Acute Mechanical Response to Anti-arrhythmic Drug Therapy (AAD and CRT)

The aim of this study is to determine if anti-arrhythmic drugs with a sodium channel-blocking mechanism exert a detrimental electromechanical effect on cardiac function in patients depending upon baseline intraventricular conduction and left ventricular function.

Amiodarone therapy is used frequently for control of ventricular arrhythmias in patients who receive painful shocks from an implantable cardioverter-defibrillator (ICD). Data in post-myocardial infarction (MI) patients and ICD patients suggest that amiodarone is mortality-neutral; it neither confers increased nor decreased mortality. However, these data are derived from patients largely with normal intraventricular conduction, manifesting as a QRS complex duration on the surface ECG <120 ms. Amiodarone, in addition to potassium-channel blocking effects, is a sodium channel-blocker. Because sodium channels mediate cardiac depolarization, and a QRS complex >120 ms is indicative of abnormal depolarization, amiodarone may not be benign in patients with such conduction defects. Patients with cardiac resynchronization therapy-defibrillators (CRT-D), who all have abnormal baseline intraventricular conduction, may therefore be adversely affected by amiodarone. Anecdotal clinical data suggest that this may be the case, but the question of amiodarone's cardiac safety profile in CRT patients has never been studied.

All patients will undergo 12-lead ECG and transthoracic echocardiography on the day of the study. These studies will be performed on patients as their previously implanted device is reprogrammed to pace in different modes. Patients will then receive an infusion of procainamide (12 mg/kg up to a maximum of 1 g) at a rate of 20 mg/min. Repeat ECG and echocardiograms will then be performed. The patient's device will be programmed to a specific setting before and after the procainamide infusion.

the procainamide will be infused at 12mcg/kg up to a max of 1 gram at a rate of 20mg/min which will take up to 1 hour to infuse

the QRS waveform measurements will be calculated on the EKG prior to and after the procainamide infusion

The RV-LV electrical activation will be assessed during the device interrogation pre and post procainamide infusion.

Inclusion Criteria: Implanted cardiac device requiring generator change and a new device Able to give informed consent Exclusion Criteria: Current membrane-active anti-arrhythmic Glomerular filtration rate (GRF)<30 milliliters (mL)/min MAP<60 mmHg Known intolerance to procainamide Pregnancy Age <18 or >85 years old Baseline QT interval >480 ms (500 ms if paced)

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