Cardiac Metabolism and Coronary Circulation (Goldhaber)

Question 1

What kind of energy/metabolism does the heart prefer to use?

Answer 1

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)

Question 2

Myocardial Oxygen Consumption (MvO2)

Answer 2

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

Question 3

Heart’s energy expenditure

Answer 3

Cellular maintenance = 20%

Electrical properties = 1%

Volume work = 15%

Pressure work = 64%

(Pressure work is more costly than volume work)

Question 4

What increases heart O2 consumption?

Answer 4

Afterload (increase in vascular resistance)

Preload

Contractility

Heart rate

Wall stress/tension

Question 5

Diseases that increase MvO2

Answer 5

Aortic stenosis (BP not necessarily high, but heart has to work harder to get blood out–increased afterload)

Hypertension

Tachycardia

Question 6

What is the blood supply for the anterior papillary muscle and the posterior papillary muscle?

Answer 6

Anterior papillary muscle: LAD and Left Circumflex artery

Posterior papillary muscle: Right coronary artery (if you lose RCA, posterior papillary muscle loses blood supply)

Question 7

Right dominant (coronary arteries)

Answer 7

Right coronary artery feeds inferior wall and posterior LV (and SA and AV nodes)

90% of people are right dominant

Question 8

Left dominant (coronary arteries)

Answer 8

Left coronary artery supplies inferior wall and posterior LV (and SA and AV nodes)

Question 9

Codominant

Answer 9

Branches of right and left coronary arteries contribute more or less equally to supply heart walls

Question 10

How do you get more oxygen to the myocardium?

Answer 10

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%

Question 11

How do we regulate coronary flow?

Answer 11

1) Adenosine
2) Autonomic Nervous System (parasympathetic –> vasodilation and sympathetic –> vasoconstriction)
3) Acidosis (pH)
4) Hyperkalemia (increased K+)
5) NO (endothelium-dependent relaxing factor)

Question 12

Flow reserve

Answer 12

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

Question 13

When do we get coronary flow to the heart muscle?

Answer 13

During diastole!

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

Question 14

Stroke Work

Answer 14

Stroke Work = Stroke Volume x Aortic Pressure

Area within the pressure-volume loop

Question 15

Cardiac minute work

Answer 15

Cardiac minute work = CO x Aortic Pressure

Two components: volume work (external) and pressure work (internal)