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.
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 S
3 and are summarized in
Table 53-2.
Conditions that result in ventricular hypertrophy produce an S
4 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).
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.