Atrioventricular Node

Issues of Concern

Atrioventricular Block

Disease involving the atrioventricular node or the His–Purkinje conduction system may impair impulse transmission from the atria to the ventricles, resulting in varying degrees of atrioventricular block. Conduction abnormalities may arise from degenerative fibrosis, ischemic injury, infiltrative cardiomyopathies, myocarditis, congenital abnormalities, medication effects, or structural conduction system disease. Second-degree atrioventricular block encompasses both nodal and infranodal conduction disturbances.

Mobitz type I (Wenckebach) most commonly reflects progressive conduction delay within the atrioventricular node itself. In contrast, Mobitz type II more often originates from disease within the His–Purkinje system distal to the atrioventricular node.[4] In Mobitz I atrioventricular block, increasing refractoriness within the atrioventricular node produces progressive PR interval prolongation until an atrial impulse fails to conduct, generating the characteristic grouped beating pattern observed on electrocardiography.[5] 

Despite similar nomenclature, Mobitz I and Mobitz II represent fundamentally different pathophysiologic entities with distinct prognostic implications. Mobitz II atrioventricular block generally reflects structural conduction system disease and carries a substantially greater risk of progression to advanced atrioventricular block or complete heart block. Contemporary guideline-directed management recommends permanent pacemaker implantation for acquired Mobitz II atrioventricular block not attributable to reversible or physiologic causes because of the elevated risk of syncope, hemodynamic compromise, and sudden cardiac death.[6] Higher-grade conduction disturbances involving the atrioventricular node and His–Purkinje system remain among the most common indications for permanent pacing worldwide and represent a major source of morbidity, particularly in aging populations with progressive conduction system degeneration.

Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common regular supraventricular tachycardia in adults and represents one of the most clinically important disorders directly involving atrioventricular nodal physiology.[7] AVNRT arises from reentry involving dual atrioventricular nodal pathways consisting of functionally distinct fast and slow conduction pathways located within transitional tissues surrounding the compact atrioventricular node. Premature atrial impulses may initiate a reentrant circuit when conduction proceeds antegrade through the slow pathway while retrograde conduction occurs through the fast pathway, producing rapid, regular tachycardia. Clinical manifestations include palpitations, chest discomfort, dyspnea, dizziness, anxiety, and syncope. Catheter ablation targeting the slow pathway remains definitive treatment and achieves high long-term success rates with low procedural complication rates.[7]

Atrioventricular Nodal Ischemia and Inferior Myocardial Infarction

Because the atrioventricular nodal artery most commonly arises from the right coronary artery, ischemia involving the atrioventricular nodal circulation may impair conduction, particularly during an inferior wall myocardial infarction. Atrioventricular block complicating acute coronary syndromes may range from transient first-degree atrioventricular block to complete heart block and carries important prognostic implications. Although atrioventricular nodal dysfunction associated with inferior myocardial infarction is often transient due to ischemia or increased vagal tone, persistent conduction abnormalities may require pacing support or permanent pacemaker implantation.

Drug-Induced Atrioventricular Nodal Dysfunction

Pharmacologic suppression of atrioventricular nodal conduction represents an important and potentially reversible cause of bradyarrhythmias and atrioventricular block. Medications commonly implicated include beta blockers, nondihydropyridine calcium channel blockers, digoxin, adenosine, amiodarone, and other antiarrhythmic agents. Excessive atrioventricular nodal suppression may precipitate symptomatic bradycardia or higher-grade conduction abnormalities, particularly in older adults, in patients with baseline conduction disease, or in individuals receiving multiple atrioventricular nodal-blocking agents. Recognition of medication-induced conduction disturbances is essential because dose adjustment or drug discontinuation may prevent unnecessary device implantation.

Procedural Atrioventricular Nodal Injury

The atrioventricular node and adjacent conduction tissues remain vulnerable during cardiac interventions involving nearby anatomic structures. Catheter ablation procedures, congenital heart surgery, septal defect interventions, and structural heart procedures, including transcatheter aortic valve replacement (TAVR), may result in transient or permanent conduction injury.[8] Conduction disturbances following TAVR remain among the most frequent procedural complications and may necessitate temporary pacing or permanent pacemaker implantation. Procedural planning, imaging guidance, and detailed understanding of atrioventricular nodal anatomy remain critical for minimizing iatrogenic conduction injury.[8]

Congenital and Genetic Conduction Disorders

Congenital atrioventricular conduction abnormalities represent another clinically important category of atrioventricular nodal dysfunction. Congenital complete heart block may occur secondary to maternal anti-Ro/Sjögren syndrome–related antigen A and anti-La/Sjögren syndrome–related antigen B autoantibodies, causing fetal conduction system injury. Inherited channelopathies and genetic conduction disorders affecting ion channel function or conduction system development may also impair atrioventricular nodal conduction and predispose patients to progressive conduction disease.[9]

Lenègre-Lev disease (often grouped as a single entity) is a progressive cardiac conduction disorder characterized by the fibrosis and sclerosis of the heart's electrical pathways.[10] This condition is a leading cause of complete heart block and the need for a pacemaker. Progressive fibrosis and sclerosis of the conduction system remain major contributors to atrioventricular conduction abnormalities in aging populations.

Infiltrative and Inflammatory Disease

Cardiac sarcoidosis, amyloidosis, myocarditis, and Lyme carditis may involve the atrioventricular node and His-Purkinje system, producing conduction abnormalities ranging from first-degree atrioventricular block to complete heart block.[11][12]

Cystic Tumor of the Atrioventricular Nodal Region

Primary cardiac tumors are exceptionally rare, occurring in approximately 0.0017% to 0.03% of autopsy series.[13] Cystic tumor of the atrioventricular nodal region (CTAVN), also termed mesothelioma of the atrioventricular node or endodermal heterotopia, is an uncommon congenital benign cardiac tumor arising near the atrioventricular nodal region within the triangle of Koch, with fewer than 100 cases reported in the literature.[14] Although histologically benign, CTAVN has substantial clinical significance given its close association with the cardiac conduction system. Progressive involvement of the atrioventricular node or penetrating His bundle may result in varying degrees of atrioventricular block, including complete heart block, junctional escape rhythms, syncope, malignant arrhythmias, and sudden cardiac death.[15]

CTAVN is recognized as one of the most important primary cardiac tumors associated with sudden death due to conduction system disruption. Diagnosis remains challenging because patients frequently present with nonspecific symptoms or unexplained conduction abnormalities years before definitive identification. While rare, CTAVN should remain within the differential diagnosis of unexplained high-grade atrioventricular block, particularly in younger individuals without typical degenerative conduction disease risk factors.[16]

Clinical Significance

The atrioventricular node plays a critical role in normal cardiac electrophysiology as the primary electrical bridge between the atrial and ventricular myocardium. Positioned at the junction of the atria and ventricles, the atrioventricular node introduces a physiologic conduction delay that allows adequate ventricular filling following atrial contraction before ventricular systole begins. This delay optimizes cardiac output and mechanical efficiency by preserving atrioventricular synchrony.

Beyond facilitating coordinated contraction, the atrioventricular node exhibits decremental conduction properties that serve as a protective “gatekeeper,” limiting the transmission of excessively rapid atrial impulses to the ventricles. This filtering function becomes particularly important during supraventricular tachyarrhythmias such as atrial fibrillation or atrial flutter, reducing the risk of dangerously elevated ventricular rates and hemodynamic compromise. The atrioventricular node also serves an important backup pacemaking role within the cardiac conduction system.

When sinoatrial node activity fails, or atrial impulse generation becomes inadequate, junctional tissues associated with the atrioventricular node can generate escape rhythms, typically at intrinsic rates of approximately 40 to 60 beats per minute, preserving ventricular activation and maintaining perfusion. Dysfunction involving the atrioventricular node or adjacent His–Purkinje system may result in clinically significant conduction disturbances ranging from first-degree atrioventricular block to complete heart block, potentially producing syncope, heart failure, reduced exercise tolerance, or sudden cardiac death. The atrioventricular node is also central to the pathophysiology of arrhythmias such as atrioventricular nodal reentrant tachycardia (AVNRT), one of the most common forms of paroxysmal supraventricular tachycardia.

Furthermore, the atrioventricular node has major procedural significance in electrophysiologic studies, catheter ablation, congenital heart interventions, and structural cardiac procedures, as inadvertent injury may result in permanent conduction abnormalities that require pacemaker implantation. The atrioventricular node also plays a substantial role in cardiovascular therapeutics and clinical decision-making. Numerous medications, including beta-blockers, nondihydropyridine calcium channel blockers, digoxin, adenosine, and antiarrhythmic agents, exert therapeutic effects by modulating atrioventricular nodal conduction. Pharmacologic atrioventricular nodal blockade remains a cornerstone strategy for ventricular rate control in atrial fibrillation and other supraventricular arrhythmias. Given its central role in cardiac electrophysiology, arrhythmogenesis, and hemodynamic regulation, preservation of atrioventricular nodal function remains essential for maintaining normal cardiovascular performance and optimizing outcomes in patients with cardiac disease.

A solid understanding of atrioventricular nodal anatomy and physiology underpins accurate diagnosis and management of the diverse conduction disturbances and tachyarrhythmias encountered in clinical practice (see Image. Common Atrioventricular Node–Related Supraventricular Arrhythmias). These include: 

• Junctional escape beat
  • A junctional escape beat or rhythm arises from the atrioventricular junction when sinus impulses fail to reach the ventricles or are excessively delayed, allowing the intrinsic junctional pacemaker (approximately 40–60 bpm) to assume control. On an electrocardiogram (ECG), a junctional escape rhythm typically appears as a regular narrow-QRS rhythm at 40 to 60 beats per minute with absent P waves or inverted P waves that may precede, be inscribed within, or follow the QRS complex due to retrograde atrial activation.[2][17] Junctional escape often emerges as a protective rhythm in the setting of excessive vagal tone, sinus node dysfunction, or high-grade atrioventricular block, when higher pacemakers fail to maintain adequate ventricular activation.
• Accelerated junctional rhythm and junctional tachycardia
  • Accelerated junctional rhythm (60–100 bpm) and junctional tachycardia (>100 bpm) are related arrhythmias arising from increased automaticity in the atrioventricular junction, often encountered with digoxin toxicity, myocardial ischemia, or in the early period after cardiac surgery.[18] In both rhythms, the atrioventricular junction serves as the primary ventricular pacemaker, producing a regular narrow-QRS rhythm on the ECG, unless a coexisting bundle-branch block is present. In patients with underlying atrioventricular block or structural conduction disease, accelerated junctional rhythms can coexist with other supraventricular tachyarrhythmias, complicating ECG interpretation.
• AVNRT
  • In or near the atrioventricular node, anatomically and functionally distinct fast and slow pathways can conduct electrical impulses. In typical (slow–fast) AVNRT, the reentrant impulse travels antegrade through the slow pathway to activate the His–Purkinje system and ventricles, then returns retrogradely via the fast pathway to the atria, often producing retrograde P waves immediately after the QRS complex on ECG. Multiple atypical AVNRT variations exist, depending on the pathway configurations. Typical AVNRT produces a short-RP narrow-complex tachycardia and may show a pseudo-R′ in lead V1 or pseudo-S waves in the inferior leads.[19] Catheter ablation of the slow pathway is first-line definitive therapy for symptomatic AVNRT.[20]
• Junctional ectopic tachycardia 
  • Junctional ectopic tachycardia (JET) is a rare focal automatic tachycardia arising from the AV junction, most often seen in infants or early after cardiac surgery.[21][22] In JET, an ectopic automatic focus within the AV junction overrides the sinus node, so that the junctional tissue, rather than the AV node, acts as a gatekeeper, dictating the ventricular rate. The junctional focus drives the ventricles at a rapid rate; atrial activity may be dissociated from ventricular activation or show retrograde conduction, rather than simple 1:1 antegrade AV conduction.[18] JET can be differentiated from AVNRT with adenosine: adenosine usually produces transient AV block without terminating JET, whereas it often terminates AVNRT by interrupting the reentrant circuit.[17][23]
• Wolff–Parkinson–White syndrome 
  • Wolff–Parkinson–White (WPW) syndrome is a pre-excitation disorder caused by an accessory pathway (typically the Bundle of Kent) that bypasses the atrioventricular node, allowing direct atrioventricular conduction and resulting in early ventricular depolarization.[24] Due to the accessory pathway bypassing the atrioventricular node’s rate-limiting function, the ventricles may be activated at very high rates during supraventricular tachyarrhythmias, which can be particularly dangerous, especially in atrial fibrillation with pre-excitation. On ECG, WPW is characterized by a short PR interval and a widened QRS complex with a slurred initial upstroke, known as the delta wave.[25]
• Atrioventricular reentry tachycardia
  • Atrioventricular reentrant tachycardia (AVRT) is a macroreentrant supraventricular tachycardia that requires an accessory pathway between the atrium and ventricle and is commonly associated with WPW. In orthodromic AVRT, the impulse travels anterogradely through the atrioventricular node and His–Purkinje system, and returns retrogradely through the accessory pathway, producing a narrow-QRS tachycardia. In antidromic AVRT, the impulse travels anterogradely through the accessory pathway, resulting in a wide-QRS tachycardia. 
  • Orthodromic AVRT is distinguished from AVNRT by the conduction pathway. In orthodromic AVRT, conduction travels through the atrium → atrioventricular node/His–Purkinje → ventricle → accessory pathway back to the atrium. In AVNRT, the reentrant circuit is confined within dual atrioventricular nodal pathways and does not require an extranodal accessory pathway. The attached media provides a visual representation.

Nursing, Allied Health, and Interprofessional Team Interventions

Optimal patient care for atrioventricular nodal disorders requires coordinated interprofessional collaboration among physicians, advanced practitioners, nurses, pharmacists, cardiac electrophysiologists, and other healthcare professionals to enhance patient safety, outcomes, and cardiovascular function. Physicians and advanced practitioners play essential roles in recognizing conduction abnormalities, evaluating arrhythmias, interpreting electrocardiographic findings, identifying reversible causes of atrioventricular nodal dysfunction, and determining appropriate medical, procedural, or device-based interventions. Electrophysiologists provide expertise in advanced diagnostic testing, catheter ablation, and management of cardiac implantable electronic devices when indicated. Nursing staff contribute substantially through cardiac rhythm monitoring, medication administration, symptom assessment, patient education, and early recognition of clinical deterioration, including symptomatic bradycardia, syncope, or hemodynamic instability. Pharmacists enhance patient safety by performing medication reconciliation, identifying atrioventricular nodal blocking agents that may worsen conduction disturbances, optimizing antiarrhythmic therapy, and monitoring for adverse drug interactions.

Effective communication and care coordination are particularly important because atrioventricular nodal dysfunction may arise from diverse etiologies, including ischemia, medication effects, infiltrative disease, structural conduction abnormalities, or procedural complications. Timely communication among emergency medicine clinicians, cardiologists, electrophysiologists, pharmacists, nurses, and rehabilitation professionals facilitates rapid diagnosis, escalation of care when pacing support becomes necessary, and implementation of individualized treatment plans. Standardized monitoring protocols, shared clinical decision-making, and coordinated longitudinal follow-up improve patient-centered care while reducing complications associated with arrhythmias, atrioventricular block, or device therapy. Interprofessional collaboration additionally strengthens patient education regarding symptom recognition, medication adherence, and long-term management strategies, ultimately enhancing team performance, cardiovascular outcomes, and overall quality of care for patients with atrioventricular nodal disorders.