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Coexistence of atrioventricular block and ventricular pre-excitation is rare. Most reported cases have been associated with structural heart disease and in many patients the atrioventricular (AV) block was incomplete.1-4
A 2 year old boy was referred for evaluation after a routine examination by his general practitioner had detected a slow pulse and a murmur. He was asymptomatic with normal growth and development. On examination he had a regular bradycardia of 65 beats/min and a grade 2 ejection murmur. The ECG showed complete AV block with an atrial rate of 115 beats/min and a ventricular rate of 65 beats/min (fig 1). The QRS duration and QT interval were normal. Echocardiography showed a structurally normal heart with normal ventricular function. A 24 hour ECG showed complete AV block throughout with an average ventricular rate of 50 beats/min at night and 65 beats/min during the day. He remained well during follow up with no change in the clinical situation, ECG, or 24 hour ECG.
At 9 years old he attended for a routine clinic appointment. His parents reported an increase in his energy and he had taken up cross country running. On examination his pulse rate was 84 beats/min. His ECG showed sinus rhythm with 1:1 AV conduction and notable ventricular pre-excitation, with a pattern predicting a left posterolateral position for the accessory pathway (fig 2). A 24 hour ECG showed 1:1 AV conduction throughout with ventricular rates of up to 135 beats/min. A Bruce protocol exercise test showed sustained 1:1 conduction with pre-excitation throughout. He exercised for 15 minutes and achieved a maximum heart rate of 209 beats/min. He has been well during a further 3½ years' follow up with persisting 1:1 conduction on all investigations.
This case appears to be unique. The AV block was presumably congenital although maternal antibody testing was negative. The development of ventricular pre-excitation at 9 years old restored 1:1 conduction, and pathway conduction seems robust. Manifestation of ventricular pre-excitation during childhood occurs at an average of 8 years old,5 so this case is probably a fortunate coincidence. It provides the ideal solution to complete AV block.