Future of Implantable Devices for Cardiac Rhythm Management

The first cardiac implantable electronic device (CIED), the electronic pacemaker, maintains cardiac contraction during bradycardia. The implantable cardioverter-defibrillator (ICD) manages ventricular tachycardia (VT) or fibrillation (VF) and saves lives primarily through the use of high-energy shocks. The cardiac resynchronization therapy (CRT) device restores interventricular and intraventricular dyssynchrony in patients with heart failure (HF). Despite >50 years of pacing and 40 years of ICD therapy, the lead remains the weakest link between the device and the patient. Although CRT reduces mortality and morbidity in HF, it is applicable only to those patients with systolic left ventricular (LV) dysfunction and wide QRS complex, especially left bundle-branch block. At best, only 70% of such patients respond, and the majority of patients without left bundle-branch block or with nonsystolic HF derive no benefit from CRT. Early detection of worsening HF with implantable sensors enables corrective therapy to avert acute decompensated HF. Implantable cardiac monitors (ICMs) allow monitoring of arrhythmias such as atrial fibrillation (AF). Despite their efficacy at eliminating the risk of sudden cardiac death (SCD) in the highest-risk patient, ICDs currently have a limited role in reducing the overall burden of SCD, and ICM has the potential for early identification of asymptomatic subjects at risk of SCD to derive benefit from ICD. An increasing cause of SCD is pulseless electric activity (PEA), and alternative management other than defibrillation will be required. This review addresses the recent exciting development of CIEDs in response to these unmet clinical needs such as leadless and endocardial pacing, subcutaneous ICD (S-ICD), low-energy multistage electrotherapy for VT and AF, intermediate-strength stimulation for PEA, early detection of VT, sensors for HF monitoring, and novel therapies for arrhythmias and HF. ### Limitations of Cardiac Pacing With Current Pacemakers and CRT Despite the significant improvements in device longevity, reliability, size/profile, and ease of implantation over the last 50 years, implanting a pacemaker …