Longitudinal dissociation and concealed electrotonic conduction as a possible mechanism of AV block.

摘要

We have read with much interest a recent report by Bhargava et al on AV block. They represented an electrocardiogram showing sinus tachycardia with sinus rate exceeding the ventricular rate suggesting atrioventricular (AV) block in a patient with old anterior wall infarction. Fig. 1 is the electrocardiogram shown in their report, in which the presence of varying PR intervals, irregular R-R intervals and P-QRS relationship not consistent with second-degree, type I AV block was seen. As represented in the upper diagram of Fig. 1, they explained that 2-level block occurred in the AV junction as the mechanism.In the electrocardiogram, sinus impulse SI is conducted to the ventricles with a normal PR interval. The next sinus impulse, S2, is conducted with a markedly long PR interval of 0.68 second. In cases of our previous report, such abrupt marked prolongation of the PR interval was explained by longitudinal dissociation in the AV junction. In this letter, attempts are made to explain the case not by 2-level AV block but by longitudinal dissociation and concealed electrotonic conduction in the AV junction as an alternative possible mechanism, as shown in the lower diagram of Fig. 1.