What are the components of an implantable pacing or defibrillation system?
How do pacemakers interact with the heart's natural rhythm to know when to and when not to pace?
What do the common pacing codes (ie, VVI, DDD) mean, and how do they affect the electrocardiogram (ECG)?
When should patients be referred for cardiac resynchronization therapy (CRT)?
How should clinicians evaluate the patient who has received an implantable cardiac defibrillator (ICD) shock?
When should a pacemaker or ICD be interrogated in the inpatient setting?
Advances in technology and the expansion of indications have greatly increased the number of patients receiving pacemakers and implantable cardiac defibrillators (ICDs). Approximately 200,000 pacemakers and 100,000 defibrillators are implanted annually for the management of cardiac arrhythmias, treatment of congestive heart failure, and the prevention of sudden cardiac death. These devices have progressed from relatively simple components with basic pacing and defibrillation features, to more advanced systems with a significant impact on patient morbidity and mortality. The increasing number and complexity of devices encountered in hospitalized patients frequently presents a clinical management challenge. The purpose of this chapter is to introduce basic concepts of pacing and defibrillation, review standard indications for cardiac rhythm devices, and highlight pertinent clinical considerations for hospitalist care of patients with these devices.
Cardiac pacing and defibrillating systems consist of pulse generators and leads. The pulse generator is the “device” that contains the battery, circuitry, and capacitors. It is typically encased in a titanium housing that ranges in size and shape depending on the manufacturer. Defibrillator pulse generators are about two to three times larger than pacemakers (Figure 129-1).
Examples of cardiac resynchronization therapy with defibrillator (CRT-D), implantable cardiac defibrillator (ICD), and pacemaker devices. Note the size difference between the defibrillator and pacemaker devices.
The leads are connected to the pulse generator at the time of implant and are attached distally to the myocardium. They are secured to the myocardium either “actively” by means of a small screw, or “passively” by means of small tines near the lead tip. Pacemaker leads consist of conducting wires, a silicone or polyurethane insulation coating, and platinum electrodes used for pacing. Defibrillation leads have one or two additional wire coils capable of delivering high-voltage impulses for defibrillation (Figure 129-2).
Examples of (A) an implantable cardiac defibrillator (ICD) lead and (B) a pacemaker lead. Note the high-voltage defibrillation coils on the ICD lead (indicated by arrows).
Technologic advancements in the field of cardiac rhythm devices have resulted in smaller batteries with increased life spans. Most batteries used in modern devices are lithium-based and are nonrechargeable with a finite life span. Typically, a pacemaker battery will last approximately 10 years, while an ICD battery will ...