Pharmacological Interventions in Cardiac Emergencies

Pharmacological Interventions in Cardiac Emergencies

As a paramedic, you carry and administer medications that can restore a heartbeat, correct a lethal rhythm, or prevent a heart attack from becoming fatal. Understanding each drug—not just its name, but why you give it, when you must not give it, and how it works—is a core competency and a patient-safety obligation.

How to Approach Cardiac Pharmacology

Organize every drug around five questions: What class is it? How does it work (mechanism)? When do I give it (indications)? When must I avoid it (contraindications)? How does it get into the body (route)? Dosing specifics are set by your medical director through your regional formulary; always follow local protocols. The goal here is to understand the clinical reasoning behind each drug so you can use it safely.

Key Cardiac Drugs in the Paramedic Formulary

Adenosine

Adenosine is an endogenous nucleoside that briefly blocks conduction through the AV node, essentially hitting a "reset button" on supraventricular tachycardia (SVT). Because its half-life is only a few seconds, it must be given as a rapid IV push followed immediately by a saline flush into a large, proximal vein. It is indicated for stable SVT that has not responded to vagal maneuvers. Contraindications include second- or third-degree heart block, sick sinus syndrome (without a pacemaker), and known hypersensitivity. Warn the patient: transient chest pressure, flushing, and a brief sense of impending doom are common and expected.

Amiodarone

Amiodarone is a broad-spectrum antidysrhythmic that works by blocking sodium, potassium, and calcium channels, as well as having beta-blocking and alpha-blocking properties. It is a first-line antidysrhythmic for ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) that persists after defibrillation and epinephrine. It is also used for stable wide-complex tachycardia. Contraindications include cardiogenic shock, severe sinus-node dysfunction, second- and third-degree AV block (without a pacemaker), and known sensitivity to amiodarone or iodine. Hypotension is a significant side effect during IV infusion.

Atropine

Atropine is a parasympatholytic (anticholinergic) agent that blocks muscarinic receptors, increasing heart rate by removing vagal tone. It is indicated for symptomatic bradycardia. It is not effective—and should not be used—in second-degree Type II (Mobitz II) or third-degree AV block, where transcutaneous pacing is the priority. Avoid atropine in patients with tachycardia.

Epinephrine

Epinephrine (adrenaline) is a catecholamine that stimulates both alpha- and beta-adrenergic receptors. In cardiac arrest, it increases coronary and cerebral perfusion pressure during CPR, making it the primary vasopressor for VF, pulseless VT, pulseless electrical activity (PEA), and asystole. In non-arrest bradycardia refractory to atropine and pacing, an epinephrine infusion may be used. Because it also dramatically increases myocardial oxygen demand, use it thoughtfully in the non-arrest patient.

Lidocaine

Lidocaine is a sodium-channel blocker (Class IB antidysrhythmic) that suppresses ventricular ectopy. It is an alternative to amiodarone for VF/pulseless VT and for stable ventricular dysrhythmias per local protocol. Signs of toxicity—tinnitus, slurred speech, seizures—occur with excessive dosing. It is contraindicated in high-degree heart block and known lidocaine allergy.

Aspirin

Aspirin inhibits platelet aggregation by irreversibly blocking cyclooxygenase (COX), reducing clot formation. In a suspected acute coronary syndrome (ACS), early aspirin administration can reduce myocardial injury. Contraindications include true aspirin allergy and active gastrointestinal bleeding. Ensure the patient can chew and swallow safely before administration.

Nitroglycerin

Nitroglycerin is a vasodilator (nitrate) that reduces preload and myocardial oxygen demand. It is indicated for chest pain associated with ACS and acute pulmonary edema. Critical contraindications: hypotension, right ventricular infarction (suspected inferior MI with right-sided involvement), and recent use of phosphodiesterase-5 inhibitors (such as sildenafil or tadalafil), which can cause severe, refractory hypotension.

Dopamine

Dopamine is a catecholamine with dose-dependent receptor effects. At lower infusion rates it has more dopaminergic effects; at moderate rates it acts primarily on beta-1 receptors (increasing cardiac output); at higher rates it has alpha-adrenergic (vasopressor) effects. It is used for hemodynamically significant hypotension and bradycardia refractory to atropine. Infusion rates are calculated in micrograms per kilogram per minute (mcg/kg/min), making accurate weight-based calculation essential.

Magnesium Sulfate

Magnesium sulfate is a mineral electrolyte that stabilizes cardiac membranes. Its primary cardiac indications are torsades de pointes (a polymorphic VT associated with a prolonged QT interval) and refractory VF/VT. It is given IV and must be administered slowly in the non-arrest patient to avoid hypotension and respiratory depression.

Safety Principles for All Cardiac Drugs

• Verify the six rights every time: right patient, drug, dose, route, time, and documentation.
• Check the formulary—protocols vary by region. Never dose from memory alone when a reference is available.
• Weight-based calculations must be double-checked. A calculation error exceeding 20% can cause serious harm or death.
• Reassess continuously after every intervention. Watch for desired effects and adverse reactions.
• Know your contraindications cold—giving nitroglycerin to a hypotensive patient or a patient who took a PDE-5 inhibitor is a preventable, potentially fatal error.