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Difficulty: HardPhysical Examination Findings

A 24-year-old male presents to the clinic to establish primary care. He is generally healthy but reports a single episode of lightheadedness that occurred while sprinting during a soccer match two weeks ago. He has no significant past medical history and takes no medications. Vital signs show a temperature of 37.0°C (98.6°F), blood pressure of 114/68 mm Hg, and heart rate of 66/min. Cardiac auscultation reveals a grade 3/6, harsh, crescendo-decrescendo systolic murmur heard best at the lower left sternal border without radiation to the carotid arteries. While assessing the patient's radial pulse and simultaneously auscultating the heart, the physician notes an occasional premature ventricular contraction (PVC). Which of the following physical examination findings during the cardiac cycle immediately following the premature beat is most specific for this patient's underlying condition?

  1. A transient decrease in the arterial pulse pressureAnswer
  2. B
    A transient increase in the arterial pulse pressure
  3. C
    A decrease in the intensity of the systolic murmur
  4. D
    A paradoxical splitting of the second heart sound
  5. E
    A complete disappearance of the systolic murmur

Answer

A transient decrease in the arterial pulse pressure
The correct answer accurately describes the Brockenbrough-Braunwald-Morrow sign, a highly specific physical examination finding for hypertrophic obstructive cardiomyopathy (HOCM). Following a premature ventricular contraction (PVC), the compensatory pause leads to increased preload and post-extrasystolic potentiation (increased contractility). In HOCM, this sudden increase in contractility exacerbates the anterior systolic motion (SAM) of the mitral valve, severely worsening the dynamic left ventricular outflow tract (LVOT) obstruction. As a result, the forward stroke volume paradoxically decreases, manifesting as a transient decrease in the arterial pulse pressure on the beat immediately following the PVC.

Step-by-Step Solution

1
Identify the likely underlying diagnosis based on the clinical vignette.
The patient is a young athlete with exertional lightheadedness and a harsh systolic murmur at the lower left sternal border that does not radiate to the carotids, which strongly suggests hypertrophic obstructive cardiomyopathy (HOCM).
Recognizing the classic presentation of HOCM is required before predicting the hemodynamic response to a premature ventricular contraction.
2
Determine the physiological changes that occur immediately following a premature ventricular contraction (PVC).
A PVC is followed by a compensatory pause, which leads to increased diastolic filling time (increased preload) and post-extrasystolic potentiation (increased myocardial contractility).
Understanding the fundamental hemodynamics of a post-PVC beat is essential for predicting physical exam findings.
3
Apply the post-PVC physiological changes to the specific pathophysiology of HOCM.
The increased myocardial contractility in the post-PVC beat severely exacerbates the anterior systolic motion (SAM) of the mitral valve, worsening the dynamic left ventricular outflow tract (LVOT) obstruction.
The dynamic nature of the LVOT obstruction in HOCM dictates that increased contractility worsens the obstruction, unlike in fixed obstructions such as valvular aortic stenosis.
4
Deduce the resulting physical examination findings on the arterial pulse.
Because the dynamic LVOT obstruction significantly worsens during the post-PVC beat, the forward stroke volume falls, which manifests clinically as a transient decrease in the arterial pulse pressure (Brockenbrough-Braunwald-Morrow sign).
This specific hemodynamic response perfectly correlates the underlying pathophysiology with the bedside physical examination.

Key Concept

The Brockenbrough-Braunwald-Morrow sign demonstrates that in hypertrophic obstructive cardiomyopathy (HOCM), increased contractility following a premature ventricular contraction paradoxically decreases the arterial pulse pressure due to worsening of the dynamic left ventricular outflow tract obstruction.
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Topics

Physical Examination Findings

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