Cardiac Cycle and ECG

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Questions and Answers

What is the primary role of the sino-atrial (SA) node in the mammalian heart?

To initiate the electrical impulses that drive the cardiac cycle. (correct)
To repolarize the atrial muscle cells.
To rapidly conduct electrical signals through the ventricles.
To delay the electrical impulse, allowing for ventricular filling.

What is the correct sequence of electrical signal transmission in the heart's conduction system, starting from the initiation of the impulse?

SA node → Bundle of His → AV node → Purkinje fibers
SA node → AV node → Purkinje fibers → Bundle of His
SA node → AV node → Bundle of His → Purkinje fibers (correct)
AV node → SA node → Bundle of His → Purkinje fibers

Why is there a conduction delay at the atrioventricular (AV) node?

To speed up the transmission of electrical signals.
To allow sufficient time for ventricular filling. (correct)
To allow for atrial repolarization before ventricular contraction.
To prevent the ventricles from contracting prematurely.

What does the QRS complex represent on an ECG?

Ventricular depolarization (B) Signup and view all the answers

What does the T wave on an ECG represent?

Ventricular repolarization (D) Signup and view all the answers

In the context of ECG interpretation, what does the P wave represent?

Atrial depolarization. (B) Signup and view all the answers

Which of the following best describes Einthoven's Triangle?

The placement of electrodes forming a triangle around the heart to record electrical activity. (C) Signup and view all the answers

What does a prolonged Q-T interval on an ECG indicate?

Increased risk of ventricular arrhythmias (D) Signup and view all the answers

Which of the following correctly describes the electrical dipole in the heart during depolarization?

A region with a negative charge moving toward a region with a positive charge. (C) Signup and view all the answers

Why are healthy heart valves described as having very little resistance?

To allow rapid and efficient blood flow with only a small pressure difference. (D) Signup and view all the answers

During which phase of the cardiac cycle is the mitral valve open, allowing blood to flow from the left atrium into the left ventricle?

Diastole (D) Signup and view all the answers

What event causes the aortic valve to open during the cardiac cycle?

When pressure in the left ventricle exceeds pressure in the aorta (D) Signup and view all the answers

In the cardiac cycle, what is 'isovolumic contraction'?

The period when the ventricles are contracting with no change in volume. (D) Signup and view all the answers

During which period of the cardiac cycle does the dicrotic notch occur, and what does it signify?

During isovolumic relaxation; it signifies the closure of the aortic valve. (A) Signup and view all the answers

What is the correct definition of end-systolic volume (ESV)?

The volume of blood remaining in the ventricle after contraction. (A) Signup and view all the answers

What factors affect stroke volume?

Preload, Afterload, & Contractility (D) Signup and view all the answers

How is ejection fraction (EF) calculated?

$EF = (EDV - ESV) / EDV * 100$ (A) Signup and view all the answers

What does the stroke work represent in the context of pressure-volume loops, and how is it determined?

The net work performed by the ventricle during one cardiac cycle; estimated by the area within the P-V loop. (C) Signup and view all the answers

In the hierarchy of pacemakers within the mammalian heart, what happens if the SA node fails and how does that impact the heart's rhythm?

The AV node takes over, resulting in a slower heart rate. (B) Signup and view all the answers

In an ECG, which of the following intervals represents the time from the beginning of atrial depolarization to the beginning of ventricular depolarization?

P-Q interval (A) Signup and view all the answers

Which of the following best describes the Frank-Starling mechanism?

Increased preload leads to increased stroke volume due to enhanced contractility. (C) Signup and view all the answers

If the conduction through the ventricular 'conduction system' was slow instead of fast, how would that impact ventricular contraction?

The base of the heart would contract before the apex. (D) Signup and view all the answers

In the context of pressure-volume loops, what does a shift of the curve to the right, with an increase in both end-diastolic volume (EDV) and end-systolic volume (ESV), typically indicate?

Increased preload, possibly due to increased venous return (B) Signup and view all the answers

What changes on the pressure-volume loop would lead you to believe the patient is suffering from heart failure?

A shift of the curve to the right, increase in end-diastolic volume (EDV) and decrease in contractility (C) Signup and view all the answers

A patient's ECG shows a consistently absent P wave, but a normal QRS complex and T wave. What is the most likely condition?

Atrial fibrillation (C) Signup and view all the answers

How would administration of a drug that selectively blocks $I_{Ks}$ potassium channels (responsible for the slow component of the delayed rectifier potassium current) be expected to affect the ECG?

Prolonged Q-T Interval (D) Signup and view all the answers

Augustus Waller conducted early ECG experiments using a dog named Jimmie. If Waller observed that Jimmie's ECG showed inverted T waves in multiple leads, what might he have incorrectly inferred about Jimmie's health, given the understanding of ECGs at that time?

Jimmie had an abnormality in ventricular repolarization. (C) Signup and view all the answers

Flashcards

Cardiac Cycle (Electrical Events)

The sequence of electrical events that occur during the cardiac cycle.

ECG

Electrical events recorded on the body surface.