Myocardial oxygen supply and demand

Heart extracts ¾ of O2 content so ↑ demand requires ↑ supply.

Supply depends on

CaO2
Coronary blood flow (proportional to pressure drop across coronary circulation i.e. aortic root pressure – downstream coronary pressure)
250mls/min at rest

These depend on:
Upstream pressure minus downstream pressure
Upstream pressure

  • LV - Mean and diastolic BP – Most flow in early diastole as B perforating arteries compressed by high pressure (systole)
  • RV - Low pressure RV gets blood supply throughout coronary cycle
Downstream pressure
  • Coronary vascular resistance (fixed (atheroma) and variable (α and ß minimal effect, local metabolites))
  • Ventricular pressures
HR (length of diastole)
Viscosity (↓ in coronary bypass)

Demand depends on:

Ventricular wall tension (afterload (ESWT) and preload (EDWT))
HR
Contractility

Anatomy

RCA supplies SA node and via posterior descending the AV node.
LCA supplies LAD (anterior and septum) and circumflex (lateral, posterior and inferior LV).

Venous drainage is via:
Thebesian veins into LV (shunt)
Coronary sinus (L) and anterior cardiac vein (R) into RA