Complete heart block and pacemaker indications

Definition. Third-degree (complete) heart block is complete failure of conduction between atria and ventricles, producing regular atrial activity with an independent escape rhythm. The escape is usually ventricular — wide QRS at 30–40 beats per minute. A nodal or junctional escape (narrow QRS, faster) means the block is higher, within the AV node or bundle of His. The lower the origin of the escape rhythm, the less reliable it is.

Causes in the elderly. Idiopathic age-related fibrosis of the conduction system (Lev and Lenègre disease) is commonest. Others: ischaemic heart disease and inferior myocardial infarction, drugs (beta-blockers, digoxin, verapamil, diltiazem, amiodarone), hyperkalaemia, calcific aortic valve disease and post-TAVI, infiltrative disease (sarcoidosis, amyloidosis), neuromuscular disease (myotonic dystrophy type 1, Kearns–Sayre syndrome), and cardiac surgery or AV junction ablation.

Clinical features. Stokes–Adams attacks (abrupt syncope without warning), presyncope, falls, fatigue, dyspnoea, angina and heart failure. Signs: slow regular pulse, cannon 'a' waves in the JVP, variable intensity of the first heart sound and a wide pulse pressure. Complete heart block is a classic cardiac cause of syncope in old age.

Class I indications for permanent pacing. (i) Acquired complete heart block not attributable to a reversible or physiological cause — regardless of symptoms. (ii) Complete heart block due to neuromuscular disease with conduction disorder (myotonic dystrophy type 1, Kearns–Sayre). (iii) Symptomatic complete heart block occurring as a consequence of guideline-directed drug therapy that must be continued.

Related Class I / IIa indications. Mobitz type II second-degree block not attributable to reversible causes should be paced regardless of symptoms (Class I); so should unresolving advanced second-degree block after cardiac surgery or AV junction ablation (Class I). Pacing is reasonable (Class IIa) in infiltrative cardiomyopathy such as cardiac sarcoidosis with Mobitz type II block, and in Mobitz type I block when symptoms are clearly attributable to the block.

Pacemaker choice and complications. DDD (dual-chamber) pacing preserves AV synchrony and is preferred in complete heart block with sinus rhythm; VVI/R is used when there is permanent atrial fibrillation. Pacing that maintains physiological ventricular activation (CRT or His-bundle pacing) should be considered when the ejection fraction is below 50% and ventricular pacing is expected more than 40% of the time (Class IIa). Complications: pneumothorax 1–2% with the subclavian approach but under 0.1% with cephalic or axillary access, tamponade under 0.2%, infection under 1%, lead displacement; early complications occur in about 7% within two weeks and later complications in up to 10%. Risk factors are female sex and low body mass index — increasing age itself is not associated with higher complication risk. In cachectic patients with thin skin or skeletal deformity, a sub-pectoral position reduces erosion.

The 2023 HRS/APHRS/LAHRS Guideline on Cardiac Physiologic Pacing establishes conduction system pacing as a recommended alternative to conventional right-ventricular pacing when a high ventricular pacing burden is anticipated — as in complete heart block. Left bundle branch area pacing (LBBAP) has largely superseded His-bundle pacing because of better capture thresholds and lead stability. Leadless pacemakers (Micra AV2, Aveir) are an option for AV block in frail older patients with poor venous access, thin skin or high infection risk.