Episode Details

1. Anatomy, Perfusion & Conduction

• Layers & Chambers: Heart layers: endocardium, myocardium, epicardium. Pericardium contains 10-15 mL of fluid. LV is 2-3x thicker than RV to pump into systemic circulation.
• Coronary Flow: Perfusion occurs primarily during diastole. LCA (branches into LAD, circumflex) supplies LV/LA/septum. RCA supplies RA/RV/posterior LV. In 90% of people, RCA supplies the AV node/bundle of His; blockages cause conduction defects.
• Electrical System: SA Node → AV Node → Bundle of His → Bundle Branches → Purkinje fibers (impulse in 0.12s).
  • P wave: Atrial depolarization.
  • QRS: Ventricular depolarization.
  • T wave: Ventricular repolarization.
  • U wave: Purkinje repolarization; prominent in hypokalemia.

2. Hemodynamics & Autonomic Control

• Metrics: CO=HR×SV (4-8 L/min). CI adjusts CO for BSA (2.8-4.2 L/min/m²).
• SV Determinants:
  • Preload: End-diastolic stretch (CVP/RV: 2-8 mmHg; PAWP/LV: 6-12 mmHg).
  • Afterload: Force opposing ejection (SVR: 800-1200).
  • Contractility: Contraction force; increased by positive inotropes, decreased by ischemia/acidosis.
• Perfusion: BP=CO×SVR. MAP=3SBP+2DBP​; must be >60 mmHg to prevent vital organ ischemia.
• Regulation: Sympathetic (β-adrenergic) increases HR/contractility; α1​ receptors vasoconstrict. Parasympathetic (vagus) slows HR. Baroreceptors inhibit sympathetic tone under pressure overload, causing vasodilation and bradycardia.

3. Monitoring, Diagnostics & Care

• Invasive Lines: Reference arterial lines to the phlebostatic axis (4th ICS, mid-chest). Too low produces falsely high BP; too high produces falsely low BP. Monitor distal extremity hourly for neurovascular compromise.
• PA Catheter: Hypokalemia, hypomagnesemia, and hypoxia increase cardiac irritability, raising ventricular dysrhythmia risk during insertion.
• Biomarkers:
  • Troponin (cTnT/cTnI): Choice for ACS; rises in 4-6 hrs, peaks 10-24 hrs, persists 10-14 days.
  • BNP / NT-pro-BNP: Distinguishes cardiac vs. respiratory causes of dyspnea.
• Procedures:
  • Cardiac Cath: Pre-op: NPO 6 hrs, check dye allergy, assess distal pulses. Post-op: monitor bleeding, maintain bedrest, assess perfusion, push fluids.
  • TEE: NPO 6 hrs; post-op: withhold oral intake until gag reflex returns.