Cardiovascular System Practice Questions

Q: Which of the following is correct about the pressure volume loop of left ventricle?

Aortic valve opens at 2. ***Aortic valve opens at 2*** - Point 2 marks the moment when **left ventricular pressure exceeds aortic pressure**, causing the aortic valve to open. - This is the transition point between **isovolumetric contraction** (1→2) and **ventricular ejection** (2→3). - From point 2 onwards, blood is actively ejected from the left ventricle into the aorta during **systole**. *1 to 2 indicates isovolumetric relaxation* - The phase from point 1 to point 2 shows an increase in **pressure at constant volume**, which represents **isovolumetric contraction**, not relaxation. - During **isovolumetric contraction**, both the mitral and aortic valves are closed, and the ventricle contracts without changing volume, building up pressure. - **Isovolumetric relaxation** occurs from point 3 to point 4, where pressure drops at constant volume after the aortic valve closes. *2 to 3 indicates ventricular diastole* - The period from point 2 to point 3 represents **ventricular ejection**, which is part of **ventricular systole**, not diastole. - During this phase, the aortic valve is open, and blood is being ejected from the left ventricle into the aorta while ventricular volume decreases. - **Ventricular diastole** includes isovolumetric relaxation (3→4) and ventricular filling (4→1). *Pulmonic valve opens at 3* - Point 3 represents the **closure of the aortic valve** at the end of ventricular ejection, not its opening. - The **pulmonic valve** is part of the right ventricular circuit, not the left ventricle; it opens during right ventricular ejection into the pulmonary artery. - This question specifically addresses the **left ventricular** pressure-volume loop.

Q: The A wave in His bundle electrogram shows presence of:

Atrial depolarization. ***Atrial depolarization*** - The **A wave** in a His bundle electrogram represents the electrical activity corresponding to **atrial depolarization**. This is the first electrical event recorded prior to ventricular activation. - It signifies the activation of the atria, preceding the impulse transmission through the AV node and His bundle. *Atrial repolarization* - **Atrial repolarization** is generally not clearly visible as a distinct wave in a His bundle electrogram, as its electrical signal is usually small and often obscured by the much larger QRS complex from ventricular depolarization. - The T-wave on a surface ECG corresponds to ventricular repolarization, and there isn't a directly analogous, easily identifiable wave for atrial repolarization in standard His bundle recordings. *AV node activation* - **AV node activation** itself is a slow electrical process that does not generate a distinct, sharply defined wave in the His bundle electrogram. - The time taken for conduction through the AV node is represented by the **AH interval**, which is the duration between the A wave (atrial activation) and the H wave (His bundle activation). *Atrial depolarization to AV node activation* - This option describes a **duration or interval**, specifically the **AH interval**, which reflects the time from the beginning of atrial activation (A wave) to the beginning of His bundle activation (H wave) and primarily represents AV nodal conduction. - The A wave itself signifies a specific electrical event (**atrial depolarization**), not the entire period from atrial depolarization up to AV node activation.

Q: The phase of cardiac action potential marked Green is related to which of the following?

Calcium entry, L channels. ***Calcium entry, L channels*** - The green phase represents **Phase 0 (rapid depolarization)** of the **SA node action potential**, which is primarily mediated by **L-type calcium channels** rather than sodium channels. - **SA node cells lack fast voltage-gated sodium channels (Nav1.5)**, making them dependent on **slow calcium influx** through L-type channels for depolarization, unlike ventricular myocytes. *Sodium entry* - **Fast sodium channels** are responsible for Phase 0 in **ventricular and atrial myocytes**, but are **absent in SA node cells**. - The rapid sodium influx creates the characteristic steep upstroke in non-pacemaker cardiac cells, which differs from the slower calcium-dependent depolarization in pacemaker cells. *Calcium entry, T channels* - **T-type calcium channels** contribute to **Phase 4 (pacemaker depolarization)** and help bring the membrane potential to threshold, not Phase 0. - These channels have **faster inactivation kinetics** compared to L-type channels and are not the primary contributors to the depolarization phase marked in green. *Mixed sodium and potassium current* - **If (funny current)** involving mixed **sodium and potassium influx** occurs during **Phase 4** and is responsible for the **spontaneous diastolic depolarization** in pacemaker cells. - This current gradually brings the membrane potential to threshold but does not mediate the actual depolarization phase shown in the green marking.

Q: Which part of ventricular action potential corresponds to ST segment in ECG?

Phase 2. ***Phase 2 (Correct Answer)*** - Phase 2 is the **plateau phase** of the ventricular action potential - Maintained by a balance of inward **calcium current (ICa)** and outward **potassium current (IK)** - Corresponds to the **ST segment** on ECG, representing the period when the entire ventricle is depolarized with no net electrical activity - This phase is responsible for the prolonged contraction of ventricular muscle *Phase 0 (Incorrect)* - Phase 0 is the rapid depolarization phase caused by opening of **fast sodium channels** - Corresponds to the **QRS complex** on ECG, not the ST segment - Represents the initial rapid upstroke of the action potential *Phase 1 (Incorrect)* - Phase 1 is the early rapid repolarization phase - Caused by inactivation of sodium channels and opening of transient outward potassium channels - Represents the brief notch after depolarization, not associated with a specific ECG component *Phase 3 (Incorrect)* - Phase 3 is the rapid repolarization phase caused by opening of **delayed rectifier potassium channels** - Corresponds to the **T wave** on ECG, not the ST segment - Represents the return of membrane potential to resting level

Q: There are two blood vessels shown below. Assuming that pressure along both the vessels is same and both of them follow linear flow pattern, what will be the amount of blood flow in A compared to B?

32 times. ***32 times*** - According to **Poiseuille's law**: Q = (ΔP × π × r⁴) / (8 × η × L), where flow is proportional to the **fourth power of radius** and inversely proportional to vessel length. - Vessel A has **double the diameter** (radius = 2r) and **half the length** (L/2) compared to vessel B: Q_A ∝ (2r)⁴/(L/2) = 32r⁴/L vs Q_B ∝ r⁴/L, giving ratio of **32**. *4 times* - This would occur with a much smaller radius difference between the vessels than what is shown. - Does not account for the **fourth power relationship** of radius with flow in Poiseuille's equation. *8 times* - This would result if vessel A had **double the diameter** but also **double the length** of vessel B. - Calculation: (2r)⁴/(2L) ÷ (r⁴/L) = 16r⁴/2L ÷ r⁴/L = **8 times**. *16 times* - This would occur if vessel A had **double the radius** but **equal length** to vessel B. - Calculation: (2r)⁴/L ÷ (r⁴/L) = 16r⁴/L ÷ r⁴/L = **16 times**.

Q: Compare the two ECG recordings taken before and after activation of low pressure atrial stretch receptors. Which reflex explains the findings?

Bainbridge reflex. ***Bainbridge reflex*** - The Bainbridge reflex, also known as the **atrial reflex**, is an increase in heart rate due to an increase in **central venous pressure**, which activates stretch receptors in the atria. - Activation of these low-pressure receptors signals the medulla to **increase sympathetic stimulation** to the heart, resulting in tachycardia, which is reflected in a faster heart rate on the ECG. *Frank Starling Law* - The Frank-Starling law of the heart describes the relationship between **end-diastolic volume** and the force of contraction. - It states that an increase in venous return stretches the ventricular myocardium, leading to a more forceful ventricular contraction, not primarily affecting heart rate. *Bezold Jarisch Reflex* - This reflex is characterized by a triad of **bradycardia, hypotension, and coronary vasodilation**. - It is triggered by ventricular mechanoreceptors, usually in response to **decreased ventricular filling** or myocardial ischemia. *Vasovagal reflex* - The vasovagal reflex is a common cause of **syncope**, characterized by **bradycardia** and **vasodilation**, leading to a drop in blood pressure. - It is often triggered by emotional stress, pain, or prolonged standing, and results in a **slowing of the heart rate**, not an increase.

Q: Phonocardiogram tracing is shown below with corresponding ECG. Identify the phase corresponding with $S_{2}$ in phonocardiogram.

Isovolumetric relaxation. ***Isovolumetric relaxation*** - **S₂ (second heart sound)** occurs due to closure of the **aortic and pulmonary semilunar valves** at the end of systole, marking the onset of isovolumetric relaxation. - On the **ECG**, S₂ corresponds to the **end of the T wave**, when ventricular pressure drops below aortic pressure causing valve closure. *Isovolumetric contraction* - This phase corresponds to **S₁ (first heart sound)** caused by closure of the **mitral and tricuspid valves** at the beginning of systole. - Occurs on the ECG around the **QRS complex**, not at the timing of S₂. *Rapid ejection* - This phase occurs **between S₁ and S₂** when blood is actively ejected from the ventricles into the aorta and pulmonary artery. - The **semilunar valves are open** during this phase, so no heart sounds are produced. *Rapid ventricular filling* - This phase occurs **after S₂** during early diastole when the **AV valves open** and blood rapidly fills the ventricles. - May be associated with **S₃ gallop** in pathological conditions, but not with S₂.

Q: Using the quadrant method, if the mean QRS vector in lead I is negative and in lead aVF is positive, what is the axis?

Right axis deviation. ***Right axis deviation*** - A **negative QRS vector in lead I** indicates that the overall electrical activity of the heart is moving away from the left arm (typically towards the right). - A **positive QRS vector in lead aVF** signifies that the electrical activity is moving towards the feet. When lead I is negative and aVF is positive, the vector points to the **lower right quadrant** of the heart, consistent with right axis deviation. *Normal axis* - A normal axis typically has a **positive QRS deflection in both lead I and lead aVF**, indicating the vector is within the normal range of -30° to +90°. - In this scenario, the negative deflection in lead I immediately rules out a normal axis. *Left axis deviation* - Left axis deviation is characterized by a **positive QRS in lead I** and a **negative QRS in lead aVF**, meaning the vector points to the upper left quadrant. - The given condition (negative lead I, positive aVF) directly contradicts the criteria for left axis deviation. *Extreme axis deviation* - Extreme axis deviation (or "northwest axis") occurs when the QRS is **negative in both lead I and lead aVF**. - The positive QRS in aVF in this case excludes extreme axis deviation.

Q: If the mean QRS vector in lead I is positive and in lead III is negative, what is the axis deviation?

Left axis deviation. ***Left axis deviation*** - A **positive QRS vector in lead I** means the overall electrical activity is moving towards the positive pole of lead I (i.e., towards the patient's left). - A **negative QRS vector in lead III** means the overall electrical activity is moving away from the positive pole of lead III. When combined, these findings indicate the axis is shifted to the left, typically between -30° and -90°. *Normal axis* - A normal axis would typically show **positive QRS vectors in both lead I and lead III**. - The electrical forces are directed generally downwards and to the left, usually between -30° and +90°. *Right axis deviation* - Right axis deviation is characterized by a **negative QRS vector in lead I** and a positive QRS vector in lead aVF or lead III. - This signifies the electrical axis is shifted to the right, usually between +90° and +180°. *Extreme axis deviation* - Extreme axis deviation (also known as "indeterminate" or "northwest" axis) is indicated by **negative QRS vectors in both lead I and lead aVF**. - This represents an axis between -90° and -180°, an unusual and often pathological finding.

Question 1

Which of the following is correct about the pressure volume loop of left ventricle?

Accepted Answer

Aortic valve opens at 2

Answer

1 to 2 indicates isovolumetric relaxation

Answer

2 to 3 indicates ventricular diastole

Answer

Pulmonic valve opens at 3

Question 2

The A wave in His bundle electrogram shows presence of:

Accepted Answer

Atrial depolarization

Answer

Atrial repolarization

Answer

AV node activation

Answer

Atrial depolarization to AV node activation

Question 3

The phase of cardiac action potential marked Green is related to which of the following?

Accepted Answer

Calcium entry, L channels

Answer

Sodium entry

Answer

Calcium entry, T channels

Answer

Mixed sodium and potassium current

Question 4

Which part of ventricular action potential corresponds to ST segment in ECG?

Accepted Answer

Phase 2

Answer

Phase 0

Answer

Phase 1

Answer

Phase 3

Question 5

There are two blood vessels shown below. Assuming that pressure along both the vessels is same and both of them follow linear flow pattern, what will be the amount of blood flow in A compared to B?

Accepted Answer

32 times

Answer

4 times

Answer

8 times

Answer

16 times

Question 6

Compare the two ECG recordings taken before and after activation of low pressure atrial stretch receptors. Which reflex explains the findings?

Accepted Answer

Bainbridge reflex

Answer

Frank Starling Law

Answer

Bezold Jarisch Reflex

Answer

Vasovagal reflex

Question 7

The structure marked $A$ begins to close by what time frame and due to what cause?

Accepted Answer

Begins to close at 10-15 hours after birth, due to withdrawal of prostaglandins

Answer

Begins to close at 10-15 hours after birth, due to expression of prostaglandins

Answer

Begins to close 4 weeks after birth, due to fall in oxygen concentration

Answer

Begins to close 4 weeks after birth, due to rise in oxygen tension

Question 8

Phonocardiogram tracing is shown below with corresponding ECG. Identify the phase corresponding with $S_{2}$ in phonocardiogram.

Accepted Answer

Isovolumetric relaxation

Answer

Isovolumetric contraction

Answer

Rapid ejection

Answer

Rapid ventricular filling

Question 9

Using the quadrant method, if the mean QRS vector in lead I is negative and in lead aVF is positive, what is the axis?

Accepted Answer

Right axis deviation

Answer

Normal axis

Answer

Left axis deviation

Answer

Extreme axis deviation

Question 10

If the mean QRS vector in lead I is positive and in lead III is negative, what is the axis deviation?

Accepted Answer

Left axis deviation

Answer

Normal axis

Answer

Right axis deviation

Answer

Extreme axis deviation

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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