Predicting postpneumonectomy FEV1. Half empty or half full?

followed by premature RB beats, we must assume that RB complexes do not express conducted sinus impulses but are, in fact, escape beats, also suggested by their short H-V interval. The diagram of Figure 1 reflects a 2:1 form of A-V nodal block. This phenomenon, however, would have been the same with any other form of second-degree A-V block provided that two levels of block occur, and no retrograde conduction of the escape impulses is manifested. Other arguments against conduction of sinus impulses through Mahaim fibers include: no delta wave is evident in RB beats, and the direction of the initial vectors of ventricular activation is the same for both the P A and RB beats.