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Impedance Mismatch Causes Conduction Block. Introduction: The impedance mismatch hypothesis has been proposed as one of the mechanisms responsible for accessory connection conduction block. Methods and Results: We describe a case in which retrograde conduction across block posters accessory connection was ablated at the atrial insertion site in the coronary sinus of, whereas Anterograde conduction was ablated at the ventricular insertion site in the left ventricle. Conclusion: The evidence supports the impedance mismatch concept as the cause of unidirectional conduction block and shows that the distal junction between the accessory connection and the myocardium is more vulnerable to ablation.

Although we have shown previously that electrical alternans of the ST segment and T wave; i.e., repolarization alternans (RA), is a marker of vulnerability to ventricular arrhythmias, the mechanism of RA in humans remains unclear. To determine the component of repolarization that is most closely associated with arrhythmogenesis, electrical alternans of the ST segment, and the early (Tearly), mid (Tmid), and late (Tlate) components of the T wave were measured using sensitive spectral analytical techniques in 35 patients undergoing electrophysiological studies (EPS). Alternans measured in each phase of repolarization was correlated with arrhythmia vulnerability as defined by; 1. The results of EPS and 2. Actuarial 20 month arrhythmia-free survival. Figure options Download full-size image Download high-quality image (58 K) Download as PowerPoint slide In EPS+ patients, the magnitude of RA increased progressively during later phases of repolarization (Figure). In contrast, EPS-patients had elevated RA levels only in late (Tlate) but not during early repolarization. Hence, RA of Tlatedid not differ significantly between EPS + and EPS–patients (Figure). Inducibility at EPS was predicted with greatest specificity by the presence of RA in early repolarization (TearlySpecificity = 0.88), compared to RA involving later components of the T wave; Tmid(0.79). Tlate(0.63). or the ST segment (0.71). Similarly, RA involving early repolarization was the most specific marker for reduced arrhythmia-free survival (Specificity's: Tearly0.87, Tmid0.83, Tlate0.58, ST 0.80). Conclusions RA of the terminal component of the T wave is present in most patients and is not necessarily a specific marker for arrhythmia vulnerability. In contrast, RA involving the early phases of repolarization (Tearly) appears 10 have the most prognostic significance. RA related arrhythmogenesis may be due to an underlying disturbance affecting early repolarization.