From the Guidelines
Heart blocks are classified into several types, including first-degree, second-degree (with subtypes Mobitz type I and Mobitz type II), and third-degree (complete) heart block, each with distinct characteristics and treatment approaches. The classification of heart blocks is based on the degree of disruption in the electrical conduction system of the heart.
Types of Heart Blocks
- First-degree heart block: characterized by a prolonged PR interval (>0.20 seconds) on an electrocardiogram (ECG), indicating delayed conduction through the AV node 1.
- Second-degree heart block: has two subtypes,
- Mobitz type I (Wenckebach): characterized by progressive prolongation of the PR interval until a beat is dropped,
- Mobitz type II: characterized by beats dropped without PR interval changes, often associated with a wide QRS complex.
- Third-degree (complete) heart block: occurs when no electrical impulses from the atria reach the ventricles, resulting in complete dissociation between atrial and ventricular rhythms.
Anatomical Classification
Heart blocks can also be classified anatomically into supra-Hisian, intra-Hisian, and infra-Hisian blocks, depending on the location of the conduction delay or block in the heart's conduction system 1.
Clinical Implications
Understanding the specific type of heart block is crucial for appropriate management, as treatment depends on the type and severity of the block, ranging from observation for first-degree block to pacemaker implantation for symptomatic high-grade blocks 1.
Causes and Risk Factors
These conditions occur due to various causes, including aging, heart disease, medications, or congenital issues, and can significantly impact morbidity, mortality, and quality of life if not properly managed 1.
From the Research
Types of Heart Block
There are several types of heart block, including:
- First-degree heart block: This type of block is characterized by a delay in the electrical conduction between the atria and ventricles, but all atrial impulses are still conducted to the ventricles 2.
- Second-degree heart block: This type of block is characterized by some, but not all, atrial impulses being conducted to the ventricles. There are two subtypes of second-degree heart block:
- Mobitz type I (Wenckebach): This type of block is characterized by a progressive delay in the electrical conduction between the atria and ventricles, followed by a dropped beat 3, 4.
- Mobitz type II: This type of block is characterized by an all-or-none conduction, where some atrial impulses are conducted to the ventricles and others are not, without any visible changes in the AV conduction time or PR intervals before and after the blocked impulse 3, 4, 5.
- Third-degree heart block (complete heart block): This type of block is characterized by a complete disruption in the electrical conduction between the atria and ventricles, resulting in no atrial impulses being conducted to the ventricles 6.
- 2:1 or 3:1 block: This type of block is characterized by a fixed ratio of conducted to non-conducted atrial impulses, and can be either nodal or infranodal in location 2, 3.