From the Guidelines
2:1 Atrioventricular (AV) block is a type of second-degree AV block where every other P wave is conducted to the ventricles, resulting in a 2:1 conduction ratio.
Key Characteristics
- This type of block cannot be classified as Mobitz I or II, as it does not exhibit the characteristic progressive PR prolongation or constant PR intervals before and after the blocked P wave, respectively 1.
- The ECG will show group beating as a result of “dropped” QRS complexes, with every other P wave being conducted to the ventricles 1.
- The level of block in 2:1 AV block is often difficult to determine and may require further evaluation, such as electrophysiological studies, to determine the site of block 1.
Clinical Significance
- 2:1 AV block may be asymptomatic or may cause symptoms related to bradycardia, such as fatigue, dizziness, or syncope 1.
- The prognosis and treatment of 2:1 AV block depend on the underlying cause and the presence of symptoms, with pacing therapy often being considered in symptomatic patients 1.
Diagnosis
- Careful evaluation of the ECG is required for the diagnosis of 2:1 AV block, with attention to the presence of group beating and the 2:1 conduction ratio 1.
- Other conditions, such as atrial bigeminy or isorhythmic dissociation, may mimic 2:1 AV block and must be excluded through careful analysis of the ECG 1.
From the Research
Definition of 2:1 Atrioventricular (AV) Block
- A 2:1 AV block is a type of second-degree AV block where every other P wave is blocked, resulting in a 2:1 ratio of P waves to QRS complexes 2, 3, 4, 5, 6.
- It cannot be classified into type I or type II second-degree AV block because there is only one PR interval to examine before the blocked P wave 4, 6.
Characteristics of 2:1 AV Block
- It can occur in either the AV node or the His-Purkinje system 4, 5.
- The site of the lesion in 2:1 block can often be determined by seeking the company it keeps, such as association with type I or type II block and the width of the QRS complex 4, 5.
- Outside of acute myocardial infarction, sustained 2:1 AV block with a wide QRS complex occurs in the His-Purkinje system in 80% of cases and 20% in the AV node 4.
Diagnosis and Treatment
- The diagnosis of 2:1 AV block requires careful analysis of the electrocardiogram and consideration of the clinical context 2, 3, 4, 5, 6.
- Infranodal block, including 2:1 AV block, requires pacing regardless of symptoms 2, 3, 6.
- Administration of atropine in patients with His-Purkinje disease may increase the degree of AV block 4.