Antidromic tachycardia due to an accessory pathway

Patient

63-year-old man with multiple risk factors hospitalized for palpitations; ECG recorded during a well-hemodynamically supported tachycardia episode;

Trace

Tachycardia of 180 bpm, with broad QRS, right delay, superior axis; very smooth ascending QRS slope in all precordial leads; atrial activity difficult to pinpoint (possible 1:1 AV ratio with atrium in the ascending branch of the T wave); this patient was referred in emergency following the diagnosis of probable ventricular tachycardia;

Trace

The termination of the tachycardia was not recorded; after the return to sinus rhythm, short PR pattern without obvious pre-excitation, possible sequela of inferior and anterolateral necrosis;

Trace

During the hospitalization, a new episode of tachycardia; narrow QRS tachycardia;

Trace

Interruption of the tachycardia upon injection of 6 mg Adenosine; after return to sinus rhythm, evidence of major pre-excitation which was masked on the previous sinus rhythm tracing; the conduction through the atrioventricular node was completely blocked by the injection of Adenosine, the conduction is now exclusively through the accessory pathway; the QRS pattern is identical to that observed on the first tachycardia suggesting that it was an antidromic tachycardia;

Exergue

Antidromic tachycardias are less frequent than orthodromic tachycardia; the impulse descends from the atrium to the ventricles through the accessory bundle and ascends in retrograde manner toward the atrium through the nodo-Hisian pathway; this is a regular wide QRS tachycardia (maximum pre-excitation pattern) with a 1:1 AV ratio;