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You are watching: The first heart sound (the "lub" of the "lub-dup") is caused by

Walker HK, hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and also Laboratory Examinations. Third edition. Boston: Butterworths; 1990.



Heart sounds room discrete to explode of listening vibrations of differing intensity (loudness), frequency (pitch), quality, and also duration. The first heart sound (S1) is created of number of high-frequency components; only the first two are typically audible. These 2 sets that audible vibrations are temporally related to closure the the mitral and also tricuspid valves. The first heart sound corresponds with convulsion of the ventricles, thus identifying the beginning of ventricular systole and the finish of mechanically diastole.


The examination must be carried out in a warm, quiet room. Place the patient in a supine position after all garments has been gotten rid of from the chest. Describe to the patient the you room going to study the heart. Heat your hands and also stethoscope, yet warn the patient that your hands might be cool in ~ first. The most comfortable and also satisfactory position for most inspectors is top top the patient"s appropriate side. Due to the fact that heart sounds may be palpable, effort to palpate the very first sound with the heel of the ideal hand and/or the fingerpads, originally at the cardiac apex and also then over the whole precordium.

The acoustic occasions should it is in analyzed only after having assessed the venous, arterial, and chest wall pulsations. The auscultatory check is commonly begun at the aortic area (second best intercostal space) and the stethoscope inched to the pulmonary area (second left intercostal space), the tricuspid area (lower left sternal border), and mitral area (cardiac apex), as displayed in figure 22.1. Monitor an identical routine for every examination, passing native one part to an additional in a particular order.


Figure 22.1

Routine areas for auscultation of the precordium.

Force yourself right into the habit of listening for one sound at a time, using an excellent care come time the love sounds exactly. Listen v the stethoscope diaphragm, pressed firmly on the chest, to finest hear the high-frequency vibrations the the very first heart sound. Concentrate for several cycles top top the quality and also intensity that the an initial heart sound, dismissing every little thing else from your mind until the sound is plainly identified and also appraised. The very first sound is generally lower in pitch 보다 the 2nd sound.

The high quality of the first heart sound (S1) and also its time connection with the 2nd heart sound (S2) do it feasible for the experienced observer to identify a definite rhythm and thus quickly distinguish between S1 and S2. In ~ normal and also slow heart rates, S1 is the first of the paired heart sounds, adhering to the much longer diastolic duration and preceding the shorter systolic period. These sounds have the right to be be separate by all at once feeling or looking at the apex advertise while listening; the an initial heart sound is synchronous v the outward thrust that the apex impulse. Through experience, the is feasible to watch the activity of the stethoscope top top the chest if listening to the love sounds in order to time systole and diastole. When the apex impulse cannot be seen or felt, the pulsation the the carotid artery deserve to be used as a guide. A finger ~ above the carotid artery will sense the palpable arterial upstroke that automatically follows the first heart sound. With rapid heart rates, however, the slight delay between the first sound and also carotid pulsation may make this exercise unsatisfactory. Usage of a more distant artery because that this purpose leads to error due to the fact that of the moment it take away the pulse wave to reach the periphery.

For exact identification of the an initial heart sound when multiple sounds room audible, relocate the stethoscope progressively from the 2nd right to the fourth left intercostal room (ICS) through inching follow me the left sternal border. Climate ask the patient to revolve to the left lateral position. Examine the apical area while the patient is in reality turning, utilizing light push with the stethoscope bell. Other auscultatory areas that might be valuable in particular situations include the epigastrium and very first or 2nd left ICS. Auscultation should likewise be perform in the sitting position, especially in emphysematous patients, since the heart sounds may be far-off or even absent in the supine position. An altering the position of the patient might accentuate sounds by bringing the love closer to the chest wall or by accelerating blood flow as result of exertion. The affect of respiration on sounds heard roughly the first heart sound need to be noted. Likewise determine whether the very first sound is separation into the two contents (mitral and also tricuspid) and, if so, which ingredient is loudest.

There is normal asynchrony in the closure the mitral (M1) and also tricuspid (T1) valves, the mitral closure preceding tricuspid closure through 20 to 30 msec (0.02 come 0.03 sec.). This produces two audible components (M1-T1) referred to as common or physiologic splitting of the first heart sound. Such narrow dividing is usually finest heard at the lower left sternal border through the stethoscope diaphragm. The tricuspid component, i beg your pardon may boost with inspiration, is ideal heard in this location however is poorly transmitted come the apical region. The mitral component, in contrast, is ideal heard at the apex yet is intense sufficient to be heard transparent the precordium.

Auscultation of love sounds have to not it is in performed as an secluded event. The an initial and 2nd heart sound are referral points for understanding the nature of details pulsations. In order come correlate the physical findings and best know cardiac physiology and anatomy, outline on a schematic diagram the love sounds in addition to the jugular venous pulse, the carotid pulse, the precordial movements, and any murmurs and extra sounds heard, as displayed in figure 22.2. Careful study that this number will illustrate countless of the points of this section concerning timing, location, and intensity of normal heart sounds in relationship to the other cardiovascular physics findings.


Figure 22.2

The regular cardiac pulsations and heart sounds. The jugular venous pulsation normally has 3 hopeful waves—a, c, and v—and 2 an unfavorable troughs—x and y. The "a" tide is approximately synchronous through the first heart sound (S1) and also (more...)

Basic Science

Figure 22.3 gift in graphic type the occasions of the cardiac cycle. The genesis the the an initial heart sound is controversial. The recent use that echophonocardiographic and intracardiac methods supports the concept, originally proposed by Leatham, that S1 is composed of two major elements temporally related to mitral and also tricuspid closure. The actual contact of the valve cusps is not believed to it is in the resource of sound. Therefore, the heart sounds most likely represent vibrations of cardiac structures and also blood in ~ the heart. This vibrations are developed during the cardiac cycle by abrupt acceleration or deceleration the a fixed of blood within the ventricles linked with suddenly tensing that the whole atrioventricular (AV) valve apparatus (i.e., papillary muscles, chordae tendineae, valve leaflets, and also rings) that stretches the surrounding structures to your elastic limits. The more rapid this forces, the enlarge the sounds and also the greater the frequency.


Figure 22.3

Events of the cardiac cycle. The very first phase of ventricular systole, isovolumic contraction, begins with the abrupt climb in left ventricular pressure and also is associated with the mitral component (M1) that the very first heart sound. The succeeding rapid ventricular (more...)

At the onset of ventricular diastole, the mitral and also tricuspid valves open, and also their corresponding leaflets separate widely. Opening of these AV valves is usually silent. Throughout ventricular filling, the leaflets of each AV valve begin to close; with the start of atrial systole, the partly closed leaflets reopen. Once atrial systole ends, the ventricle recoils and the leaflets close. Following closure, the AV valves room stretched towards the atrium by the inert of the ventricular blood mass. Once the AV valves reach their best excursion, the blood volume is abruptly checked (decelerated). These events set into activity a stretch-recoil sequence. The subsequent vibrations the this cardiohemic system create discrete sound in the audible variety that room heard on the chest wall surface as the very first heart sound that is composed of the mitral closure sound (M1) and the tricuspid closure sound (T1).

The areas on the chest wall surface to which assorted acoustic occasions are preferentiallytransfer incorporate the 2nd right ICS, the second and third left ICS, the fourth and fifth left ICS, the epigastrium, and also the cardiac apex. Determinants responsible for this transmission incorporate the size and also position that the love in the thorax; the existence of fluid in, or fibrous thickening of, the pericardium; and the position and degree that aeration that the lungs.

Normal love sounds will certainly differ substantially in miscellaneous chest wall locations and patient positions. In the region of the apex, because that example, heart sounds room usually loud since the heart is in direct contact with the anterior wall of the thorax. In patients with thick chest walls or pulmonary emphysema, heart sounds might be poorly heard or inaudible. They space heard more plainly if the patience bends front or lies top top the left side and also is examined at the point of maximal expiration. In young persons with thin and also elastic chests, love sounds room heard with greater intensity 보다 in older topics whose chest walls space thicker and also stiffer. If one or both lungs space retracted by disease, love sounds end an area that the heart not spanned by the lung will certainly seem intensified. Therefore, prior to attributing abnormal heart sounds to an illness of the heart, to exclude, such factors as these. In addition, several various patient location (e.g., supine, left lateral, sitting, and, occasionally, prone) should be used during auscultation.

Cardiac auscultation is extremely daunting because the person auditory mechanism is no well suited because that the inexplicable vibratory characteristics of heart sounds and also murmurs. Mindful training, suitable use that a great stethoscope, and concentration top top selected parts of the cardiac cycle can assist improve auscultation. A an excellent stethoscope must have actually ear tips that fit snugly, a bending in the earpieces the aligns them appropriately with the ear canals, dual tubes 25 come 30 centimeter (10 come 12 in) in length and 3 mm (.125 in) in internal diameter, a trumpet bell, and also a diaphragm the attenuates low-frequency vibrations but does not change high-frequency vibrations. Because auscultation is substantially influenced by elevator noise, the check is finest carried the end in a quiet room.

Hearing the contents of the very first heart sound relies on the capacity of the ear to integrate the frequency and also intensity that the vibrations consisting of the sound. The ear have the right to detect 2 sounds be separated by an interval that as small as 0.02 second. A according to sound, however, may momentarily deafen the ear, with the an outcome that an almost simultaneous pass out sound might not be heard. For proper appreciation of the high-pitched components of the an initial sound, the diaphragm that the stethoscope need to be applied with enough pressure to leave a mark (after-ring) ~ above the chest when it is removed.

Clinical Significance

The very first sound have to be evaluated as to its quality, intensity, and degree that splitting. The normal very first heart sound is audible in each of the four standard listening areas, and also its intensity and also quality will commonly differ in each of these auscultatory areas. The an initial heart sound has actually a booming quality and also is lower-pitched, duller, and longer than the 2nd heart sound. That is usually louder in ~ the apex 보다 is the 2nd sound. In ~ the base, however, both components of the 2nd sound are typically louder than the very first sound (see thing 23, The 2nd Heart Sound). In ~ the reduced left sternal border, whereby the tricuspid closure sound (T1) is best heard, splitting of S1 is finest evaluated.

The intensity (amplitude or loudness) that the first heart sound is impacted by the position of the AV valve leaflets at end diastole (i.e., PQ interval of the electrocardiogram), and therefore your closing velocity, the pressure of ventricular contractility and the anatomical problem of the valves.

The soot of the very first sound is generally related come the place of the AV valves at the beginning of ventricular systole. The an initial sound is commonly louder in topics with a short PQ interval 보다 in those through a long PQ interval. The shorter the PQ interval, the more comprehensive is the separation the the AV valve cusps when ventricular systole begins and the later on is valve closure. This outcomes in a much more rapid valve-closing motion and also increased strongness of S1 Maximal strongness of S1 occurs v PQ intervals of 80 come 120 msec (0.08 to 0.12 sec.). Together the PQ interval progressively increases, there is a reduction in the intensity of S1. In ~ PQ intervals higher than 200 msec (0.20 sec.) (first-degree love block), there is much less separation the the AV valves, i m sorry have currently begun come close with atrial relaxation. Therefore, when ventricular systole begins, there is less excursion that the AV valves, and S1 occurs earlier. Due to the fact that less pressure is used to the AV valves, your closing velocity is reduced, bring about a softer S1. Although raised intensity of the an initial sound might be expected with shortening of the PQ interval, this walk not apply to the quick PQ interval of the Wolff–Parkinson–White syndrome, due to the fact that the beginning of ventricular contraction occurs later than is suggested by the beginning of the electrocardiographic "delta wave."

A loud an initial heart sound is a hallmark the hemodynamically far-ranging mitral stenosis. Mobile yet stiff mitral leaflets create a according to S1 uneven the leaflets are heavily calcified. The according to S1 is due mainly to higher excursion of the leaflets during closure, because elevated left atrial pressure has actually kept the leaflets relatively wide apart. In addition, stiff, noncompliant leaflets and chordae tendineae appear to resonate with boosted amplitude. A similar mechanism is responsible for the according to S1 in patients with left atrial myxoma.

Conditions that increase myocardial contractility, including hyperadrenergic claims (e.g., exercise, anxiety, anemia, fever, pregnancy, and also thyrotoxicosis), likewise tend come be associated with a according to S1. The prime element in increasing the strongness of S1 in these problems is the increased rate of pressure advancement in the ventricles. The first sound likewise tends to it is in louder in young people and in patients v thin chest walls.

Decreased soot of S1 occurs in problems that cause the AV valves to close before ventricular systole or if there is a palliation in the rate of intraventricular press development. First-degree love block is the most common reason of a soft S1. Holosystolic mitral regurgitation, ventricular septal defect, and acute aortic regurgitation likewise reduce the intensity of S1. In both holosystolic regurgitation and also ventricular septal defect, the intensity of S1 might be diminished or masked by the murmur itself, the isovolumic period may be absent, or the rate of rise of intraventricular pressure might be blunted. In acute serious aortic regurgitation, S1 is most typically diminished because preclosure the the mitral valve occurs together a result of the rapid increase in left ventricular filling pressure.

A to decrease in the intensity of S1 is additionally associated v myocardial depression (e.g., cardiomyopathy, myxedema, acute myocardial infarction, and also cardiogenic shock) since the rate of intraventricular pressure breakthrough is reduced. Pulmonary emphysema, because of the boosted amount the lung organization interposed in between the chest wall and the heart, additionally tends to attenuate S1.

Beat-to-beat sport in the strongness of S1 take place in conditions that differ the PQ interval (e.g., second-degree AV block, Wenckebach type), the visibility of AV dissociation (e.g., finish heart block and also junctional or ventricular tachycardia), or throughout variable prices of intraventricular pressure development (e.g., atrial fibrillation and also pulsus alternans). S1 strongness may likewise vary in electrical alternans.

Splitting of the very first heart sound right into its two audible components, M1 and also T1, is a normal finding top top cardiac auscultation. The M1–T1 term is normally separated by 20 to 30 msec. The fact that the very first heart sound is split may be useful in certain disease states. Because that instance, a loud tricuspid ingredient of the an initial heart sound may be heard in patients through Ebstein"s anomaly, right atrial myxoma, atrial septal defect, and also the straight-back syndrome. The mitral component of the very first heart sound is extremely loud and may it is in heard throughout the precordium in patients v mitral stenosis.

Wide dividing of the very first sound is virtually always abnormal. The break-up may be increased to 60 msec in patients with appropriate bundle branch block, Ebstein"s anomaly, or other problems in which there is electrical delay in activitation of one of the 2 ventricles (e.g., ventricular ectopic beats, ventricular tachycardia, AV block v idioventricular rhythm, and also left ventricular pacing). Splitting of the first sound is no characteristic the left bundle branch block because there is no significant hold-up in start of left ventricular contraction. Mechanically delays in closure of the mitral valve (e.g., mitral stenosis and left atrial myxoma) or the tricuspid valve (e.g., ideal atrial myxoma) may cause abnormal splitting of the first heart sound.

Sounds occurring roughly the time that S1 that need to be identified from a split very first sound encompass an atrial gallop or fourth heart sound (S4), one ejection sound (ES), and very early systolic click. The fourth heart sound, which forms the S4–S1 complex, is a low-pitched, late diastolic (presystolic) sound. The S4 might emanate from either the left or best ventricle. When left-sided, the much more common occurrence, that is confined to the cardiac apex whereby it is connected with palpable presystolic distention the the apex impulse. The is finest heard v the bell that the stethoscope inserted lightly end the apex, barely do an air seal, and is attenuated with increased pressure ~ above the bell (i.e., creation of a diaphragm). It is usually diminished in intensity v standing (i.e., lessened venous return).

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The ejection sound that forms the S1–ES complicated is a high-pitched, early on systolic sound. It may be heard in ~ the basic where dividing of S1 is not heard or in ~ the cardiac apex if it emanates native the aorta or aortic valve. There is no trustworthy maneuver the will distinguish these 2 acoustical events. The systolic click that mitral valve prolapse, in contrast, occurs later in systole 보다 the ejection sound, and varies in place in systole with certain maneuvers that adjust the form of the left ventricle.