Heart block disrupts the heart’s natural electrical rhythm by interfering with the signal transfer from the upper chambers (atria) to the lower chambers (ventricles). This interruption occurs at the atrioventricular (AV) node, which acts as a gateway for electrical impulses. The result is a heart that beats too slowly or irregularly, potentially leading to symptoms like dizziness, fainting, or shortness of breath. Treatment depends entirely on the severity of the electrical disruption and the presence of associated symptoms.
Classifying Heart Block Severity
The degree of heart block is classified into three main levels based on the extent of electrical signal delay or failure. First-degree heart block is the mildest form, where the electrical impulse is delayed passing through the AV node, but every signal still reaches the ventricles. This delay is observed on an electrocardiogram (ECG) but typically causes no symptoms.
Second-degree heart block involves an intermittent failure of the electrical signal to reach the ventricles, resulting in skipped beats. This level is divided into Type I (Wenckebach), where the delay gets progressively longer until a beat is dropped, and Type II (Mobitz II), where beats are dropped suddenly. Type I is less risky, while Type II carries a higher risk of progressing to a complete block.
Third-degree heart block, or complete heart block, is a total failure of electrical conduction between the atria and the ventricles. The chambers beat independently, forcing the ventricles to rely on a slower, backup rhythm. This uncoordinated and very slow heart rate severely compromises the heart’s ability to circulate blood.
Non-Invasive Management for Mild Heart Block
For the mildest forms of heart block, such as first-degree and asymptomatic second-degree Type I, aggressive intervention is avoided in favor of careful observation. Patients are managed through regular follow-up and monitoring. Diagnostic tools like a Holter monitor, a portable ECG device, may be used periodically to track the heart’s rhythm and assess for progression.
A thorough review of the patient’s current medications is a central component of management. Certain drugs, including beta-blockers, calcium channel blockers, and Digoxin, can slow the heart rate and worsen conduction delay. A cardiologist may adjust the dosage, switch medications, or discontinue the offending drug to see if the heart block improves. Addressing underlying causes, such as thyroid dysfunction or electrolyte imbalances, is also a primary focus. If the heart block is stable, asymptomatic, and not caused by structural heart disease, this observational approach is often the only treatment required.
Permanent Solutions: Pacemaker Implantation
When heart block progresses to symptomatic second-degree Type II or third-degree heart block, the definitive long-term treatment is a permanent pacemaker. A pacemaker is a small, battery-powered electronic device designed to stabilize the heart’s rhythm by delivering precise electrical impulses. It consists of a pulse generator, placed beneath the skin near the collarbone, and thin wires called leads that are threaded through a vein directly to the heart muscle.
The device constantly monitors the heart’s native electrical activity (sensing) and only delivers an electrical signal (pacing) if the heart’s own rhythm is too slow or fails. This ensures the ventricles contract at a sufficient rate to meet the body’s demands, preventing pauses. The implantation procedure is minimally invasive, often performed under local anesthesia, and takes only a few hours.
The choice of device depends on the patient’s specific needs. Single-chamber or dual-chamber pacemakers are the most common types. A single-chamber device uses one lead, while a dual-chamber device uses two leads to pace both the right atrium and the right ventricle. The dual-chamber system is often preferred because it maintains natural coordination between the chambers, optimizing pumping efficiency. Pacemaker technology has a high success rate in restoring a reliable heart rhythm and improving the quality of life for patients.
Acute and Temporary Interventions
When a patient presents with severe symptoms like fainting, shock, or hemodynamic instability due to advanced heart block, immediate temporary interventions are necessary for stabilization. The goal is to rapidly increase the heart rate until a permanent solution, such as a pacemaker, can be implemented.
Emergency medications can acutely speed up the heart rate. Atropine is often the first-line drug, administered intravenously to block the effects of the vagus nerve and increase conduction through the AV node. However, Atropine is generally ineffective for Type II or third-degree heart blocks that occur lower in the conduction system. If Atropine fails, other medications like Isoproterenol may be used, though these are typically reserved for patients at low risk for coronary artery disease.
The most reliable temporary intervention is pacing. Transcutaneous pacing is the quickest method, delivering electrical impulses externally through pads placed on the chest and back. While often uncomfortable, this provides immediate, life-saving support. For more prolonged support, a transvenous pacemaker is inserted through a vein, offering a more reliable and less painful means of pacing the heart until a permanent device can be surgically implanted.