Sinus Captures in Nodal Rhythm

Report:

Junctional rhythm 42/min

Sinus capture beats

AV dissociation with interference

Concealed conduction

Comment:

The sinus captures are only possible after sufficient distance from the preceding QRS complex has rendered the AV node amenable to conduction. That the preceding (junctional) impulse had penetrated the AV node is attested by the prolonged PR interval of the capture beat. This is an example of concealed conduction (of the junctional impulse to the AV node): concealed, because it is not manifest per se, but only by its effect (prolonged PR interval) on the subsequent beat.

Without obvious captures – capture beats are always early - one can rarely be sure whether the sinus P waves are actually conducted or merely present in isorhythmic AV dissociation (Fig 31a).

It is likely that this patient’s bradycardia is the result of ß-blocker therapy.

Nodal rhythm? The usefulness of this term is in provoking pedants into explaining why the term should no longer be used. Not many clinicians care whether the impulses come from the node proper or its (“junctional”) surroundings. Not any more than they would want to know if you come from New York or greater New York area.

Fig 31b. One cannot be sure that the upper strip is conducted sinus rhythm in view of what happens in the lower strip: gradual immersion of the obviously dissociated P waves into the junctional complexes at the almost the same rate. Isorhythmic dissociation is common in double bradycardias.

Fig 32. 65 year old man with COAD (COPD, now CAL), ventilated following a laparotomy. Xylocaine 75 mg IV was given to abolish suctioning-induced hypotension a few minutes after the middle strip was recorded. What happened then? Why?