Four years after production of the first transistor in 1954, C. W. Lillehei, a cardiothoracic surgeon, and Earl Bakken, an electrical technician, developed the first battery-operated system to pace the heart. This was followed just 2 years later by the introduction of the first implantable, battery-powered permanent pacemaker (PPM). Further advancements in technology ultimately led to the development of the implantable cardioverter-defibrillator (ICD) in the early 1980s, which was subsequently FDA approved for use in 1985. With continuing technological advancements, modern cardiac implantable electronic devices (CIEDs) have become extraordinarily sophisticated and bear only a slight resemblance to their early predecessors. More than 1.5 million Americans have PPMs and 500,000 have ICDs. In addition to permanently implanted cardiac devices, the heart can be paced temporarily using pads placed on the skin (transcutaneous pacing) or via leads placed through a central vein (transvenous pacing), into the esophagus (esophageal pacing), or onto the surface of the heart (epicardial pacing). People with CIEDs span a large age range, from the very young to the elderly. Adults with CIEDs frequently have coronary artery disease (50%), hypertension (20%), and diabetes (10%). Generally speaking, pacing is indicated for patients with disorders of the sinoatrial (SA) node (i.e., unable to initiate a sinus beat) and/or atrioventricular (AV) node (i.e., unable to properly conduct a sinus impulse). Most recently, in 2001, the FDA-approved devices to pace both the atria and ventricles (biventricular pacing, also known as cardiac resynchronization therapy [CRT]). ICDs are implanted for people who have a history of, or are at risk for, malignant ventricular arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF).

To better understand the function of cardiac pacemakers and defibrillators, it is important to have a basic understanding of the cardiac cycle. Chapter 7 covers cardiac electrophysiology and the cardiac cycle. It may be useful to review these topics as they are essential to understanding how pacemakers and ICDs function. In brief, the heart must coordinate the contractions of the atria and ventricles to pump efficiently. The impulse for this coordinated series of contractions originates in the SA node, an area of the heart often referred to as the intrinsic cardiac pacemaker. Located in the right atrial appendage, the SA node is responsible for initiating the wave of electrical depolarization that leads to atrial contraction and, ultimately, ventricular filling. Firing of the SA node produces the “P” wave on the electrocardiogram (ECG) tracing. The signal is next propagated to the AV node, located in the lower aspect of the right atrium, where it is delayed before being conducted to the ventricles via the bundle of His and the Purkinje fibers (collectively known as the His-Purkinje system). Depolarization and contraction of the ventricles produces the “QRS” complex on the ECG tracing. The “T” wave represents the ventricular refractory (recovery) period and follows the QRS complex on the ECG tracing. A perturbation at any point along the conducting pathway may disrupt the heart’s coordinated timing and lead to hemodynamic compromise (bradycardia, heart block, hypotension, etc.). In many instances, patients with conduction disease are candidates for either temporary pacing or permanent CIED therapy.

Indications for pacing and defibrillation are beyond the scope of knowledge required for the anesthesia technician; however, the indications for permanent and temporary pacing are provided as a reference below.

Pacemakers can be used to pace a single chamber (i.e., either the right atrium or right ventricle), two chambers (i.e., both the right atrium and right ventricle, known as dual-chamber pacing), or multiple chambers (i.e., the right atrium and both ventricles, known as biventricular pacing), depending on the number and placement of leads. Implanted pacemakers have two main components, the pulse generator (“box”) and the lead(s). For PPMs, the generator is typically implanted in the upper chest area just underneath the clavicle (collar bone). The leads are connected to the generator and are inserted through a vein into the heart, where they make contact with the heart muscle (myocardium) and are fixed in position.

As stated earlier in the chapter, ICDs are generally implanted in patients at risk of developing malignant ventricular arrhythmias. The ICD senses VT or VF and responds by delivering therapy (shock) to terminate the arrhythmia. In general, if the ICD senses VT, it will first attempt to overdrive pace the heart (i.e., increase the heart rate) to break the rhythm. If overdrive pacing is unsuccessful, shocks of sequentially higher energy will be automatically administered. If the ICD detects VF, the ICD will deliver a high-energy shock to terminate the rhythm.

The term pacemaker generally brings to mind a permanently implanted device as described above. While this is the most commonly encountered pacing system, there are several available devices that can be used temporarily, during emergencies, when long-term pacing is unlikely to be necessary or until more permanent pacing can be established. External pacing modalities include transcutaneous, transvenous, epicardial, and transesophageal. Many of these pacing modalities are especially important in the perioperative period and are widely used by anesthesiologists. The anesthesia technician should gain basic familiarity with these modalities of temporary pacing and especially with the temporary external pacing box (Fig. 44.1).