Atrial fibrillation (AFib) and syncope are distinct medical events that frequently occur together. AFib can definitively cause syncope, and this combination represents a serious medical situation requiring immediate attention. Syncope, commonly known as fainting, is the temporary loss of consciousness and muscle tone, which is typically self-recovering. When AFib is the underlying cause, it signals a profound disruption in the heart’s ability to supply blood to the brain. Addressing this syncopal episode requires rapid assessment and targeted intervention to stabilize the heart rhythm and prevent future occurrences.
Understanding Atrial Fibrillation and Syncope
Atrial fibrillation (AFib) is an irregular heart rhythm characterized by chaotic electrical signals originating in the heart’s upper chambers, the atria. Instead of a coordinated contraction, the atria quiver at rates often exceeding 400 beats per minute, significantly reducing the heart’s overall efficiency. This disorganized activity disrupts the normal flow of blood into the lower chambers, the ventricles, and out to the body.
Syncope is defined as a transient loss of consciousness caused by insufficient blood flow to the brain, known as cerebral hypoperfusion. This temporary reduction in blood supply causes the brain to shut down briefly, leading to fainting and a loss of postural tone. While many causes of syncope are relatively benign, when a cardiac arrhythmia like AFib is involved, it indicates a far more serious hemodynamic problem.
The Hemodynamic Link Causing Loss of Consciousness
The most direct mechanism linking AFib to syncope is the development of a rapid ventricular rate (RVR). In AFib, chaotic electrical signals from the atria bombard the atrioventricular (AV) node, the electrical gateway to the ventricles. When the AV node allows too many impulses to pass through, the ventricles begin beating rapidly and irregularly, often exceeding 100 beats per minute.
This RVR drastically shortens the time available for the ventricles to relax and fill with blood between beats. Because the ventricles cannot fill properly, the amount of blood pumped out (stroke volume) is severely diminished.
The resulting sudden reduction in Cardiac Output causes a rapid drop in systemic blood pressure. This acute hypotension starves the brain of oxygen and nutrients, initiating cerebral hypoperfusion and resulting in syncope. Furthermore, the disorganized atrial contraction itself can reduce cardiac output by 20% to 30%, which is compounded by the rapid ventricular rate.
Differentiating Syncope from Other AFib Symptoms
It is important for patients to distinguish true syncope from other common, less severe symptoms of AFib. Syncope is the complete, temporary loss of consciousness. Many people with AFib report pre-syncope, which is the sensation of feeling faint without passing out. Pre-syncope symptoms typically include dizziness, lightheadedness, blurred vision, and a feeling of weakness.
Other frequent complaints associated with AFib include heart palpitations (the feeling of a racing, fluttering, or pounding heart) and fatigue. These symptoms are caused by the heart’s inefficient and irregular beating pattern. However, the occurrence of full syncope is a qualitative shift in severity. It confirms a dramatic failure of the cardiovascular system to maintain sufficient blood pressure for brain function, signifying an acute, severe reduction in cardiac output that warrants immediate medical evaluation.
Immediate Medical Action and Treatment
Any episode of syncope, especially in a person with known or suspected AFib, should be treated as a medical emergency. A healthcare provider will perform a thorough evaluation, beginning with a detailed history and physical examination. Diagnostic tools like an electrocardiogram (ECG) confirm the presence of AFib and identify other abnormalities.
Diagnosis and Stabilization
Further investigation may involve prolonged monitoring with a Holter or implantable loop recorder to capture the rhythm disturbance. Immediate treatment goals focus on stabilizing the patient, primarily by controlling the ventricular rate with medication to allow the heart chambers more time to fill. If the patient is unstable, electrical cardioversion may be used to deliver a controlled shock to reset the heart to a normal rhythm. Long-term management involves addressing the underlying AFib through medications, such as rate or rhythm control drugs, and potentially procedures like catheter ablation.