Temporary cardiac pacing has been used in both prevention and termination of supraventricular and ventricular tachyarrhythmias [5]. Atrial pacing is often effective in terminating atrial flutter and paroxysmal nodal supraventricular tachycardia [6]. Atrial pacing in the ICU setting is most frequently performed when temporary epicardial electrodes have been placed during cardiac surgery. A critical pacing rate (usually 125% to 135% of the flutter rate) and pacing duration (usually about 10 seconds) are important in the successful conversion of atrial flutter to sinus rhythm [7,8]. This method is often effective in patients with classic atrial flutter; however, it is typically ineffective for atypical or type II atrial flutter (rate 400 beats per minute, P waves upright in the inferior leads).

In some clinical situations pacing termination of atrial flutter may be more attractive than synchronized cardioversion, which requires sedation with its attendant risks. Pacing termination is the treatment of choice for atrial flutter in patients with epicardial atrial wires in place after cardiac surgery. It may be preferred as the means to convert atrial flutter in patients on digoxin and those with sick sinus syndrome, as these groups often demonstrate prolonged sinus pauses after DC cardioversion [9].

Temporary pacing has proved lifesaving in preventing paroxysmal polymorphic ventricular tachycardia in patients with prolonged QT intervals (torsades de pointes), particularly when secondary to drugs. Temporary cardiac pacing is the treatment of choice to stabilize the patient while a type I antiarrhythmic agent exacerbating ventricular irritability is metabolized [10]. In this situation, the pacing rate is set to provide a mild tachycardia. The effectiveness of cardiac pacing probably relates to decreasing the dispersion of refractoriness of the ventricular myocardium (shortening the QT interval).

Temporary ventricular pacing is also frequently successful in terminating ventricular tachycardia [11]. If ventricular tachycardia must be terminated urgently, cardioversion is mandated. However, in less urgent situations, conversion of ventricular tachycardia via rapid ventricular pacing may be useful. The success of this technique depends on the setting in which ventricular tachycardia occurs as well as the type of pacing used (rapid overdrive pacing or programmed extrastimulation). Programmed stimulation techniques are usually effective in terminating ventricular tachycardia in a patient with remote myocardial infarction or in the absence of heart disease. This technique is less effective when ventricular tachycardia complicates acute myocardial infarction or cardiomyopathy. Rapid ventricular pacing is most successful in terminating ventricular tachycardia when the ventricle can be “captured” (asynchronous pacing for 5 to 10 beats at a rate of 50 beats per minute greater than that of the underlying tachycardia). Extreme caution is advised, as it may be accompanied by acceleration of ventricular tachycardias in more than 40% of patients; a cardiac defibrillator should be immediately available at the bedside.

Temporary atrial pacing electrodes allow accurate diagnosis of tachyarrhythmias when the morphology of the P wave and its relation to the QRS complexes cannot be determined from the
surface electrocardiogram (ECG) [12,13]. A recording of the atrial electrogram is particularly helpful in a rapid, regular, narrow-complex tachycardia in which the differential diagnosis includes atrial flutter with rapid ventricular response, and AV nodal reentrant or other supraventricular tachycardia. This technique is also useful to distinguish wide-complex tachycardias in which the differential diagnosis includes supraventricular tachycardia with aberrant conduction, sinus tachycardia with bundle branch block, and ventricular tachycardia.

To record an atrial ECG, the limb leads are connected in the standard fashion and a precordial lead (usually V₁) is connected to the proximal electrode of the atrial pacing catheter or to an epicardial atrial electrode. A rhythm strip is run at a rapid paper speed, simultaneously demonstrating surface ECG limb leads as well as the atrial electrogram obtained via lead V₁. This rhythm strip should reveal the conduction pattern between atria and ventricles as antegrade, simultaneous, retrograde, or dissociated.

Temporary pacing may be used therapeutically or prophylactically in acute myocardial infarction. Recommendations for temporary cardiac pacing have been provided by a Task Force of the American College of Cardiology and the American Heart Association (Table 5-2) [14]. Bradyarrhythmias unresponsive to medical treatment that result in hemodynamic compromise require urgent treatment. Patients with anterior infarction and bifascicular block or Mobitz type II second-degree AV block, while hemodynamically stable, may require a temporary pacemaker, as they are at risk for sudden development of complete heart block with an unstable escape rhythm.

Prophylactic temporary cardiac pacing has aroused considerable debate for the role it may play in complicated anterior wall myocardial infarction [15]. Thrombolytic therapy or percutaneous coronary intervention, when indicated, should take precedence over placement of prophylactic cardiac pacing, as prophylactic pacing has not been shown to improve mortality. Transthoracic (transcutaneous) cardiac pacing is safe and usually effective [16, 17, 18 and 19] and would be a reasonable alternative to prophylactic transvenous cardiac pacing, particularly soon after thrombolytic therapy has been administered.

When right ventricular involvement complicates inferior myocardial infarction, cardiac output may be very sensitive to ventricular preload. Because coordinated atrial transport may be required for maintenance of effective stroke volume, AV sequential pacing is frequently the pacing modality of choice in patients with right ventricular infarction [20,21].

Some of the many transvenous pacing catheters available for use in the critical care setting are illustrated in Figure 5-1. Pacing catheters range in size from 4 French (Fr) (1.2 mm) to 7 Fr (2.1 mm). In urgent situations, or where fluoroscopy is unavailable, a flow-directed flexible balloon-tipped catheter (Fig. 5-1, top) may be placed in the right ventricle using ECG guidance. After advancing the catheter into the right ventricle, the balloon can be deflated and the catheter tip advanced to the right ventricular apex. While the balloon-tipped catheter may avoid the need for fluoroscopy, placement may be ineffective in the setting of low blood flow during cardiac arrest or in the presence of severe tricuspid regurgitation. Stiff catheters (Fig. 5-1, middle) are easier to manipulate but require insertion under fluoroscopic guidance.

A flexible J-shaped catheter (Fig. 5-1, bottom), designed for temporary atrial pacing, is also available [22]. This lead is positioned by “hooking” it in the right atrial appendage under fluoroscopic guidance, providing stable contact with the atrial endocardium. Either the subclavian or internal jugular venous approach may be used.

A multilumen pulmonary artery catheter is available with a right ventricular lumen. Placement of a small (2.4 Fr) bipolar pacing lead through the right ventricular lumen allows intracardiac pressure monitoring and pacing through a single catheter [23]. Details on its use and insertion are described in Chapter 4.

An esophageal “pill” electrode allows atrial pacing and recording of atrial depolarizations without requiring central venous cannulation. As mentioned, detecting atrial depolarization aids in the diagnosis of tachyarrhythmias. Esophageal pacing has also been used to terminate supraventricular tachycardia and atrial flutter [24]. Because the electrode can be uncomfortable and may not give consistent, stable capture, the esophageal electrode is typically limited to short-term use for diagnosis of arrhythmias in pediatric patients.