Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 281: What is the function of chordae tendineae?

A. Opens A-V valve
B. Prevents regurgitation (Correct Answer)
C. Helps contraction of papillary muscles
D. Passes action potential to papillary muscles

Explanation: **Explanation:** The **chordae tendineae** (colloquially known as "heartstrings") are strong, fibrous cords that connect the papillary muscles of the ventricles to the leaflets of the Atrioventricular (AV) valves (Mitral and Tricuspid). **1. Why Option B is correct:** During ventricular systole, the pressure within the ventricles rises sharply, forcing the AV valves to close. The chordae tendineae act as "tethers." When the papillary muscles contract, they pull on these cords, preventing the valve cusps from eversion (prolapsing) into the atria. By maintaining the structural integrity of the closed valve against high ventricular pressure, they **prevent the backflow (regurgitation) of blood** into the atria. **2. Why other options are incorrect:** * **Option A:** AV valves open **passively** due to the pressure gradient when atrial pressure exceeds ventricular pressure; chordae tendineae do not play an active role in opening them. * **Option C:** The papillary muscles contract independently as part of the ventricular myocardium; the chordae tendineae are passive structures moved by this contraction, not the cause of it. * **Option D:** Action potentials are conducted via the **Purkinje fibers**. Chordae tendineae are collagenous structures and do not conduct electrical impulses. **High-Yield Clinical Pearls for NEET-PG:** * **Rupture of Chordae Tendineae:** Often a complication of **Infective Endocarditis** or **Acute Myocardial Infarction**, leading to acute, severe mitral regurgitation and heart failure. * **First Heart Sound (S1):** Produced by the closure of AV valves; the tensioning of the chordae tendineae contributes to the vibrations heard as S1. * **Papillary Muscle Dysfunction:** Most commonly involves the **posteromedial papillary muscle** because it has a single blood supply (usually RCA), making it more susceptible to ischemia than the anterolateral muscle (dual supply).

Question 282: All are effects of sympathetic stimulation except?

A. Increased conduction velocity
B. Increased heart rate
C. Increased refractory period (Correct Answer)
D. Increased contractility of heart

Explanation: **Explanation:** Sympathetic stimulation of the heart is mediated primarily by **Norepinephrine** acting on **$\beta_1$-adrenergic receptors**. This activation triggers a Gs-protein-cAMP-Protein Kinase A pathway, which enhances the influx of $Ca^{2+}$ and $Na^+$ ions. **Why "Increased refractory period" is the correct answer:** Sympathetic stimulation actually **decreases** the refractory period. By increasing the rate of repolarization (via activation of potassium channels) and accelerating the recovery of sodium channels, the heart can beat at a faster rate. A shorter refractory period allows the cardiac tissue to be ready for the next impulse sooner, which is essential for tachycardia. **Analysis of Incorrect Options:** * **Increased conduction velocity (Positive Dromotropy):** Sympathetic activity increases the rate of conduction through the AV node and His-Purkinje system by increasing the rate of rise of the action potential. * **Increased heart rate (Positive Chronotropy):** It increases the slope of the prepotential (Phase 4) in the SA node, reaching the threshold faster and increasing the firing frequency. * **Increased contractility (Positive Inotropy):** It increases $Ca^{2+}$ influx through L-type channels and enhances $Ca^{2+}$ release from the sarcoplasmic reticulum, leading to more forceful contractions. **High-Yield Clinical Pearls for NEET-PG:** * **Parasympathetic (Vagal) Effect:** Opposite to sympathetic; it increases the refractory period (specifically in the AV node) and decreases heart rate/conduction. * **Lusitropic Effect:** Sympathetic stimulation also has a positive lusitropic effect (increased rate of relaxation) due to the phosphorylation of **phospholamban**, which speeds up $Ca^{2+}$ reuptake. * **Key Receptor:** $\beta_1$ is the predominant receptor in the heart; $\beta_2$ is also present but in smaller proportions.

Question 283: Which heart sound is referred to as the "atrial sound"?

A. S1
B. S2
C. S3
D. S4 (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. S4** The **Fourth Heart Sound (S4)** is known as the **atrial sound** because it occurs during the late phase of ventricular diastole, coinciding with **atrial systole** (atrial contraction). As the atrium contracts to push the final 20–30% of blood into the ventricle, it creates vibrations in the ventricular wall, valves, and blood. #### Why S4 is the Atrial Sound: * **Mechanism:** It is produced when the atrium contracts against a **stiff or non-compliant ventricle** (e.g., in left ventricular hypertrophy or systemic hypertension). * **Timing:** It occurs just before S1 (presystolic). * **Requirement:** A functional atrium is necessary; therefore, **S4 is absent in Atrial Fibrillation.** #### Analysis of Incorrect Options: * **A. S1 (First Heart Sound):** Known as the "lub" sound, it is caused by the closure of the Atrioventricular (Mitral and Tricuspid) valves at the beginning of ventricular systole. * **B. S2 (Second Heart Sound):** Known as the "dup" sound, it is caused by the closure of the Semilunar (Aortic and Pulmonary) valves at the beginning of ventricular diastole. * **C. S3 (Third Heart Sound):** Known as the **ventricular gallop**, it occurs during the early rapid filling phase of diastole. While it can be physiological in children and athletes, in older adults, it often indicates congestive heart failure. #### NEET-PG High-Yield Pearls: * **S4 is always pathological** (unlike S3, which can be physiological). * **Triple Rhythm/Gallop:** The presence of S3 or S4 along with S1 and S2 creates a gallop rhythm. * **Best heard with:** The **bell** of the stethoscope at the apex in the left lateral decubitus position. * **Phonocardiogram:** S4 corresponds to the interval between the P wave and the QRS complex on an ECG.

Question 284: C-type natriuretic peptide is found in which of the following locations?

A. Brain
B. Kidney
C. Pituitary
D. All of the above (Correct Answer)

Explanation: **Explanation:** The Natriuretic Peptide family consists of three main hormones: ANP (Atrial), BNP (Brain), and **CNP (C-type)**. While ANP and BNP are primarily cardiac in origin and act as circulating hormones, CNP functions differently, acting mainly as a paracrine mediator. **Why "All of the above" is correct:** C-type natriuretic peptide (CNP) has a unique distribution compared to its counterparts. It is the most common natriuretic peptide found in the **Central Nervous System**, with high concentrations in the **Brain** and the **Pituitary gland**. Additionally, it is synthesized in **Vascular Endothelial cells** and the **Kidneys** (specifically in the nephron), where it plays a role in local vasodilation and remodeling. Because it is expressed in all these tissues, option D is the correct choice. **Analysis of Options:** * **Brain:** CNP is highly concentrated in the hypothalamus and various brain regions, where it acts as a neuromodulator. * **Pituitary:** It is found in high levels in the anterior pituitary, influencing the secretion of other hormones. * **Kidney:** It is produced locally in the renal tubules, contributing to the regulation of electrolytes and water, though its systemic diuretic effect is weaker than ANP. **High-Yield Clinical Pearls for NEET-PG:** * **Source:** Unlike ANP/BNP (Heart), CNP is primarily from **Endothelium** and **Neural tissue**. * **Potency:** CNP is the most potent **venodilator** of the three peptides but has the **least natriuretic/diuretic** activity. * **Bone Growth:** CNP is a major regulator of endochondral ossification; mutations in its receptor (NPR-B) can lead to skeletal dysplasia (Achondroplasia). * **Receptor:** CNP binds specifically to the **NPR-B** receptor (linked to guanylyl cyclase).

Question 285: Vagal stimulation of the heart causes all, EXCEPT:

A. Decreased heart rate
B. Decreased force of heart contraction
C. Decreased cardiac output
D. Decreased R-R interval in ECG (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Decreased R-R interval in ECG**. **1. Why Option D is correct:** Vagal stimulation involves the release of **Acetylcholine (ACh)**, which acts on **M2 receptors** in the heart. This leads to a decrease in the firing rate of the SA node (Negative Chronotropy). In an ECG, the **R-R interval** represents the time between two consecutive heartbeats. When the heart rate decreases, the time between beats increases. Therefore, vagal stimulation causes an **increased R-R interval**, not a decreased one. **2. Why other options are incorrect:** * **Option A (Decreased heart rate):** Vagal fibers primarily innervate the SA and AV nodes. Stimulation slows the rate of diastolic depolarization, leading to a lower heart rate (Bradycardia). * **Option B (Decreased force of contraction):** While vagal innervation to the ventricles is sparse, it significantly decreases atrial contractility and indirectly reduces ventricular contractility by inhibiting sympathetic effects (Negative Inotropy). * **Option C (Decreased cardiac output):** Cardiac Output = Stroke Volume × Heart Rate. Since vagal stimulation decreases both heart rate and (to a lesser extent) stroke volume, the overall cardiac output falls. **Clinical Pearls for NEET-PG:** * **Vagal Escape:** If the vagus nerve is stimulated continuously, the ventricles may eventually start beating at their own intrinsic rhythm (Idioventricular rhythm) to prevent cardiac standstill. * **Right vs. Left Vagus:** The **Right Vagus** primarily innervates the **SA node** (affects rate), while the **Left Vagus** primarily innervates the **AV node** (affects conduction/prolongs PR interval). * **Mechanism:** ACh increases **K+ conductance** (hyperpolarization) and decreases **cAMP**, inhibiting Ca2+ and If (funny) channels.

Question 286: Occlusion of the common carotid artery on both sides leads to what change in heart rate and blood pressure?

A. Increase in HR and BP (Correct Answer)
B. Increase in BP and decrease in HR
C. Decrease in HR and BP
D. No effect on BP and HR

Explanation: ### Explanation **Underlying Concept: The Baroreceptor Reflex** The correct answer is **A (Increase in HR and BP)**. This phenomenon is explained by the **Baroreceptor Reflex**, a rapid-acting mechanism for blood pressure (BP) regulation. The carotid sinuses, located at the bifurcation of the common carotid arteries, contain high-pressure baroreceptors. When both common carotid arteries are occluded, the blood flow to the carotid sinuses drops significantly. The baroreceptors perceive this as a **systemic drop in blood pressure**. In response, the firing rate of the **Hering’s nerve** (branch of Glossopharyngeal nerve, CN IX) decreases. This signals the Nucleus Tractus Solitarius (NTS) in the medulla to: 1. **Increase Sympathetic outflow:** Leading to vasoconstriction (increasing Total Peripheral Resistance and BP) and increased contractility. 2. **Decrease Parasympathetic (Vagal) tone:** Leading to an increase in Heart Rate (HR). --- **Analysis of Incorrect Options:** * **Option B:** While BP does increase, HR does not decrease. A decrease in HR (reflex bradycardia) would only occur if the baroreceptors sensed *high* pressure. * **Option C:** This would occur if the carotid sinus was externally massaged (simulating high pressure), not occluded. * **Option D:** Occlusion triggers a potent compensatory reflex; it is never hemodynamically neutral. --- **High-Yield NEET-PG Pearls:** * **Receptor Location:** Carotid sinus (CN IX) and Aortic arch (CN X). * **The "Buffer" Nerves:** CN IX and CN X are called buffer nerves because they prevent extreme fluctuations in BP. * **Carotid Sinus Massage:** Clinically used to terminate Paroxysmal Supraventricular Tachycardia (PSVT) by stimulating the baroreceptors to increase vagal tone and slow the HR. * **Denervation:** If the carotid sinus nerves are cut, the brain perceives "zero" pressure, leading to a massive, sustained increase in BP and HR.

Question 287: What is the normal duration of the PR interval?

A. 0.12 - 0.2 seconds (Correct Answer)
B. 0.2 - 0.3 seconds
C. 0.3 - 0.4 seconds
D. 0.4 - 0.5 seconds

Explanation: The **PR interval** represents the time taken for electrical impulses to travel from the SA node, through the atria, and across the AV node to the ventricles. ### Why Option A is Correct The normal PR interval ranges from **0.12 to 0.20 seconds** (equivalent to 3 to 5 small squares on standard ECG paper). This duration accounts for the physiological **AV nodal delay**, which is crucial as it allows the atria to contract and fully empty their blood into the ventricles before ventricular systole begins. ### Why Other Options are Incorrect * **Options B, C, and D:** These durations (>0.20 seconds) are pathologically prolonged. A PR interval greater than 0.20 seconds indicates a conduction delay, most commonly diagnosed as **First-degree Heart Block**. ### High-Yield Clinical Pearls for NEET-PG * **Measurement:** It is measured from the *beginning of the P wave* to the *beginning of the QRS complex*. * **Short PR Interval (<0.12s):** Seen in pre-excitation syndromes like **Wolff-Parkinson-White (WPW) syndrome** (due to accessory pathways bypassing the AV node) and Lown-Ganong-Levine (LGL) syndrome. * **Prolonged PR Interval (>0.20s):** Seen in First-degree AV block, hyperkalemia, and digitalis toxicity. * **PR Segment vs. PR Interval:** The PR *segment* is the isoelectric line between the end of the P wave and the start of the QRS; it represents the actual delay at the AV node. The PR *interval* includes atrial depolarization (P wave). * **PR Depression:** A classic diagnostic sign for **Acute Pericarditis**.

Question 288: Protein C activation causes which of the following?

A. Promotion of clotting
B. Inactivation of factor II
C. Activation of factor X
D. Inactivation of factor V (Correct Answer)

Explanation: **Explanation:** Protein C is a vitamin K-dependent plasma protein that serves as a natural anticoagulant. Its activation is triggered when **Thrombin** binds to **Thrombomodulin** on the endothelial cell surface. Once activated (forming Activated Protein C or APC), it works alongside its cofactor, **Protein S**, to maintain blood fluidity. **Why Option D is Correct:** Activated Protein C (APC) exerts its anticoagulant effect by proteolytically **inactivating Factors Va and VIIIa**. These factors are essential cofactors in the coagulation cascade: Factor Va is required for the prothrombinase complex (to form thrombin), and Factor VIIIa is required for the intrinsic tenase complex. By inactivating them, Protein C effectively shuts down the amplification of the clotting cascade. **Why Other Options are Incorrect:** * **Option A:** Protein C is an **anticoagulant**, meaning it inhibits clotting rather than promoting it. * **Option B:** Factor II (Prothrombin) is inactivated by direct thrombin inhibitors (like Heparin/Antithrombin III), not by Protein C. * **Option C:** Factor X is an enzyme in the common pathway; Protein C inhibits the *cofactors* (V and VIII) that help activate Factor X, rather than activating it. **NEET-PG High-Yield Pearls:** * **Factor V Leiden:** The most common inherited cause of hypercoagulability (thrombophilia). It involves a mutation in Factor V that makes it **resistant** to inactivation by Protein C. * **Warfarin-Induced Skin Necrosis:** Since Protein C has a shorter half-life than other clotting factors (II, VII, IX, X), starting Warfarin can cause a transient pro-coagulant state, leading to microvascular thrombosis and skin necrosis. * **Mnemonic:** Protein **C** and **S** **C**ut **S**tops (they cut/inactivate the cofactors to stop clotting).

Question 289: Blood pressure is measured in which artery?

A. Axillary artery
B. Carotid artery
C. Brachial artery (Correct Answer)
D. Radial artery

Explanation: **Explanation:** The **brachial artery** is the standard vessel used for measuring systemic arterial blood pressure using a sphygmomanometer. This is primarily due to its anatomical location: it is superficial enough to be easily compressed against the humerus and is situated at the level of the heart, which minimizes hydrostatic pressure errors. During auscultation, the stethoscope is placed over the brachial artery in the cubital fossa to listen for **Korotkoff sounds**, which indicate systolic and diastolic pressure. **Analysis of Options:** * **Axillary Artery (A):** While it is a proximal continuation of the brachial artery, its deep location in the axilla makes it inaccessible for routine non-invasive cuff measurement. * **Carotid Artery (B):** Used primarily for assessing pulse character and strength (especially in emergencies), but it is never used for cuff-based BP measurement due to the risk of stimulating carotid sinus baroreceptors, which can cause bradycardia or syncope. * **Radial Artery (D):** Commonly used for feeling the peripheral pulse or for **invasive** intra-arterial blood pressure monitoring (Arterial Line). However, it is not the standard site for routine non-invasive measurement. **High-Yield Clinical Pearls for NEET-PG:** * **Level of the Heart:** If the arm is held above the heart level, BP readings will be falsely low; if below, they will be falsely high. * **Cuff Size:** A cuff that is too small/narrow gives a falsely high reading (common in obese patients), while a cuff that is too large gives a falsely low reading. * **Osler’s Maneuver:** Used to detect "Pseudohypertension" in elderly patients with severely atherosclerotic (calcified) arteries that do not collapse with cuff inflation.

Question 290: What is the most important factor determining myocardial O2 consumption?

A. Myocardial fibre tension (Correct Answer)
B. Cardiac output
C. Blood volume
D. Heart rate

Explanation: **Explanation:** The primary determinant of myocardial oxygen consumption ($MVO_2$) is **myocardial fiber tension** (wall stress). According to the **Law of Laplace** ($T = P \times r / 2h$), wall tension is directly proportional to intraventricular pressure and the radius of the chamber. Since the heart must generate significant tension to overcome afterload and eject blood, this "pressure work" is metabolically expensive, accounting for nearly 50% of total $MVO_2$. **Analysis of Options:** * **A. Myocardial fibre tension (Correct):** It represents the internal work of the heart. Factors increasing wall tension (like systemic hypertension or aortic stenosis) significantly escalate oxygen demand. * **B. Cardiac Output:** While related, CO is a measure of "volume work" (external work). The heart is remarkably efficient at moving volume; a doubling of stroke volume increases $MVO_2$ far less than a doubling of systolic pressure. * **C. Blood Volume:** This affects preload (End Diastolic Volume). While increased preload increases tension via the Laplace Law (increased radius), it is a secondary factor compared to the tension required to generate systolic pressure. * **D. Heart Rate:** This is a major determinant because it dictates the number of tension-generating cycles per minute. However, on a "per-beat" basis and in terms of absolute magnitude, wall tension remains the most critical factor. **High-Yield Clinical Pearls for NEET-PG:** * **Pressure Work vs. Volume Work:** Pressure work (afterload) is much more oxygen-consuming than volume work (preload). This is why patients with **Aortic Stenosis** (pressure overload) develop angina much earlier than those with **Aortic Regurgitation** (volume overload). * **Determinants of $MVO_2$:** The big three are **Wall Tension** (highest impact), **Heart Rate**, and **Contractility** (Inotropy). * **Basal Metabolism:** Even at rest, the heart extracts 70-80% of oxygen from coronary blood, meaning any increase in demand must be met by increasing coronary blood flow, not extraction.

Practice by Chapter

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