Skip to Main Content


Key Clinical Questions

  • image What are the components of an implantable pacing or defibrillation system?

  • image How do pacemakers interact with the heart’s natural rhythm to know when to and when not to pace?

  • image What do the common pacing codes (ie, VVI, DDD) mean, and how do they affect the electrocardiogram (ECG)?

  • image When should patients be referred for cardiac resynchronization therapy (CRT)?

  • image How should clinicians evaluate the patient who has received an implantable cardiac defibrillator (ICD) shock?

  • image When should a pacemaker or ICD be interrogated in the inpatient setting?

Advances in technology and the expansion of indications have greatly increased the numbers 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 2 to 3 times larger than pacemakers (Figure 136-1).

Figure 136-1

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 136-2).

Figure 136-2

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).

Many of the long-term complications related to cardiac rhythm devices are specific to transvenous leads. These complications include infection, malfunction, or venous stenosis. Lead extraction required as a result ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.