Atrial Fibrillation and Understanding Ventricular Rate

Atrial fibrillation (AFib) is a common type of irregular heartbeat characterized by rapid and disorganized electrical activity in the atria. During AFib, the atrial rate can range from 350 to 600 beats per minute, significantly faster than the normal heart rhythm. However, the ventricular rate, which is the rate at which the lower chambers of the heart pump blood to the body, typically falls between 100 and 160 beats per minute. This rate can vary depending on the individual's condition and whether they are receiving treatment to control their heart rhythm.

Impact of Ventricular Rate on Symptoms

The severity of AFib symptoms often depends on how fast the ventricular rate is. When the ventricular rate remains within a controlled range, some patients may experience minimal or no symptoms at all. On the other hand, if the ventricular rate accelerates beyond 150 beats per minute, individuals may develop symptoms such as chest pain (angina) or signs of congestive heart failure. This occurs because the heart is unable to pump efficiently, leading to reduced blood flow and increased pressure within the heart chambers.

Effects on Cardiac Output

During atrial fibrillation, the atria lose their coordinated contraction, which can reduce cardiac output by 20% or more compared to when the heart is in normal sinus rhythm. This decrease in efficiency can lead to fatigue, shortness of breath, and other symptoms associated with poor circulation.

Pulse Deficit and Fast Ventricular Rates

One notable phenomenon that can occur with a high ventricular rate is a pulse deficit, where the pulse rate measured at the wrist is lower than the actual heart rate. This discrepancy happens because some heartbeats are too weak to generate a detectable pulse in the peripheral arteries. Either the ventricular contractions are insufficient to open the aortic valve fully, or the resulting blood pressure changes are too subtle to be felt externally. As a result, healthcare providers may observe a difference between the heart rate heard through a stethoscope and the pulse rate measured manually.