Dual chamber sensing has been proposed in implantable defibrillators a
s an additional diagnostic modality for enhanced differentiation of ve
ntricular and supraventricular tachycardias. A patient with different
rates of wide QRS complex tachycardias is described in whom a tiered t
herapy implantable defibrillator with atrial sensing capability was im
planted. Atrial diagnostic data in this patient enabled definitive dia
gnosis of his ventricular tachycardias and guided management decisions
of his arrhythmia.