Complete heart block (or third-degree AV heart block)
A colleague showed me an unusual looking ECG on a patient with no cardiac symptoms. We asked a cardiologist for advice and he diagnosed Complete Heart Block (CHB). As the patient was well he was referred to cardiology clinic the following day for a pacemaker.
Complete heart block is the most serious type of AV heart block. This is an abnormal heart rhythm (arrhythmia) that happens when there is a complete absence of electrical impulses (AV conduction) between the atria and ventricles.
Normally a back-up system keeps ventricles beating (junctional or ventricular escape rhythm), but the ventricles beat much slower than normal. This can affect the flow of blood to the body and brain and will cause symptoms of confusion, collapse, dizziness, breathlessness and tiredness.
Alternatively, the patient may suffer ventricular standstill leading to syncope (if self-terminating) or sudden cardiac death (if prolonged).
What causes complete heart block?
Most people with complete heart block have an underlying heart condition like coronary heart disease, cardiomyopathy or congenital heart disease.
It can also be caused by ageing of the electrical pathways in your heart (meaning you’re more likely to get it if you’re older), electrolyte imbalances, and some medicines (e.g. calcium-channel blockers, beta-blockers, digoxin)
The patient will have severe bradycardia (slow heartbeat) with independent atrial and ventricular rates, i.e. AV dissociation on ECG-see below.
Example of complete heart block
The atrial rate is approximately 100 bpm.
The ventricular rate is approximately 40 bpm.
The two rates are independent; there is no evidence that any of the atrial impulses are conducted to the ventricles.
Patients require urgent admission for cardiac monitoring, backup temporary pacing and usually insertion of a permanent pacemaker.