Prehospital Nitroglycerin Safety in Inferior ST Elevation Myocardial Infarction

Abstract

Patients with inferior ST elevation myocardial infarction (STEMI), associated with right ventricular infarction, are thought to be at higher risk of developing hypotension when administered nitroglycerin (NTG). However, current basic life support (BLS) protocols do not differentiate location of STEMI prior to NTG administration. We sought to determine if NTG administration is more likely to be associated with hypotension (systolic blood pressure < 90 mmHg) in inferior STEMI compared to non-inferior STEMI. We conducted a retrospective chart review of prehospital patients with chest pain of suspected cardiac origin and computer-interpreted prehospital ECGs indicating "ACUTE MI." We included all local STEMI cases identified as part of our STEMI registry. Univariate analysis was used to compare differences in proportions of hypotension and drop in systolic blood pressure ≥ 30 mmHg after nitroglycerin administration between patients with inferior wall STEMI and those with STEMI in another region (non-inferior). Multiple variable logistic regression analysis was also used to assess the study outcomes while controlling for various factors. Over a 29-month period, we identified 1,466 STEMI cases. Of those, 821 (56.0%) received NTG. We excluded 16 cases because of missing data. Hypotension occurred post NTG in 38/466 inferior STEMIs and 30/339 non-inferior STEMIs, 8.2% vs. 8.9%, p = 0.73. A drop in systolic blood pressure ≥ 30 mmHg post NTG occurred in 23.4% of inferior STEMIs and 23.9% of non-inferior STEMIs, p = 0.87. Interrater agreement for chart review of the primary outcome was excellent (κ = 0.94). NTG administration to patients with chest pain and inferior STEMI on their computer-interpreted electrocardiogram is not associated with a higher rate of hypotension compared to patients with STEMI in other territories. Computer interpretation of inferior STEMI cannot be used as the sole predictor for patients who may be at higher risk for hypotension following NTG administration.

Adverse events from nitrate administration during right ventricular myocardial infarction: a systematic review and meta-analysis

“…It would be reasonable to expect a higher rate of adverse events as the penumbra increases; this comparison may make RVMI appear unsafe, whereas the increased risk may be instead due to increased area of infarction (regardless of RVMI being the additional region involved). This theory is supported by the results of Robichaud et al , where isolated inferior infarction was the safest at 6.10% and the rate of adverse events in concomitant inferior and RVMI was actually lower than the rate in concomitant inferior and other myocardial infarctions at 8.14% compared with 8.40%, respectively 12…”

“…Two factors mean the synthesised result for nitroglycerin 400 μg sublingual may be overstating the actual risk. First, McConnell et al compared joint inferior and RVMI with isolated inferior infarction 12 13. It would be reasonable to expect a higher rate of adverse events as the penumbra increases; this comparison may make RVMI appear unsafe, whereas the increased risk may be instead due to increased area of infarction (regardless of RVMI being the additional region involved).…”

“…For all other infarctions, it is commonly accepted that adverse events from nitrates—the primary of which is hypotension—are transitory and respond favourably to fluid challenge, and therefore nitrates remain widely recommended as a first-line analgesic for angina 1 2. Over the past 5 years, larger cohort studies, cumulatively including 1050 patients, concluded that nitrate administration to combined inferior and RVMI was not associated with a different rate of adverse events, suggesting that this topic merits systematic review 12 13…”

Right Ventricular Myocardial Infarction and Adverse Events from Nitrates: A Narrative Review

“…The overall hypotension rate was 8.2%, suggesting that hypotension will occur in one in every 12 patients who are administered glyceryl trinitrate, and that this will be regardless of the region where the infarction is occurring. The paper concluded "although it is widely recommended in the medical literature to use caution when administering nitroglycerin to patients with inferior STEMI, the only study supporting this statement is a retrospective cohort study published in 1989 by Ferguson et al" (5).…”

Eletrocardiogram gate time in patients with thoracic pain in the emergency

“…Because nitroglycerin may precipitate hypotension in patients with acute lower-wall and associated VRIG STEMI, its prehospital administration routine may not be safe. 15 Oxygen therapy has been commonly used in the initial treatment of patients with STsegment elevation myocardial infarction, based on the belief that supplemental oxygen may increase the oxygen supply to the ischemic myocardium and, therefore, reduce myocardial injury, which is supported by laboratory studies and an early clinical study. Other studies, however, have suggested a potential adverse physiological effect of supplemental oxygen, with reduced coronary blood flow, increased coronary vascular resistance, and the production of reactive oxygen species that contribute to vasoconstriction and reperfusion injury.…”