A pulse deficit is the difference between the heart’s actual rate of contraction (apical pulse) and the rate of the pulse felt in a peripheral artery (radial pulse). This discrepancy indicates the heart’s efficiency in pushing blood throughout the body. A deficit signals that not every heartbeat is strong enough to create a detectable pressure wave at the wrist. The presence of a pulse deficit suggests a problem with the heart’s rhythm or the force of its contractions. In a healthy cardiovascular system, the central heart rate matches the peripheral pulse rate exactly, resulting in a zero pulse deficit.
Understanding the Two Pulse Measurements
The calculation of a pulse deficit relies on comparing two distinct measurements: the Apical Pulse (AP) and the Radial Pulse (RP). The Apical Pulse represents the true rate of ventricular contraction and is determined by listening directly over the heart. This measurement is taken using a stethoscope placed at the point of maximal impulse (PMI). Counting the “lub-dub” heart sounds heard at this spot for a full minute provides the most accurate measure of the heart’s pace.
The Radial Pulse is a peripheral pulse measured at the wrist over the radial artery, on the thumb side of the forearm. It is felt by lightly pressing the pads of the index and middle fingers against the artery. This measurement reflects the number of pressure waves that successfully travel from the heart and reach the extremities.
The Simultaneous Measurement Procedure
Determining a pulse deficit requires the simultaneous measurement of both the apical and radial pulses, necessitating two examiners working in coordination. One examiner uses a stethoscope to auscultate the Apical Pulse over the PMI. The second examiner simultaneously palpates the Radial Pulse on the patient’s wrist.
The procedure begins with the two examiners agreeing on a starting signal. A single timer is used to count for a full 60 seconds to ensure accuracy, especially when an irregular rhythm is suspected. The examiner listening to the heart counts every “lub-dub” sound, representing a single heart contraction. The examiner at the wrist counts every pressure wave felt, and the Apical Pulse count will always be equal to or greater than the Radial Pulse count.
Once both rates are recorded, the pulse deficit is calculated using the formula: Pulse Deficit = Apical Pulse Rate – Radial Pulse Rate. For example, if the apical rate is 84 beats per minute and the radial rate is 72 beats per minute, the pulse deficit is 12. This difference signifies that 12 heart contractions were too weak to generate a palpable pulse at the wrist. A deficit exceeding 10 beats per minute is considered clinically significant.
Clinical Significance and Related Conditions
A pulse deficit is a significant clinical finding because it indicates a reduction in the heart’s ability to effectively circulate blood to the periphery. The underlying mechanism is that some ventricular contractions are too weak or occur too early in the cardiac cycle. These weak contractions fail to generate enough pressure to open the aortic valve fully and push a detectable blood volume wave into the radial artery. A much lower pressure is sufficient to merely close the mitral valve, creating a heart sound without a corresponding pulse.
The most common cause of a pulse deficit is Atrial Fibrillation (A-Fib). This arrhythmia is characterized by chaotic, rapid, and irregular electrical activity in the heart’s upper chambers. In A-Fib, the ventricles beat irregularly and quickly, resulting in varying diastolic filling times. When the filling time is too short, the left ventricle does not fill sufficiently, and the ensuing contraction lacks the force needed to create a peripheral pulse.
Other conditions that can lead to a pulse deficit include premature ventricular contractions (PVCs) and severe heart failure, where the heart muscle is too compromised to contract forcefully. A higher pulse deficit in patients with A-Fib is often correlated with a reduced capacity for physical exercise. The presence of a deficit serves as a warning sign of compromised cardiac output and requires thorough medical evaluation to address the root cause.