Third-degree heart block, also known as complete heart block, is a severe interruption of the heart’s electrical signaling system. This profound disruption prevents electrical impulses from traveling properly through the heart. This condition requires prompt medical evaluation.
Understanding Third-Degree Heart Block
The heart’s rhythm relies on precisely timed electrical signals that originate in the sinoatrial (SA) node, often called the heart’s natural pacemaker. These impulses normally travel from the SA node through the atria, the heart’s upper chambers, and then pass through a relay station known as the atrioventricular (AV) node. The AV node ensures the electrical signal reaches the ventricles, the heart’s lower pumping chambers, in an organized manner.
In third-degree heart block, a complete electrical disconnect prevents impulses from the atria from reaching the ventricles. The SA node’s signals do not conduct to the ventricles. As a result, the ventricles generate their own electrical impulses, beating independently and much more slowly than the atria. This uncoordinated beating significantly reduces the heart’s ability to pump blood effectively.
Recognizing the Signs and Symptoms
Symptoms of third-degree heart block often stem from the heart’s inability to pump sufficient blood. A common indicator is severe bradycardia, an abnormally slow heart rate, typically less than 45-50 beats per minute. This slow rate may be perceived as a weak or unusually slow pulse.
Individuals may experience dizziness, lightheadedness, or fainting spells (syncope). These symptoms occur because the brain does not receive adequate oxygen-rich blood due to inefficient pumping. A general lack of energy, tiredness, or weakness is also frequently reported.
Reduced blood flow to the lungs can lead to shortness of breath, especially during physical activity. Some people might feel palpitations, an irregular heartbeat, even if the rate is very slow. Chest pain or discomfort can also occur, indicating reduced blood supply to the heart muscle. In severe instances, inadequate oxygen to the brain may result in confusion or disorientation. These symptoms warrant immediate medical attention.
How It Is Diagnosed
Medical professionals confirm third-degree heart block primarily through diagnostic tools. The definitive test is an electrocardiogram (ECG or EKG). An ECG displays the heart’s electrical activity, revealing a complete dissociation between P waves (atrial activity) and QRS complexes (ventricular activity). This means atrial and ventricular electrical events occur independently.
A physical examination also provides important clues, as a healthcare provider can check the patient’s pulse and blood pressure, which may reveal very slow or irregular heartbeats. To assess for intermittent symptoms that might not be present during a single office visit, a Holter monitor or event monitor may be used. These portable devices continuously record the heart’s electrical activity over a longer period, typically 24 hours to several weeks, helping to capture irregular rhythms. Blood tests might be conducted to exclude other underlying conditions or electrolyte imbalances that could contribute to heart rhythm disturbances, though they are not diagnostic for the block itself.
Immediate Steps and Treatment
If symptoms suggest third-degree heart block, call emergency services immediately. Delaying medical attention can have serious consequences due to the heart’s compromised pumping ability.
Upon arrival at a medical facility, initial management often involves temporary measures to stabilize the heart rate. Medications like atropine may be administered to temporarily increase the heart rate by affecting the electrical pathways. In some cases, temporary transcutaneous or transvenous pacing might be initiated, where external or internal electrical impulses are delivered to stimulate the heart to beat at a more appropriate rate. These temporary interventions aim to improve blood flow and stabilize the patient while a definitive treatment plan is prepared.
The definitive treatment for third-degree heart block is typically the implantation of a permanent pacemaker. A pacemaker is a small, battery-powered device surgically placed under the skin, usually near the collarbone. This device sends regular electrical impulses to the heart, ensuring it beats at a consistent and normal rate, thereby overcoming the electrical disconnect between the atria and ventricles. After pacemaker implantation, patients typically undergo follow-up appointments to monitor the device’s function and ensure optimal heart rhythm.