Pain Management in Inferior Wall STEMI
Morphine sulfate (2-4 mg IV with increments of 2-8 mg IV repeated at 5-15 minute intervals) is the analgesic of choice for pain management in inferior wall STEMI. 1, 2
Primary Analgesic Approach
Morphine remains a Class I recommendation (highest level) for STEMI patients because these patients either have received reperfusion or are not candidates for reperfusion, and continuing pain requires relief in either case 1
The standard dosing protocol is 2-4 mg IV initially, with increments of 2-8 mg IV repeated at 5-15 minute intervals as needed 1, 2
Morphine provides multiple benefits beyond analgesia: it relieves pain, reduces anxiety, decreases work of breathing, and has favorable hemodynamic effects without the profound preload reduction seen with nitrates 3
Nitroglycerin Use and Critical Contraindications
Before administering morphine, patients should receive up to 3 doses of sublingual or aerosol nitroglycerin at 3-5 minute intervals until pain is relieved or low blood pressure limits its use 1
Nitroglycerin is absolutely contraindicated in inferior wall STEMI if right ventricular infarction is present, as this can precipitate cardiovascular collapse 1, 4
Additional nitroglycerin contraindications include: systolic blood pressure <90 mmHg or ≥30 mmHg below baseline, extreme bradycardia (<50 bpm), or tachycardia without heart failure (>100 bpm) 1, 4
For inferior wall STEMI specifically, always obtain right-sided ECG leads (V3R, V4R) to rule out right ventricular involvement before administering nitroglycerin 4
Additional Pain Management Options
Acetaminophen 500 mg orally every 6 hours can be added if additional pain control is needed beyond morphine 3
If post-infarction pericarditis develops and is not adequately controlled with aspirin alone, colchicine 0.6 mg every 12 hours orally can be added 3
Absolute Contraindications for Pain Management
NSAIDs (both non-selective and COX-2 selective agents) are absolutely contraindicated during hospitalization for STEMI due to increased risk of mortality, reinfarction, hypertension, heart failure, and myocardial rupture 1, 3
Any NSAIDs the patient was taking before STEMI should be discontinued immediately at presentation 1
Glucocorticoids should be avoided for treatment of pericarditis after STEMI as they are potentially harmful 3
Safety Considerations with Morphine
While morphine is the drug of choice, monitor for potential adverse effects including respiratory depression, hypotension (particularly in ambulatory patients), bradycardia, nausea, vomiting, and urinary retention 2
Use caution and reduced doses in elderly patients, those with renal or hepatic impairment, or patients with CNS depression 2
Recent observational data suggest potential concerns about morphine delaying antiplatelet absorption and possibly affecting reperfusion, but no prospective randomized trials have demonstrated adverse outcomes, and morphine remains the guideline-recommended analgesic 5, 6, 7
One large study of 969 anterior STEMI patients found no significant difference in major adverse cardiovascular events at 1 year between those who received morphine (26.2%) versus those who did not (22.0%), with similar all-cause mortality rates 5
Adjunctive Considerations for Inferior Wall STEMI
Aspirin (non-enteric) should be given as soon as possible unless the patient has known aspirin allergy or active gastrointestinal hemorrhage 1
Oral beta-blockers should be administered within the first 24 hours in patients without contraindications such as signs of heart failure, low-output state, or increased risk for cardiogenic shock 1, 3
For inferior wall STEMI with bradycardia and hypotension, atropine 0.5-0.6 mg IV (not exceeding 2.5 mg cumulative dose over 2.5 hours) may be indicated, as bradycardia in this setting can worsen ventricular arrhythmias 8