This case highlights the possibility of parasystolic fusion of upper and lower pacemakers during transitions between sinus rhythm and isorhythmic A-V dissociation in a patient with congenital heart disease.
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May aid ECG interpretation in congenital heart disease rhythm transitions; leaves open mechanistic validation in larger cohorts.
A 15-year-old boy with congenital heart disease showed two types of wide QRS complexes in the limb leads. One type appeared during sinus rhythm with a QRS axis of ca. -45°, and the other during isorhythmic A-V dissociation with a QRS axis of ca. +110°. Transitions between the two rhythms were gradual, and several intermediate QRS complexes intervened. Possibility of parasystolic fusion of upper and lower pacemakers during transitions was discussed.
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Kimiaki Nakamoto (1972) studied this question.
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