From the Guidelines
Sinoatrial (SA) block, specifically type 2, is characterized by blocked conduction between the sinus node and adjacent atrial tissue, resulting in multiple electrocardiographic manifestations, including "group beating" of atrial depolarization and sinus pauses. According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1, SA block is a type of sinus node dysfunction that can manifest as sinus bradycardia, ectopic atrial bradycardia, or sinus pause.
Key Characteristics of SA Block Type 2
- Blocked conduction: Between the sinus node and adjacent atrial tissue
- Electrocardiographic manifestations: "Group beating" of atrial depolarization and sinus pauses
- Comparison to sinus arrest: SA block type 2 is distinct from sinus arrest, which is characterized by no evidence of sinus node depolarization
Comparison to Sinus Arrest
- Sinus arrest: No evidence of sinus node depolarization, whereas SA block type 2 has evidence of blocked conduction between the sinus node and adjacent atrial tissue
- Clinical implications: SA block type 2 may require different management strategies compared to sinus arrest, depending on the underlying cause and severity of the condition
In summary, SA block type 2 is a specific type of sinus node dysfunction characterized by blocked conduction between the sinus node and adjacent atrial tissue, resulting in distinct electrocardiographic manifestations. It is distinct from sinus arrest and may require different management strategies. The 2018 ACC/AHA/HRS guideline provides a comprehensive framework for evaluating and managing patients with bradycardia and cardiac conduction delay, including those with SA block type 2 1.
From the Research
Characteristics of Sinoatrial (SA) Block
- Sinoatrial block is a condition where there is a blockage of electrical impulses from the sinoatrial node to the atria 2
- There are three types of SA block: first-degree, second-degree, and third-degree, with second-degree being further divided into two types: Wenckebach (type 1) and Mobitz (type 2) 2, 3
- Type 2 second-degree SA block is characterized by a long pause that is less than twice the normal PP interval, without progressive shortening of the atrial cycle before the block 3
Comparison to Sinus Arrest
- Sinus arrest is a condition where there is a complete cessation of electrical impulses from the sinoatrial node, resulting in a pause in the ECG tracing 4, 2
- Sinus arrest can be distinguished from second-degree SA block by its irregular periodicity, whereas second-degree SA block has a more regular periodicity 2
- Both conditions can cause symptoms such as dizziness and syncope, and can be diagnosed using electrocardiography and Holter monitoring 4, 2
Diagnostic Features of Type 2 SA Block
- The presence of a long pause that is less than twice the normal PP interval, without progressive shortening of the atrial cycle before the block 3
- The PP interval that follows the long pause is slightly longer than the one that precedes the pause 3
- First-degree SA block may also be present, which can affect the duration of the long pause and the following PP interval 3