Dissociation with interference in the presence of 2:1 atrioventricular block

Abstract

Two cases are reported which present dissociation with interference in the presence of 2:1 atrioventricular block. This arrhythmia differs from ordinary dissociation with interference in that the automatic ventricular rhythm is slower than the sinus rhythm, but is faster than the sinoauricular half rhythm. Dissociation with interference combined with 2:1 atrioventricular block is a well-defined arrhythmia which shows the following characteristic features: 1. 1. Dissociated action of the atria and ventricles. The regular ventricular rhythm is occasionally interrupted by shorter ventricular cycles. 2. 2. The ventricular complexes which conclude the shorter cycles show a fixed relationship to a preceding atrial wave, thus suggesting that they are due to conducted atrial excitations. They may or may not differ in shape from the regular ventricular beats. 3. 3. The P wave of the conducted beats show a distinct time relationship to the preceding automatic ventricular beat. Only those atrial impulses are conducted which fall late in diastole after the refractory state of the bundle, caused by transmission of an automatic ventricular excitation, has ended. 4. 4. The refractory period of the bundle can be estimated from the shortest R-P interval of the conducted sinoauricular beats. This “critical” R-P interval may be close to, but is mostly longer than, one sinus period. Complete atrioventricular dissociation develops instead of dissociation with interference when the critical R-P interval plus the time required for conduction of a sinoauricular excitation is longer than the automatic ventricular period. Complete atrioventricular dissociation of this type should not be mistaken for complete atrioventricular block.