[Junctional reciprocating "fast-slow" reentry tachycardias. Diagnostic characterization and therapeutic...

The typical electrocardiographic pattern of "fast-slow" junctional reciprocating tachycardias is characterized by RP' interval longer than the P'R interval, with P wave negative in the inferior leads. The most common substrates of this arrhythmia are: an atypical (fast-slow) intranodal reentry; a reentry by a posteroseptal accessory pathway with decremental properties, which is responsible for the permanent form of junctional reciprocating tachycardia (PJRT). Usually unresponsive to pharmacological therapy, these arrhythmias are often observed in young people. A variable degree of cardiac dysfunction, as a consequence of reversible tachycardia-induced cardiomyopathy, can occur in some patients. An endocavitary electrophysiologic evaluation is required to define the arrhythmogenic substrate. The occurrence of second degree A-V block with persistence of tachycardia is diagnostic of A-V node reentry, while the occasional (spontaneous or induced) appearance of pure posterior septal pre-excitation is in favour of PJRT. Suggestive of PJRT is the identification of 2 sequences of retrograde activation in the same patients during ventricular pacing at increasing rates. Due to the usual unresponsiveness of these tachycardias to pharmacological treatment, surgical interruption of the reentry circuit is often necessary. Such a goal can be reached by means of transcatheter techniques.