Pacemaker-ICD/Drug Interaction

When a drug is prescribed for a patient with a permanent pacemaker or an implantable cardioverter defibrillator (ICD), consideration must be given to the potential interactions. Drug effect on pacemaker performance is usually thought to cause an increase or decrease in pacing threshold. From a practical view, Class IC drugs must be used cautiously in pacemaker patients, especially in those who are pacemaker-dependent. The possibility of a rise in threshold should always be considered in these patients, and the pacemaker output should be programmed to allow an adequate pacing margin of safety. In such patients, automatic output regulation would be particularly useful. Two-third of ICD recipients are treated with antiarrhythmic drugs to reduce the frequency of ventricular tachycardia/ventricular fibrillation (VT/VF) recurrences and enhance quality of life. However, antiarrhythmic drugs may alter ventricular defibrillation threshold (DFT). Class I agents that work primarily by slowing ventricular conduction velocity increase DFT. Class III agents that work primarily by prolonging ventricular action potential duration decrease DFT. Antiarrhythmic drugs with a balance of class I and class III actions (such as amiodarone) may increase or decrease DFT. Besides affecting DFT, antiarrhythmic drugs may also alter arrhythmia cycle length and frequency, pacing thresholds, and post-shock excitability. Finally, interactions between the ICD and the pacemaker may result in sensing problems, leading to multiple counting and inappropriate shocks, VF nondetection, sensing or capture failure post defibrillation, and pacemaker reprogramming induced by defibrillator discharge.