Cardiovascular Critical Care I
ii.
Can lead to severe cardiogenic shock
iii.
SAM is more of a dynamic obstruction in which the degree of obstruction and flow gradient is
dependent on heart rate, cardiac contractility, and ventricular preload volume.
| (a) | In an underfilled LV, there is physically less distance between the mitral valve and septum, |
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thus generating an increased risk of obstruction because the LVOT is generally narrower
at the onset of systole, particularly if the mitral valve leaflet is affected.
| (b) | Increasing cardiac contractility and heart rate increases LVOT obstruction and gradient |
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by inducing a stronger contraction, increasing the contact between the septum and mitral
leaflets, and increasing the rate of systolic attempts.
iv.
For patients with SAM who have a potential for obstructive physiology, management involves
maintaining normal or increased LV preload and low heart rates.
| (a) | Acute hypotension is best managed with phenylephrine or vasopressin (pure |
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vasoconstrictors) to selectively increase SVR without increasing contractility or heart
rate. Concomitant β-blocker use may also be considered to improve cardiac filling.
| (b) | Inotropes and vasopressors that mediate increases in heart rate or contractility should be |
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avoided, if possible, because they may be harmful and worsen the LVOT.
| (c) | Afterload-reducing agents (e.g., ACE inhibitors, ARBs, non-dihydropyridines) should be |
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used with caution (if at all).
Septal defects can be acquired (i.e., postinfarction ventricular septal defect) or can be congenital.
Diagnosed predominantly by ECHO using a bubble study. If the patient presents in a seemingly
low cardiac output state, a left-to-right intracardiac shunt should be suspected if Svo2 saturations
are greater than Scvo2 saturations.
Important principles
Goals include minimizing the degree of intracardiac shunt while maintaining adequate cardiac
output. It is generally favored to accept a right-to-left intracardiac shunt while recognizing that
partial pressure of arterial oxygen (Pao2) saturations will be somewhat decreased and reflective
of venous and arterial blood mixing in the LV before ejection.
ii.
Decreasing right-sided cardiac filling pressures can augment left-to-right intracardiac shunting
of blood. Administration of venodilators (i.e., nitrates) or aggressive diuresis could augment
left-to-right intracardiac shunts and lead to clinical deterioration.
iii.
Intravenous medications should preferably be filtered to minimize the risk of air/particulate
embolus traveling through to the left side of the heart, being ejected, and causing a potential
stroke.
| d. | Treatment may include surgical correction or percutaneous catheter placement of a closure device. |
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