Aortic stenosis (AS) is a condition where the heart’s aortic valve becomes stiff and narrowed, preventing it from opening fully. This valve sits between the heart’s main pumping chamber, the left ventricle, and the aorta, the body’s largest artery. When the valve is narrowed, the heart must work much harder to push blood out to the rest of the body. This disruption of normal, smooth blood flow creates distinct, unusual sounds known as heart murmurs that a healthcare provider can detect with a stethoscope. The specific sound of an aortic stenosis murmur offers important clues about the underlying mechanical problem in the heart.
The Mechanism Behind the Characteristic Sound
The sound of aortic stenosis originates from the physical disturbance of blood flow across the restricted valve opening. Normally, blood flows in a smooth, organized pattern called laminar flow. When the aortic valve leaflets cannot open completely, the passage for blood narrows significantly.
As the left ventricle contracts, it forces blood at high pressure through this constricted opening, creating a high-speed jet. This jet immediately encounters the wider space of the aorta, causing the smooth flow to break down into chaotic, disorganized motion known as turbulent flow.
This turbulence involves the formation of swirling eddies and vortices past the narrowed valve. The rapid, irregular vibration of these blood particles and surrounding structures generates sound waves that travel through the chest wall, becoming the audible “whooshing” or “swishing” sound detected by the stethoscope.
The creation of this turbulent flow is directly related to the pressure difference, or gradient, across the valve. The left ventricle must generate a much higher pressure to push blood through the narrowed valve into the lower-pressure aorta, driving the high-velocity jet and the resulting turbulent sound production.
A Detailed Description of the Aortic Stenosis Murmur
The aortic stenosis murmur is classified as a systolic ejection murmur, meaning it occurs during systole, the phase when the heart contracts to push blood out. It begins shortly after the first heart sound and ends before the second heart sound.
The intensity follows a distinct crescendo-decrescendo pattern, often described as a diamond shape. The sound starts softly, rapidly increases to a peak loudness, and then gradually fades away. This pattern mirrors the blood flow dynamics: the sound becomes louder as the left ventricle accelerates flow and softer as the flow decelerates toward the end of the contraction.
The sound is typically described as harsh, rough, or coarse, often having a medium to high pitch due to the high pressure and velocity of the blood jet. A healthcare provider listens for this sound most clearly at the right upper sternal border, near the second intercostal space, the primary listening area for the aortic valve.
A defining characteristic is its tendency to radiate upward into the neck. The sound frequently travels along the carotid arteries, which helps distinguish it from other heart murmurs.
Interpreting the Murmur and Assessing Severity
The specific features of the aortic stenosis murmur provide a preliminary assessment of the valve disease’s impact.
Timing of Peak Intensity
The timing of the murmur’s peak intensity within the systolic phase offers clues about the degree of obstruction. In mild aortic stenosis, the peak loudness occurs relatively early in systole. As the severity of the valve narrowing progresses, the heart requires more time to overcome the resistance, causing the peak intensity to shift later in systole. A murmur that peaks closer to the second heart sound suggests a more advanced stage of the disease.
Loudness and Correlation
Additional heart sounds can accompany the murmur and suggest greater severity, such as a diminished or absent second heart sound component related to the aortic valve closing. While the murmur’s loudness generally correlates with severity, this is not always a reliable measure. In cases of extremely severe stenosis, the heart muscle may weaken and fail to pump enough blood, paradoxically leading to a quieter murmur.
Confirmation and Diagnosis
Hearing this characteristic murmur is not sufficient for a definitive diagnosis or assessment of the disease’s degree; it serves as a sign that prompts further investigation. Imaging studies, specifically an echocardiogram (ultrasound of the heart), are necessary. These studies measure the actual size of the valve opening and the pressure gradient across the valve, which are the established ways to confirm the diagnosis and determine the extent of the obstruction.