Safety and Effectiveness of Field Nitroglycerin in Patients with Suspected ST Elevation Myocardial Infarction

Abstract

Objective: While widely used in the treatment of cardiac conditions, only limited data characterize out-of-hospital nitroglycerin (NTG) use. We sought to determine the safety of out-of-hospital sublingual NTG administered for suspected ST-segment elevation myocardial infarction (STEMI) and its effect on the patient's pain score. Methods: We prospectively identified adult patients with suspected STEMI transported by paramedics to three percutaneous Coronary Intervention PCI-capable hospitals in a large urban-suburban emergency medical services (EMS) system. We compared patients who received field NTG to those who did not. The primary outcome was the change in systolic blood pressure (SBP) between initial EMS measurement and emergency department (ED) triage vital signs. Secondary outcomes included the frequency of hypotension (SBP < 100 mmHg) and bradycardia (HR < 60) on ED arrival, drop in SBP ≥ 30 mmHg, out-of-hospital cardiac arrest (OHCA), and the change in pain score compared to an a priori threshold of −1.39. Results: Among 940 EMS transports for suspected STEMI, we excluded 160 for initial SBP < 100 mmHg, leaving 780 subjects for the analysis. Median age was 67 with 61% male. NTG was administered to 340 (44%) patients. The median change in SBP was −10 mmHg (IQR −27, 2) and −3 mmHg (IQR −20, 9) in patients treated with and without NTG, respectively. The median difference in the decrease in SBP was 6 mmHg (95% CI 3, 9 mmHg). The frequencies of ED hypotension and bradycardia, the drop in SBP ≥ 30 mmHg, and the OHCA did not differ between groups. For patients with an initial pain score > 0, the average change in pain score for patients treated with NTG was −2.6 (95% CI −3.0, −2.2), while patients who did not receive NTG had a change in pain score of −1.4 (95% CI −1.8, −1.0). Conclusion: In this cohort, field NTG did not result in a clinically significant decrease in blood pressure when compared with patients who did not receive NTG. However, NTG did cause a clinically significant reduction in pain.

Key words:

• ST elevation myocardial infarction
• emergency medical services
• nitrates
• pharmacology