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AtrioventricularEdit

I can provide a neutral, evidence-based encyclopedia-style article on the topic. The term atrioventricular refers to the junction between the atria and ventricles in the heart’s electrical system, most prominently involving the atrioventricular (AV) node and the conduction pathway that coordinates the timing of atrial and ventricular contraction. This conduction axis is essential for efficient cardiac output, allowing time for ventricular filling while maintaining a reliable heart rate.

Anatomy and physiology

Components of the atrioventricular conduction axis

  • Atrioventricular node Atrioventricular node: the primary slow-conducting relay between the atria and ventricles, located at the lower part of the right atrial septum near the opening of the coronary sinus.
  • Atrioventricular bundle (bundle of His) Bundle of His: the pathway that transmits impulses from the AV node into the interventricular septum, connecting to the purkinje system.
  • Right and left bundle branches: subdivisions of the His-Purkinje system that rapidly deliver impulses to the right and left ventricles.
  • Purkinje fibers: the terminal network that ensures rapid and uniform ventricular activation.
  • Accessory pathways (in some individuals): alternative conduction routes that can bypass the AV node, contributing to certain arrhythmias such as Wolff-Parkinson-White syndrome Wolff-Parkinson-White syndrome.

Location and structural characteristics

The AV node resides in the right atrium, near the junction of the atrial septum and the tricuspid annulus. It sits within the fibrous annulus that separates the atria from the ventricles, which helps regulate conduction between chambers. The His bundle traverses the atrioventricular junction and penetrates the interventricular septum before dividing into the bundle branches. Together, these components form the core of the AV conduction axis, enabling coordinated timing between atrial contraction and subsequent ventricular contraction.

Electrophysiology and conduction properties

Conduction through the AV node is deliberately slow relative to other portions of the conduction system. This delay, typically on the order of approximately 100–250 milliseconds, creates the physiologic PR interval on electrocardiograms (ECGs) and provides time for ventricular filling after atrial systole. The slow conduction also creates a refractory period that helps prevent rapid reentrant circuits. Beyond the AV node, the His-Purkinje network conducts impulses rapidly to ensure nearly simultaneous activation of both ventricles.

Function in normal cardiac rhythm

In normal rhythm, the sinoatrial node Sinoatrial node generates impulses that travel through the atria to the AV node, which delays the impulse before transmitting it to the ventricles via the His-Purkinje system. This sequence ensures that atrial contraction precedes ventricular contraction and that the ventricles fill efficiently before they pump blood to the lungs and the rest of the body.

Clinical significance

Atrioventricular block

Atrioventricular block refers to impaired conduction between the atria and ventricles and is categorized by degree and pattern: - First-degree AV block: uniformly prolonged PR interval (greater than 200 ms) without dropped beats; typically asymptomatic but can indicate underlying conduction system disease. - Second-degree AV block Mobitz type I (Wenckebach): progressive lengthening of the PR interval followed by a dropped ventricular beat; often intermittent and may be tolerated in some individuals. - Second-degree AV block Mobitz type II: sudden dropped beats with a relatively stable PR interval; more likely to progress to complete block and may require intervention. - Third-degree AV block (complete heart block): complete dissociation between atrial and ventricular activity; ventricles beat independently at an intrinsic rate, which often necessitates pacemaker therapy.

Arrhythmias related to AV conductions

  • AV nodal reentrant tachycardia (AVNRT): a common paroxysmal supraventricular tachycardia arising from a reentrant circuit within or near the AV node; catheter-based ablation targeting slow pathway tissue is a common treatment AV node and AV nodal reentrant tachycardia.
  • AV reciprocating tachycardias (AVRT): involve accessory pathways that create a reentrant circuit between atria and ventricles; Wolff-Parkinson-White syndrome Wolff-Parkinson-White syndrome is a classic example, often treated with ablation of the accessory pathway Catheter ablation.
  • Atrial fibrillation with rapid ventricular response: the AV node governs the rate at which atrial impulses reach the ventricles, and rate control strategies often aim to modulate AV nodal conduction Atrial fibrillation.

Diagnostic approaches

  • Electrocardiography (ECG or EKG): primary tool to assess PR interval, AV block patterns, and signs of tachyarrhythmias.
  • Electrophysiology study (EPS): invasive testing to map conduction properties, identify reentrant circuits, and guide ablation or pacing strategies.
  • Holter monitoring and event recorders: provide long-term assessment of intermittent conduction abnormalities or arrhythmias.
  • Imaging and structural assessment: echocardiography or MRI may be used to evaluate underlying structural heart disease that can influence AV conduction.

Therapeutic and interventional options

  • Pacemaker therapy: used to treat symptomatic high-grade AV block or to maintain heart rate in certain conduction diseases.
  • Catheter ablation: targeted destruction or modification of conduction tissue to prevent reentrant circuits or eliminate accessory pathways Catheter ablation.
  • Pharmacologic management: antiarrhythmic medications or rate-control drugs may be used to manage symptoms or modify AV nodal conduction in certain scenarios.

See also