Cardiac murmurs should be evaluated as to intensity (grades 1 to 6), timing (systolic or diastolic), location, transmission, and quality (musical, vibratory, or blowing):
- Grade 1: barely audible
- Grade 2: soft but easily audible
- Grade 3: moderately loud; no thrill
- Grade 4: loud; thrill present
- Grade 5: loud; audible with stethoscope barely on chest
- Grade 6: loud; audible with stethoscope not touching the chest
The murmur grade is recorded as 1/6, and so on. The next step in evaluating a murmur is its classification in relation to S1and S2. The three types of murmurs are systolic, diastolic, and continuous. An infant with no murmur may still have significant cardiac disease.
Most heart murmurs are systolic, occurring between S1 and S2. Systolic murmurs are either ejection or regurgitation murmurs. They are a normal finding during the routine physical exam of a healthy infant. Studies have shown that as many as 90% of healthy children have a benign murmur at some time.
The blood flow causes ejection murmurs through stenotic or deformed valves or increased flow through normal valves. Regurgitant systolic murmurs begin with S1, with no interval between S1 and the beginning of the murmur. Regurgitation murmurs generally continue throughout systole. Regurgitation systolic murmurs are caused by blood flow from a chamber at a higher pressure throughout the systole than in the receiving chamber. Regurgitation systolic murmurs are associated with only three conditions:
- ventricular septal defects (VSDs)
- mitral regurgitation
- tricuspid regurgitation
Diastolic murmurs are classified according to their timing in relation to heart sounds as early diastolic, mid-diastolic, or pre-systolic. They are usually pathologic. They result from aortic regurgitation and pulmonary insufficiency. With aortic regurgitation, the murmur is high-pitched and blowing. It begins with the second heart sound and is loudest in early diastole. It may be missed because it is often very soft or may be mistaken for breath sounds because of its high pitch. Bounding pulses are present.
The murmur of pulmonary insufficiency is a distinctive diastolic murmur. It is low-pitched, early in onset, and of short duration. It ends well before the first heart sound. It occurs with postoperative TOF, pulmonary hypertension, postoperative pulmonary valvotomy for pulmonary stenosis, or other deformities of the pulmonary valve.
Mid-diastolic murmur results from abnormal ventricular filling. Due to stenosis, the murmur results from turbulent flow through the tricuspid or mitral valve. They are associated with mitral stenosis or large left-to-right shunt VSD or PDA, producing relative mitral stenosis secondary to increased flow across the normal-sized mitral valve. It is seen in the atrial septal defect (ASD), total or partial anomalous pulmonary venous return (TAPVR, PAPVR), endocardial cushion defects, or abnormal stenosis of the tricuspid valve.
Most continuous murmurs are not audible throughout the cardiac cycle. They begin in systole and extend into diastole. They are a pathologic finding. They can be produced in rapid blood flow, high-to-low pressure shunting, and localized arterial obstruction.
The most significant is the PDA high-to-low shunting. The patency of the ductus is normal in the first 24 hours of life, but a few weeks later, a patent ductus is abnormal. It is more common in girls (sex ratio of 3:2), tends to affect siblings, and may be a complication of maternal rubella. It is six times more common in infants born at high altitudes and more common in premature infants. There may be a vigorous pericardial activity, a systolic thrill, and bounding pulses if the ductus is large. There may be symptoms of congestive heart failure (CHF).