Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 931: The 'a' wave in jugular venous pressure is due to?

A. Atrial filling
B. Atrial relaxation
C. Atrial contraction (Correct Answer)
D. Ventricular relaxation

Explanation: ***Atrial contraction*** - The **a wave** in jugular venous pressure (JVP) corresponds to the increase in right atrial pressure due to **atrial systole** (contraction). - This pushes blood against the closed tricuspid valve and back into the great veins, causing a visible pulsation. *Atrial filling* - **Atrial filling** occurs during diastole and contributes to the overall increase in atrial pressure but is not the primary cause of the a wave. - This phase is more related to the **v wave** (due to ventricular contraction pushing blood into the atria against a closed tricuspid valve) and the **y descent** (due to tricuspid valve opening and rapid ventricular filling). *Atrial relaxation* - **Atrial relaxation** follows **atrial contraction** and is associated with the **x descent** on the JVP waveform, representing the decrease in right atrial pressure as the atrium relaxes and the tricuspid valve moves away from the atrium during ventricular systole. - It results in a fall in pressure not a rise, so it cannot be the a wave. *Ventricular relaxation* - **Ventricular relaxation** (early diastole) is primarily responsible for the **y descent**, which occurs as the tricuspid valve opens and blood rapidly empties from the atrium into the ventricle. - This phase of the cardiac cycle is related to falling pressures within the right atrium and ventricle, not the initial pressure rise seen in the **a wave**.

Question 932: What does the first heart sound correspond to?

A. Mitral valve opening
B. Mitral valve closing (Correct Answer)
C. Aortic valve closing
D. Pulmonary valve closing

Explanation: ***Mitral valve closing*** - The **first heart sound (S1)** is primarily caused by the simultaneous **closure of the mitral and tricuspid valves** at the beginning of ventricular systole. - Mitral valve closure is the dominant component of S1 due to higher pressures in the left heart. *Mitral valve opening* - **Valve opening** is typically a silent event that does not produce an audible heart sound. - Abnormal sounds associated with valve opening, like an opening snap, occur in cases of **stenotic valves**. *Aortic valve closing* - The **aortic valve closes** at the end of ventricular systole, contributing to the **second heart sound (S2)**. - S2 also includes the closure of the **pulmonic valve**. *Pulmonary valve closing* - The **pulmonary valve closes** at the end of ventricular systole, contributing to the **second heart sound (S2)** along with the aortic valve. - This occurs after S1, not during it.

Question 933: At which point in the cardiac cycle does the closure of the mitral valve begin? (Refer to the diagram showing points A, B, C, and D)

A. Point A: Closure of the mitral valve (Correct Answer)
B. Point B: Opening of the aortic valve
C. Point C: Closure of the aortic valve
D. Point D: Opening of the mitral valve

Explanation: ***Point A: Closure of the mitral valve*** - As indicated in the Wigger's diagram, "Point A" directly corresponds to the event labeled "**Mitral Valve Closes**" in the "Pressure" section. - This closure signifies the beginning of **isovolumic contraction**, where ventricular pressure rises rapidly after filling and before the aortic valve opens. *Point B: Opening of the aortic valve* - The **opening of the aortic valve** occurs after the mitral valve has closed and the ventricular pressure has exceeded aortic pressure. - This point marks the beginning of the **ejection phase** of systole, not the closure of the mitral valve. *Point C: Closure of the aortic valve* - The **closure of the aortic valve** occurs at the end of ventricular ejection, initiating isovolumic relaxation. - This event is represented by the **dicrotic notch** and the second heart sound (S2), significantly later than mitral valve closure. *Point D: Opening of the mitral valve* - The **opening of the mitral valve** happens during ventricular diastole, allowing blood to flow from the atrium into the ventricle. - This occurs after the aortic valve has closed and ventricular pressure falls below atrial pressure, marking the beginning of **ventricular filling**.

Question 934: How would left ventricular failure affect the pressure-volume loop of the left ventricle?

A. Increased end-diastolic volume and decreased stroke volume (Correct Answer)
B. Increased end-diastolic volume with no change in stroke volume
C. Decreased end-diastolic volume with no change in stroke volume
D. Decreased end-diastolic volume and mildly decreased stroke volume

Explanation: ***Increased end-diastolic volume and decreased stroke volume*** - In **left ventricular failure**, the heart's pumping ability is impaired, leading to incomplete ejection of blood and a subsequent increase in the **end-diastolic volume (EDV)** as blood accumulates. - Due to the reduced contractility and inefficient ejection, the **stroke volume (SV)**, which is the volume of blood pumped out per beat, decreases significantly. *Increased end-diastolic volume with no change in stroke volume* - While **left ventricular failure** does lead to an increased **end-diastolic volume (EDV)** due to impaired pumping, it invariably results in a **reduced stroke volume (SV)**, not an unchanged one. - No change in stroke volume would imply that despite filling more, the heart maintains its ejection efficiency, which is contrary to the definition of heart failure. *Decreased end-diastolic volume with no change in stroke volume* - A **decreased end-diastolic volume (EDV)** would indicate less filling of the ventricle, often seen in conditions like hypovolemia or restrictive cardiomyopathy, which is not characteristic of **left ventricular failure**. - As explained, **left ventricular failure** is characterized by increased EDV and decreased SV. *Decreased end-diastolic volume and mildly decreased stroke volume* - **Left ventricular failure** predominantly causes an **increased end-diastolic volume (EDV)** due to incomplete emptying, rather than a decrease. - The decrease in **stroke volume (SV)** in heart failure is typically substantial rather than mild, reflecting the significant impairment in cardiac function.

Practice by Chapter

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