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Carotid Doppler & Aortic Stenosis

What information can we glean from a pulse? This question was the center of discussion for many clinicians in the 19th and early 20th centuries. Without advanced imaging, clinicians suspected that small variations in the nature of the pulse could map directly to cardiac disease. However, this information was only retrievable through the palpation of the pulse until German physiologist Karl von Vierordt invented the sphygmograph in 1854, transforming the palpation of a pulse into a graphical tracing.



This offered a window into the circulatory system and created an enormous opportunity to diagnose cardiac disease more precisely and non-invasively. The visual changes seen in the pulse in patients with aortic stenosis were some such insights. In aortic stenosis, the upstroke of the pulse can take on a more rounded and less steep slope, known as pulsus parvus et tardus. As described in a 1909 medical textbook A System of Medicine, the pulse in mild to moderate aortic stenosis "may not shew any abnormal features," but as the AS progresses to severe, "the waves will become more infrequent and tardy."


In his 1913 medical text Diseases of the Heart and Aorta, Dr. Aurthur Douglas Hirschfelder noted that the pulsus tardus was most associated with aortic stenosis and had a characteristic waveform that was dampened and delayed as compared to a normal pulse.



This was evidenced in a carotid pulse tracing of a patient with aortic stenosis:




In 1962, physician Brian Robinson from St. George's Hospital in London sought to further characterize the carotid pulse in patients with aortic stenosis. He fitted them with a neck cuff and compared his findings to that of an autopsy, an operation, or cardiac catheterization.



A normal tracing was shown below:



This was compared to a tracing with severe aortic stenosis, where the acceleration phase is more gradual and the peak is more rounded:



Another study from the 1970s corroborated this, showing that the rate of rise of the carotid upstroke (acceleration time) was highly correlated with the aortic valve area and the mean gradient across the aortic valve. In severe aortic stenosis with a high gradient ( > 50 mmHg), the rate of rise was much slower at 328 mmHg per second compared to 626 with a normal gradient.



This concept was demonstrated in the ultrasound era as well. A retrospective study from 1996 looked at carotid Doppler waveforms and acceleration times in aortic stenosis patients and how they compared to controls. Below is a normal carotid waveform. Note the sharp rise of the initial upstroke:




Now compare this to a rounded, delayed upstroke in someone with critical aortic stenosis:




They found that these signs (delayed acceleration time and rounded waveform) were 100% specific for severe aortic stenosis and about 80% sensitive.



When evaluating cardiac function and the degree of aortic stenosis, the morphology and acceleration time can be very valuable. A normal common carotid Doppler has a very sharp rise, a sharp peak, and a velocity in the 50 cm to 100 cm per second range. Younger patients generally have higher flow velocities. Velocities also vary with the physiological state, higher with exercise and lower with rest, and are higher with carotid stenosis or severe atherosclerosis.


Example of normal carotid doppler. Note the very rapid systolic rise and very sharp peak.

Acceleration time and waveform shape seem to change with aortic stenosis while peak velocity usually does not, unless the patient has a severely reduced ejection fraction at which time it may. This was determined in patients with severe aortic stenosis who underwent aortic valve replacements. There was no difference in peak velocities measured in the internal carotid artery before and after valve replacement.


Here is an example of pulsus parvus et tardus from the internal carotid artery:


via https://pubmed.ncbi.nlm.nih.gov/24524745/

In very low flow states, the carotid waveform appears more triangular, and can have significantly reduced peak velocity as seen here:







With a handheld probe, carotid Doppler is a simple test that can be acquired in almost every person and incorporated into the physical exam. It can give information on heart rate, rhythm, cardiac output, fluid responsiveness, and aortic stenosis or regurgitation.


Here is a normal carotid Doppler, with a sharp upstroke:



And some in patients with severe aortic stenosis:






In atrial fibrillation, note the irregular rhythm and variable size and velocity of the carotid upstrokes:





How have you used carotid doppler in your clinical practice?


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Get a copy of The POCUS Manifesto to learn more about point-of-care ultrasound. And get a copy of There's a Nest in My Chest! for the kids!




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