Heart block is a condition where the electrical signals that regulate the heartbeat are disrupted, causing the heart to beat too slowly or irregularly. This disruption affects the heart’s natural rhythm, impacting its ability to efficiently pump blood throughout the body. Different types of heart block manifest distinct patterns of electrical signal disruption.
The Heart’s Electrical System: A Foundation
The heart’s rhythmic pumping action relies on a specialized electrical system. This system begins with the sinoatrial (SA) node, often called the heart’s natural pacemaker, located in the upper right chamber. The SA node generates electrical impulses that spread across the upper chambers, the atria, causing them to contract.
These impulses then travel to the atrioventricular (AV) node, situated between the atria and the lower chambers, the ventricles. The AV node acts as a relay station, momentarily delaying the electrical signal. This brief delay allows the atria to fully empty their blood into the ventricles before the ventricles contract. From the AV node, the impulse moves through the Bundle of His and into Purkinje fibers, which rapidly distribute the electrical signal throughout the ventricles, prompting their coordinated contraction.
Understanding the Degrees of Heart Block
Heart blocks are categorized by the severity and pattern of electrical signal disruption. In first-degree heart block, electrical impulses from the upper to the lower chambers are delayed, but every signal successfully passes through.
Second-degree heart block involves some electrical signals from the atria failing to reach the ventricles, resulting in skipped beats. Mobitz Type I, also known as Wenckebach, is characterized by a progressive lengthening of the electrical signal’s travel time until one impulse is completely blocked, causing a dropped beat.
In contrast, Second-degree Mobitz Type II heart block involves consistent electrical signal delays, but beats are intermittently dropped without a preceding pattern of increasing delay. This type is considered more concerning because it can unpredictably worsen to a complete heart block.
Third-degree heart block, also known as complete heart block, represents the most severe form. Here, there is a complete failure of electrical signals to pass from the atria to the ventricles. The atria and ventricles beat independently of each other, with the ventricles relying on a slower, backup electrical rhythm to maintain pumping action.
Key Indicators and When to Seek Medical Attention
Symptoms associated with heart block can vary widely depending on the type and severity, and some individuals may not experience any symptoms. Common indicators include dizziness or lightheadedness, fatigue, and shortness of breath. Some people may also experience fainting spells, chest discomfort, or heart palpitations, which are sensations of irregular or skipped heartbeats.
These symptoms are not exclusive to heart block and can indicate various underlying health issues. Any new or worsening symptoms warrant medical evaluation. Immediate medical attention is advisable if severe dizziness, fainting, significant chest pain, or severe difficulty breathing occurs.
Diagnostic Approaches: Visualizing Electrical Activity
Medical professionals rely on specific diagnostic tools to differentiate and diagnose heart blocks. The primary tool is the electrocardiogram (ECG or EKG), which records the heart’s electrical activity, revealing delays or blocks that characterize different types of heart block.
For symptoms that occur intermittently, a Holter monitor may be used, which is a portable ECG device worn for 24 to 48 hours to continuously record heart rhythms. An event recorder serves a similar purpose but can be worn for weeks or months, activated by the patient when symptoms are felt. In more complex cases, an electrophysiology (EP) study might be performed for a more detailed analysis of the heart’s electrical system.