What kind of energy/metabolism does the heart prefer to use?
Free fatty acids (FFA) via oxidative metabolism (through citric acid cycle)
(Rather than glucose via aerobic glycolysis, so clycogen is just stored since we have robust supply of FFA for heart to use)
Myocardial Oxygen Consumption (MvO2)
Amount of oxygen the heart must consume in order to perform work
MvO2 varies very well just as it's needed to match cardiac minute work
Heart's energy expenditure
Cellular maintenance = 20%
Electrical properties = 1%
Volume work = 15%
Pressure work = 64%
(Pressure work is more costly than volume work)
What increases heart O2 consumption?
Afterload (increase in vascular resistance)
Diseases that increase MvO2
Aortic stenosis (BP not necessarily high, but heart has to work harder to get blood out--increased afterload)
What is the blood supply for the anterior papillary muscle and the posterior papillary muscle?
Anterior papillary muscle: LAD and Left Circumflex artery
Posterior papillary muscle: Right coronary artery (if you lose RCA, posterior papillary muscle loses blood supply)
Right dominant (coronary arteries)
Right coronary artery feeds inferior wall and posterior LV (and SA and AV nodes)
90% of people are right dominant
Left dominant (coronary arteries)
Left coronary artery supplies inferior wall and posterior LV (and SA and AV nodes)
Branches of right and left coronary arteries contribute more or less equally to supply heart walls
How do you get more oxygen to the myocardium?
Have to increase FLOW by decreasing coronary vascular resistance
Myocardium already extracts a huge percentage of oxygen from the coronary blood (65-75% compared to rest of the body which is 25%), and during exercise extracts 90%
How do we regulate coronary flow?
2) Autonomic Nervous System (parasympathetic --> vasodilation and sympathetic --> vasoconstriction)
3) Acidosis (pH)
4) Hyperkalemia (increased K+)
5) NO (endothelium-dependent relaxing factor)
Normal coronary vessels can increase flow 3-4 times to meet normal demands.
This increased potential is called coronary flow reserve
Can measure by inserting catheter into coronary artery then adding adenosine to cause max dilation then measure what the diff in flow is, and get difference which is coronary flow reserve
When do we get coronary flow to the heart muscle?
80% of flow occurs during diastole at basal heart rate
Flow ceases and can even reverse (go back into artery) during systole
Reactive hyperemia occurs with each beat
Stroke Work = Stroke Volume x Aortic Pressure
Area within the pressure-volume loop
Cardiac minute work
Cardiac minute work = CO x Aortic Pressure
Two components: volume work (external) and pressure work (internal)