The correct answer is: B. 130 mm Hg.

Figure 7 provides an explanation.

Figure 7

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Figure 7

Answer choice A is an incorrect choice because the CW Doppler is showing the MR signal as noted by the characteristic envelope shape (as opposed to the LVOT signal). The MR signal will provide the LV-to–left atrium (LA) gradient, not the LVOT gradient.

Answer choice B is the correct choice. After one correctly identifies that the CW Doppler signal in this case is the MR signal, the LV-LA gradient is calculated to be 265 mm Hg (4V²). The left ventricular systolic pressure (LVSP) is then estimated by the formula LV-LA gradient + estimated LA pressure (assumed to be 10-15 mm Hg), which calculates to 275 mm Hg (265 + 10 mm Hg). The LVOT gradient is then estimated by the formula estimated LVSP – systolic BP, which reveals the correct answer choice of 130 mm Hg (275 – 145 mm Hg).

Answer choices C and D are incorrect choices.

Accurate measurement of the LVOT gradient is critical in the diagnosis and management of HOCM. Apical imaging with color and CW Doppler provides the necessary information to assess LVOT obstruction. When using CW, special caution should be taken to localize and differentiate the LVOT gradient from the MR gradient, and to identify characteristic signal patterns of MR in HOCM (Figure 8).

Figure 8

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Figure 8

Differentiating the HOCM MR Signal From the LVOT Signal

The appearance of the HOCM MR and LVOT signals can be confusing and the differentiation can be challenging. If the MR signal is mistaken as an LVOT signal, the LVOT gradient can be overestimated. The features listed in Table 1 help differentiate these signals:

Table 1

Differentiating the HOCM MR Signal From Other Causes of MR

• Most other MR signals (except mitral valve [MV] prolapse) have onset at the isovolumetric contraction (IVC) phase and last until isovolumetric relaxation (IVR; i.e., pansystolic MR).
• HOCM MR begins after IVC during the ejection phase but persists until IVR.
• This gives the HOCM MR signal its characteristic initial curved appearance, which is different from most other MR signals.

In HOCM, LV ejection is followed by LVOT obstruction and then onset of MR due to the SAM of the MV and disruption of coaptation between the two leaflets. This sequence of events in HOCM has been referred to as the eject-obstruct-leak sequence.

Educational grant support provided by: Bristol Myers Squib
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References

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3. Woo A, Jedrzkiewicz S. The mitral valve in hypertrophic cardiomyopathy: it's a long story. Circulation 2011;124:9-12.
4. Adelman AG, McLoughlin MJ, Marquis Y, Auger P, Wigle ED. Left ventricular cineangiographic observations in muscular subaortic stenosis. Am J Cardiol 1969;24:689-97.