The Initial Vibrations of the First Heart Sound

Observations on the mechanism of atrial gallop rhythm

An atrial gallop sound is a frequent finding in hypertensive cardiovascular disease, myocardial infarction, and in the presence of a prolonged atrioventricular conduction time. In view of evidence relating this sound to a ventricular pressure wave resulting from atrial contraction, modification of this hemodynamic event was studied by means of tourniquet pooling of blood in the extremities. In the 18 patients studied, this maneuver caused striking changes in the intensity and timing of the atrial gallop. Analysis of these changes helps explain the frequent appearance of this triple rhythm in severe hypertensive cardiovascular disease.

Echophonocardiographic study of the initial low frequency component of the first heart sound

To investigate the genesis of the initial low frequency component of the first heart sound that precedes the high frequency vibrations associated with closure of the atrioventricular valves, echophonocardiograms of 36 persons were recorded. These included 10 normal subjects and 26 patients with various types of heart disease including mitral valve replacement. Electrocardiograms demonstrated normal sinus rhythm in 23 subjects, atrial fibrillation in 9, complete atrioventricular block in 2 and atrial flutter in 2. In the phonocardiogram, the low frequency component of the first heart sound followed the onset of the QRS complex and preceded the first high frequency component of this sound. The low frequency component occurred simultaneously with the beginning of the final fast closing movement of the mitral valve on the echocardiogram and was found both in normal rhythm and in arrhythmias. However, in arrhythmias its intensity varied on a beat to beat basis, being loudest after a short RR interval or when atrial systole occurred very close to the expected time of ventricular systole. In patients in whom apexcardiograms were recorded, the low frequency component was coincident with or very close to the onset of ventricular systole. It is concluded that the low frequency component of the first heart sound represents vibrations caused by contraction of the left ventricle and deceleration of antegrade blood flow across the mitral valve. Neither atrial contraction nor mitral valve tension is necessary for the production of this soft initial component.

"Presystolic" augmentation of diastolic heart sounds in atrial fibrillation

In the presence of atrial fibrillation, the diastolic murmur of mitral stenosis can appear augmented during early systole before the mitral valve closure sound. This phenomenon has previously been thought to be due to increased blood flow velocity across the narrowing mitral valve orifice. We have observed patients in whom the third heart sound (S3) gallop, the diastolic flow murmur of atrial septal defect and mitral insufficiency and the initial muscular component of the first heart sound become more intense during this period with short, critically timed cycle lengths. This phenomenon appears to be neither peculiar to nor indicative of mitral stenosis and is probably a direct result of the initial muscular contraction of an underfilled ventricle. Either the contraction itself or the sudden deceleration of the rapidly moving flow of blood across the atrioventricular orifice may produce the sound.

Mitral components of the first heart sound

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Kinetocardiogram, phonocardiogram, and arterial pulse waves during acute hemodynamic changes

The effects of drugs that produce known hemodynamic alterations were assessed on externally recorded pulse waves, heart sounds, and the relationship of these to each other and to the electrocardiogram.

The shape of the carotid pulse and the carotid-femoral pulse-wave transmission time difference showed changes that could be related to alterations in central arterial distensibility. The ratio of the second to the first positive inflection, and of the incisura to the first positive inflection of the carotid pulse wave, increased following use of drugs which raised mean arterial pressure and decreased after those which lowered blood pressure. The carotid-femoral transmission time difference decreased with vasopressor agents, increased with amyl nitrite and hexamethonium, and showed no consistent change after isoproterenol.

Left ventricular ejection time, measured from the carotid pulse, changed in relation to heart rate, increasing with cardiac slowing and decreasing when the rate accelerated. The ejection time index remained unchanged except for a slight increase following amyl nitrite and a decrease after hexamethonium.

Alterations in isovolumic contraction time approximately paralleled changes in diastolic pressure. The ratio of diastolic pressure to isovolumic contraction time provides an index of the rate of rise of left ventricular pressure. The quotient of diastolic pressure divided by isovolumic contraction time increased with adrenergic stimulation (isoproterenol) and decreased after ganglion blockade. It was not significantly changed by angiotensin II, methoxamine, or amyl nitrite.

The interval between the onset of QRS and the beginning of the first heart sound (Q-S 1 ), shortened considerably after isoproterenol and moderately following amyl nitrite. It increased after hexamethonium and remained essentially unchanged following angiotensin II or methoxamine. These results suggest that the Q-S 1 interval may reflect ventricular contractility in the absence of mitral valvular disease.

The amplitude of the first heart sound appeared to be a sensitive indicator of ventricular contractility increasing with isoproterenol and amyl nitrite, decreasing with hexamethonium and remaining unchanged following use of angiotensin II or methoxamine.

Relationship of heart sounds to acceleration of blood flow

A concept has been presented that abrupt acceleration or deceleration of blood flow is associated with an energy source sufficient to displace the mass of the heart, and that, consequently, this mass will oscillate at a sum of frequencies that are a function of chamber mass and restoring forces. Induced pressure transients may be observed in all chambers, the lower frequencies appearing on conventional pressure tracings, the higher frequencies as intracardiac sound.

Using high frequency response instrumentation in dogs, intravascular sound has been compared with pressure and flow events throughout the cardiac cycle.

(1) The first component of the first heart sound occurs during early isometric ventricular contraction and is associated with lower frequency pressure transients that may berecorded from all chambers of the heart. The left atrial "c-wave" is one of these transients.

(2) The second component of the first heart sound occurs during ventricular ejection, and appears to be a function of acceleration of aortic blood flow.

(3) The second heart sound begins significantly before aortic valve closure, while forward flow is still going on, and is proportional to the magnitude of deceleration of blood flow.

(4) The third heart sound appears only in the presence of left ventricular failure at the time of rapid ventricular filling, and is associated with a low frequency wave recordable from the central aorta. The production of these transients is presumed to be deceleration of inflow as the limits of ventricular relaxation are reached.

(5) A fourth sound arises coincident with pressure transients in other chambers as atrial systole further distends the left ventricle.

It is proposed that acceleration and deceleration of blood flow is a sufficient and necessary condition for the origin of cardiovascular sound transients.

The Normal Apex Cardiogram

The configuration of the apex cardiogram and its temporal relationship to the electrocardiogram, phonocardiogram, carotid pulse, and jugular venous pulse were analyzed in 25 normal subjects. In two patients with rheumatic valvular disease simultaneous electrocardiograms, phonocardiograms, left intraventricular pressure and apex cardiograms were obtained. In all cases the apex cardiogram showed a characteristic and reproducible contour in both its systolic and diastolic components. The curves of the apex cardiogram display all consecutive phases of the cardiac cyle; contraction-and-emptying and relaxation-and-filling. It bears a constant relationship to the phonocardiogram and is more useful as a reference tracing for acoustic events than the electrocardiogram, carotid pulse, or jugular venous pulse. The onset of the systolic wave of the apex cardiogram precedes the rise of left intraventricular pressure and mitral valve closure. The maximal systolic peak of the apex cardiogram occurs simultaneously with the onset of left ventricular ejection and the rise of the carotid pulse pressure. Small deflections are frequently inscribed on the apex cardiogram at the time of mitral, tricuspid, and aortic valve closure.

The wave form of the apex cardiogram is caused primarily by movements of the left ventricle against the chest wall. It is thus a translation of the sequence of hemodynamic events occurring in the underlying left ventricle. The inaccuracy of the jugular venous pulse for timing right- and left-sided cardiac events is emphasized.

The Tricuspid Component of the First Heart Sound in Mitral Stenosis

The sound of tricuspid valve closure has been identified in 35 of 40 phonocardiograms of patients with mitral valve disease. Identification of the sound is facilitated by the delay of closure of the mitral valve thus separating these 2 components of the first heart sound. When the ventricular rhythm is irregular due to atrial fibrillation, the intensity of the sound is inversely proportional to the length of the preceding diastolic interval. When the sound of tricuspid closure is accentuated, it may be identified by auscultation as the initial component of a split first sound mesial to the apex. Measurement of the interval from the onset of the QRS complex of the electrocardiogram to the "first heart sound" should be made to the mitral component of the first sound when this can he identified on the phonocardiogram.

Relation of the first and second heart sounds to events in the cardiac cycle

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The Effect of Cycle Length on the Time of Occurrence of the First Heart Sound and the Opening Snap in Mitral Stenosis

Phonocardiography is often more valuable than electrocardiography in timing mechanical events in the cardiac cycle. This study shows that the opening and closing of the mitral valve are related to the length of the previous heart cycle as demonstrated by the variations occuring in auricular fibrillation. These variations in valve action are controlled by the pressure gradient between left auricle and ventricle.