Overdriving by pacing to suppress ventricular ectopic activity

Abstract

Summary o 1. Six patients were overdriven from ventricular electrodes in an attempt to suppress different types of ectopic activity. 2. In four patients overdriving was successful in preventing ectopic beats; in two of these, overdriving suppressed life-threatening arrhythmias that could not previously be suppressed by drugs. 3. Ectopics with fixed coupling, triggered by the basic cardiac rhythm, could easily be suppressed by overdriving. Those with variable coupling, due to a parasystolic focus, were often not completely suppressed by overdriving. 4. The rates needed to suppress ventricularectopic activity were slower than those expected from the coupling interval in the patients with fixed coupled ectopic beats. These patients showed abnormal ST segments and/or T wave. The QT interval (corrected for increased duration of the QRS and for rate) was much longer than normal. These long QT intervals became normal at rates needed to suppress ectopic activity. 5. In patients, whose ectopics had variablecoupling, the rates expected to suppress ventricular ectopic beats led to fusion (paced plus ectopic) beats. The QT interval was normal in these patients. 6. The clinical implications are discussed.Overdriving at relatively slow rates is likely to be successful in preventing multiple ectopic beats in patients with fixed coupling and long QT intervals.