Heart sounds are the noises made by the beating heart and the flow of blood through its chambers. When a doctor listens to your chest with a stethoscope, they hear two main sounds, often described as “lub-dub.” The first sound, S1, marks the beginning of the heart’s pumping phase, while the second sound, S2, signals the end of this phase and the start of the filling period. The S2 sound can sometimes be heard as two distinct components, known as a “split S2,” which can be a normal variation or indicate an underlying heart condition.
The Mechanics of Heart Sounds
The first heart sound, S1, is produced by the simultaneous closure of the mitral and tricuspid valves, which separate the atria from the ventricles. This closure occurs as the ventricles begin to contract, preventing blood from flowing backward into the atria. The sound is heard as a single “lub.”
The second heart sound, S2, is created by the closure of the aortic and pulmonic valves as the ventricles finish ejecting blood. The aortic valve closes first (A2), followed shortly by the pulmonic valve (P2). These two components are heard as one fused sound during expiration, but they can separate during inspiration.
During inhalation, chest cavity pressure decreases, allowing more blood to flow into the right side of the heart. This increased blood volume in the right ventricle prolongs its emptying time, delaying the closure of the pulmonic valve (P2). Simultaneously, reduced intrathoracic pressure slightly decreases blood return to the left side, causing the aortic valve (A2) to close slightly earlier. This temporal separation of A2 and P2 creates the audible physiological split S2, which merges back into a single sound during exhalation.
Conditions Leading to an Abnormal Split S2
Beyond normal physiological splitting, a split S2 can indicate various heart conditions. These appear as different patterns.
A “wide and persistent split” occurs when the delay between A2 and P2 is exaggerated and remains noticeable even during exhalation. This pattern can be caused by conditions that prolong right ventricular emptying, such as a right bundle branch block (RBBB), where electrical impulses are delayed in reaching the right ventricle, or pulmonary stenosis, a narrowing of the pulmonary valve that obstructs blood flow out of the right ventricle.
A “fixed split” occurs when the split between A2 and P2 remains constant and does not vary with respiration. This type of split is associated with an atrial septal defect (ASD), a hole in the wall between the heart’s upper chambers. The ASD causes a continuous shunt of blood from the left atrium to the right atrium, leading to a persistent overload of the right ventricle and a consistent delay in pulmonic valve closure, regardless of the respiratory cycle.
A “paradoxical split,” also known as a reversed split, occurs when the pulmonic valve (P2) closes before the aortic valve (A2). The split may become more apparent during expiration and disappear during inspiration. Conditions that delay left ventricular emptying can cause this, such as a left bundle branch block (LBBB), which delays electrical activation of the left ventricle, or severe aortic stenosis, a significant narrowing of the aortic valve that impedes blood flow out of the left ventricle.
When a Split S2 Signals Concern
While a physiological split S2 is a normal finding, certain characteristics signal an underlying medical concern. If a split S2 is heard consistently, regardless of breathing, or if its pattern changes from the normal physiological response, it warrants medical attention. A new or changing split S2, especially when accompanied by other symptoms, should prompt a visit to a healthcare professional.
Individuals might experience symptoms such as shortness of breath, fatigue, chest pain, or fainting. These symptoms, when combined with an abnormal split S2, suggest a need for further evaluation. A doctor will perform a physical examination, including listening to the heart, and may recommend additional diagnostic tests. These tests can include an electrocardiogram (ECG) to assess the heart’s electrical activity or an echocardiogram, which uses sound waves to create images of the heart’s structure and function, to determine the cause of the abnormal heart sound.