Murmurs

Jack Rychik

INTRODUCTION

A murmur is an auditory vibration produced by turbulent flow within the cardiac structures. A murmur may be physiologic (i.e., a normal finding) or pathologic.

Heart Sounds

Variations in the normal heart sounds, as well as adventitious heart sounds, may be associated with murmurs and are essential clues to diagnostic interpretation of the murmur.

First Heart Sound (S₁)

The S₁ is produced by closure of the mitral and tricuspid valves, in that order. The mitral component and tricuspid component are best heard at the apex and the lower sternal border region, respectively.

The intensity of the S₁ is accentuated in conditions characterized by increased cardiac output and a short PR interval because in these circumstances maximal excursion of the leaflets occurs during closure.
Wide splitting of the S₁ with a delayed tricuspid component may be noted in patients with tricuspid stenosis, Ebstein anomaly, right bundle branch block, or when there is pacing of the left ventricle.

Second Heart Sound (S₂)

The S₂ is produced by closure of the aortic valve (A₂) immediately followed by closure of the pulmonic valve (P₂) and is best heard at the base of the heart. The P₂ is normally softer than the A₂ and is less widely transmitted. Splitting of the S₂ is normally appreciated during quiet respiration. Inspiration results in two physiologic phenomena: an increased capacitance of the lung vasculature, with a greater period of systole for the right ventricle relative to the left ventricle, and increased venous return to the right-sided structures. Both of these phenomena result in delayed closure of the pulmonic valve.

In mild forms of aortic or pulmonic stenosis, the A₂ or the P₂ may be soft.
The S₂ is single and loud in the following circumstances: when there is fusion of the two components, such as in severe pulmonary hypertension; when there is only one semilunar valve, such as in atresia of either the aortic or the pulmonic valves or truncus arteriosus; and when the P₂ is inaudible because of an anteriorly positioned aorta, such as in tetralogy of Fallot or transposition of the great arteries.
Abnormally wide splitting of the S₂ is noted in the conditions listed in Table 53-1.

TABLE 53-1 Common Causes of Abnormally Wide Splitting of the Second Heart Sound (S₂)

Atrial septal defect

Mild pulmonic stenosis

Complete right bundle branch block

Left ventricular paced beats

Massive pulmonary embolus

Third Heart Sound (S₃) and Fourth Heart Sound (S₄) Heart sounds are occasionally heard during ventricular diastole. Early rapid filling of the ventricle, which follows the opening of the atrioventricular valve, may produce the third heart sound (S₃); ventricular filling related to the forceful expulsion of blood from the atrium into the ventricle with atrial contraction may produce the fourth heart sound (S₄). These sounds are best heard at the apex with the bell of the stethoscope. An audible S₃ may be normal in infants and young children, whereas an audible S₄ is distinctly abnormal.

Conditions that cause ventricular volume overload produce an abnormally prominent S₃ and are summarized in Table 53-2.
Conditions that result in ventricular hypertrophy produce an S₄ and are summarized in Table 53-3.

Characteristics of a Murmur

Phase. Murmurs are described as being systolic (occurring during systole following S₁, corresponding with ventricular contraction), diastolic (occurring during diastole following S₂, corresponding with ventricular relaxation), or continuous (occurring throughout the cardiac cycle).
Length and timing. Murmurs are described as having a short, medium, or long duration and occurring in the early, mid-, or late part of the cardiac cycle. The terms “holosystolic” and “pansystolic” refer to a murmur that begins with S₁ and ends with S₂.
Peak intensity (grade) is summarized in Table 53-4.
Variation in intensity. The term “crescendo” implies that the murmur starts low and builds to a peak; “decrescendo” implies that the murmur starts at its greatest intensity and subsequently diminishes. The term “crescendodecrescendo” is used to describe a murmur that starts low, builds to a peak, and then diminishes over the course of the murmur (i.e., a “diamond-shaped” murmur).
Location and radiation. The location of the murmur is described in relation to a chest wall landmark such as the sternum or intercostal spaces (e.g., the left upper sternal border of second intercostal space). The direction of projection (i.e., the radiation) is also noted (e.g., originating at the apex of the heart and radiating toward the left axilla).

TABLE 53-2 Conditions Causing a Prominent Third Heart Sound (S₃)

Physiologic (infants and children)

Congestive heart failure

Ventricular septal defect, with large pulmonary to systemic flow (Qp-to-Qs) ratio

Mitral insufficiency

Tricuspid insufficiency

Hyperdynamic ventricle with high output (e.g., anemia, thyrotoxicosis, arteriovenous fistula)

TABLE 53-3 Conditions Causing a Prominent Fourth Heart Sound (S₄)

Left ventricular outflow tract obstruction (e.g., aortic stenosis)

Right ventricular outflow tract obstruction (e.g., pulmonic stenosis)

Hypertrophic cardiomyopathy

Heart block (atrium contracting against a closed valve)

Physical Maneuvers

The following maneuvers can alter the characteristics of a murmur:

Supine position. Having the patient lie supine increases venous return to the heart and augments murmurs that are volume dependent (e.g., those associated with aortic stenosis or pulmonic stenosis; functional murmurs). Pericardial rubs are diminished when the patient is supine because the visceral and parietal membranes move away from each other when the heart shifts posteriorly in the chest.
Valsalva maneuver. Forced exhalation against a closed glottis or straining with the mouth and nose closed increases the intrathoracic pressure and reduces venous return to the heart. During the Valsalva maneuver, the two components of S₂ become single, and volume-dependent murmurs are attenuated.

TABLE 53-4 Grading of Murmurs

Grade	Description
I	Very soft, no thrill
II	Easily audible, of moderate intensity, no thrill
III	Prominent intensity but no thrill
IV	Loud murmur accompanied by a thrill
V	Very loud murmur accompanied by a thrill; heard with the stethoscope partially off the chest wall
VI	Very loud murmur accompanied by a thrill; heard with the stethoscope completely off the chest wall

DIFFERENTIAL DIAGNOSIS LIST

Functional or Innocent Murmurs

Still murmur
Cervical venous hum
Peripheral pulmonic stenosis

Physiologic Murmurs

High cardiac output states
Arteriovenous fistula

Pathologic Murmurs

Ventricular septal defect (VSD)—nonrestrictive and restrictive
Atrial septal defect (ASD)
Patent ductus arteriosus (PDA)
Pulmonic stenosis
Aortic stenosis
Coarctation of the aorta

DIFFERENTIAL DIAGNOSIS DISCUSSION

Still Murmur (Innocent “Flow” Murmur)

Etiology

This sound, described in the early 20th century by Dr. George Frederick Still of Great Ormond Street Children’s Hospital, London, is one of the most common findings in the physical examination of a normal child. It is heard in children between 2 years of age and early adolescence and may even persist into adulthood. Although its cause is uncertain, some evidence points to turbulent flow across the left ventricular outflow tract as the source.

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