Cardiovascular System Practice Questions

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.

Q: The normal amplitude of the marked wave is usually less than \qquad mm in the chest leads.

5. ***5*** - The marked waves in the provided ECG are **U waves**, indicated by the arrows. Normal U waves in chest leads (V1-V6) are typically small and positive, with a characteristic amplitude of **less than 1-2 mm**, often described as less than 5 mm. - Prominent U waves (amplitude > 1.5-2 mm or > 25% of the T wave amplitude in the same lead) can indicate **hypokalemia**, but the question asks for the normal amplitude limit. *10* - An amplitude of 10 mm for a U wave in chest leads is considered **abnormally large** and would typically suggest underlying pathology, most commonly **hypokalemia**. - Normal U waves are usually **subtle** and much smaller than other ECG waves like the R wave or T wave. *15* - An amplitude of 15 mm for a U wave is significantly higher than the normal range and would be considered a **pathological finding**, strongly indicative of severe electrolyte imbalance such as **severe hypokalemia**. - Such prominent U waves are easily visible and can even be larger than the T waves, which is an abnormal sign. *20* - An amplitude of 20 mm for a U wave is an **extremely large** and highly abnormal finding, suggesting very severe underlying cardiac or electrolyte disturbances, far exceeding what is considered normal. - This magnitude could indicate a critical medical condition and requires immediate attention.

Q: The marked part of the ECG called as 'X' points to which phase of cardiac action potential?

Phase 2. ***Phase 2*** - The **ST segment** (marked as 'X') corresponds to **Phase 2 (plateau phase)** of the ventricular cardiac action potential. - During this phase, **calcium influx** balances **potassium efflux**, creating an **isoelectric line** on the ECG with no net voltage change. *Phase 0* - Represents **rapid depolarization** due to **sodium influx**, corresponding to the **QRS complex** on ECG. - This phase shows a sharp upstroke in action potential, not the flat isoelectric segment marked as 'X'. *Phase 3* - Represents **repolarization** due to **potassium efflux**, corresponding to the **T wave** on ECG. - This phase shows downward deflection on ECG, unlike the flat ST segment marked as 'X'. *Phase 4* - Represents the **resting potential** maintained by **Na+/K+ ATPase pump**, corresponding to the **TP segment** on ECG. - This is the baseline between cardiac cycles, not the ST segment elevation/depression area marked as 'X'.

Question 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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

Question 9

The normal amplitude of the marked wave is usually less than \qquad mm in the chest leads.

Accepted Answer

5

Answer

10

Answer

15

Answer

20

Question 10

The marked part of the ECG called as 'X' points to which phase of cardiac action potential?

Accepted Answer

Phase 2

Answer

Phase 0

Answer

Phase 3

Answer

Phase 4

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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