PERITACHYCARDIC SYNCOPAL LEFT-BUNDLE-BRAN CH BLOCK - A NEW SYNDROME

The authors report four observations: three are essentially clinical c ases where substained rate dependant left bundle branch block can indu ce syncope, where as there is no syncope when the same supraventricula r tachycardia at the same frequency has narrow QRS complexes. The four th case demonstrates the dramatic decrease of arterial electrophysiolo gical slowly accelerated atrial pacing in a patient investigated for a lose of consciousness of unknown origin. The hemodynamic impairment d ue to intermittent left bundle branch block has been demonstrated even in patients with normal ventricular function. If there are critical h emodynamic events such as during fast supraventricular rythms occurenc e of a left bundle branch block may determinate a dramatic decrease of arterial pression, with syncope. Syncope of supraventricular tachycar dias might be induced not only by very fast rate but also by functiona l left bundle branch block. It might have some interesting application s in the diagnosis of syncope when coexist electrophysiological datas of supraventricular arythmia substrate and frequence dependant left bu ndle branch block.