Presentation on Class 2 Drugs: Beta Blockers

Introduction

• Focus: Class 2 antiarrhythmic drugs known as beta blockers
• Objectives:
  • Describe usage and effects of beta blockers
  • Understand impact on cardiac status and care

Beta Blockers Overview

• Von Williams Classification: Class 2 agents
• Target: Action potential of pacemaker cells affecting heart rate
• Key Properties of Cardiac Cells:
  • Contractility: Ability to shorten and return to original length
  • Automaticity: Ability to depolarize spontaneously
  • Excitability: Ability to depolarize in response to an impulse
  • Conductivity: Ability to conduct electrical impulses

Mechanism of Action

• Beta Adrenergic Receptor Antagonists
• Indirectly block pacemaker cell current and calcium channels
• Decrease slope of phase 4, reducing impulse firing rate
• Effects: Decreased automaticity, prolonged AV node repolarization, increased refractory period

Types of Beta Receptors

• Beta 1 Receptors:
  • Located in heart, kidneys, eyes
  • Increase heart rate, conduction, automaticity, and contractility
• Beta 2 Receptors:
  • Located in lungs, vascular smooth muscle, GI tract
  • Cause vasodilation, bronchial dilation, increased intestinal motility
• Alpha Receptors: Cause vasoconstriction

Effects of Beta Blockers

• Heart Effects:
  • Decrease heart rate, automaticity, contractility
  • Negative chronotropic, dromotropic, and inotropic effects
• Secondary Actions:
  • Inhibit pro-arrhythmic depolarization, enhance ACE inhibitors

Generations of Beta Blockers

• First Generation: Non-selective (e.g., propranolol)
• Second Generation: Beta 1 selective (e.g., bisoprolol)
• Third Generation: Vasodilator properties (e.g., carvedilol)

Indications for Use

• Arrhythmia Control: Atrial fibrillation, tachycardia, QT syndrome
• Other Uses: Ischemic heart disease, hypertension, heart failure

Contraindications

• Heart conduction issues, asthma, severe peripheral vascular disease
• Caution in lung conditions, some diabetes patients

Adverse Effects

• Respiratory distress, CNS effects, impotence, nausea
• Worsening heart failure initially

Oxygen Supply and Demand

• Beta blockers reduce heart oxygen demand and increase supply
• Target heart rate: 55-60 bpm at rest, <100 bpm during exercise

Specific Beta Blockers

• Propranolol: Non-selective, high brain uptake
• Atenolol: Beta 1 selective, strong cardioselective properties
• Bisoprolol: Highly beta 1 selective, effective in heart failure
• Carvedilol: Third generation, affects alpha and beta receptors
• Metoprolol: Second generation, moderate cardioselectivity

Conclusion

• Beta blockers are crucial in cardiac care, reducing mortality in several conditions including angina and heart failure.
• Must be selected and dosed carefully considering individual patient profiles and potential adverse effects.