Nitrates for RVMI: time for a re-think?
Current guidelines recommend that when right ventricular myocardial infarction (RVMI) is present, nitrates should not be administered. The advice is predicated upon the risk that decreasing preload in an already compromised right ventricular ejection fraction may further reduce cardiac output and cause hypotension; however, question marks hang over the quality of evidence that informed this recommendation. New studies have been published in this domain—so it is time to revisit the topic.
The authors undertook a systematic review to answer the question ‘Is nitrate administration to patients with RVMI associated with increased adverse events compared with nitrate administration to patients with myocardial infarctions only in other regions?’ Six databases were systematically searched in May 2022 and two investigators independently assessed for quality and bias and extracted data in accordance with the Joanna Briggs Institute tools and methods. Risk ratios and 95% confidence intervals (CI) were calculated, and meta-analysis performed on two studies (others lacked the rigour for meta-analysis).
Outcomes included haemodynamics, Glasgow Coma Score, syncope, cardiac arrest, and death. No cardiac arrests or death occurred in the RVMI group. Meta-analysis was possible only for the two studies that looked at sublingual nitroglycerin 400 μg (2 studies, n=1050) but no statistically significant differences in relative risk were found between inferior infarction with RVMI and MI infarction without RV involvement. The relative risk was 1.31 with sublingual nitroglycerin but the 95% CI crossed the null effect line (0.81 to 2.12, p=0.27), with an absolute effect of 3 additional adverse events/100 treatments, suggesting that current guidelines are not supported by the evidence, though limitations need to be considered.
The samples combined inferior and RVMI so the safety of nitrates in isolated RVMI cannot be determined. Likewise, the severity or clinical significance of hypotension cannot be determined, and definitions of hypotension were not agreed among studies so affected reporting. Most of all though, the certainty of evidence under the GRADE criteria is very low and did not consider the benefits of nitrates.
Factors influencing traumatic cardiac arrest outcomes
Traumatic cardiac arrest (TCA) is uncommon, accounting for around 6% of all cardiac arrests. Despite specific management guidelines, outcomes from TCA remain poor with survival rates typically between 2–8%. Victims of TCA are predominantly male and generally younger than those who suffer medical cardiac arrest. Factors that are associated with improved outcomes in medical cardiac arrest, such as cardiac motion on ultrasound, initial rhythm other than asystole, and bystander-witnessed arrest are also associated with improved outcome in TCA. In addition, specific predictive factors for good outcomes in TCA have been described including falls, rather than motor vehicle crashes, location of cardiac arrest (short distance to hospital), and low Injury Severity Score (ISS).
This retrospective study reviewed the Royal Brisbane and Women's Hospital database from 2008–2021 and included all TCA. They analysed the data to identify factors that contributed to survival and then further analysed outcomes pre- and post-TCA guideline changes in 2016. Patients were categorised by prehospital and in-hospital arrest, prehospital return of spontaneous circulation (ROSC), and year in relation to TCA management protocol changes.
A total of 101 patients met the inclusion criteria, of which 84 had a cardiac arrest prehospital. Most patients were male, with a median age of 47 years (range 18–83 years). Surprisingly, 25 patients survived to hospital discharge, of which 13 were discharged to another hospital or rehabilitation facility, and 12 were discharged home.
This study demonstrated an overall survival rate of 25% to hospital discharge, with a trend towards increased survival following 2016 guideline changes. ISS and age were not found to be associated with a positive outcome following TCA in this cohort. Mechanism of injury, response to intervention and location of cardiac arrest were important. No patients survived if they did not achieve ROSC by hospital arrival, which questions the role of aggressive management beyond the emergency department.