Anterior Wall of heart (right ventricle) is supplied by RCA, but on lead V1-V4..

[cooldude89]

Anterior Wall of heart in anatomy is (right ventricle) supplied by RCA, but on lead V1-V4 anterior wall infarction is by LAD on pg 298 first aid.

How is it that leads v1-v4 show anterior wall infarction via LAD of anterior wall (right ventricle) but the blood supply of right ventricle is RCA??

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[Phloston]

Anterior Wall of heart in anatomy is (right ventricle) supplied by RCA, but on lead V1-V4 anterior wall infarction is by LAD on pg 298 first aid.

How is it that leads v1-v4 show anterior wall infarction via LAD of anterior wall (right ventricle) but the blood supply of right ventricle is RCA??

Anterior wall infarction via the LAD is referring to primarily the anterior left ventricle / anterior septal region. So if you infarct the LAD, you infarct the anterior left ventricle and apex. If you get an anterior infarction of the RCA, it's probably because you knocked out the acute marginal artery, a branch of the RCA, which runs over the anterior RV. Either that or you knocked out the RCA just proximal to the acute marginal but distal to the PDA branch-point (assuming right-dominance).

I've seen this in practice questions actually. If you infarct the LAD, they might ask for which vessel could supply collateral flow to maintain perfusion to the anterior heart. If a patient has long-term ischaemia, the acute marginal of the RCA and the LAD show anastamoses.

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An easy way to remember which marginal is which: just remember LO (like "low"). The LCA gives off the obtuse marginal. The RCA gives off the acute one.

Look at this image here and how the acute marginal of the RCA swings "acutely" across the anterior heart, and it's proximity to the LAD: http://en.wikipedia.org/wiki/Right_marginal_branch_of_right_coronary_artery

 

[cooldude89]

ok thanks

 

[Old Style Nanny]

An equally valid and simpler explanation is that ECG doesn't really look at the right ventricle. For all practical purposes, LV predominates thanks to its heft. So, chest leads V1-V4 are clearly going to show only LV infarcts - hence, LAD.

I highly doubt this would be tested on step 1, but if you want to pick up a RV infarct, you have to see for changes only in V1. This is the only lead that is over RV and the only chest lead that is useful here (the other one is of course the bipolar lead III because of its orientation but this is clearly beyond the scope of Step 1).

 

[OveractiveBrain]

Anterior Wall of heart in anatomy is (right ventricle) supplied by RCA, but on lead V1-V4 anterior wall infarction is by LAD on pg 298 first aid.

How is it that leads v1-v4 show anterior wall infarction via LAD of anterior wall (right ventricle) but the blood supply of right ventricle is RCA??

Back up. Until your cards rotation in your internal medicine residency follow this:

1. RCA = RV = II, III, and aVF = Inferior Infarct
2. LAD = Anterior Wall and Septum = V1, V2, V3, and V4; V1,2 = Septal, V3,V4 = Anterior
3. Left Cx = Lateral Wall = V5, and V6

So "inferior wall infarct" is going to be shown as ST segment elevation in II, III, and aVF and is a product of RCA occlusion

"anterior wall infarct" is going to be shown as ST segment elevation in V3 and V4, may involve V1,V2, or V5, and is either the LAD or one of its branches; the larger the infarct (the more Vs it includes) this proximal the lesion, and the more likely the main LAD is involved.

"lateral wall infarct" is going to be shown as an ST segment elevation in V5 and V6, may show in lead I, and is an occlusion of the left circumflex artery.

"posterior wall infarct" is going to be shown as an ST segment depression in V1-V4 and you cannot tell which vessel is involved until you cath.


BONUS...
1. Depression in V1-V4 may be a POSTERIOR infarct, and can be supplied by either Left Cx or RCA (you dont know until you cath)

 

[Phloston]

"posterior wall infarct" is going to be shown as an ST segment depression in V1-V4 and you cannot tell which vessel is involved until you cath.


BONUS...
1. Depression in V1-V4 may be a POSTERIOR infarct, and can be supplied by either Left Cx or RCA (you dont know until you cath)

Lol. Make sure you say this twice, but the second time as a "bonus" so that we can really feel the heat of it.

I'm glad you mentioned this btw because, although I recall having heard it before, that wasn't on the top of my mind, so I'm glad you refreshed it.