Transvenous Cardiac Pacing

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 (SVC) and the right atrium (RA). 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 RA and left atrium (LA) 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 the following advantages over the transcutaneous method:

• Enhanced patient comfort
• Greater reliability
• 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.

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. ^[1] 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). ^{[2, 3]}

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. ^[4]

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 (VT). 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

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.

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 subsequently 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, with A standing for “atrium,” V for “ventricle,” and D for “dual-chamber” (meaning that both the RA and the right ventricle [RV] can be paced)
• Position II - The same letters listed above are used refer to the chamber or chambers sensed, with S standing for “single-chamber” (meaning that the pacemaker can pace only one chamber) and O indicating 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, with I indicating 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, with R indicating 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), indicating that rate modulation is not available or is not used
• Position V - This position refers to multisite pacing, with A indicating 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 RV, 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

Updated guidelines on cardiac pacing and cardiac resynchronization therapy (CRT) were published in August 2021 by the European Society of Cardiology (ESC) and European Heart Rhythm Association (EHRA) in Europace. ^{[5, 6]} Emphasis has been placed on patient-centered care, shared decision making, and appropriate workup/testing prior to pacemaker implantation.

New recommendations include those for pacing after syncope, pacing following transcatheter aortic valve implantation (TAVI), CRT for heart failure (HF) and for prevention of pacing-induced cardiomyopathy, and pacing in various infiltrative and inflammatory diseases of the heart, as well as in different cardiomyopathies. ^{[5, 6]} New sections include those on pacing the His bundle (HBP) and the left bundle branch (LBB), as well as on evaluation of suspected or documented bradycardia or conduction system disease.

Select Key Messages

Cardiac pacing

Cardiac pacing is indicated in patients with:

• Sinus node dysfunction (SND), including those with bradycardia–tachycardia type of SND, when symptoms are clearly attributed to bradyarrhythmia

• Sinus rhythm (SR) and permanent or paroxysmal third- or second-degree type 2 or high-degree atrioventricular block (AVB), irrespective of symptoms

Single-lead ventricular pacing is indicated in the setting of permanent atrial fibrillation (AF) and permanent or paroxysmal AVB.

In the setting of syncope and unexplained falls, determine the diagnosis using available diagnostic methods before considering pacemaker therapy.

Cardiac resynchronization therapy

CRT is recommended in patients with symptomatic HF and left ventricular (LV) ejection fraction (EF) ≤35% despite optimal medical therapy (OMT) who are in SR and have LBB block (LBBB) QRS morphology, when QRS duration is ≥150 ms. Consider CRT in these patients when QRS duration is 130–149 ms.

In the setting of non-LBBB QRS morphology, less convincing evidence exists for the benefit of CRT, especially with normal PR and QRS duration < 150 ms. CRT should not be used in patients with HF and QRS duration < 130 ms unless ventricular pacing is needed.

Consider CRT in those with permanent AF, symptomatic HF, LVEF ≤35%, and QRS ≥130 ms who remain in New York Heart Association (NYHA) class III or ambulatory IV despite OMT.

Consider AV junction (AVJ) ablation for those with AF and CRT when at least 90-95% effective biventricular pacing is not achievable.

For patients with high-degree AVB and an indication for cardiac pacing who have HF with reduced EF (HFrEF) (LVEF < 40%), the ESC/EHRA recommend CRT rather than right ventricular (RV) pacing.

His bundle pacing

HBP may:

• Result in normal or near-normal ventricular activation; it is an attractive alternative to RV pacing

• Be considered for select patients with AVB and LVEF >40%, who are anticipated to have >20% ventricular pacing

• Correct ventricular conduction in a subset of patients with LBBB; thus, it may be used in lieu of biventricular pacing for HBP-based CRT in select patients

In patients offered HBP, individual consideration should be given for implanting an RV lead used as “backup” for pacing. In patients treated with HBP, tailor the device programming to the specific requirements of HBP.

Consider implantation of a leadless pacemaker when no upper extremity venous access exists, when the risk of device pocket infection is particularly heightened, and in patients on hemodialysis.

TAVI, other surgeries, and perioperative considerations

Undergoing TAVI raises the risk of developing AVB. Base decisions regarding post-TAVI cardiac pacing on preexisting and new conduction disturbances. Consider ambulatory electrocardiographic (ECG) monitoring for 7-30 days or electrophysiologic studies (EPS) in post-TAVI patients who have new LBBB or progression of a preexisting conduction anomaly, but who do not yet have any indication for a pacemaker.

In patients undergoing surgery for endocarditis or tricuspid valve surgery who have or develop AVB under surgery, consider placing epicardial pacing leads during surgery.

To reduce the risk of complications:

• Administer preoperative antibiotics before cardiovascular implantable electronic device (CIED) procedures

• Chlorhexidine–alcohol should be preferred for skin antisepsis

• Attempt cephalic or axillary vein access as first choice

• Avoid heparin bridging in CIED procedures to minimize the risk of hematoma and pocket infection

• Consider use of an antibiotic-eluting envelope in CIED reintervention procedures to lower the infection risk

Radiation therapy can be offered to patients with a pacemaker or CRT—provided individualized treatment planning and risk stratification is done beforehand and the device is interrogated as recommended around the period of radiation therapy.

For more information, please go to Transcutaneous Cardiac Pacing and Cardiac Resynchronization Therapy.

Go to 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: Developed by the Task Force on cardiac pacing and cardiac resynchronization therapy of the European Society of Cardiology (ESC) With the special contribution of the European Heart Rhythm Association (EHRA) for full details.