Mechanisms of Paroxysmal Supraventricular Tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is a common arrhythmia in patients with and without organic heart disease. It has generally been believed to reflect either reentrant mechanisms or rapid firing of ectopic foci. Recent clinical and experimental observations have suggested that most PSVT appears to reflect reentrance.¹⁻⁶In man, the occurrence of reentrance has been demonstrated in the sinus node,⁷⁻⁹atrium,⁹atrioventricular node,¹⁻⁶and possibly the His bundle.¹⁰ Longitudinal dissociation of a conducting structure (for example, the atrioventricular node) allows reentry to occur¹¹⁻¹⁴(Fig 1, left). With dissociation into two pathways, a premature impulse encounters refractoriness (unidirectional block) in one pathway and conducts slowly in the other pathway. The previously blocked pathway recovers for retrograde conduction during the period of slow conduction. If the two pathways are connected by a final common pathway, the impulse can reenter the previously blocked pathway and return to the chamber of origin. While conducting retrograde,