Inferior STEMI? Check the right ventricle before you reach for nitro

#The call

A 58-year-old man, crushing chest pain for forty minutes, pale and diaphoretic. Your first 12-lead shows ST elevation in II, III and aVF with reciprocal depression in aVL. Inferior STEMI. His pressure is 104/68 and he's asking for something for the pain.

Nitroglycerin is in your hand, and on most chest-pain calls it would be a reasonable next step. On this one, it's the decision the whole call turns on.

#Why the right ventricle changes the plan

The right coronary artery supplies the inferior wall in most people, and in many of them it also supplies the right ventricle. When it's blocked high enough, both territories are affected. Estimates vary, but right ventricular infarction, or right-ventricular involvement, is found in up to half of inferior infarctions, and in a smaller share it's large enough to change the patient's haemodynamics.

The right ventricle is a thin-walled, low-pressure pump. When it's ischaemic, it can't push blood through the lungs on its own effort, so the left ventricle's output comes to depend on preload: venous return filling a struggling right heart.

Nitroglycerin is a venodilator. It pools blood in the veins and lowers preload, which is exactly what helps a congested left heart and exactly what a failing right heart can't afford. The result can be a sudden, deep drop in pressure a few minutes after the dose.

The patient who looked stable at 104 systolic can be at 70 before you've finished packaging him.

#Finding it in the field

You don't need a full right-sided ECG. One lead answers the question.

1. Keep the limb leads where they are.
2. Move the V4 electrode to the same landmark on the right side of the chest: fifth intercostal space, right midclavicular line.
3. Record a strip, and label it V4R so the receiving team doesn't read it as a normal V4.
4. Put V4 back and carry on.

It takes under a minute, and it's worth doing on every inferior STEMI before a preload-reducing drug.

#What counts as positive

• ST elevation of 1 mm or more in V4R is the usual threshold for right-ventricular involvement.
• ST elevation in lead III greater than in lead II on the standard 12-lead is a supporting clue.
• The classic bedside picture is hypotension with clear lungs and distended neck veins, but don't wait for all three: by the time the triad is obvious, the pressure has often already fallen.

Right-sided ST changes can fade within hours of onset, so the first strip is the one that counts.

#If the pressure has already dropped

If nitro was given before right-ventricular involvement was recognised, or the patient presents hypotensive, the priorities are:

• Stop any further nitrates, and avoid other drugs that reduce preload.
• Lay the patient flat if their breathing allows.
• Follow your service's directive for hypotension, which for a right-ventricular infarct usually means a cautious fluid bolus with reassessment of pressure and lung sounds after each one.
• Pre-alert the receiving PCI centre with the V4R finding. It changes their plan too.

Medication names, doses and thresholds differ between services. Your medical directive is the authority, not this post.

#How Imedica scores this moment

This exact decision is one of the moments in Imedica's inferior STEMI scenario. The physician who wrote it set the rules like this:

Action at this moment	Verdict
Right-sided lead V4R before any nitrate	Correct
Fluid bolus after the pressure drops, within three minutes	Correct
The same bolus, given late	Suboptimal
Nitroglycerin with right-ventricular involvement	Harmful

A harmful choice changes the patient: the monitor shows the pressure falling, and the call continues from there. The debrief then explains why, with the directive behind each verdict.

#For training leads

Right-ventricular infarction is a classic example of a low-frequency, high-consequence decision. Most crews know the rule. Fewer have had to apply it under time pressure, with a patient asking for pain relief and a partner already drawing up the next drug.

That gap between knowing and doing is what scenario practice is for. If your team's readiness data shows cardiac medication decisions coming back late or harmful, this is a good case to start with.

Drafted for Imedica Field Notes. Physician review of this article is pending.