia associated with significant symptoms and with supraventricular tachycardia and high-degree AV block unresponsive to appropriate pharmacological management Class 2  may be acceptable or necessary • Asymptomatic acquired third-degree AV block with ventricular rate > 40 beats per minute • Bifascicular or trifascicular block accompanied by syncope that is attributed to transient complete heart block after other plausible causes of syncope have been reasonably excluded • Asymptomatic Mobitz II second-degree AV block • Asymptomatic Mobitz I second-degree AV block within the His–Purkinje system (requires electrophysiological evaluation) 2