The human pulse is the rhythmic expansion and contraction of an artery as blood is pushed through the circulatory system by the heart. While a peripheral pulse, such as the radial pulse at the wrist, measures the wave of blood pressure in the arteries, the apical pulse measures the heart rate directly at its source. This measurement is taken over the heart’s apex and provides the true count of ventricular contractions. The apical pulse is considered the most accurate method for determining heart rate, helping healthcare professionals assess overall cardiovascular function.
Defining the Apical Pulse and Identifying the Point of Maximal Impulse
The apical pulse is a direct reflection of the mechanical contraction of the heart’s ventricles, particularly the left ventricle. This measurement is taken over the apex of the heart, which is the lower, pointed end of the organ. The physical impulse felt or heard at this specific spot is known as the Point of Maximal Impulse (PMI) or the apex beat.
In most adults, the PMI is anatomically located at the intersection of the fifth intercostal space and the mid-clavicular line on the left side of the chest. The fifth intercostal space is the gap between the fifth and sixth ribs, and the mid-clavicular line is an imaginary vertical line drawn down from the midpoint of the collarbone. Because this location is directly over the left ventricle’s tip, it is the most reliable site to detect the heart’s actual beat.
The Technique for Measuring Apical Heart Rate
Measuring the apical heart rate requires a stethoscope and a watch or timer with a second hand to auscultate the heart sounds accurately. The patient should be positioned comfortably, either lying flat (supine) or sitting upright. Sometimes a slight turn to the left side can make the impulse easier to hear. After locating the Point of Maximal Impulse (PMI) on the chest, the diaphragm of the stethoscope is placed firmly over this area.
The healthcare professional listens for the distinct “lub-dub” sounds, which represent one complete heartbeat. The “lub” sound (S1) is the closing of the mitral and tricuspid valves, while the “dub” (S2) is the closing of the aortic and pulmonic valves. Each “lub-dub” sequence counts as one beat, and the rate is determined by counting the number of sequences that occur in one minute. Counting for a full 60 seconds is the standard practice for an apical rate measurement, especially if the heart rhythm is irregular.
Clinical Situations Requiring an Apical Assessment
An apical pulse assessment is often preferred in clinical situations where peripheral pulse checks may be unreliable. For infants and young children, an apical assessment is the standard method because their small size makes it difficult to palpate a peripheral pulse. The apical rate is also the preferred measure for patients with known cardiovascular conditions, such as certain arrhythmias, where the peripheral pulse may not reflect the heart’s true contraction rate.
This measurement is also employed before administering specific cardiac medications, such as digitalis, which can significantly alter the heart rate. A precise apical rate measurement is needed to ensure the drug can be safely given. If a patient’s peripheral pulse is weak, irregular, or difficult to locate due to factors like obesity or poor circulation, the apical pulse provides necessary direct and reliable heart rate data.
The Significance of a Pulse Deficit
Peripheral pulses, such as the radial pulse, measure the pressure wave created when blood is ejected into the arteries. The apical pulse, however, measures the mechanical contraction itself. In a healthy person, the apical rate and the peripheral pulse rate should be identical, meaning every heart contraction generates a palpable pressure wave.
A “Pulse Deficit” occurs when the apical heart rate is higher than the peripheral pulse rate, signifying that some heart contractions are too weak to create a detectable pulse wave. This deficit suggests inefficient heart function because not every beat is strong enough to push a sufficient volume of blood into the circulation. A difference of more than 10 beats per minute between the two rates is considered a significant pulse deficit.
This difference is frequently observed in conditions like atrial fibrillation, where the heart’s upper chambers contract rapidly and irregularly, leading to varying stroke volumes. To accurately measure a pulse deficit, two healthcare professionals must simultaneously count the apical and radial pulses for a full minute. The resulting deficit is calculated by subtracting the radial rate from the apical rate, indicating compromised cardiac output that warrants further medical evaluation.