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Treating patients with suspected RVI

Currently, the REMSA protocol for acute coronary syndrome (ACS) reads:

For patients with evidence of an inferior wall MI as indicated on their 12 lead ECG (ST elevations in II, III and AVF), consider risks of NTG-related pre-load reduction and hypotension in patients with right ventricular injury.

This statement is designed to allow the clinician latitude based upon assessment and clinical presentation to treat in a manner the paramedic feels is most appropriate. Protocols are intended to be a guideline. However, it does allow for some ambiguity. Hopefully we can take some time to clear this up.

First, let’s decide what types of patients fall into the ACS protocol. Patients who present with chest pain, shortness of breath, unexplained hypotension, unexplained abdominal pain, back pain in the scapular or subscapular region, epigastric pain, neck or jaw pain, generalized weakness, syncope, complaint of tightness in the chest, nausea, vomiting, sweating that is unusual, and any other presentation that is systemically abnormal should be considered ACS patients.

Once we have included a patient into the ACS protocol we have standard or traditional treatments for ACS, or MONA. The order should actually be O12ANA.

O

Oxygen is applied to the patient to supplement and guard for hypoxia. American Heart Association no longer advises high flow oxygen for ACS in the absence of hypoxia, but no studies have shown that high flow oxygen does any harm.

12

12 leadECG should be acquired. In three instances a right sided 12 lead, or right sided quick look should be acquired.

  1. A patient presenting with all signs and symptoms leading the paramedic to believe they may have cardiac ischemia, but shows no ST changes on standard left sided 12 lead.
  2. 12 lead shows ST elevation in leads II, III, aVF (inferior STEMI)
  3. 12 lead showing ST depression in the V leads, possible reciprocal changes from a posterior MI.

A

Aspirin inhibits prostaglandins, it inhibits the formation of blood clots

N

Nitroglycerin – The rationale for giving nitroglycerin has been it will vasodilate both sides of the systemic circulation, reducing both preload (venous return) and afterload (systemic resistance), which reduces the workload on the heart and oxygen consumption. It is also thought to vasodilate the coronary circulation, which improves coronary artery circulation, both direct and collateral, increasing oxygen delivery to ischemic tissues. The protocol adds nitroglycerin should be used with caution in any patient with presumptive evidence of right ventricular infarction because of the profound effect on preload.

A

Analgesia – Some have questioned the efficacy of morphine in MI, but the American Heart Association still grants it a Class IC classification (consensus opinion intervention is useful and effective) with the stated precaution: “Use with caution in right ventricular infarction.” Again, due to the vasodilatory effects.

 

You may say, “Wow that’s great but what I want to know is; what do I do when my interpretation of the 12 lead is inferior infarct? ” We will address this after a short review of cardiac circulation.

With inferior MI, either the right coronary artery (RCA) or the left circumflex coronary artery (LCX) may contain the culprit lesion. In patients with inferior MI who have right ventricular infarction, the culprit artery virtually always is the RCA. Such patients, including those in whom ECG evidence of right ventricular MI is masked, are at increased risk for death, shock, and arrhythmias, including atrioventricular block. This is why it is important to isolate the infarct and rule out, or in, RVI. Thirty to 50% of patients experiencing an inferior wall infarct may also have involvement of the right ventricle. Right ventricular infarctions seldom exist alone; they are almost always seen with an inferior infarct. The coronary artery involved is usually an occluded right coronary artery (RCA). When the inferior wall of the left ventricle is deprived of blood through RCA occlusion, it makes sense to ask whether the right ventricle is also involved, since an RVI can present distinct treatment challenges for you as the paramedic in the field.

A 12-lead tracing that shows ST segment elevation in any of the inferior leads (II, III or aVF), or relative ST segment depression in V2 or V3 compared with lead V1, should immediately trigger acquisition of a right-sided 12-lead. ST segment elevation in V4R is considered to be diagnostic for right ventricular infarction; however, any ST elevation in the right V-leads 3 through 6 should signal suspicion for a right-sided MI. Evidence of acute right ventricular infarction is important, not only because it identifies the RCA as harboring the culprit lesion, but especially because it predicts a greatly increased morbidity and mortality.

So what do I do for the ACS patient?

Obtain a 12 lead. If the 12 lead ECG shows ST elevation in leads II, III, aVF, or ST depression in the V leads, a right sided 12 lead should be done. A right sided ECG should also be considered when a patient presents as ACS but no ST segment changes are noted in the standard ECG.

If the right sided ECG shows evidence of RVI then fluid should be administered to maintain SBP of 100 mmHg. The American Heart Association’s Handbook of Emergency Cardiovascular Care, Guidelines CPR-ECC 2005 states  nitroglycerin is contraindicated in RVI. Therefore, nitroglycerin should be withheld.

If NTG is administered before an RVI is recognized and hypotension results, fluids should be given. As much as two to three liters of normal saline may be required to restore preload to adequate levels, but less is usually adequate. As always, when administering fluids, lung sounds and oxygenation should be monitored.

If adequate blood pressure and cardiac output cannot be maintained with fluids alone, dopamine is the drug of choice with hypotension and signs of cardiogenic shock. Shunt to the Cardiogenic Shock protocol.

Critical care paramedics can consider replacing morphine with fentanyl for analgesia in the presence of RVI.

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