GPT CVS Notes

Question 1

What are the five phases of the cardiac cycle?

Answer 1

Atrial systole, Isovolumetric contraction, Ventricular ejection, Isovolumetric relaxation, Early ventricular filling.

Question 2

What causes the first heart sound (S1)?

Answer 2

Closure of the AV valves (mitral and tricuspid) at the start of ventricular systole.

Question 3

What causes the second heart sound (S2)?

Answer 3

Closure of the semilunar valves (aortic and pulmonary) at the start of ventricular diastole.

Question 4

What three factors influence stroke volume?

Answer 4

Preload (EDV), Afterload (resistance), and Contractility (strength of contraction).

Question 5

Describe the cardiac conduction pathway in order.

Answer 5

SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers.

Question 6

What ion influx causes Phase 0 in ventricular myocyte action potential?

Answer 6

Fast Na⁺ influx.

Question 7

What ions contribute to the plateau phase (Phase 2) in ventricular myocyte action potential?

Answer 7

Ca²⁺ influx balanced with K⁺ efflux.

Question 8

What ion movement causes repolarization in ventricular myocytes?

Answer 8

K⁺ efflux (outflow).

Question 9

What is unique about the SA node action potential compared to ventricular myocytes?

Answer 9

SA node has no Phase 1 or 2; Phase 0 is due to Ca²⁺ influx, and it has spontaneous depolarization via funny current (Na⁺ influx).

Question 10

What is the resting membrane potential of ventricular myocytes?

Answer 10

Approximately −90 mV.

Question 11

What is the resting membrane potential of SA node pacemaker cells?

Answer 11

Approximately −60 mV (unstable resting potential).

Question 12

What causes the spontaneous depolarization (Phase 4) in SA node cells?

Answer 12

Funny current (If) Na⁺ influx and T-type Ca²⁺ channels.

Question 13

What is the Frank-Starling law?

Answer 13

Increased ventricular filling (preload) increases contraction strength and stroke volume up to a physiological limit.

Question 14

How do sympathetic and parasympathetic stimulation affect the heart?

Answer 14

Sympathetic (β1 receptors) increases HR and contractility; Parasympathetic (vagus nerve) decreases HR.

Question 15

What is the formula for cardiac output?

Answer 15

Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV).

Question 16

What does ejection fraction (EF) represent and how is it calculated?

Answer 16

EF = Stroke Volume (SV) / End-Diastolic Volume (EDV); measures % of blood ejected per beat (~55-70%).

Question 17

Which cardiac cycle phase corresponds to the P wave on ECG?

Answer 17

Atrial systole (atrial depolarization).

Question 18

What ions are involved in the pacemaker action potential’s Phase 0?

Answer 18

Calcium (Ca²⁺) influx via L-type channels.

Question 19

What factors increase myocardial oxygen demand?

Answer 19

Increased heart rate, contractility, afterload, preload, wall tension, and hypertrophy.

Question 20

When does coronary perfusion primarily occur during the cardiac cycle?

Answer 20

During diastole.

Question 21

What does the pressure-volume loop demonstrate?

Answer 21

Relationship of ventricular volume and pressure throughout the cardiac cycle, illustrating preload, afterload, contractility, stroke volume, and ejection fraction.

Question 22

What causes the “funny current” in SA node cells?

Answer 22

Slow Na⁺ influx via hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

Question 23

What does isovolumetric contraction mean?

Answer 23

Ventricles contract with all valves closed, building pressure but no volume change.

Question 24

What does isovolumetric relaxation mean?

Answer 24

Ventricles relax with all valves closed, pressure drops but volume remains constant.

Question 25

What is the mechanism of action of GTN spray, including the role of GTP?

Answer 25

GTN is converted to nitric oxide (NO), which activates guanylate cyclase. This enzyme converts GTP into cGMP. Increased cGMP causes smooth muscle relaxation and vasodilation, especially of veins. This reduces preload and myocardial oxygen demand, relieving angina.