Pharmacology I Drugs Used to Treat Arrhythmias

Arrhythmias Needing Treatment: Atrial Fibrillation/Flutter (AF) Supraventricular Tachycardia (SVT) Ventricular Tachycardia (VT)

Drug Classifications: Ia Used For: Used to treat SVT, AF, VT Mechanism: Blocks Na+ Channels (slows action potential) ECG Effects: QRS and Q-T interval Examples: Quinidine (Quinora), Procainamide (Pronestyl), Disopyramide (Norpace)

Other Effects: Class Ia Slight increase in resting HR Causes peripheral vasodilation Which decreases TPR Which decreases BP Supresses PVC’s Quinidine Toxicity: Prolonged Q-T: Causes polymorphic VT –”Torsades de Pointe” Syncope

Exercise Capacity: Class Ia Drugs (ACSM Manual) No Change in Exercise Tolerance Exercise ECG: Prolonged Q-T intervals “False Positive” ST changes Exercise HR/BP unaffected

Drug Classification: Ib Used For: VT Mechanism: Blocks Na+ channels ECG Effects: Decreased Q-T Interval Examples: Lidocaine (Xylocaine), Tocainide (Tonocard), Phenytoin (Dilantin)

Other Effects: Class Ib Increases Preload Decreases Contractility (Reduces Ejection Fraction) Lidocaine Toxicity: May reduce CO and BP excessively Nevertheless: Well tolerated by CHF patients NO Significant Exercise Effects

Drug Classification: II Used For: SVT and AF Mechanism: Blocks Beta receptors for SNS and Adrenal stimulation ECG Effects: Prolong P-R interval and reduce HR Examples - Beta Adrenergic Blockers: Inderal, Lopressor, Corzide

Other Effects: ß-Blockers Reduce risk of prolonged Q-T intervals Reduces all types of tachycardias Adverse Effects: May disrupt glucose control and Hypoglycemic symptoms in Diabetics May exacerbate Cardiac failure in CHF Sudden Withdrawal is DANGEROUS

Exercise Effects: II Very Common Cardiac Drugs Exercise Tolerance: Improved in patients with angina Decreased in non-anginal patients Exercise ECG: HR and ischemic changes Hemodynamics: HR and BP at rest and Exercise

Drug Classification: III Used For: SVT, VT and AF Mechanisms: Na+/K+ channel blocker and many others ECG Effect: Prolong Q-T Examples: NAPA, Amiodarone

Other EffectsIII Other Effects: III Slows HR Decreases TPR (BP too) Increases Coronary Artery blood flow Slightly reduces contractility ADVERSE: symptomatic sinus brady, AV blocks, sinus arrest

Exercise Effects: III Exercise Tolerance: No change Exercise ECG: Decreased HR Hemodynamics: Decreased HR

And Finally: Class IV

Drug Classification: IV Used For: SVT and AF Mechanisms: Ca++ Channel Blockers ECG Effects: Decrease HR and Increase PR- Interval Examples: Verapamil (Calan), Diltiazem (Cardizem)

Other Effects: Class IV Used more for other cardiac effects – especially hypertension and ischemia Uncontrolled AF: Reduces Ventricular rate in AF (>100) Adverse Effects: Hypotension, bradycardia and rarely, ventricular asystole

Exercise Effects: IV Exercise Tolerance: Improved in patients with angina Exercise ECG: Reduced HR and ischemic ST changes Hemodynamics: Reduced blood pressure

What About Digitalis?

Cardiac Glycosides: Nightshade plant… Used For: SVT and AF Mechanisms: Inhibits Na+/K+- ATPase activity (maintains resting potential…) ECG Effects: QRS and Q-T Examples: Lanoxin

Other Effects: Digitalis Most commonly used to treat CHF Great Risk of Toxicity: Serum levels monitored closely Tachyarrhythmias Anorexia “Halo Vision” when looking at lights

Exercise And Digitalis: Exercise Tolerance: Improved in patients with CHF or AF ECG Effects: “Scooping” ST segment Hemodynamics: Some decrease in patients with AF /CHF