Cardiac Pharmacology

Comprehensive vocabulary flashcards covering cardiovascular pharmacology, Vaughan-Williams antiarrhythmic classifications, mechanism of action, clinical indications, contraindications, adverse effects, and dosing protocols.

Vaughan-Williams Antiarrhythmic Classification System

A classification scheme categorizing antiarrhythmics into Class IA and IB (Sodium Channel Blockers that widen the QRS and prolong the QT), Class II (Beta-Blockers that prolong the PR interval and cause bradycardia), Class III (Potassium Channel Blockers that prolong the QT interval), Class IV (Calcium Channel Blockers that prolong the QT interval and cause bradycardia), and Miscellaneous agents (such as Adenosine and Digoxin).

Adenosine

A nucleoside antiarrhythmic that binds to Adenosine $A_1$ receptors, causing an efflux of potassium and inhibiting calcium influx in slow potential cells, hyperpolarizing autorhythmic cells (SA/AV node) and slowing AV conduction. It is the first-line medication for stable narrow-complex SVT.

Adenosine Administration and Dosing

Administered as a rapid IV/IO push followed immediately by a rapid $20\,\text{mL}$ fluid flush (ideally using a 3-way stopcock). The adult 1st dose is $6\,\text{mg}$; if ineffective, the 2nd dose is $12\,\text{mg}$. Initial doses should be reduced by half in patients on dipyridamole or carbamazepine, heart transplant recipients, or if given via central venous access.

Adenosine Contraindications

Contraindicated in atrial fibrillation (A-Fib), atrial flutter (A-Flutter), Torsades de Pointes, poison/drug-induced tachycardia, 2nd- or 3rd-degree AV blocks, and Wolff-Parkinson-White (WPW) syndrome.

Albuterol

A sympathetic beta agonist with preference for $\beta_2$ adrenergic receptors. It is indicated for bronchospasm, allergic reactions/anaphylaxis, and hyperkalemia.

Albuterol Dosing

For bronchospasm: $2.5\,\text{mg} / 3\,\text{mL}$ via small-volume nebulizer (SVN), repeated every $15\text{--}20\,\text{minutes}$ as needed. For hyperkalemia: $10\text{--}20\,\text{mg}$ via large-volume nebulizer (LVN) over $15\,\text{minutes}$, repeated as needed.

Amiodarone

A Class III antiarrhythmic that slows potassium efflux to delay myocardial repolarization. Indicated for VF/pulseless VT unresponsive to CPR, defibrillation, and epinephrine, as well as recurrent stable VT with a pulse.

Amiodarone Cardiac Arrest Dosing

For VF/pulseless VT unresponsive to CPR, shock delivery, and epinephrine: 1st dose is $300\,\text{mg}$ IV/IO push; 2nd dose is $150\,\text{mg}$ IV/IO push if needed.

Amiodarone Infusion Protocols

For life-threatening arrhythmias with a pulse: 1st dose is a rapid infusion of $150\,\text{mg}$ over $10\,\text{minutes}$ ($15\,\text{mg/min}$, repeatable every $10\,\text{minutes}$); followed by a slow infusion of $360\,\text{mg}$ IV over $6\,\text{hours}$ ($1\,\text{mg/min}$); and a maintenance infusion of $540\,\text{mg}$ over $18\,\text{hours}$ ($0.5\,\text{mg/min}$). Terminal half-life lasts up to $40\,\text{days}$.

Aspirin

An NSAID and cyclooxygenase (COX) inhibitor. It blocks the COX enzyme from acting upon arachidonic acid, preventing the generation of thromboxane $A_2$ and thereby inhibiting platelet activation and aggregation in acute coronary syndromes.

Aspirin Administration and Dosing

Administered as $160\text{--}325\,\text{mg}$ PO of non-enteric coated chewable tablets. Enteric-coated formulations must be avoided when treating acute ischemic cardiac symptoms.

Atropine

A parasympatholytic anticholinergic agent that selectively blocks muscarinic acetylcholine receptors, suppressing parasympathetic vagal tone and allowing sympathetic tone to increase heart rate.

Atropine Bradycardia Dosing

Given as $1\,\text{mg}$ IV push every $3\text{--}5\,\text{minutes}$ ($3\,\text{minutes}$ in severe clinical instability) up to a maximum total of $0.04\,\text{mg/kg}$ or $3\,\text{mg}$. Doses below $0.5\,\text{mg}$ must be avoided because they may cause paradoxical slowing of the heart rate.

Calcium Chloride

An essential element and electrolyte solution indicated for hyperkalemia, hypocalcemia, adverse effects from calcium channel blocker overdose, and hypotension secondary to diltiazem administration.

Calcium Chloride Dosing and Precautions

Dosed at $0.5\text{--}1\,\text{g}$ slow IV over $3\text{--}5\,\text{minutes}$ (or $250\text{--}500\,\text{mg}$ for diltiazem-induced hypotension). Rapid injection can cause severe bradycardia, coronary spasm, and asystole. Precipitates when mixed with sodium bicarbonate.

Captopril

An ACE inhibitor that prevents the conversion of angiotensin I to angiotensin II, resulting in systemic vasodilation and reduced renal water retention. Indicated for severe CHF with hypertension alongside nitrates and CPAP, dosed at $25\,\text{mg}$ PO.

Diazepam

A benzodiazepine that binds to GABA receptors, triggering an influx of chloride ions to cause central nervous system depression. Indicated for tachycardia from stimulant overdose, sustained seizures, anxiety, and sedation at adult doses of $2.5\text{--}10\,\text{mg}$ slow IV/IO/IM in $2.5\,\text{mg}$ increments.

Diltiazem

A Class IV antiarrhythmic (calcium channel blocker) that slows action potentials in autorhythmic cardiac cells by inhibiting calcium channels. It is the first-line medication for atrial fibrillation and atrial flutter with rapid ventricular response (ventricular rates $>150\,\text{bpm}$).

Diltiazem Dosing

Administered IV as a 1st dose of $0.25\,\text{mg/kg}$ (maximum single dose $20\,\text{mg}$), followed by a 2nd dose of $0.35\,\text{mg/kg}$ (maximum single dose $25\,\text{mg}$) if rate control is not achieved.

Dobutamine

A synthetic sympathetic agonist with alpha- and beta-adrenergic action whose inotropic (contractility) properties are significantly more pronounced than its chronotropic (rate) properties. Indicated for cardiac pump failure (CHF) with hypotension.

Dobutamine Dosing and Restrictions

Administered as an IV infusion at $2\text{--}20\,\mu\text{g/kg/min}$, titrated so baseline heart rate does not increase by more than $10\%$. It must not be mixed with sodium bicarbonate and is contraindicated in uncorrected hypovolemia.

Dopamine

A sympathetic alpha- and beta-adrenergic agonist that functions as a rate-dependent vasopressor with positive inotropic, chronotropic, and dromotropic effects. Indicated for CHF, hypotensive shock, and second-line for symptomatic bradycardia after atropine.

Dopamine Dosing and Contraindications

Infused at $2\text{--}20\,\mu\text{g/kg/min}$ titrated carefully to patient response (never infused wide open). Contraindicated in uncorrected hypovolemia and pheochromocytoma; must never be mixed with sodium bicarbonate.

Enalapril

An ACE inhibitor that prevents the production of angiotensin II, decreasing systemic vascular resistance and fluid retention. Indicated for severe CHF with hypertension at an initial dose of $2.5\,\text{mg}$ PO titrated up to $20\,\text{mg}$ PO.

Epinephrine 1:10,000

A powerful endogenous sympathetic agonist stimulating both alpha- and beta-adrenergic receptors. It increases heart rate, myocardial contractility, systemic vascular resistance, and coronary perfusion pressure.

Epinephrine 1:10,000 Indications and Dosing

Indicated for cardiac arrest ($1\,\text{mg}$ IVP/IOP every $3\text{--}5\,\text{minutes}$) and for symptomatic bradycardia, normovolemic hypotension, or severe anaphylaxis ($2\text{--}10\,\mu\text{g/min}$ infusion prepared by mixing $1\,\text{mg}$ into a $1{,}000\,\text{mL}$ IV bag).

Fentanyl

A synthetic Schedule II opioid agonist providing analgesia and sedation through opiate receptor binding. It is markedly more potent than morphine ($100\,\mu\text{g}$ of fentanyl equals $10\,\text{mg}$ of morphine).

Fentanyl Dosing and Administration

Administered at $1\,\mu\text{g/kg}$ to a maximum single dose of $100\,\mu\text{g}$ via IV, IO, IM, or IN (maximum $1\,\text{mL}$ volume per nare), repeatable every $5\text{--}10\,\text{minutes}$ PRN. Must be pushed slowly to prevent chest wall rigidity.

Furosemide

A loop diuretic that blocks the reabsorption of sodium, chloride, and water within the loop of Henle in the kidney tubules, accelerating urine production. Indicated for acute pulmonary edema (with SBP $>90\text{--}100\,\text{mmHg}$) and hypertensive emergencies.

Furosemide Dosing

Dosed at $0.5\text{--}1\,\text{mg/kg}$ IV over $1\text{--}2\,\text{minutes}$; can be doubled to $2\,\text{mg/kg}$ slowly over $1\text{--}2\,\text{minutes}$ if there is no response. For new-onset pulmonary edema with suspected hypovolemia, administer $<0.5\,\text{mg/kg}$ slow IV.

Glucagon

A polypeptide hormone that binds glucagon receptors and stimulates adenylate cyclase to increase intracellular cAMP, which up-regulates calcium channels in SA and AV nodal cells independent of beta-adrenergic receptors.

Glucagon Toxicology Dosing

Indicated specifically for symptomatic bradycardia caused by beta-blocker or calcium channel blocker toxicity. Dosed at $3\text{--}10\,\text{mg}$ slow IV over $3\text{--}5\,\text{minutes}$, followed by an IV infusion of $3\text{--}5\,\text{mg/hr}$.

Labetalol

A non-cardioselective beta-blocker that competitively antagonizes $\beta_1$, $\beta_2$, and $\alpha_1$ adrenergic receptors, resulting in slowing of the heart rate and systemic blood pressure reduction through peripheral vasodilation.

Labetalol Dosing and Contraindications

Administered as $10\,\text{mg}$ IV/IO push over $1\text{--}2\,\text{minutes}$, repeatable every $10\,\text{minutes}$ up to a maximum dose of $150\,\text{mg}$ (titrated to SBP $140\text{--}150\,\text{mmHg}$). Contraindicated in STEMI patients showing signs of heart failure, low cardiac output, or cardiogenic shock risk.

Lidocaine

A Class IB antiarrhythmic that blocks fast voltage-gated sodium channels in cardiac tissue, slowing ventricular depolarization and decreasing abnormal automaticity.

Lidocaine Ventricular Arrhythmia Dosing

For cardiac arrest from VF/pVT: initial dose is $1\text{--}1.5\,\text{mg/kg}$ IV/IO push; refractory VF may receive $0.5\text{--}0.75\,\text{mg/kg}$ every $5\text{--}10\,\text{minutes}$ up to a max of $3\,\text{mg/kg}$. A perfusing arrhythmia may receive a maintenance infusion of $1\text{--}4\,\text{mg/min}$ ($30\text{--}50\,\mu\text{g/kg/min}$).

Magnesium Sulfate

An essential electrolyte and mineral that acts as a physiological calcium antagonist, functioning similarly to a calcium channel blocker. It stabilizes excitable cardiac membranes.

Magnesium Sulfate Cardiac Indications and Dosing

Indicated during cardiac arrest only when Torsades de Pointes (TdP) or hypomagnesemia is suspected ($1\text{--}2\,\text{g}$ diluted in $10\,\text{mL}$ IV/IO). For pulsatile TdP: $1\text{--}2\,\text{g}$ in $50\text{--}100\,\text{mL}$ over $5\text{--}60\,\text{minutes}$, followed by a maintenance infusion of $0.5\text{--}1\,\text{g/hr}$.

Metoprolol

A cardioselective $\beta_1$-adrenergic receptor blocker that reduces heart rate, contractility, and cardiac output, lowering myocardial oxygen demand in tachyarrhythmias and acute myocardial infarction.

Metoprolol Dosing

Administered as $5\,\text{mg}$ slow IV every $5\,\text{minutes}$ up to 3 total doses (maximum $15\,\text{mg}$), titrated to a systolic blood pressure between $140\text{--}150\,\text{mmHg}$ and/or a heart rate below $150\,\text{bpm}$.

Midazolam

A short-acting benzodiazepine that binds GABA receptors, increasing chloride conductance to induce sedation, anxiolysis, muscle relaxation, and anterograde amnesia. Indicated for seizures, RSI induction, chemical restraint, and post-intubation bucking.

Midazolam Seizure and RSI Dosing

For active seizures: adult dose is $0.1\,\text{mg/kg}$ in $2\,\text{mg}$ IV/IO increments (maximum single dose $5\,\text{mg}$) or $5\,\text{mg}$ IM/IN. For RSI induction: $0.1\text{--}0.3\,\text{mg/kg}$ IV/IO (maximum $10\,\text{mg}$). For endotracheal tube bucking: $0.05\,\text{mg/kg}$ slow IV/IO over $1\text{--}2\,\text{minutes}$.

Morphine

A natural opioid Schedule II narcotic that binds central opiate receptors to produce analgesia, sedation, and mild venodilation, which lowers cardiac preload. Indicated for ischemic chest pain refractory to nitroglycerin.

Morphine Acute Coronary Syndrome Dosing

For STEMI: initial dose of $2\text{--}4\,\text{mg}$ slow IV/IO, repeatable at $2\text{--}8\,\text{mg}$ every $5\text{--}15\,\text{minutes}$. For NSTEMI-ACS: dosed at $0.1\,\text{mg/kg}$ slow IV/IO or IM up to a maximum of $10\,\text{mg}$. Contraindicated in systolic blood pressures below $90\,\text{mmHg}$.

Nitroglycerin

An organic nitrate and potent vascular smooth muscle relaxant that promotes venous dilation (reducing preload and myocardial wall tension) and dilates coronary arteries to enhance myocardial collateral blood flow.

Nitroglycerin Contraindications

Contraindicated in hypotension (SBP $<90\,\text{mmHg}$ or $\ge 30\,\text{mmHg}$ below baseline), severe bradycardia ($<50\,\text{bpm}$), extreme tachycardia ($>100\,\text{bpm}$), right ventricular infarction (RVI), phosphodiesterase-5 inhibitor use within 48 hours, and increased intracranial pressure.

Nitroglycerin Dosing and Handling

Dosed at $0.4\,\text{mg}$ sublingually via tablet or spray every $5\,\text{minutes}$ up to 3 total doses (maximum $1.2\,\text{mg}$). Sublingual spray canisters must never be shaken because shaking alters metered valve delivery.

Norepinephrine

A potent sympathomimetic amine with predominant $\alpha$-adrenergic receptor agonism and modest $\beta_1$ activity, producing intense peripheral vasoconstriction and mild inotropic stimulation without significant chronotropy.

Norepinephrine Dosing and Adverse Reactions

Administered as a continuous IV/IO infusion at $0.1\text{--}0.5\,\mu\text{g/kg/min}$ for normovolemic hypotension, septic shock, or cardiogenic shock. Extravasation causes severe localized tissue necrosis.

Ondansetron

A competitive and selective serotonin $5\text{-HT}_3$ receptor antagonist located centrally in the chemoreceptor trigger zone and peripherally on vagal nerve terminals, used to prevent and manage nausea and vomiting.

Ondansetron Dosing and Adverse Effects

Administered at $4\text{--}8\,\text{mg}$ slow IV, IM, or PO. Can cause hypotension, tachycardia, extrapyramidal reactions, and dose-dependent prolongation of the QT interval.

Procainamide

A Class IA antiarrhythmic that blocks fast sodium channels, prolonging action potential duration, slowing conduction velocity, and suppressing automaticity. Indicated for stable monomorphic VT with a pulse and pre-excitation rhythms like Wolff-Parkinson-White.

Procainamide Four Endpoints of Administration

Infused at $20\,\text{mg/min}$ (or up to $50\,\text{mg/min}$ in urgent situations) and must be stopped immediately when: 1. The arrhythmia is terminated; 2. Severe hypotension ensues; 3. The QRS complex widens by more than $50\%$ of its baseline; or 4. The maximum cumulative dose of $17\,\text{mg/kg}$ is reached.

Sodium Bicarbonate

A systemic alkalinizing agent that dissociates to provide bicarbonate ions, buffering excess hydrogen ions ($\text{H}^+$) to raise blood pH and reverse metabolic acidosis manifestations. Indicated for hyperkalemia and bicarbonate-responsive intoxications (TCAs, aspirin, cocaine, DKA).

Sodium Bicarbonate Dosing and Contraindications

Dosed at $1\,\text{mEq/kg}$ IV bolus for suspected systemic acidosis and $50\,\text{mEq}$ IV bolus for hyperkalemia. It is contraindicated for routine administration in undifferentiated cardiac arrest and forms insoluble precipitates when co-infused with calcium salts.

Verapamil

A non-dihydropyridine Class IV antiarrhythmic and calcium channel blocker that slows L-type calcium influx in SA and AV nodal tissues, slowing AV nodal conduction and prolonging refractory periods.

Verapamil Dosing and Precautions

Given as a 1st dose of $2.5\text{--}5\,\text{mg}$ IV/IO bolus over $2\text{--}3\,\text{minutes}$, followed by a 2nd dose of $5\text{--}10\,\text{mg}$ after $15\text{--}30\,\text{minutes}$ if needed (maximum total dose $20\,\text{mg}$). Produces a more profound hypotensive response than diltiazem and can cause severe cardiogenic shock or heart block if given concurrently with beta-blockers.