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You are watching: The first of two heart sounds (lubb) occurs when the

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



Heart sounds are discrete explode of auditory vibrations of varying intensity (loudness), frequency (pitch), quality, and duration. The very first heart sound (S1) is written of number of high-frequency components; just the very first two are typically audible. These 2 sets of audible vibrations space temporally related to closure that the mitral and tricuspid valves. The very first heart sound coincides with contraction of the ventricles, thus identifying the onset of ventricular systole and also the end of mechanically diastole.


The examination need to be performed in a warm, quiet room. Location the patience in a supine place after all clothes has been removed from the chest. Describe to the patient that you space going to examine the heart. Warm your hands and also stethoscope, however warn the patient the your hands might be cool in ~ first. The many comfortable and also satisfactory place for most assessors is ~ above the patient\"s right side. Since heart sounds may be palpable, attempt to palpate the an initial sound v the hoe of the appropriate hand and/or the fingerpads, at first at the cardiac apex and also then end the whole precordium.

The acoustic events should it is in analyzed only after having actually assessed the venous, arterial, and also chest wall pulsations. The auscultatory check is commonly started at the aortic area (second best intercostal space) and the stethoscope inched come the pulmonary area (second left intercostal space), the tricuspid area (lower left sternal border), and mitral area (cardiac apex), as shown in number 22.1. Monitor an the same routine because that every examination, passing indigenous one part to another in a details order.


Figure 22.1

Routine locations for auscultation that the precordium.

Force yourself right into the habit that listening because that one sound at a time, using an excellent care come time the love sounds exactly. Listen with the stethoscope diaphragm, pressed steady on the chest, to finest hear the high-frequency vibrations that the very first heart sound. Concentration for several cycles ~ above the quality and also intensity of the an initial heart sound, dismissing everything else from your mind till the sound is plainly identified and also appraised. The an initial sound is typically lower in pitch than the 2nd sound.

The quality of the very first heart sound (S1) and also its time partnership with the second heart sound (S2) do it feasible for the competent observer to identify a identify rhythm and also thus conveniently distinguish in between S1 and S2. At normal and also slow heart rates, S1 is the first of the paired heart sounds, adhering to the longer diastolic duration and coming before the shorter systolic period. This sounds deserve to be separated by all at once feeling or looking in ~ the apex impulse while listening; the very first heart sound is synchronous through the external thrust of the apex impulse. With experience, that is possible to watch the movement of the stethoscope top top the chest while listening come the heart sounds in order to time systole and also diastole. When the apex impulse cannot be viewed or felt, the pulsation that the carotid artery can be provided as a guide. A finger top top the carotid artery will sense the palpable arterial upstroke that instantly follows the first heart sound. With quick heart rates, however, the slight hold-up between the very first sound and carotid pulsation might make this practice unsatisfactory. Usage of a more distant artery because that this purpose leads come error since of the moment it bring away the pulse wave to with the periphery.

For precise identification the the very first heart sound when multiple sounds are audible, relocate the stethoscope slowly from the second right to the fourth left intercostal room (ICS) through inching along the left sternal border. Climate ask the patient to revolve to the left lateral position. Study the apical area while the patience is in reality turning, making use of light push with the stethoscope bell. Various other auscultatory locations that may be beneficial in certain situations encompass the epigastrium and very first or second left ICS. Auscultation should also be performed in the sit position, particularly in emphysematous patients, because the love sounds may be distant or even absent in the supine position. An altering the place of the patient might accentuate sound by happen the love closer come the chest wall or by accelerating blood flow due to exertion. The influence of respiration on sound heard about the very first heart sound need to be noted. Also determine even if it is the very first sound is break-up into that two contents (mitral and tricuspid) and, if so, which ingredient is loudest.

There is common asynchrony in the closure the mitral (M1) and tricuspid (T1) valves, the mitral closure preceding tricuspid closure by 20 to 30 msec (0.02 come 0.03 sec.). This produces 2 audible materials (M1-T1) referred to as normal or physiologic splitting of the an initial heart sound. Together narrow separating is usually best heard at the lower left sternal border v the stethoscope diaphragm. The tricuspid component, which may rise with inspiration, is finest heard in this location yet is poorlytransfer to the apical region. The mitral component, in contrast, is finest heard at the apex yet is intense sufficient to it is in heard transparent the precordium.

Auscultation of love sounds have to not it is in performed as an diverted event. The first and second heart sounds are recommendation points for knowledge the nature of particular pulsations. In order come correlate the physical findings and also best understand cardiac physiology and anatomy, summary on a schematic chart the heart sounds together with the jugular venous pulse, the carotid pulse, the precordial movements, and also any murmurs and also extra sound heard, as presented in number 22.2. Careful study that this figure will illustrate plenty of of the point out of this section concerning timing, location, and intensity of typical heart sounds in relation to the various other cardiovascular physical findings.


Figure 22.2

The common cardiac pulsations and heart sounds. The jugular venous pulsation typically has 3 optimistic waves—a, c, and v—and 2 an unfavorable troughs—x and y. The \"a\" wave is approximately synchronous with the very first heart sound (S1) and (more...)

Basic Science

Figure 22.3 presents in graphic type the occasions of the cardiac cycle. The genesis of the very first heart sound is controversial. The recent use that echophonocardiographic and also intracardiac methods supports the concept, initially proposed by Leatham, the S1 is composed of two major elements temporally related to mitral and tricuspid closure. The actual contact of the valve cusps is not thought to be the resource of sound. Therefore, the love sounds most likely represent vibrations that cardiac structures and also blood in ~ the heart. These vibrations are developed during the cardiac bicycle by abrupt acceleration or deceleration that a massive of blood in ~ the ventricles linked with sudden tensing of the entire atrioventricular (AV) valve device (i.e., papillary muscles, chordae tendineae, valve leaflets, and rings) the stretches the neighboring structures to your elastic limits. The much more rapid these forces, the louder the sounds and also the higher the frequency.


Figure 22.3

Events that the cardiac cycle. The first phase of ventricular systole, isovolumic contraction, starts with the abrupt rise in left ventricular pressure and also is associated with the mitral component (M1) of the an initial heart sound. The succeeding fast ventricular (more...)

At the onset of ventricular diastole, the mitral and tricuspid valves open, and also their corresponding leaflets different widely. Opening of this AV valves is generally silent. Throughout ventricular filling, the leaflets of every AV valve begin to close; with the beginning of atrial systole, the partially closed leaflets reopen. When atrial systole ends, the ventricle recoils and the leaflets close. Complying with closure, the AV valves room stretched towards the atrium by the inert of the ventricular blood mass. As soon as the AV valves with their best excursion, the blood volume is abruptly checked (decelerated). This events set into movement a stretch-recoil sequence. The succeeding vibrations of this cardiohemic system create discrete sound in the audible selection that room heard top top the chest wall surface as the first heart sound that is created of the mitral closure sound (M1) and the tricuspid closure sound (T1).

The locations on the chest wall to which miscellaneous acoustic occasions are preferentially transmitted encompass the second right ICS, the 2nd and third left ICS, the fourth and also fifth left ICS, the epigastrium, and also the cardiac apex. Factors responsible because that this transmission include the size and position of the love in the thorax; the presence of fluid in, or fibrous thickening of, the pericardium; and the position and also degree of aeration of the lungs.

Normal love sounds will differ considerably in miscellaneous chest wall surface locations and patient positions. In the region of the apex, for example, heart sounds room usually loud since the heart is in direct call with the anterior wall surface of the thorax. In patients with thick chest wall surfaces or pulmonary emphysema, love sounds might be poorly heard or inaudible. They room heard more plainly if the patience bends front or lies ~ above the left side and is check at the point of maximal expiration. In young persons with thin and also elastic chests, heart sounds are heard with higher intensity than in older subjects whose chest walls room thicker and also stiffer. If one or both lungs are retracted by disease, heart sounds over an area the the heart not extended by the lung will certainly seem intensified. Therefore, before attributing abnormal love sounds to an illness of the heart, to exclude, such determinants as these. In addition, several various patient positions (e.g., supine, left lateral, sitting, and, occasionally, prone) must be used during auscultation.

Cardiac auscultation is extremely daunting because the human auditory mechanism is no well suited for the unusual vibratory attributes of love sounds and also murmurs. Mindful training, suitable use of a an excellent stethoscope, and also concentration top top selected sections of the cardiac bicycle can help improve auscultation. A an excellent stethoscope must have ear tips the fit snugly, a bending in the earpieces that aligns them correctly with the ear canals, twin tubes 25 to 30 cm (10 come 12 in) in length and also 3 mm (.125 in) in inner diameter, a trumpet bell, and a diaphragm the attenuates low-frequency vibrations but does not transform high-frequency vibrations. Because auscultation is substantially influenced by background noise, the check is best carried the end in a quiet room.

Hearing the components of the very first heart sound counts on the ability of the ear to incorporate the frequency and intensity the the vibrations comprising the sound. The ear can detect two sounds be separate by an interval the as small as 0.02 second. A according to sound, however, might momentarily deafen the ear, v the result that an nearly simultaneous pass out sound might not it is in heard. For suitable appreciation of the high-pitched materials of the first sound, the diaphragm of the stethoscope need to be applied with sufficient pressure to leaving a mark (after-ring) ~ above the chest once it is removed.

Clinical Significance

The first sound need to be evaluated as to its quality, intensity, and degree that splitting. The normal first heart sound is audible in every of the four standard listening areas, and its intensity and also quality will typically differ in every of this auscultatory areas. The an initial heart sound has actually a booming quality and is lower-pitched, duller, and longer than the 2nd heart sound. The is typically louder at the apex than is the 2nd sound. At the base, however, both materials of the 2nd sound are generally louder than the an initial sound (see thing 23, The second Heart Sound). At the reduced left sternal border, where the tricuspid closure sound (T1) is ideal heard, splitting of S1 is finest evaluated.

The intensity (amplitude or loudness) that the an initial heart sound is affected by the place of the AV valve leaflets at end diastole (i.e., PQ expression of the electrocardiogram), and also therefore your closing velocity, the pressure of ventricular contractility and also the anatomical problem of the valves.

The soot of the an initial sound is mainly related to the place of the AV valves in ~ the onset of ventricular systole. The an initial sound is normally louder in topics with a short PQ interval than in those with a lengthy PQ interval. The much shorter the PQ interval, the wider is the separation the the AV valve cusps as soon as ventricular systole begins and also the later is valve closure. This results in a an ext rapid valve-closing motion and increased strongness of S1 Maximal intensity of S1 occurs through PQ intervals the 80 come 120 msec (0.08 come 0.12 sec.). As the PQ interval increasingly increases, over there is a palliation in the intensity of S1. In ~ PQ intervals greater than 200 msec (0.20 sec.) (first-degree love block), there is much less separation of the AV valves, which have already begun come close through atrial relaxation. Therefore, as soon as ventricular systole begins, over there is less excursion of the AV valves, and also S1 wake up earlier. Due to the fact that less force is used to the AV valves, your closing velocity is reduced, leading to a softer S1. Although raised intensity the the first sound might be meant with shortening the the PQ interval, this walk not use to the short PQ interval of the Wolff–Parkinson–White syndrome, due to the fact that the start of ventricular contraction occurs later on than is shown by the beginning of the electrocardiographic \"delta wave.\"

A loud an initial heart sound is a hallmark of hemodynamically far-reaching mitral stenosis. Mobile however stiff mitral leaflets create a according to S1 uneven the leaflets are heavily calcified. The according to S1 is due mainly to greater excursion that the leaflets during closure, since elevated left atrial pressure has actually kept the leaflets fairly wide apart. In addition, stiff, noncompliant leaflets and also chordae tendineae show up to resonate with boosted amplitude. A comparable mechanism is responsible because that the loud S1 in patients through left atrial myxoma.

Conditions that rise myocardial contractility, consisting of hyperadrenergic says (e.g., exercise, anxiety, anemia, fever, pregnancy, and also thyrotoxicosis), additionally tend come be linked with a loud S1. The prime factor in enhancing the intensity of S1 in these conditions is the boosted rate that pressure advance in the ventricles. The very first sound additionally tends to it is in louder in young people and also in patients v thin chest walls.

Decreased soot of S1 wake up in conditions that reason the AV valves come close prior to ventricular systole or if there is a reduction in the rate of intraventricular press development. First-degree love block is the most common cause of a soft S1. Holosystolic mitral regurgitation, ventricular septal defect, and also acute aortic regurgitation likewise reduce the strongness of S1. In both holosystolic regurgitation and ventricular septal defect, the soot of S1 might be decreased or masked by the murmur itself, the isovolumic duration may it is in absent, or the price of climb of intraventricular pressure may be blunted. In acute major aortic regurgitation, S1 is most commonly diminished since preclosure the the mitral valve occurs together a result of the rapid increase in left ventricular filling pressure.

A decrease in the strongness of S1 is additionally associated with myocardial depression (e.g., cardiomyopathy, myxedema, acute myocardial infarction, and cardiogenic shock) due to the fact that the rate of intraventricular pressure development is reduced. Pulmonary emphysema, due to the fact that of the raised amount of lung tissue interposed between the chest wall and the heart, also tends come attenuate S1.

Beat-to-beat sports in the strongness of S1 take place in conditions that differ the PQ term (e.g., second-degree AV block, Wenckebach type), the presence of AV dissociation (e.g., complete heart block and also junctional or ventricular tachycardia), or during variable prices of intraventricular pressure advancement (e.g., atrial fibrillation and pulsus alternans). S1 soot may likewise vary in electric alternans.

Splitting of the an initial heart sound right into its 2 audible components, M1 and T1, is a normal finding ~ above cardiac auscultation. The M1–T1 interval is generally separated through 20 to 30 msec. The truth that the an initial heart sound is split may be useful in certain condition states. Because that instance, a loud tricuspid ingredient of the an initial heart sound might be heard in patients with Ebstein\"s anomaly, ideal atrial myxoma, atrial septal defect, and also the straight-back syndrome. The mitral ingredient of the very first heart sound is incredibly loud and may be heard transparent the precordium in patients through mitral stenosis.

Wide separating of the very first sound is practically always abnormal. The separation may be increased to 60 msec in patients with best bundle branch block, Ebstein\"s anomaly, or other problems in which over there is electrical delay in activitation of among the 2 ventricles (e.g., ventricular ectopic beats, ventricular tachycardia, AV block with idioventricular rhythm, and left ventricular pacing). Dividing of the an initial sound is no characteristic the left bundle branch block due to the fact that there is no significant delay in beginning of left ventricular contraction. Mechanical delays in closure the the mitral valve (e.g., mitral stenosis and left atrial myxoma) or the tricuspid valve (e.g., best atrial myxoma) may cause abnormal splitting of the first heart sound.

Sounds occurring roughly the time the S1 that should be identified from a split an initial sound incorporate an atrial gallop or 4th heart sound (S4), an ejection sound (ES), and very early systolic click. The fourth heart sound, which creates the S4–S1 complex, is a low-pitched, late diastolic (presystolic) sound. The S4 might emanate from one of two people the left or right ventricle. As soon as left-sided, the much much more common occurrence, the is confined come the cardiac apex wherein it is linked with palpable presystolic distention that the apex impulse. The is finest heard with the bell the the stethoscope placed lightly end the apex, barely make an wait seal, and also is attenuated with raised pressure top top the bell (i.e., creation of a diaphragm). The is usually decreased in intensity through standing (i.e., decreased venous return).

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The ejection sound that develops the S1–ES complicated is a high-pitched, early systolic sound. It might be heard at the base where dividing of S1 is no heard or in ~ the cardiac apex if the emanates native the aorta or aortic valve. Over there is no reputable maneuver the will identify these 2 acoustical events. The systolic click that mitral valve prolapse, in contrast, occurs later in systole than the ejection sound, and also varies in location in systole with details maneuvers that readjust the form of the left ventricle.