Master the board step 3

Master the Boards: USMLE Step 3
The following table shows the effect of venous return on murmurs.
Effect of Change in Venous Return
Valvular Lesion
Increase (squat, leg raise)
Decrease (stand, Valsalva)
Aortic stenosis (AS) Increased murmur Decreased murmur
Aortic regurgitation (AR) Increased murmur Decreased murmur
Mitral stenosis (MS) Increased murmur Decreased murmur
Mitral regurgitation (MR) Increased murmur Decreased murmur
Ventricular septal defect (VSD) Increased murmur Decreased murmur
Hypertrophic obstructive
cardiomyopathy (HOCM)
Decreased murmur
Increased murmur
Mitral valve prolapse (MVP) Decreased murmur Increased murmur
Effects of Handgrip and Amyl Nitrate
Handgrip is a maneuver that increases afterload by compressing the arteries
of the arm by contracting the muscles of the arm. Handgrip does not significantly
increase venous return to the heart: the veins of the arms are not as large
as those of the legs, so compressing them does not make much difference in
venous return to the heart. Handgrip, because it increases afterload, essentially
functions as the opposite of an ACE inhibitor, worsening the murmurs of
conditions that would get better with an ACE inhibitor. For instance, AR and
MR are treated with ACE inhibitors, because afterload reduction increases the
forward flow of blood into the aorta. Handgrip will, therefore, worsen AR
and MR murmurs by pushing blood backward into the heart. Handgrip will
make the murmurs of AR and MR louder and more intense. The same is true
for VSD. Handgrip worsens the murmur of VSD, because more blood now
goes from the left ventricle into the right ventricle.
Amyl nitrate is a vasodilator that decreases afterload by dilating peripheral
arteries. Amyl nitrate has the opposite effect of handgrip. Giving amyl nitrate
is like giving an ACE inhibitor or ARB. If handgrip worsens AR and MR, then
amyl nitrate improves AR and MR.
Handgrip improves or lessens the murmurs of MVP and HOCM. The murmurs
of MVP and HOCM lessen when the left ventricular chamber is larger
or more full. What happens to the size of the left ventricular (LV) chamber if
there is increased afterload? The LV chamber will not empty and, therefore,
the LV will be larger. A larger LV chamber relieves or lessens the obstruction
in HOCM.
Amyl nitrate will do the opposite. It increases ventricular emptying and,
therefore, decreases the size of the LV. Amyl nitrate worsens the murmurs of
MVP and HOCM by increasing the obstruction and the degree of prolapse of
the valves in MVP.
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