Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 721: The recording of cardiac cycle is drawn below. Which of the following is correct about $X$ and $Y$ shown in the image?

A. $X=$ Pre-ejection period and $Y=$ LV ejection time (Correct Answer)
B. $X=$ Pre-ejection period and $Y=$ Electromechanical systole
C. $X=$ LV ejection time and $Y=$ Pre-ejection period
D. $X=$ Electromechanical systole and $Y=$ LV ejection time

Explanation: ***X = Pre-ejection period and Y = LV ejection time*** - **X** corresponds to the **pre-ejection period (PEP)**, which is the time from the onset of ventricular depolarization (Q wave on ECG) to the opening of the aortic valve (AO). It includes the **isovolumetric contraction time**. - **Y** corresponds to the **left ventricular (LV) ejection time (LVET)**, which is the interval from the opening of the aortic valve (AO) to its closure (AC), during which blood is ejected into the aorta. *X = Pre-ejection period and Y = Electromechanical systole* - While X correctly represents the **pre-ejection period**, Y is not the **electromechanical systole**. - **Electromechanical systole** is the total time from the Q wave on the ECG to the closure of the aortic valve (AC), encompassing both PEP and LVET. *X = LV ejection Time and Y = Pre-ejection period* - This option incorrectly identifies X as **LV ejection time** and Y as the **pre-ejection period**. - The diagram clearly shows X precedes Y, with X representing the initial phase of ventricular contraction before ejection. *X = Electromechanical systole and Y = LV ejection time* - This option incorrectly identifies X as **electromechanical systole**. X is only a part of the electromechanical systole (the pre-ejection period). - While Y correctly identifies the **LV ejection time**, the initial part of the statement is incorrect.

Question 722: The following diagram represents flow in compliant versus non-compliant aorta. This shows operation of:

A. Windkessel effect (Correct Answer)
B. Ohm's law
C. Poiseuille's law
D. Frank-Starling mechanism

Explanation: ***Windkessel effect*** - The diagram perfectly illustrates the **Windkessel effect**, where the **elasticity of the aorta** allows it to expand during systole to store blood and then recoil during diastole to maintain continuous blood flow. - In a **compliant aorta**, during systole, 100% of the blood enters, but only 50% immediately flows forward as the aorta expands. During diastole, the aortic valves close, and the stored blood (the other 50%) is propelled forward due to the aorta's retraction, maintaining distal blood flow. *Ohm's law* - Ohm's law, when applied to circulation, describes the relationship between **blood flow (I)**, **pressure difference (ΔP)**, and **vascular resistance (R)** (I = ΔP/R). - This diagram focuses on the aorta's physical properties and blood buffering, not primarily on resistance or pressure gradients due to flow. *Poiseuille's law* - Poiseuille's law calculates **fluid flow rate** through a cylindrical tube, heavily dependent on the **vessel radius**, length, and fluid viscosity. - While relevant to blood flow dynamics in general, it does not explain the specific phenomenon of elastic energy storage and release by the aorta during the cardiac cycle. *Frank-Starling mechanism* - The Frank-Starling mechanism describes the heart's ability to **change its force of contraction** in response to changes in **venous return** and **end-diastolic volume**. - This mechanism is about cardiac muscle physiology and pump function, not the vascular mechanics of the aorta, as depicted.

Question 723: Which of the following dissociation curve mentioned is for myoglobin?

A. Green (Correct Answer)
B. Purple
C. Red
D. None

Explanation: ***Green*** - The **green curve** represents **myoglobin**, which has a much higher affinity for oxygen than hemoglobin. It binds oxygen at very low partial pressures and releases it only when oxygen levels are significantly depleted, as in active muscle tissue. - Myoglobin's dissociation curve is typically **hyperbolic** due to its single oxygen-binding site, reflecting its role in oxygen storage rather than transport. *Purple* - The **purple curve** represents normal **hemoglobin**, which exhibits a **sigmoidal** shape due to its **cooperative binding** of oxygen. This allows hemoglobin to efficiently load oxygen in the lungs and unload it in tissues. - Hemoglobin has a lower oxygen affinity than myoglobin and is designed for oxygen transport, adapting its binding based on oxygen partial pressure. *Red* - The **red curve** likely represents a **right-shifted hemoglobin dissociation curve**, indicating **decreased oxygen affinity**. This shift facilitates oxygen unloading to tissues. - Right shifts occur due to increased temperature, decreased pH (Bohr effect), increased 2,3-DPG, or increased CO₂. These physiological adaptations help deliver more oxygen to metabolically active tissues. *None* - This option is incorrect because the **green curve** clearly represents the characteristic oxygen dissociation curve for myoglobin.

Question 724: The pressure-volume loop of left ventricle tracing of the patient indicates:

A. Systolic dysfunction
B. Diastolic dysfunction (Correct Answer)
C. Decreased atrial compliance
D. Increased atrial compliance

Explanation: ***Diastolic dysfunction*** - The pressure-volume loop for the patient is shifted to the **left and upward** relative to the control loop, indicating higher left ventricular pressure for a given volume during diastole. - The **end-diastolic pressure-volume relationship (EDPVR)**, shown by the lower right curve, is steeper for the patient, meaning the ventricle is **stiffer or less compliant** during filling. *Systolic dysfunction* - Systolic dysfunction would be characterized by a **reduced stroke volume** (narrower loop horizontally) and a **lower ejection fraction**, often accompanied by a shift to the right due to increased end-diastolic volume. - The **end-systolic pressure-volume relationship (ESPVR)**, which represents contractility, would be shifted downwards and to the right in systolic dysfunction, indicating impaired contractility. *Decreased atrial compliance* - Decreased atrial compliance would primarily affect **atrial pressures** and the force of atrial contraction, which might indirectly impact ventricular filling, but is not directly represented by the ventricular pressure-volume loop's morphology in this manner. - The primary indicator of atrial compliance is often via atrial pressure-volume relationships or specific atrial function studies, not the ventricular loop's overall shift. *Increased atrial compliance* - Increased atrial compliance would allow the atria to accommodate more volume at lower pressures, potentially *improving* ventricular filling if the ventricle itself is compliant, but it would not explain the **elevated ventricular diastolic pressures** seen in the patient's tracing. - This condition would typically lead to lower atrial pressures, which is the opposite of what would contribute to the observed ventricular diastolic dysfunction.

Question 725: Which of the following is correct about the point marked $Z$ on the cardiac cycle?

A. Mitral valve opens
B. Tricuspid valve opens
C. Aortic valve opens (Correct Answer)
D. Mid systolic click

Explanation: ***Aortic valve opens*** - At point Z, the **left ventricular pressure (LVP)** curve (solid red line) intersects and surpasses the **aortic pressure (AP)** curve (dashed line), marking the moment the **aortic valve opens** and blood begins to be ejected into the aorta. - This event signifies the transition from **isovolumetric contraction** to rapid **ventricular ejection phase** during systole. *Mitral valve opens* - The **mitral valve opens** during diastole, when the **left ventricular pressure (LVP)** falls below the **left atrial pressure (LAP)**, allowing ventricular filling. - This event would typically occur much later in the cardiac cycle, around point 5 or 6, after the aortic valve closes. *Tricuspid valve opens* - The **tricuspid valve opens** during diastole when the right ventricular pressure falls below the right atrial pressure. This event is not directly depicted for the left side of the heart in this Wigger's diagram. - It plays a role in right heart filling and is not related to the events occurring at point Z in the left heart cycle. *Mid systolic click* - A **mid-systolic click** is typically associated with **mitral valve prolapse**, occurring during mid-systole as the mitral leaflets prolapse into the left atrium. - Point Z represents the beginning of ejection, not a valvular abnormality.

Question 726: Which of the following is correct about the 'X' marking in Arterial Waveform?

A. Closure of mitral valve
B. Closure of aortic valve (Correct Answer)
C. Closure of tricuspid valve
D. Rapid filling of left ventricle

Explanation: ***Closure of aortic valve*** - The "X" marking in the arterial waveform, also known as the **dicrotic notch**, represents the brief reversal of blood flow in the aorta due to the **closure of the aortic valve**. - This event signifies the end of systole and the beginning of diastole in the arterial pressure waveform. *Closure of mitral valve* - The closure of the mitral valve occurs at the **beginning of ventricular systole** and is not directly represented as a dicrotic notch on an arterial pressure waveform. - Mitral valve closure is associated with the first heart sound (S1) and changes in left ventricular pressure, not a notch in the arterial waveform. *Closure of tricuspid valve* - The closure of the tricuspid valve also occurs at the **beginning of ventricular systole**, similar to the mitral valve, only on the right side of the heart. - This event is not reflected as a dicrotic notch in the systemic arterial pressure waveform. *Rapid filling of left ventricle* - Rapid filling of the left ventricle occurs during **early diastole**, when the mitral valve is open. - This phase is associated with changes in ventricular pressure, but not with the dicrotic notch, which signifies arterial pressure changes due to aortic valve closure.

Question 727: Which of the following is correct about the pressure volume loop of left ventricle?

A. 1 to 2 indicates isovolumetric relaxation
B. 2 to 3 indicates ventricular diastole
C. Aortic valve opens at 2 (Correct Answer)
D. Pulmonic valve opens at 3

Explanation: ***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.

Question 728: The A wave in His bundle electrogram shows presence of:

A. Atrial depolarization (Correct Answer)
B. Atrial repolarization
C. AV node activation
D. Atrial depolarization to AV node activation

Explanation: ***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.

Question 729: The lead of ECG marked as $X$ is called:

A. Lewis lead (Correct Answer)
B. V4R
C. aVR
D. V_{a}

Explanation: ***Lewis lead*** - This image displays the placement of electrodes for a **Lewis lead** ECG, used to enhance the detection of **atrial activity**, particularly for P waves. - The Lewis lead involves placing the right arm electrode (usually from a standard ECG setup) at the **right sternal border in the second intercostal space**, and the left arm electrode at the **right parasternal border in the fourth intercostal space**. *V4R* - **V4R** is a right-sided precordial lead used to detect **right ventricular infarction** and is placed in the fifth intercostal space at the right midclavicular line. - The electrode placement shown in the image is not consistent with V4R. *aVR* - **aVR** is an augmented unipolar limb lead that records electrical activity from the **right arm** relative to the average of the left arm and left leg electrodes. - It is not a chest lead placement, and therefore does not correspond to the image. *V_{a}* - **V_{a}** is not a standard or recognized ECG lead designation in clinical practice. - The commonly used precordial leads are denoted as V1 through V6.

Question 730: The phase of cardiac action potential marked Green is related to which of the following?

A. Sodium entry (Correct Answer)
B. Calcium entry, T channels
C. Calcium entry, L channels
D. Mixed sodium and potassium current

Explanation: ***Sodium entry*** - The green phase represents **Phase 0 (rapid depolarization)** of the cardiac action potential, characterized by rapid influx of **sodium ions through voltage-gated sodium channels**. - This sudden sodium entry causes the characteristic steep upstroke of the action potential, rapidly depolarizing the cell membrane from resting potential to positive values. *Calcium entry, T channels* - **T-type calcium channels** contribute to **pacemaker cell depolarization** and early phases of action potential in some cardiac cells, but are not the primary mechanism during Phase 0. - These channels have different kinetics and voltage dependence compared to the fast sodium channels responsible for rapid depolarization. *Calcium entry, L channels* - **L-type calcium channels** are responsible for **Phase 2 (plateau phase)**, which occurs after the initial rapid depolarization phase marked in green. - These channels open more slowly and maintain prolonged depolarization, but do not contribute significantly to the rapid upstroke of Phase 0. *Mixed sodium and potassium current* - **Mixed sodium and potassium current** (funny current or **If**) is characteristic of **pacemaker cells** during Phase 4, contributing to spontaneous diastolic depolarization. - This current is responsible for the gradual rise to threshold in SA node cells, not the rapid depolarization phase shown in green.

Practice by Chapter

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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