The heart, a continuously working muscle, provides blood circulation throughout the body. While its rhythmic pumping is largely internal, a specific physical sign known as the Point of Maximal Impulse (PMI) offers a direct, tangible connection to its activity. The PMI is simply the location on the chest wall where the heart’s beat can be felt most strongly. This subtle sensation is a fundamental part of a physical examination, providing healthcare professionals with immediate insights into cardiac function without requiring invasive procedures. Observing and feeling the PMI helps clinicians begin to understand the heart’s size, strength, and position within the chest.
Understanding the Point of Maximal Impulse (PMI)
The PMI, often called the apical impulse, represents the outward thrust of the left ventricle as it contracts during systole, pushing against the chest wall. This impulse is primarily caused by the apex, or tip, of the heart rotating forward and striking the chest during this phase of the cardiac cycle. In a healthy adult, the PMI is typically found in the fifth intercostal space (the space between the fifth and sixth ribs) at or just medial to the midclavicular line (an imaginary line drawn vertically down from the middle of the collarbone). This location is approximately 7 to 9 centimeters from the midsternal line.
A normal PMI typically presents as a brief, gentle tap, usually lasting less than two-thirds of systole. Its size is generally small, measuring about 1 to 2.5 centimeters in diameter, or roughly the size of a penny. The impulse should be discrete and localized, representing a single outward movement per cardiac cycle. While the PMI is usually associated with the left ventricle’s apex, other areas of the heart can produce the maximal impulse in certain conditions, such as severe right ventricular enlargement.
How Healthcare Professionals Assess the PMI
Healthcare professionals assess the PMI primarily through palpation, which involves feeling the chest wall with their fingers. They may also use inspection, visually observing the chest for any visible pulsations. To optimize the assessment, the patient is usually positioned supine, often with the upper body elevated at a 15 to 30-degree angle. Sometimes, asking the patient to roll slightly to the left (left lateral decubitus position) can make the PMI more easily palpable by bringing the heart closer to the chest wall. Asking the patient to exhale completely and hold their breath can also enhance visibility and palpation.
During palpation, the examiner uses the pads of their fingers, which are sensitive to pulsations. They systematically feel the precordium, the area over the heart, to locate the PMI. The assessment focuses on several characteristics: its precise location, its size or diameter, its amplitude or vigor (how strong it feels), and its duration (how long the impulse lasts during systole). The timing of the impulse relative to the cardiac cycle is also important to note. While listening with a stethoscope, the healthcare professional can correlate the felt impulse with the first heart sound (S1), which marks the beginning of systole.
What the PMI Can Indicate About Heart Health
Deviations from a normal PMI can signal various underlying heart conditions, making it a valuable diagnostic clue. A displaced PMI, particularly one shifted laterally (outward) or inferiorly (downward) from its usual position, often indicates an enlarged heart, a condition known as cardiomegaly. Left ventricular hypertrophy (LVH), where the left ventricular muscle wall thickens due to increased workload from conditions like hypertension or aortic stenosis, commonly causes the PMI to shift laterally. In significant enlargement, the PMI might even be felt closer to the armpit. Pregnancy or a high diaphragm can also displace the PMI upward and to the left.
An increased size or force of the PMI, often described as a “heave” or “thrust,” suggests that the ventricle is working harder to pump blood. A forceful and sustained PMI can indicate left ventricular hypertrophy resulting from pressure overload conditions like high blood pressure or aortic stenosis, where the aortic valve narrows and impedes blood flow from the heart. This sustained impulse means the outward movement lasts throughout systole, rather than being a brief tap. In contrast, a forceful yet hyperdynamic PMI, characterized by a fast impulse with a large amplitude that quickly terminates, can be seen in states of increased cardiac output, such as exercise, anemia, or hyperthyroidism.
Abnormal characteristics of the PMI can also provide insights. A dyskinetic or uncoordinated PMI, involving a larger area than normal, might suggest ventricular dysfunction, such as an aneurysm following a heart attack. The presence of a “thrill,” a vibratory sensation felt over the PMI, indicates turbulent blood flow and can suggest a heart murmur, often related to valvular abnormalities like aortic stenosis or mitral regurgitation.
In some instances, the PMI may be absent or difficult to locate. This can occur in individuals with a thick chest wall, obesity, emphysema, or conditions like pericardial effusion where fluid surrounds the heart, dampening the impulse. In chronic obstructive pulmonary disease (COPD), the PMI might be felt in the xiphoid or epigastric area due to right ventricular hypertrophy.