The heart produces sounds, often described as a “lub-dub,” which provide valuable information about its function and valve health. Medical professionals use a stethoscope to assess these sounds for variations.
The Heart’s Rhythmic Sounds
The familiar “lub-dub” represents two primary heart sounds, known as S1 and S2. S1 is produced by the closing of the mitral and tricuspid valves, which separate the atria from the ventricles at the beginning of the heart’s contraction phase. Following S1, S2 marks the closing of the aortic and pulmonic valves. These valves are located at the exits of the left and right ventricles, ensuring that blood flows forward into the body and lungs.
Decoding a Split S2
A “split S2” occurs when the two components of the S2 sound, originating from the closure of the aortic valve (A2) and the pulmonic valve (P2), are heard separately rather than as a single, unified sound. Normally, the aortic valve closes slightly before the pulmonic valve, but the difference in timing is usually too small to distinguish. This separation becomes audible when the closure of these two valves is delayed or prolonged, causing the “dub” to briefly split into two discernible parts.
The left ventricle, which pumps blood to the entire body, operates under higher pressure, leading to the earlier closure of the aortic valve. Conversely, the right ventricle, which pumps blood to the lungs, operates under lower pressure. This pressure difference means the pulmonic valve typically closes a fraction of a second after the aortic valve, and when this slight delay becomes more pronounced, the S2 split becomes noticeable.
When a Split S2 is Normal
A split S2 can be a normal finding, particularly during inspiration, and is referred to as a physiological split. During inhalation, the chest cavity expands, leading to a temporary decrease in pressure within the chest. This change allows more blood to return to the right side of the heart, increasing the volume of blood the right ventricle must pump. Consequently, it takes slightly longer for the right ventricle to eject this increased volume, which delays the closure of the pulmonic valve.
At the same time, the increased blood volume in the lungs during inspiration can slightly reduce the amount of blood returning to the left side of the heart, causing the aortic valve to close a little earlier. The combination of a slightly earlier aortic valve closure and a slightly delayed pulmonic valve closure widens the interval between A2 and P2, making the split audible. This normal splitting pattern disappears or narrows significantly during exhalation as the physiological changes reverse. This respiratory variation distinguishes a normal split S2 from those that may signal an underlying health issue.
When a Split S2 Signals Concern
While a physiological split S2 is a normal variant, certain types of S2 splitting can indicate underlying heart conditions and warrant medical evaluation. When a split S2 is consistently wide and does not change with breathing, it is known as a fixed split S2. This type of splitting strongly indicates an atrial septal defect (ASD), a congenital hole in the wall separating the heart’s upper chambers. The presence of an ASD causes a continuous flow of blood from the left atrium to the right atrium, leading to constant volume overload in the right ventricle and a sustained delay in pulmonic valve closure, regardless of the respiratory cycle.
Another concerning pattern is a wide split S2 that remains wide during both inspiration and expiration but still varies with respiration; this is often associated with conditions that delay the emptying of the right ventricle, such as a right bundle branch block (RBBB) or pulmonic stenosis. In RBBB, electrical signals to the right ventricle are delayed, causing it to contract and empty later than the left ventricle, which delays pulmonic valve closure.
A paradoxical or reversed split S2 occurs when the splitting is wider during exhalation and becomes single or narrows during inhalation, which is the opposite of the normal pattern. This happens when the aortic valve closure (A2) is delayed, causing it to close after the pulmonic valve (P2). Conditions that can cause this include severe aortic stenosis, which obstructs blood flow from the left ventricle, or a left bundle branch block (LBBB), which delays the electrical activation and contraction of the left ventricle. Any persistent or unusual S2 splitting should be assessed by a healthcare professional to determine its cause and implications.