The second heart sound is caused as a result of one of the following:
Closure of tricuspid and mitral valve.
Closure of aortic and pulmonic valves.
Closure of the pulmonic and mitral valve.
Closure of the aortic and tricuspid valve.
Answers
Answer:
closure of arotic and pulmonic valve
Explanation:
Heart sounds are produced from a specific cardiac event such as closure of a valve or tensing of a chordae tendineae. Many pathologic cardiac conditions can be diagnosed by auscultation of the heart sounds. Note that heart sounds are discrete, short audible events from a specific cause — different from a heart murmur. A murmur is due to turbulence of blood flow and can, at times, encompass all of systole or diastole.
The main normal heart sounds are the S1 and the S2 heart sound. The S3 can be normal, at times, but may be pathologic. A S4 heart sound is almost always pathologic. Heart sounds can be described by their intensity, pitch, location, quality and timing in the cardiac cycle.
Intensity: Heart sounds can be described as increased in intensity (loud), decreased in intensity (soft) or absent.
Pitch: Heart sounds can be described as high pitched (heard best with the diaphragm of the stethoscope).
Location: The location of the heart sound can help determine the etiology. The standard listening posts (aortic, pulmonic, tricuspid and mitral) apply to both heart sounds and murmurs. For example, the S1 heart sound — consisting of mitral and tricuspid valve closure — is best heard at the tricuspid (left lower sternal border) and mitral (cardiac apex) listening posts.
Listening-posts
Timing: The timing can be described as during early, mid or late systole or early, mid or late diastole.
Although terms such as “click,” “snap” or “knock” are sometimes used, they have no specific quality or meaning. They will be referenced in the following sections.
First Heart Sound (S1)
The first heart sound results from the closing of the mitral and tricuspid valves. The sound produced by the closure of the mitral valve is termed M1, and the sound produced by closure of the tricuspid valve is termed T1. The M1 sound is much louder than the T1 sound due to higher pressures in the left side of the heart; thus, M1 radiates to all cardiac listening posts (loudest at the apex), and T1 is usually only heard at the left lower sternal border. This makes the M1 sound the main component of S1.
Split_S1
CLINICAL PEARL: A split S1 heart sound is best heard at the tricuspid listening post, as T1 is much softer than M1.
The M1 sound occurs slightly before T1. Because the mitral and tricuspid valves normally close almost simultaneously, only a single heart sound is usually heard. However, in about 40% to 70% of normal individuals — as well as in certain cardiac conditions — a “split S1” sound can be appreciated. This occurs when the mitral valve closes significantly before the tricuspid valve, allowing each valve to make a separate audible sound. Inspiration delays the closure of the tricuspid valve in a normal person, due to increased venous return, thereby enhancing the splitting of the S1 sound.
A split S1 sound is common in the setting of a right bundle branch block or ventricular tachycardia/premature ventricular contractions, or PVCs, with a right bundle branch block morphology. A RBBB causes the electrical impulse to reach the left ventricle before the right ventricle. Dyssynchrony then occurs, resulting in the left ventricle contracting before the right ventricle, thus the pressures in the LV rise before that of the right ventricle.
This delays the closure of the tricuspid valve, resulting in a split S1 sound. A left bundle branch block has the opposite effect on S1. In this setting, the electrical impulse reaches the RV before the LV, thus the pressure in the RV rises before that of the LV. This forces the tricuspid valve closed earlier, resulting in complete overlap of M1 and T1, and thus no audible split S1 sound.
CLINICAL PEARL: A RBBB results in a widened split S1, whereas a LBBB results in the absence of a split S1.
Four factors affect the intensity of the first heart sound. Because the M1 portion of S1 is much louder than T1, it is only important to discuss what affects the intensity of M1.