nitroglycerin contraindicated in right side heart myocardial infarction

[Oh_Gee]

in the sketchy video for nitrates, they say nitroglycerin is contraindicated in right side heart myocardial infarction. why is that? i googled around but can't find anything.

is it because nitroglycerin decrease preload which is bad for right side MI b/c that means it gets even less blood return?

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[Fallot101]

Yes.

 

[iBS1972]

That's correct. Right-sided heart failure (ex. from MI) is what people call "preload dependent". Acutely, we try to improve the patient's hemodynamic state by increasing cardiac output of the heart. For the right side, we do this by increasing preload, which would increase wall tension, and thus stroke volume (Frank-Starling Curve). If you give nitroglycerin, you dilate the vessels so less blood returns to the heart (increased venous capacitance->more blood distributed to venous system), decreased stroke volume of right heart.
In regards to afterload, afterload is not the problem in the situation you are describing, ie. right sided MI or right heart failure due to right sided MI. But, in the case of right heart failure due to chronic advanced pulmonary disease (quite common), afterload reduction is an important factor of treatment because increased afterload from increased pulmonary resistance is the primary cause of the heart failure. As you might expect, you use care at achieving a balance between dilating the pulmonic vessels with dilating systemic vessels.

Hope this helps!

 

[Oh_Gee]

That's correct. Right-sided heart failure (ex. from MI) is what people call "preload dependent". Acutely, we try to improve the patient's hemodynamic state by increasing cardiac output of the heart. For the right side, we do this by increasing preload, which would increase wall tension, and thus stroke volume (Frank-Starling Curve). If you give nitroglycerin, you dilate the vessels so less blood returns to the heart (increased venous capacitance->more blood distributed to venous system), decreased stroke volume of right heart.
In regards to afterload, afterload is not the problem in the situation you are describing, ie. right sided MI or right heart failure due to right sided MI. But, in the case of right heart failure due to chronic advanced pulmonary disease (quite common), afterload reduction is an important factor of treatment because increased afterload from increased pulmonary resistance is the primary cause of the heart failure. As you might expect, you use care at achieving a balance between dilating the pulmonic vessels with dilating systemic vessels.

Hope this helps!

if the right heart isn't working, wouldn't it be better to give nitrates so that the heart gets less volume? what's the point of giving more blood (increased preload) to a ventricle that won't work?

 

[iBS1972]

if the right heart isn't working, wouldn't it be better to give nitrates so that the heart gets less volume? what's the point of giving more blood (increased preload) to a ventricle that won't work?

You are correct, the heart will not be pumping well, and giving more preload would put more stress on the right heart and may lead to further damage due to increased O2 demand-supply mismatch. But, without giving more preload, there's not much else you can do to make the right heart pump more (in the case of right heart failure due to MI). So you're left with two options: A. do as much as you can to preserve right heart function while risking death or organ damage (ex. brain) from decreased cardiac output aka perfusion aka blood, OR B. make the right heart work a bit harder (even if it means causing more damage to cardiac myocytes) but keeping the patient alive.

A living person with a relatively crappier heart is (usually) better than a dead person with a relatively less crappy heart.

 

[Oh_Gee]

You are correct, the heart will not be pumping well, and giving more preload would put more stress on the right heart and may lead to further damage due to increased O2 demand-supply mismatch. But, without giving more preload, there's not much else you can do to make the right heart pump more. So you're left with two options: A. do as much as you can to preserve right heart function while risking death or organ damage (ex. brain) from decreased cardiac output aka perfusion aka blood, OR B. make the right heart work a bit harder (even if it means causing more damage to cardiac myocytes) but keeping the patient alive.

A living person with a relatively crappier heart is (usually) better than a dead person with a relatively less crappy heart.

thanks!