right sided vs left sided blockage?

Whoever told you that is wrong.

Where they're coming from (i beleive) is that a 'right sided' (meaning 'right coronary artery' or 'inferior' MI) can (~40-50% of the time) involve the right ventricle. These patients are sensitive to meds (esp. nitro) and can be more likely to become hypotensive...(requiring fluid bolus, etc.). Can make for a difficult patient to treat w/meds.

But it's all relative really.

Ask this person if a 'small' rt sided mi is worse than a 'massive' lt sided MI. I'd be very intetrested in the answer...

But again...i think they're talking about the potential hemodynamic compromise that can accompany inferior MI (~40% of the time...)

RCA supplies SAN.

This is a good point. However, the RCA doesnt always feed the SA-node...so to make this blanket statement is a bit misleading. Also, the chances of an RCA/inferior MI knocking out the SA-node are small(real...but small). In contrast, the potential for RV involvement is much higher (~40-50%)...and i beleive this is from where the OP's question stems...because these RV MI's are harder to treat with 'standard' meds (ie nitro).
(...And the potential for blocks and lethal arrhythmias can just as easily stem from the left coronary system...)

Again, i think the question is loaded and that it's all relative.
Is the vessel dominant? Is the occlusion proximal? Distal? Any collateral circulation? etc.

Whoever thinks an RCA lesion is worse than a left-main lesion (for example)(because you 'could potentially knock-out the SA-node') would be hard pressed to convince me. Forget the SA node, if you shut down the Left main the patient's done.

I think the OP's teacher (or text-book) could have better phrased the question as "...what are some potential complications of right coronary artery MI's..."
Sure..they can be very bad and lethal(duh)...but so can left coronary occlusions(ummm duh again)...for various reasons.

Should've mentioned (didnt because i wanted to get my numbers right first) that in almost half of patients the SA-node actually gets its blood supply from the CIrcumflex artery...which is, of-course, a branch of the left coronary system...

Since when??? I think you may be getting your coronary arteries confused.

Right sided MI's are sometimes worse than left, esp if there is Right Ventricle involvement, because then you play a game of drown the patient, to maintain flow into the left side of the heart, then you have to VERY CAUTIOUSLY diurese them. Right sided MI's have a higher mortality, and really are about as bad as you can get if you are the nurse trying to take care of them. The RV infarct patient gets his/her perfusion from the central venous pressure if the RV is severely infarcted. I cared for a gentleman who closed off his RCA graft shortly after CABG surgery, and his CVP read 25mm Hg at one point prior to sending him to the Cath Lab for a stent and balloon pump. The patient had bonafide BP's in the 60/30 range, and was pretty moderately 3rd spaced only 48hours post-op.

.....

Only if the patient is in heart failure/pulmonary edema..otherwise diuresing someone w/MI isnt part of the recipe...

I think a bigger drug to watch is nitro...because you (ideally) will be giving it to most MI patients who can tolerate it...

This is my understanding from paramedic school.

Right sided MI is sometimes described as more severe and less common than left sided MI specifically in the pre-hospital environment. The number of interventions that a paramedic can perform for an MI is significantly limited by the hallmark hypotension that is very common in right sided MI. The three common prehospital preload reducing agents used to treat AMI (Morphine, Nitro, and Nitro paste) are all contraindicated with systolic BP's less than 90.

Right sided MI's have a tendency to progress to bradycardic rhythms, and on to brady PEA and Asystole. The only real treatment for this bradycardia is Dopamine, Epinephrine, or pacing; all of which significantly increase the myocardial oxygen demand, which serves to worsen the area and severity of the infarction. So it is really a lose-lose situation in many cases.

Severe hypotension is less common in left sided MI, so it does not prevent the majority of prehospital treatments. Often, the usage of preload reducing agents can reduce the ischemia and keep the injury from progressing. If not, the ventricular and septal wall ischemia often leads to severe ventricular dysrhythmias (V-fib and V-tach). These can sometimes be corrected by defibrillation, cardioversion, Amiodarone, or Lidocaine. Depending on the severity, the left MI can cause pulmonary edema. Usage of CPAP, as well as Nitro and Morphine can help with this, and the patient would be receiving the Nitro and Morphine anyway as long as their blood pressure holds. Once someone survives the initial dangers of dysrhythmias in a left sided MI their prognosis is usually favorable, but they will often have resultant CHF.

First lets discuss "dominace". The RCA gives rise to the PDA and PLV. In 75% of Patients the PDA arises from the RCA, the other 20-25% of the time the PDA comes off the Circ making the left system dominant. The size of the PDA often feeds the RV (right ventricle). In total RCA occussions in AMI's (inferior wall MI's) with 75% being dominate the chance of RV infarcts are high. With the RV unable to move blood forward to the Pulmonary art and to the LV the BP drops. The treatment is large volumes of FLUID and no nitrates. The symptoms are usually low BP and brady dysrythmias. The conus branch feeds the SA node and 95% of the time comes from the proximal or ostial RCA. Sometimes it is amomous and comes from the CIRC or has a separte ostium.

The left main branches into 2 vessels, the LAD and the CIRC. in 20-25% of the population the CIRC feeds the PDA which feeds the RV and causes an INFEIROR WALL MI. Usually the Circ and margianals (OM's) cause lateral wall MI's). MI's on the Left cause ANTERIOR MI's either Anterior septial (LAD and diagionals) or Anterior lateral (circ and OM's). Posterior wall MI's (missed very frequently) are usually large circ's or large RCA's with a PLV.

All MI's have high risk... even NON-STEMIS. Initially they are from sudden death but days out can still be from ventricular rupture, tamponade or papulary mussle rupture. However with the advent of inteventional cardiology over the past 15-20 years, mortality has dropped significantly.