Thursday, June 25, 2015

Study group discussion: Fluids in inferior wall myocardial infarction

Why are fluids indicated in inferior wall MI?

Inferior wall MI is associated with severe hypotension. So first, correct the hypotension, then, thrombolyse.

Yes, but any reason for the hypotension?

Because inferior wall has vagal plexus. Patients with inferior wall MI are parasympathetic i.e. high vagal tone.

Yup. Patients with acute inferior wall MI tend to be "parasympathetic" and have a high vagal tone. This explains the sinus bradycardia and lower blood pressure manifested by such patients.

In severe cases of acute inferior-wall myocardial infarction with RV involvement, the forward delivery of blood from the RV to the LV may be insufficient to fill the LV, resulting in low blood pressure even if the LV is intact.

Chemoreceptor activation in the myocardium actuates vagal (parasympathetic) efferent discharge, known as the Bezold-Jarisch reflex, which causes bradycardia and vessel dilation that may further lower blood pressure. Adenosine may accumulate in the infarct zone secondary to a local inhibition of adenosine deaminase, for which aminophylline may act pharmacologically as an antagonist. The hemodynamic changes resemble many of those seen with pericardial constriction or tamponade. Patients with this condition respond well to an infusion of normal sodium chloride solution. Improvement with such infusion compensates for failure of the pumping action of the RV; it reduces vagal tone, and it deactivates the pressure sensors that were sending a hormonal signal to the kidneys to retain salt.

1 comment:

  1. It is also why nitroglycerin is contraindicated in RV infarction. Reduces preload enough to cause severe hypotension. Patients with anteroinferior infarct with AV block may benefit from atropine :)

    ReplyDelete

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