Key result
Atypical preexcitation ECG patterns implicate Mahaim fiber or septal bypass conduction across five cases.
Why the study?
Electrocardiographic manifestations suggestive of conduction through Mahaim fibers or septal bypass in concealed preexcitation and WPW pattern cases require detailed description and analysis.
Case Report (n=5)
Specific ECG manifestations in cases of concealed preexcitation and WPW pattern can indicate conduction through Mahaim fibers or septal bypass.
Should not yet alter ECG interpretation in concealed preexcitation; leaves open prospective validation of Mahaim or septal bypass mechanisms.
One case of concealed preexcitation and four cases of Wolff-Parkinson-White (WPW) pattern (including one questionable case) n which the electrocardiographic (ECG) manifestations were highly suggestive of the conduction through Mahaim fibers or septal bypass are described. ECGs of Case 1 did not demonstrate preexcitation but showed a peculiar arrhythmia consisting mainly of the sequence of trigeminy and quadrigeminy due to the occurrence of "supraventricular premature beat" which is preceded by inverted P wave and often showed aberrant conduction of right bundle branch block (RBBB) pattern and occasional anterograde conduction failure. Atrial reciprocal rhythm (ARR) related to the presence of concealed bypass which is essentially capable only of retrograde conduction, that is, a concealed preexcitation, was the most likely mechanism. Intermittent conduction through the left-sided Mahaim fibers was the most likely mechanism of aberrant conduction of ventricular reciprocal beat (VRB). Case 2 was type A WPW pattern associated with short PR interval. After daily intravenous drip infusion of digitalis (Cedilanid), which has been generally considered to depress the atrio-ventricular (A-V) conduction and accelerate the anomalous bypass conduction, PR interval gradually prolonged to 0.16 sec, while type A WPW pattern with decreased size of initial delta wave remained. This finding was considered to favor the mechanism of either combination of A-V nodal bypass and left-sided Mahaim fibers or left-sided Mahaim fibers alone rather than left-sided (type A) Kent bundle. Case 3 was believed to be type A WPW pattern due to anomalous conduction through left-sided Mahaim fibers. However, concomitant RBBB could not be wholly excluded in Cases 2 and 3 (particularly, in Case 2). Regarding Case 4, it was impossible to label as type A WPW pattern without the aid of intracardiac recordings and pacing study because such a QRS pattern seems to have been labelled as atypical RBBB. Case 5 was considered to be atypical case associated with normal PR interval. WPW pattern of A-V junctional escape beats was indicative of the conduction through Mahaim fibers or septal bypass.
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Izumi et al. (1979) conducted a case report in Concealed preexcitation and Wolff-Parkinson-White (WPW) pattern (n=5). Conduction through Mahaim fibers or septal bypass was evaluated on Electrocardiographic manifestations and arrhythmia mechanisms. ECG manifestations in five cases of concealed preexcitation and WPW pattern suggested conduction through Mahaim fibers or septal bypass as the underlying mechanism.
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