Thread by @nickmmark

#CriticalCare non-COVID teaching case:
An elderly man is admitted to the surgical ICU for monitoring after an uncomplicated kidney transplant. You notice this funny pattern on his arterial line tracing. What’s going on here?
#FOAMcc #FOAMed
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What’s going on here?
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This is pulsus alternans: an alternating strong & weak pulse.

Based on the A-line tracing POCUS was performed that reveled a markedly reduced EF. Coronary angiography showed no obstruction and a diagnosis of stress CM was made. The patient recovered with medical therapies.
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At first glance, differentiating pulsus alternans from exaggerated pulse pressure variation (PPV) can be tricky
*pulsus alternans occurs every other beat
*PPV occurs with the respiratory cycle

Slowing down the display can differentiate: This is what increased PPV looks like
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Pulsus alternans was first described by Traube in 1872.

Despite 150 yrs of research, the mechanism is not precisely known.

There are two theories, related to either beat-to-beat variation in pre-load or in contractility.

academic.oup.com/cardiovascres/…
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The *pre-load theory* is that impaired contractility (causing a weak pulse) leads to an increased end diastolic volume at the next systole. With more filling, the next contraction ejects more blood (causing a strong pulse) due to the Frank-Starling principle.
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The alternative *contractility theory* is that residual cytoplasmic Ca2+ after a weak systole causes a stronger cardiac contraction on the next beat.

Whatever the mxn, pulsus alternans is associated with poor systolic function.
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🥡Points:
🫀Pulsus alternans on an arterial line tracing can be a useful diagnostic clue for decreased systolic fxn
1⃣📟 See this new ICU OnePager on arterial Lines for more onepagericu.com
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📚Historical/literary note:
DH Lawrence beautifully describes Pulsus Alternans in Sons and Lovers:
"…he felt her pulse. There was a strong stroke and a weak one, like a sound and its echo. That was supposed to betoken the end."

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