Results

Their search strategy found five studies that met the inclusion criteria. Of the five studies, two used nitroglycerin 400 μg sublingual as their treatment and could be meta-analyzed. One was a small study (n=46) by McConnell et al, conducted in the UK and had 19 RVMIs. The other was a larger Canadian study (n=1,004) by Robichaud et al and included 86 patients in the cohort with an RVMI.

Key Results

There was no statistical difference observed in adverse events with the administration of nitrates based upon the region of cardiac infarction.

• Primary Outcome: Adverse event rates of combined inferior and RVMI
  • Relative risk 1.31 (95 percent CI 0.81 to 2.12)
  • Adverse events reported were categorized as transient and minor.

EBM Commentary

1. Pillars of Salt and Sand: In the systematic review and meta analysis, the authors point out that the “don’t give nitrates in RVMI patients” recommendation seems to stem from the 1989 Ferguson, et. al., study of 40 patients. That retrospective study reported 20 patients with an inferior MI and hypotension after getting nitrates, and 20 patients with an inferior MI who weren’t hypotensive after receiving nitrates. In the first group (hypotension), 15/20 patients had ECG evidence of RV involvement. Only 2/20 patients in the second group (non-hypotension) had ECG evidence of RV involvement. As is often the case, when you go back to the primary literature that informs guideline recommendations you discover it’s not high-level evidence.
2. Papers Meta-Analyzed: Arguably the most compelling study included in the analysis (SRMA) is the one by Robichaud et al (n=1,004).3 It looked at the administration of 400 ug of sublingual nitroglycerin in MI patients who were categorized as inferior MI, inferior plus RVMI, inferior plus other territory, and MI’s involving only non-inferior/RVMI territories. What it demonstrated was that there was no increased risk to any of those subgroups when given nitrates. Interestingly, nitrate administration appeared to be safest in patients experiencing an isolated inferior MI. The other paper meta-analyzed is the other smaller study (n=46) by McConnell et al.⁴ It was only published as an abstract presented at a conference. The SRMA authors were able to contact the study team, get the original study data, and incorporate that into their meta-analysis. McConnell’s findings are congruent with the larger Robichaud et al study.
3. Benefits: The SRMA only looked at the potential harms of administering nitrates to patients with acute MIs. The hypotension observed is often transient, easily managed, and unlikely to be clinically meaningful (i.e., a monitor-oriented outcome). None of the studies included in the SRMA looked at the benefits of nitrate administration such as analgesia balanced against the risks of transient hypotension. The AHA recommends giving patients with ischemic discomfort up to three doses of sublingual or aerosol nitroglycerin until pain is relieved or low blood pressure limits its use (Class I, LOE B). This recommendation is much stronger than the Class III, LOE C provided for the contraindication of nitrates in RVMIs.

Bottom Line

It is reasonable to administer nitrates to patients with an RVMI. Be prepared to manage the potential transient hypotension when giving nitrates regardless of the infarct territory.