complete heart block
In complete heart block the road between the upper and lower chambers is shut entirely — no atrial signal gets through to the ventricles at all. Left without instructions from above, the ventricles fall back on a slow, built-in backup pacemaker just to keep some blood flowing. The two halves of the heart now beat to their own separate drums, completely out of step.
On the ECG this “atrioventricular dissociation” shows P waves marching at their own steady rate and QRS complexes appearing independently and more slowly, with no fixed relationship between them. The escape rhythm rescuing the ventricles is typically only 20 to 40 beats a minute and may be unreliable, risking long pauses.
Complete block is dangerous: the slow, fragile escape rhythm can cause fainting, heart failure or sudden death. Common causes are age-related degeneration of the conduction system, a heart attack involving the conduction tissue, and certain drugs. The treatment is urgent pacing — temporary at first if needed, then a permanent pacemaker.
An older man presents with recurrent blackouts; his ECG shows P waves at 80 and QRS complexes at 35 with no connection between them, and a permanent pacemaker resolves the syncope.
Independent atrial and ventricular rates on the ECG are the signature of complete block.
The telltale sign is atrioventricular dissociation: P waves and QRS complexes march at independent rates. Most symptomatic complete block requires a permanent pacemaker.