Cardiovascular Board Review

A continuous cardiac murmur

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A 45-year-old woman presents with shortness of breath that has been progressively worsening for 3 weeks. She has no history of medical conditions and is taking no medications. Her blood pressure is 132/68 mm Hg, pulse 90 beats per minute, respirations 14 per minute, and oxygen saturation 95% on room air by pulse oximetry.

Physical examination reveals clear lung fields and no jugular venous distention or peripheral edema. However, she has a grade 3 of 6 continuous murmur audible over the entire precordium that does not change in intensity with respiration.

1. Which of the following is the likely cause of this patient’s cardiac murmur?

  • Ventricular septal defect
  • Atrial septal defect
  • Ruptured sinus of Valsalva aneurysm
  • Aortic regurgitation
  • Patent ductus arteriosus
  • Pulmonic stenosis

Table 1 summarizes the characteristics of the murmurs caused by these various cardiac defects.

Ventricular septal defect causes murmurs that are characteristically holosystolic and heard best at the lower left sternal border with radiation to the right lower sternal border, which overlies the defect.

The murmur of restrictive ventricular septal defect is most often holosystolic because the pressure difference between the ventricles is generated almost instantly at the onset of systole with a left-to-right shunt continuing throughout ventricular contraction. In contrast, nonrestrictive ventricular septal defects generally do not generate a murmur, since pressure is equalized across the defect. This left-to-right shunting may lead to right ventricular volume overload, resulting in delayed closure of the pulmonary valve and a widely split S2. Irreversible pulmonary hypertension with shunt reversal may occur if the defect remains untreated.1

Atrial septal defect. The most characteristic feature of atrial septal defect is a fixed split S2 resulting from right ventricular volume overload due to left-to-right atrial shunting of blood flow. As flow is shunted from the left to the right atrium and subsequently into the right ventricle, ejection of excess blood through the pulmonary valve produces a midsystolic flow murmur, heard best over the left upper sternal border, that may radiate to the back.

Ruptured sinus of Valsalva aneurysm. The pressure is higher in the aorta than in the right atrium throughout the cardiac cycle, and if a shunt is created between the two structures by a ruptured sinus of Valsalva aneurysm, the blood flow across this shunt throughout the cardiac cycle produces a continuous murmur. In contrast, if a sinus of Valsalva aneurysm ruptures into the right ventricle, the murmur is accentuated in diastole and attenuated in systole, and is often associated with pounding pulses and a thrill along either the left or right sternal border.1

Aortic regurgitation causes a diastolic murmur as blood flows retrograde into the left ventricle through the incompetent aortic valve. This murmur is usually described as a blowing, decrescendo murmur heard best at the third left intercostal space.

Patent ductus arteriosus is a communication between the descending thoracic aorta and the pulmonary artery that fails to close at birth. The hallmark murmur associated with this defect is a continuous “machine-like” murmur located at the upper left sternal border, often radiating down the left side of the sternum into the back. Of note, increasing the systemic pressure by the Valsalva maneuver or handgrip exercise will increase the diastolic component of the continuous murmur associated with ruptured sinus of Valsalva aneurysm, helping to differentiate it from patent ductus arteriosus.2

Pulmonic stenosis causes a systolic murmur heard best at the second intercostal space along the left sternal border and having a crescendo-decrescendo intensity and harsh quality. As the right ventricle takes longer to eject its blood volume through the stenotic pulmonary valve, the delay in closure between the aortic and pulmonary valve is widened, resulting in a significant splitting of the S2. In addition, any maneuver that increases preload will also increase the intensity of the murmur.3

Our patient has a murmur that is continuous, is heard across the entire precordium, and has no respiratory variation. These features are most consistent with a sinus of Valsalva aneurysm that has ruptured into the right atrium.

The 2008 update of the joint American College of Cardiology and American Heart Association guidelines4 recommends further evaluation of diastolic or continuous murmurs with echocardiography, as these murmurs are most often signs of a pathologic condition. In addition, echocardiography is warranted to evaluate grade 3 or higher systolic murmurs and those that are holosystolic.4

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