Heart block

Heart block is a problem with the electrical signals that coordinate the heartbeat. The signal normally travels from the heart's upper chambers (atria) to the lower chambers (ventricles) in a precise sequence. In heart block, this signal is slowed down or blocked — sometimes intermittently, sometimes completely.

Heart block is different from "blocked arteries" (coronary artery disease), which is about blood supply rather than electrical signalling.

Types

• First-degree heart block — the electrical signal is slowed but every beat still gets through. Often has no symptoms; often found incidentally on ECG.
• Second-degree heart block — some signals don't get through. Divided into Mobitz type I (Wenckebach — usually benign) and Mobitz type II (more concerning; can progress).
• Third-degree (complete) heart block — no signals get through from atria to ventricles. A backup rhythm takes over but is usually slow. This is a medical emergency.

Symptoms

First-degree block often causes no symptoms. Higher-grade block can cause:

• Slow heartbeat
• Dizziness or lightheadedness
• Fainting (syncope)
• Tiredness, reduced exercise capacity
• Chest discomfort
• Shortness of breath
• In complete heart block: collapse, possible cardiac arrest

Causes

• Ageing-related changes in the heart's electrical system
• Coronary artery disease (heart attack can damage the conduction system)
• Heart failure
• Inflammatory or infiltrative heart diseases (myocarditis, sarcoidosis, amyloidosis)
• Certain medicines — beta-blockers, calcium-channel blockers, digoxin
• Electrolyte imbalances — especially high potassium
• Congenital heart block (present from birth, sometimes from maternal lupus)
• Infections — Lyme disease; in India, sometimes rheumatic heart disease or Chagas-like illnesses
• After cardiac surgery or catheter procedures

Diagnosis

• ECG — the first and most important test
• Holter monitor — a 24-48 hour ECG recording for intermittent block
• Event recorder or implantable loop recorder — for infrequent symptoms
• Echocardiogram — to check the heart's structure
• Blood tests — electrolytes, thyroid, kidney function
• Exercise testing or electrophysiology study in selected cases

Treatment

• First-degree — usually no treatment; monitor
• Mobitz I second-degree — often monitored; treatment only if symptomatic
• Mobitz II or complete heart block — usually needs a pacemaker (a small device implanted under the skin near the collarbone that sends electrical signals to the heart). Pacemaker implantation is a routine procedure, widely available across Indian cardiac centres.
• Reversible causes — stopping or adjusting offending medicines, treating electrolyte problems, treating underlying infection
• Emergency treatment — for unstable complete heart block, temporary pacing and hospital admission

People with pacemakers live normal lives with regular cardiology follow-up for battery and device checks. The pacemaker battery lasts 5-15 years depending on the model and usage.