Heart Conduction Disorders and Blocks
What are conduction disorders?
The heart beats through coordinated electrical impulses. These normally start in the sinus node, spread through the atria and pass through the atrioventricular (AV) node and specialised conduction pathways to the ventricles. A conduction disorder occurs when an impulse is delayed or interrupted along this system.
The effects range from an incidental ECG finding to a very slow rhythm requiring urgent treatment. The location and degree of block are more important than the word "block" alone.
What symptoms can occur?
- Dizziness or near-fainting.
- Fainting or unexplained falls.
- Fatigue and reduced exercise capacity.
- Breathlessness.
- A slow pulse or pauses.
Many conduction abnormalities cause no symptoms and are found during a routine ECG.
What are the main types?
First-degree AV block
Electrical conduction from the atria to the ventricles is delayed, but each atrial impulse is conducted. It is often asymptomatic. Its importance depends on the extent of delay and the patient's circumstances.
Second-degree AV block
Some atrial impulses fail to reach the ventricles. In Mobitz type I, conduction usually becomes progressively slower before an impulse is blocked. In Mobitz type II, an impulse may be blocked without that progressive pattern. Mobitz II and advanced AV block require particular attention because they may progress to complete block.
Third-degree or complete AV block
Atrial impulses do not reach the ventricles. The ventricles rely on a slower escape rhythm. This can cause fainting and circulatory instability and may require pacemaker treatment.
Bundle branch and fascicular blocks
Right or left bundle branch block affects the spread of electricity through the ventricles. A fascicular block affects part of the left-sided conduction system. Some are incidental, while others accompany structural heart disease. A bundle branch block does not automatically mean that a pacemaker is needed.
What causes conduction abnormalities?
Causes include age-related degeneration, coronary artery disease and myocardial infarction, cardiomyopathies, myocarditis, previous heart surgery and some congenital conditions. Certain medicines and electrolyte abnormalities may also interfere with conduction.
How are they diagnosed?
An ECG identifies the type and location of the abnormality. Holter or longer monitoring may reveal intermittent blocks and help link symptoms with the rhythm. Echocardiography evaluates underlying heart disease. Blood tests, exercise testing, cardiac MRI or an electrophysiological study may be appropriate in selected cases.
How are they treated?
Asymptomatic low-risk abnormalities may need observation. Potentially reversible causes should be addressed and medication reviewed. A permanent pacemaker is often indicated for significant AV block when no reversible cause is present, and may also be appropriate when a documented conduction problem causes symptoms.
Selected patients with heart failure and electrical dyssynchrony may benefit from cardiac resynchronisation therapy. This is different from routine pacemaker treatment and is not needed for every bundle branch block.
When is urgent assessment needed?
Unexplained fainting, particularly with a known conduction abnormality, needs prompt evaluation. Fainting with chest pain, severe breathlessness, confusion or a very slow pulse requires emergency care. Call 112.
Assoc. Prof. Sezen Bağlan Uzunget, MD — Cardiologist
This content is educational. Treatment is individualised according to symptoms, ECG findings and the underlying condition.
Türkçe: Kalp İleti Blokları