Transvenous Cardiac Pacing

Updated: Feb 19, 2016
  • Author: Ali A Sovari, MD, FACP, FACC; Chief Editor: Vincent Lopez Rowe, MD  more...
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Overview

Background

This article describes transvenous cardiac pacing. In a healthy heart, electrical impulses are generated in the sinoatrial (SA) node (sinus node), which is near the junction of the superior vena cava and the right atrium. The specialized cells of the SA node generate electrical impulses faster than other parts of the conduction system and with automaticity; therefore, these cells are usually the dominant natural pacemakers of the heart. The impulse is then conducted through the right and left atria and reaches the atrioventricular (AV) node.

The AV junction, which is at the base of the interatrial septum and extends into the interventricular septum, has two main parts: the AV node in the upper part, and the bundle of His in the lower part. In a healthy heart, the AV node is the only electrical connection between the atria and the ventricles. The inherent delay in transmitting the electrical impulse from the atria to the ventricles provides the appropriate diastolic duration to enable ventricular filling.

The His bundle divides into the left and right bundle branches and then into the Purkinje fibers, which conduct the impulse rapidly through the ventricles to produce rapid and simultaneous ventricular contractions. In general, symptomatic abnormalities of the conduction system are the main indications for cardiac pacing, a method by which a small pulsed electrical current is artificially delivered to the heart.

Of the several methods for temporary pacing of the heart (transcutaneous, transvenous, transesophageal, transthoracic, and epicardial), transvenous and transcutaneous cardiac pacing are the most commonly used. The main factor that dictates the use of one approach instead of another is the urgency of the need for pacing.

In an emergency where a patient is experiencing cardiac symptoms or asystole, transcutaneous pacing is the method of choice. Nevertheless, transvenous pacing has several advantages over the transcutaneous method: enhanced patient comfort, greater reliability, and the ability to pace the atrium. However, because transvenous pacing requires central venous access, it cannot be initiated as fast as transcutaneous pacing can, and it is associated with several complications that result from obtaining venous access.

A common scenario is one in which transcutaneous pacing is employed first in an emergency, followed by transvenous placement of a lead that will enable a longer period of pacing and evaluation in patients who may require permanent pacing later during their hospitalization.

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Indications

Transvenous cardiac pacing can be used as a bridge to permanent pacing when permanent pacing is not available, when the pacing need is only temporary, or when further evaluation is required. Therefore, all indications for permanent cardiac pacing are indications for transvenous pacing as well. Temporary pacing is appropriate when a permanent pacemaker must be replaced, repaired, or changed or when permanent pacing fails. In emergencies (eg, asystole), transcutaneous pacing may be the most appropriate type of temporary pacing.

Recommended indications for cardiac pacing can be complex and depend on a combination of presenting symptoms and electrocardiographic (ECG) findings. These recommendations, along with their level of supporting evidence, are well summarized by the American College of Cardiology (ACC) and the American Heart Association (AHA). [1, 2]

Because transvenous pacing is a temporary method, it may be indicated for treating a reversible condition for which permanent pacing is contraindicated. For example, Ho et al reported using transcutaneous pacing in patients with bradycardia due to hypothermia. [3]

Temporary cardiac pacing is occasionally used to determine whether a patient requires permanent pacing. However, patients treated with cardiac pacing may become pacemaker-dependent and exhibit asystole when pacing is terminated, even though they may not have experienced asystole in the absence of pacing.

Although temporary transvenous cardiac pacing is indicated primarily for the treatment of bradycardia and various types of heart block, intermittent overdrive pacing can also be used as an antitachycardic treatment for a variety of atrial and ventricular tachycardias, such as postoperative atrial flutter or monomorphic ventricular tachycardia. Pacing is also used to prevent bradycardia-dependent tachycardias, such as torsades de pointes. Reversible causes of heart block that may call for temporary cardiac pacing include the following:

  • Injury to the SA node or other parts of the conduction system after cardiac surgery (injuries that occur after coronary bypass surgery tend to be temporary, but those sustained after valve surgery or cardiac transplant may not be reversible)
  • Chest and cardiac trauma associated with either temporary SA node or AV node dysfunction
  • Metabolic and electrolyte derangements (eg, hyperkalemia)
  • Drug-induced bradyarrhythmia (eg, digitalis toxicity); if treatment with the drug must be continued and there is no alternative, permanent pacing should be considered
  • Other diseases (eg, Lyme disease, bacterial endocarditis) that may be associated with temporary damage to the SA node or the AV node
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Contraindications

In general, temporary cardiac pacing should not be considered for asymptomatic patients who have a fairly stable rhythm (eg, a first-degree AV block or a Mobitz I or stable escape rhythm). For example, pacing an asymptomatic patient with a stable escape rhythm may render that individual dependent on pacing, and withholding pacing may then cause asystole.

Although the aforementioned rhythms are stable for the most part, there are exceptions (eg, a Mobitz I rhythm with a wide QRS may originate from an infra-AV nodal area and therefore may progress to complete heart block). When in doubt, having transcutaneous pacing ready for use in emergencies may be reasonable.

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Technical Considerations

In 1974, the ACC and the AHA proposed a three-digit code system for categorizing the basic functions of pacemakers. The North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG) continued to expand these codes, and the coding system was last updated in 2002. Currently, pacemaker function is described by means of the following position codes, which are generic and are used for all brands of pacemakers:

  • Position I - This position indicates the chamber or chambers paced; A stands for “atrium,” V for “ventricle,” and D for “dual-chamber” (meaning that both the right atrium and the right ventricle can be paced)
  • Position II - The same letters listed above are used refer to the chamber or chambers sensed; S stands for “single-chamber” (meaning that the pacemaker can pace only 1 chamber), and O indicates that the pacemaker lacks sensing capability (it may be used in asynchronous pacing)
  • Position III - This position indicates how the pacemaker responds to a sensed event; I indicates that the sensed event inhibits the pacemaker output, T that the sensed event triggers the output, and D that both capabilities are available; dual response is possible only in a dual-chamber pacemaker—for example, a sensed event in the atrium can inhibit the output in the atrium and trigger the output in the ventricle, and in such cases, ventricular output usually occurs with a delay to mimic the normal PR interval and may be inhibited if the atrial pulse is conducted normally through the AV node
  • Position IV - This position indicates programmability and rate modulation capability; R indicates that the rate can be changed, depending on whether the patient is active, and O, which may not be explicitly mentioned (ie, DDD is understood to be equivalent to DDDO), indicates that rate modulation is not available or is not used
  • Position V - This position refers to multisite pacing; A indicates that the pacemaker can pace multiple sites in one or both atria, V that it can pace multiple sites in one or both ventricles, D that it can pace multiple sites in both the atria and the ventricles, and O that the multisite capability is not available or is not used

These position codes are used to describe pacemaker modes, as follows:

  • VVI mode - The device paces and senses the right ventricle, and a sensed event in the ventricle inhibits the pacemaker from pacing or producing any output
  • AAI mode - The pacemaker paces and senses the atrium, and the sensing of an event (eg, sensing atrial activity within 1 second) inhibits the pacemaker from pacing
  • DDD mode - The pacemaker paces both the atria and the ventricles; it can sense both chambers, and the response can be both triggering or inhibitory
  • DDDR mode - The pacemaker has all the capabilities of the VVI, AAI, and DDD modes, as well as rate modulation capability
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