From the Guidelines
Heart blocks are classified into three main types: first-degree, second-degree, and third-degree, with treatment depending on the type and symptoms, and can result from various causes including aging, heart disease, and medications, as outlined in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Classification of Heart Blocks
The classification of heart blocks is based on the severity of the conduction disruption, with first-degree being the mildest and third-degree being the most severe.
- First-degree heart block is characterized by a prolonged PR interval (>200 ms) on ECG, as defined in the 2018 ACC/AHA/HRS guideline 1.
- Second-degree heart block comes in two forms: Mobitz type I (Wenckebach), where PR intervals progressively lengthen until a beat is dropped, and Mobitz type II, where PR intervals remain constant but some P waves fail to conduct to the ventricles, as described in the guideline 1.
- Third-degree (complete) heart block is the most severe, with complete dissociation between atrial and ventricular activity, as impulses from the atria cannot reach the ventricles, and is defined in the guideline as "no evidence of atrioventricular conduction" 1.
Causes and Symptoms of Heart Blocks
Heart blocks can result from various causes, including:
- Aging
- Heart disease
- Medications like beta-blockers
- Electrolyte abnormalities Symptoms of heart blocks can range from mild to severe and include:
- Fatigue
- Dizziness
- Syncope
- Cardiac arrest if left untreated ### Treatment of Heart Blocks Treatment of heart blocks depends on the type and symptoms, ranging from observation for asymptomatic first-degree block to pacemaker implantation for symptomatic high-grade blocks, as recommended in the 2018 ACC/AHA/HRS guideline 1.
- Asymptomatic first-degree heart block may not require treatment
- Symptomatic second-degree and third-degree heart blocks may require pacemaker implantation Recognizing the patterns of heart blocks is crucial for appropriate management, and the 2018 ACC/AHA/HRS guideline provides a comprehensive framework for the evaluation and management of patients with bradycardia and cardiac conduction delay 1.