Even in this age of high-tech medicine, physical exam is still a great starting point for assessing the severity of aortic stenosis (AS) even if you are not a skilled cardiologist like most.

Start out by listening over the right clavicle. If you don’t hear a systolic murmur, you can be pretty confident that your patient doesn’t have moderate to severe AS (>98% sensitivity, LR 0.10)¹.

After you hear a systolic murmur,  look for combination of findings that may increase the likelihood of moderate to severe AS: slow carotid artery upstroke, reduced carotid artery volume, maximal murmur intensity at the second right intercostal space, and reduced intensity of the second heart sound.  The presence of 3 or 4 of these signs increases the likelihood of moderate to severe AS (LR 40)^, with less than 3 not helping much¹.

When considered individually, many of the signs we often attribute to significant AS² may not be as helpful in part because most of us are not skilled cardiologists and over the years the cause of AS has changed from primarily rheumatic heart disease-related to that advancing age and valve degeneration³.  

So it may not be surprising that murmur intensity (eg grade 3/6 or above) may have a poor sensitivity and is an unreliable predictor of the severity of AS when patients with left ventricular failure are also studied³.  Remember also that the absence of the 2^nd sound may not distinguish between moderate and severe AS⁴. 

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References

1. Etchells E, Glenns V, Shadowitz S, et al. A bedside clinical prediction rule for detecting moderate or severe aortic stenosis. J Gen Intern Med 1998;13:699-704. https://link.springer.com/article/10.1046/j.1525-1497.1998.00207.x
2. Etchells EE, Bell C. Robb KV. Does this patient have an abnormal systolic murmur? JAMA 1997;277:564-71. https://www.ncbi.nlm.nih.gov/pubmed/10376577
3. Das P, Pocock C, Chambers J. The patient with a systolic murmur: severe aortic stenosis may be missed during cardiovascular examination. Q J Med 2000;93:685-8. https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/qjmed/93/10/10.1093_qjmed_93.10.685/1/930685.pdf?Expires=1500852139&Signature=TwyO6Z4fUfbPc1yiA~2xZC7jOjed0juH604DshdvRYy~VqeNQ57Sv1yE-LNsImthgQogkawMruBPdXn6PvVCVmdvXxE9QsMzQYhZ13JqXDTQhRiPBcsIBKDdROr~xbz0gp0nv-zEmjCp1M8-CXjrlVnjVtwJ6q2nIPTRW5h-CUOnDAmf8vCeJHRi2M9Dt3a4vGALDJQPaETvxKDfoADamBDtZHzzoCIH3OyXT3–jHRtv9AJI2uHlzN79Vzkh~oIrR-rI5mkHle3Yz0R3qIBY0l4P3PssMng~v-IXMNKS~Ghjav8YFTigHN23aEA5yUYllsC7hR25L6h9PA0SZP3QA__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q
4. Aronow WS, Kronzon I. Prevalence and severity of valvular aortic stenosis determined by Doppler echocardiography and its association with echocardiographic and electrocardiographic left  ventricular hypertrophy and physical signs of aortic stenosis in elderly patients. Am J Cardiol 1991;67:776-7. https://www.ncbi.nlm.nih.gov/pubmed/1826070