orthodromic vs antidromic avrt

Kana Ai Author

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30-12-2024

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Orthodromic vs. Antidromic Atrioventricular Reciprocating Tachycardia (AVRT): Understanding the Differences

Atrioventricular reciprocating tachycardia (AVRT) is a type of supraventricular tachycardia (SVT) characterized by a rapid heart rhythm originating from a re-entrant circuit involving the atrioventricular (AV) node and an accessory pathway. Understanding the difference between orthodromic and antidromic AVRT is crucial for appropriate diagnosis and management. These variations differ significantly in their electrocardiographic (ECG) characteristics and clinical presentation.

Understanding the Basics: The Accessory Pathway

At the heart of AVRT lies an accessory pathway – an abnormal electrical connection between the atria and ventricles. This pathway bypasses the AV node, the natural gatekeeper regulating the electrical impulses between the atria and ventricles. The presence of this accessory pathway allows for the creation of a re-entrant circuit, leading to the rapid heart rhythm seen in AVRT.

Orthodromic AVRT:

In orthodromic AVRT, the impulse travels down the normal AV node pathway to the ventricles, and then back up the accessory pathway to the atria. Think of it as the "normal" pathway going down and the accessory pathway coming back up.

• ECG Characteristics: The QRS complex typically appears narrow, resembling a normal sinus rhythm because the ventricles are activated via the normal AV node pathway. The P wave is usually retrograde (inverted or abnormally shaped) and may be buried within the QRS complex or follow it. The PR interval may be shortened or normal.

• Clinical Presentation: Patients with orthodromic AVRT often experience palpitations, dizziness, and shortness of breath. The tachycardia is typically well-tolerated, though prolonged episodes can lead to more significant symptoms.

Antidromic AVRT:

In antidromic AVRT, the impulse travels down the accessory pathway to the ventricles, and then back up the normal AV node pathway to the atria. This is the reverse of orthodromic AVRT.

• ECG Characteristics: The QRS complex is typically wide and bizarre due to the rapid activation of the ventricles via the accessory pathway, which may have a slower conduction velocity than the normal pathway. The P wave may be hidden within the QRS complex, preceding it, or following it.

• Clinical Presentation: Antidromic AVRT can be more symptomatic than orthodromic AVRT because the rapid ventricular activation via the accessory pathway can lead to hemodynamic compromise, including hypotension and syncope (fainting). This is a more serious form of AVRT.

Here's a table summarizing the key differences:

Diagnosis and Management:

Accurate diagnosis of AVRT relies on a thorough history, physical examination, and ECG analysis. Electrophysiological studies (EPS) are often performed to confirm the diagnosis, identify the location and characteristics of the accessory pathway, and guide treatment strategies. Treatment options may include medication, catheter ablation (to destroy the accessory pathway), or both.

Conclusion:

Orthodromic and antidromic AVRT represent distinct variations of AVRT, differing significantly in their ECG characteristics and clinical implications. Understanding these differences is critical for healthcare professionals to provide timely and appropriate diagnosis and management of this arrhythmia. The potential for hemodynamic instability in antidromic AVRT underscores the importance of prompt recognition and intervention.