Ventricular pacing, intermittent

The purpose of inspecting the connector block is to determine that the connector and pin are firmly in contact. If the pin of the pacing lead is not firmly in the connector block, intermittent or permanent disruption of the circuit occurs. In Figure 18.6, the chest radiograph demonstrates a dual-chamber pacemaker with a lower pin that is only partially advanced. At presentation, the patient had intermittent failure to capture the ventricle and intermittent failure to deliver a ventricular pacing output. 

Interference with ventricular pacing occurred in a patient with a pacemaker who developed severe procainamide toxicity with a serum concentration of 36 ptglml the QRS widened from 0.20 to 0.26 sec and a delay of 0.18 sec appeared between the pacing stimulus and the QRS. Subsequently, periodic variation of the Wenkenbach type developed in the stimulus-QRS interval with intermittent failure to pace. Failure of pacemaker inhibition also occurred. Administration of 160 mM sodium bicarbonate intravenously led to immediate improvement in the abnormalities (37 ). 

Distinguishing intermittent ventricular pacing from PVCs... 

If your patient has intermittent ventricular pacing, the paced ventricular complex will have a pacemaker spike preceding it, as shown in the shaded area of the top electrocardiogram... 

Vecchia L, Ometto R, Finocchi G, Vincenzi M. Torsade de pointes ventricular tachycardia during low dose intermittent dobutamine treatment in a patient with dilated cardiomyopathy and congestive heart failure. Pacing Clin Electrophysiol 1999 22(2) 397-9. 

Fig. 4.91 A. Biventricular thres hold testing the left side of the strip show biventricular capture as the threshold is decreased intermittent capture of either the RV or LV occurs as indicated by a change in morphology. B. With continued decrease in output total loss of ventricular occurs, (from Belott PH Implantation Techniqnes for Cardiac resynchronization Therapy Barold SS, Mugica J Fifth Decade of Cardiac Pacing. Armonk NY Futura. 2004 pp 22)...

Fig. 18.6 Posteroanterior radiograph (A) and close-up view (B) from a patient with intermittent failure to pace. Comparison of the upper and lower pins reveals that the lower of the two unipolar leads is not completely advanced. This difference is more evident on the close-up view. By convention, the lower of the two leads in the connector block is the ventricular lead, so that this patient must have had intermittent or permanent ventricular failure to output. An unrelated ohservation (arrowhead on 6 A) is the shallow positioning of the atrial lead, i.e., the J is much wider than 90°. (From Hayes DL. Pacemaker radiography. In Furman S, Hayes DL, Holmes DR Jr, editors. A practice of cardiac pacing, third edition. Mount Kisco [NY] Futura Publishing, 1993 361 100. Used with permission of Mayo Foundation for Medical Education and Research.)...

The most obvious finding is the low amplitude signals being sensed in the VF and VT-1 zones, and that the ventricular escape is barely 20 b.p.m. with complete heart block. The low amplitude signals are caused by a loose set screw in the pacing/sensing lead port. These potentials result because the loose set screw intermittently makes and breaks contact with the lead. These potentials also inhibit pacing. Note the lack of these potentials on the shock EGM. 

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