Third-degree heart block is a serious cardiac condition requiring immediate medical attention. Recognizing its signs is important for prompt intervention, which can significantly affect outcomes. This heart rhythm disorder disrupts the heart’s electrical signaling. Understanding these indicators enables individuals to seek timely care.
Understanding Third-Degree Heart Block
Third-degree heart block, also known as complete heart block, is a severe disruption of the heart’s electrical conduction system. The heart’s rhythm is typically controlled by electrical impulses originating in the sinoatrial (SA) node, often called the natural pacemaker. These impulses then travel through the atria and reach the atrioventricular (AV) node, which acts as a gateway to the ventricles. From the AV node, the signals pass into the ventricles, prompting them to contract and pump blood.
In third-degree heart block, the electrical signals from the atria do not reach the ventricles at all, leading to a complete dissociation between atrial and ventricular activity. This means the atria and ventricles beat independently of each other. The SA node continues to generate impulses for the atria, but these impulses are completely blocked from reaching the ventricles.
When this block occurs, the ventricles must generate their own, slower electrical rhythm, known as an escape rhythm, to maintain some blood circulation. This ventricular escape rhythm is typically much slower and less reliable than the normal heart rate, often ranging from 20 to 40 beats per minute, which is insufficient to meet the body’s demands. The lack of coordinated pumping between the atria and ventricles results in significantly reduced blood flow throughout the body.
Key Indicators and Symptoms
Third-degree heart block often manifests with a range of noticeable symptoms that arise from the heart’s inability to pump blood effectively. Profound fatigue, often constant and debilitating, is a common indicator. Individuals may also experience dizziness, lightheadedness, or syncope (fainting) if the brain is deprived of oxygen.
Shortness of breath is another frequent symptom, often experienced during minimal exertion, as the heart struggles to circulate oxygenated blood efficiently. Chest pain, sometimes described as angina, may also be present due to the heart muscle not receiving enough oxygen. Confusion or a general sense of disorientation can develop. In severe instances, third-degree heart block can lead to sudden cardiac arrest if the ventricular escape rhythm fails entirely or is too slow to sustain life.
Less common symptoms include palpitations, which might feel like skipped beats or an irregular, slow rhythm. While the overall heart rate is slow, the independent atrial contractions can sometimes be felt. Swelling in the legs and ankles (peripheral edema) can develop over time due to poor circulation and fluid retention. A general sense of weakness may also be present. These symptoms can appear suddenly or worsen rapidly, requiring medical evaluation.
Confirmation by Medical Professionals
Medical professionals diagnose third-degree heart block primarily using an Electrocardiogram (ECG or EKG). This non-invasive test records the heart’s electrical activity, providing a visual representation of its rhythm. An ECG tracing characteristic of third-degree heart block shows a complete dissociation between P waves (atrial activity) and QRS complexes (ventricular activity). The P waves and QRS complexes “march” independently, with no consistent relationship.
The atrial rate, indicated by P waves, typically remains normal or slightly elevated (60-100 beats per minute). The ventricular rate, indicated by QRS complexes, is very slow and regular, usually 20 to 40 beats per minute. This slow ventricular rate reflects the escape rhythm generated by the ventricles themselves. The lack of a consistent PR interval further confirms the complete block of electrical signals.
Beyond the ECG, a thorough physical examination is conducted. Professionals may note a very slow and regular pulse, a sign of the underlying bradycardia, and specific heart sounds. Blood tests may also be performed to rule out reversible causes like electrolyte imbalances (e.g., hyperkalemia) or certain medications (e.g., beta-blockers, calcium channel blockers, digoxin). These evaluations confirm the diagnosis and guide management.
Urgent Action and Next Steps
If someone experiences symptoms suggestive of third-degree heart block, immediate action is necessary. The most critical step is to call emergency services, such as 911, without delay. This condition is a medical emergency that requires prompt professional intervention and specialized care. Attempting to self-transport to a hospital is not advisable, as the individual’s condition could rapidly worsen, potentially leading to syncope or cardiac arrest during transit.
For someone who has fainted, basic first aid measures can be applied while waiting for emergency personnel. Lay the person down gently, elevate their legs slightly, and loosen any tight clothing around their neck or chest. These steps can help improve blood flow to the brain. Once paramedics arrive, provide them with as much information as possible, including a detailed account of the symptoms observed, any relevant medical history, and a list of current medications the individual is taking.
It is important to remember that third-degree heart block cannot be self-treated. It requires medical diagnosis and intervention, often involving a pacemaker to regulate the heart’s rhythm. Seeking immediate emergency medical care is the most appropriate response to suspected symptoms.