Hardware for the Heart: The Increasing Impact of Pacemakers, ICDs, and LVADs

Trauma, battery failure, and intrinsic pacer malfunction can cause PMT such as runaway pacemaker.  Application of a magnet has been shown effective only in some cases.^3,30 Definitive therapy with emergent pacer reprogramming or surgical disconnection of pacer leads from the generator may be warranted.

Failure to capture occurs when the device electrical impulse is insufficient to depolarize the heart. Battery failure, generator failure, electrode impedance (from fibrosing of the electrodes), lead fracture or malposition, and long QT syndrome are all causes of failure to capture.²⁹ Chest X-ray, ECG, device interrogation, and electrolyte measurement are imperative. The patient with intrinsic generator failure usually requires admission and surgical correction or replacement.³

Oversensing occurs when the device incorrectly interprets artifactual electricity as intrinsic cardiac depolarization. This results in a lack of cardiac stimulation by the pacemaker and can lead to heart block. Shivering, fasciculations from depolarizing neuromuscular blockade, and external interference can cause oversensing. Nonmedical causes include cell phones, security gates, Taser guns, magnets, and iPods.²⁸ Iatrogenic causes include electrosurgery, LVADs, radiation therapy, magnetic resonance imaging (MRI), cardioversion, and lithotripsy.^31,32 Treatment involves withdrawing the offending agent, then either placing a magnet over the generator to activate its asynchronous mode or temporary overdrive pacing.^26,28,31

Undersensing occurs when the pacer fails to sense intrinsic cardiac activity. The result is competitive asynchronous activity between the native cardiac depolarization and the pacemaker impulses. Introduction of new intrinsic rhythms from lead complications (lead fracture, lead migration), ischemia (premature ventricular contraction, premature atrial contraction), or underlying cardiac disease (atrial fibrillation, right BBB [RBBB], LBBB) can precipitate undersensing.^4,5,30 These patients are prone to arrhythmias and decompensation of cardiac function. Management requires identifying the cause of the underlying arrhythmia.²⁹ Chest X-ray, ECG, device interrogation, and electrolyte measurement are useful diagnostics for patients with new arrhythmias or ischemia.^3,14,27

Conclusion

To assist the EP in evaluating a patient with a suspected pacemaker problem, we propose the algorithm presented in Figure 3.

Recent advancements and the increased prevalence of pacemakers require the EPs to be facile with their operating systems and morbidity. A detailed history and physical examination, along with utilization of simple diagnostics and device interrogation, can prove sufficient to diagnose most pacemaker-related complaints. Acute coronary syndrome and serious infections may be subtle, so a high level of suspicion should be maintained. With a knowledgeable EP and a supportive team, pacemaker complications can be successfully managed.

Managing Implantable Cardioverter Defibrillator Shock Complications

Dustin G. Leigh, MD; Cameron R. Wangsgard, MD; Daniel Cabrera, MD

Dr Leigh is a chief resident, department of emergency medicine, Mayo Clinic, Rochester, Minnesota. Dr Wangsgard is a chief resident, department of emergency medicine, Mayo Clinic, Rochester, Minnesota. Dr Cabrera is an assistant professor of emergency medicine, Mayo Clinic, Rochester, Minnesota.

Disclosure: The authors report no conflict of interest.

Introduction

Despite significant advances in emergency medical care and resuscitation techniques, sudden cardiac death remains a major public health problem, accounting for approximately 450,000 deaths annually in the United States.¹ Moreover, the vast majority of people who suffer an out-of-hospital cardiac arrest will not survive. This is often the end result of fatal ventricular arrhythmias, including ventricular fibrillation (VF) and ventricular tachycardia (VT). The most effective therapy is rapid electrical defibrillation.²

During the 1970s, Mirowski and Mower developed the concept of an implantable defibrillator device that could monitor and analyze cardiac rhythms with automatic delivery of defibrillating shocks after detecting VF.^3,4 In 1980, the first clinical implantation of a cardiac defibrillation device was performed. Development continued steadily until the 1996 the Multicenter Automatic Defibrillator Implantation Trial was prematurely aborted when a statistically significant reduction in mortality (54%) was recognized in patients who received ICD therapy instead of antiarrhythmic therapy.^5,6 This was followed by large prospective, randomized, multicenter studies establishing that ICD therapy is effective for primary prevention of sudden death.⁷ Based on these developments, the ICD has rapidly evolved from a therapy of last resort for patients with recurrent malignant arrhythmias to the standard of care in the primary and secondary prevention of sudden cardiac death, and more recently as cardiac resynchronization devices in patients with congestive heart failure (CHF).³

These developments have led to a dramatic increase in the use of the ICD for monitoring and treatment of VT and VF. The dismal survival rate after cardiac arrest provides a strong impetus to identify high risk patients of sudden cardiac death resulting from VF/VT by primary prevention with an ICD.^2,5 More than 100,000 ICDs are implanted annually in the United States.¹ As a result of increased prevalence, the EP will often encounter patients who have received an ICD shock or complication of the device. Thus, experienced a general knowledge of implantation, components, complications, and acute management is crucial for clinicians who may care for these patients.