Third-degree heart block, also known as complete heart block, is a severe interruption of the heart’s electrical system requiring immediate medical attention. It occurs when the electrical signal generated in the upper chambers (atria) cannot pass through the atrioventricular (AV) node to reach the lower chambers (ventricles). This electrical disconnect means the atria and ventricles beat independently, resulting in a slow and unreliable heart rate. The heart’s ability to pump blood effectively is severely compromised, necessitating prompt intervention.
Recognizing the Urgency
A third-degree heart block is a medical emergency because the resulting severely slowed heart rate (bradycardia) drastically reduces the heart’s output of blood. The ventricles rely on a slower, less dependable “escape rhythm” originating lower in the conduction system, often resulting in a rate as low as 30 to 40 beats per minute. This prevents sufficient oxygenated blood from reaching the brain and other vital organs, leading quickly to severe symptoms.
Common symptoms signaling the need for emergency treatment include syncope (fainting), severe dizziness or lightheadedness, profound fatigue, shortness of breath, or chest pain. Without rapid intervention, this lack of blood flow can lead to cardiovascular collapse, heart failure, or sudden cardiac arrest. The presence of these severe symptoms requires immediate transport to a facility capable of advanced life support.
Initial Stabilization and Temporary Measures
The immediate goal in the emergency setting is to stabilize the patient and raise the heart rate until a permanent solution can be implemented. Medications are sometimes used as a temporary bridge, though their effectiveness in complete heart block is often limited. Atropine can be administered intravenously to block the vagus nerve’s slowing effect on the heart, but it often fails to significantly increase the rate when the block is located below the AV node. Other medications, such as isoproterenol, dopamine, or epinephrine, may be used as intravenous infusions to temporarily stimulate a faster heart rate in unstable patients.
If medications are ineffective, temporary pacing is the next step to control the heart rhythm. Transcutaneous pacing involves placing external pads on the chest and back to deliver electrical impulses through the skin, stimulating the heart muscle. This is a rapid but often painful procedure that must be started quickly to maintain an adequate heart rate until a more stable method can be put in place. A more reliable alternative is transvenous temporary pacing, which involves inserting a thin wire (lead) through a vein and guiding it into the heart’s right ventricle. This lead connects to an external pacemaker generator, providing a more stable and less painful method of electrical stimulation until the definitive procedure can be scheduled.
The Definitive Solution: Permanent Pacing
For nearly all patients with acquired third-degree heart block, the definitive and long-term treatment is the surgical implantation of a permanent pacemaker. This small, battery-powered device continuously monitors the heart’s electrical activity. When the heart rate drops below a preset minimum, the pacemaker delivers an electrical impulse to trigger a contraction. This ensures a consistent and sufficient heart rate to maintain adequate blood flow.
The implantation procedure is typically performed under local anesthesia. A small incision is made, usually below the collarbone, where the pacemaker generator (containing the battery and circuitry) is placed beneath the skin in a “pocket.” One or more insulated wires, called leads, are threaded through a vein near the collarbone and guided with X-ray imaging into the heart chambers.
The type of pacemaker depends on the patient’s needs, but a dual-chamber device is often selected. A dual-chamber pacemaker uses two leads—one in the right atrium and one in the right ventricle—to coordinate the contractions of both upper and lower chambers. This coordination, known as AV synchrony, results in a more natural and efficient heartbeat compared to a single-chamber device. Once the leads are positioned and tested, they are secured and connected to the generator.
Post-Procedure Care and Monitoring
Recovery from permanent pacemaker implantation involves specific precautions to allow the leads to securely integrate with the heart tissue. For the first few weeks, patients should avoid lifting anything heavier than ten pounds and refrain from raising the arm on the implant side above shoulder level. These restrictions help prevent the leads from dislodging before scar tissue forms. The incision site must be kept clean and dry, and patients should monitor the area for signs of infection, such as redness, swelling, or unusual pain.
Long-term management requires regular follow-up appointments to ensure the device is functioning correctly and to check battery life. Checkups are typically scheduled every six to twelve months, and many modern pacemakers allow for remote monitoring. The non-rechargeable battery has an expected lifespan, often ranging from 5 to 15 years, depending on how frequently the device is required to pace the heart. When the battery nears depletion, a minor procedure replaces the generator while leaving the existing leads in place.
Patients must be aware of electromagnetic interference. While most household and office electronics do not pose a threat, devices with strong magnetic fields (like security metal detectors or large industrial motors) should be approached with caution. Cell phones and other wireless devices should be kept at least six inches away from the pacemaker site. Patients should always carry their pacemaker identification card, which provides device details for medical personnel and security.