Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 651: Myocardial contractility is increased by:

A. Atropine
B. Decreased end diastolic volume
C. Increased heart rate from 70 to 150 beats/min (Correct Answer)
D. Reduced arterial pH to 7.3

Explanation: ### Explanation **Correct Answer: C. Increased heart rate from 70 to 150 beats/min** This phenomenon is known as the **Bowditch Effect** (also called the Treppe or Staircase phenomenon). When the heart rate increases, the time available for the Na+/K+ ATPase pump to remove sodium and the Na+/Ca2+ exchanger to remove calcium from the sarcoplasm decreases. This leads to a progressive accumulation of intracellular calcium ions ($Ca^{2+}$) within the sarcoplasmic reticulum. With each subsequent contraction, more $Ca^{2+}$ is released, thereby increasing myocardial contractility (inotropy). **Analysis of Incorrect Options:** * **A. Atropine:** Atropine is a muscarinic antagonist. While it increases heart rate (chronotropy) by blocking vagal tone at the SA node, it has **no direct effect** on ventricular contractility, as the ventricles lack significant parasympathetic innervation. * **B. Decreased end-diastolic volume (EDV):** According to the **Frank-Starling Law**, a decrease in EDV leads to decreased stretching of cardiac muscle fibers, resulting in a *weaker* force of contraction. * **D. Reduced arterial pH (Acidosis):** Acidosis acts as a **negative inotrope**. High levels of $H^+$ ions compete with $Ca^{2+}$ for binding sites on Troponin C and inhibit the slow inward calcium current, thereby reducing contractility. **High-Yield NEET-PG Pearls:** * **Anrep Effect:** An increase in ventricular contractility following an increase in afterload (aute compensation). * **Digitalis Mechanism:** Increases contractility by inhibiting Na+/K+ ATPase, which indirectly increases intracellular $Ca^{2+}$ (similar end-result to the Bowditch effect). * **Hyperkalemia:** High extracellular potassium decreases the resting membrane potential, leading to decreased excitability and contractility (heart stops in diastole).

Question 652: The Hb-O2 dissociation curve is shifted to the left by which of the following?

A. Metabolic acidosis
B. Increased temperature
C. Increased PCO2
D. Decreased 2,3-DPG (Correct Answer)

Explanation: **Explanation:** The Hemoglobin-Oxygen (Hb-O2) dissociation curve represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **leftward shift** indicates an **increased affinity** of hemoglobin for oxygen, meaning oxygen binds more tightly and is less easily released to the tissues. **Why Option D is Correct:** **2,3-Diphosphoglycerate (2,3-DPG)** is a byproduct of glycolysis in RBCs that binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and promoting oxygen release. Therefore, a **decrease in 2,3-DPG** stabilizes the "R" (Relaxed) state, increasing oxygen affinity and shifting the curve to the **left**. **Why Other Options are Incorrect:** * **A. Metabolic Acidosis:** A decrease in pH (increased $H^+$ ions) decreases Hb affinity for $O_2$ (the **Bohr Effect**), shifting the curve to the **right**. * **B. Increased Temperature:** Higher temperatures denature the bond between hemoglobin and oxygen, facilitating $O_2$ unloading and shifting the curve to the **right**. * **C. Increased $PCO_2$:** High $CO_2$ levels lead to increased $H^+$ production and direct carbamino-hemoglobin formation, both of which shift the curve to the **right**. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**- $CO_2$ increase, **A**- Acidosis, **D**- 2,3-DPG increase, **E**- Exercise, **T**- Temperature increase). * **Fetal Hemoglobin (HbF):** Shifts the curve to the **left** because it has a poor binding affinity for 2,3-DPG, allowing the fetus to extract $O_2$ from maternal blood. * **Stored Blood:** Levels of 2,3-DPG decrease in stored blood, causing a left shift; this is why massive transfusions can temporarily impair tissue oxygen delivery.

Question 653: Which of the following changes does NOT occur in the blood as it passes through the systemic capillaries?

A. Increase in hematocrit
B. Decrease in pH
C. Shift of the oxygen dissociation curve to the left (Correct Answer)
D. Increase in protein content

Explanation: **Explanation:** The correct answer is **C (Shift of the oxygen dissociation curve to the left)**. In the systemic capillaries, the blood undergoes changes that facilitate oxygen unloading to the tissues. This requires a **rightward shift** of the oxygen-hemoglobin dissociation curve (the **Bohr Effect**), driven by increased $PCO_2$, increased $[H^+]$ (decreased pH), and increased temperature. A leftward shift would increase hemoglobin's affinity for oxygen, hindering its release to the tissues. **Analysis of Incorrect Options:** * **A. Increase in hematocrit:** As blood passes through capillaries, the "Chloride Shift" (Hamburger phenomenon) occurs. $HCO_3^-$ leaves the RBCs while $Cl^-$ enters. This increase in intracellular osmotic pressure causes water to enter the RBCs, making them swell and slightly increasing the hematocrit in venous blood compared to arterial blood. * **B. Decrease in pH:** Tissues produce $CO_2$ as a metabolic byproduct. When $CO_2$ enters the blood, it reacts with water to form carbonic acid, which dissociates into $H^+$ and $HCO_3^-$, thereby lowering the pH (making it more acidic). * **D. Increase in protein content:** Due to hydrostatic pressure, a small amount of protein-free fluid filters out of the capillaries into the interstitial space (ultrafiltration). This leads to a relative increase in the concentration of plasma proteins in the capillary blood. **High-Yield NEET-PG Pearls:** * **Bohr Effect:** Shift to the **Right** (occurs at **Tissues**). Mnemonic: **CADET**, face Right! (**C**O2, **A**cid, 2,3-**D**PG, **E**xercise, **T**emperature). * **Haldane Effect:** Occurs at the **Lungs**; oxygenation of hemoglobin promotes the dissociation of $CO_2$ from hemoglobin. * **Chloride Shift:** $Cl^-$ moves **into** RBCs in systemic capillaries and **out** of RBCs in pulmonary capillaries.

Question 654: Which of the following is a vasoconstrictor?

A. Nitric Oxide (NO)
B. Prostaglandin I2 (PGI2)
C. Angiotensin II (Correct Answer)
D. Atrial Natriuretic Peptide (ANP)

Explanation: **Explanation:** **Angiotensin II** is one of the most potent endogenous **vasoconstrictors** in the body. It is a key component of the Renin-Angiotensin-Aldosterone System (RAAS). It acts primarily on **AT1 receptors** located on vascular smooth muscle cells, leading to an increase in intracellular calcium, which results in systemic vasoconstriction and an increase in total peripheral resistance (TPR) and blood pressure. **Analysis of Incorrect Options:** * **Nitric Oxide (NO):** Formerly known as Endothelium-Derived Relaxing Factor (EDRF), it is a potent **vasodilator**. It works by stimulating soluble guanylyl cyclase, increasing cGMP levels, which leads to smooth muscle relaxation. * **Prostaglandin I2 (PGI2):** Also known as **Prostacyclin**, it is produced by vascular endothelial cells. It is a powerful **vasodilator** and inhibitor of platelet aggregation. * **Atrial Natriuretic Peptide (ANP):** Released by the cardiac atria in response to stretch (volume overload), ANP promotes **vasodilation** and natriuresis (sodium excretion) to lower blood pressure. **High-Yield NEET-PG Pearls:** * **Potent Vasoconstrictors:** Angiotensin II, Endothelin-1 (most potent), Norepinephrine, Vasopressin (V1 receptors), and Thromboxane A2. * **Potent Vasodilators:** Nitric Oxide, Bradykinin, Histamine, Adenosine, and VIP (Vasoactive Intestinal Peptide). * **Clinical Correlation:** ACE inhibitors and ARBs (Angiotensin Receptor Blockers) are used in hypertension to prevent the vasoconstrictive effects of Angiotensin II.

Question 655: A person's electrocardiogram (ECG) shows no P wave, but has a normal QRS complex and a normal T wave. Where is the individual's pacemaker located?

A. Sinoatrial (SA) node
B. Atrioventricular (AV) node (Correct Answer)
C. Bundle of His
D. Purkinje system

Explanation: **Explanation:** The presence of a normal QRS complex and T wave in the absence of a P wave indicates a **Junctional Rhythm**, where the pacemaker is located in the **Atrioventricular (AV) node**. 1. **Why the AV Node is correct:** In a normal cardiac cycle, the SA node initiates the impulse, causing atrial depolarization (P wave). If the SA node fails or its impulse is blocked, the AV node takes over as the latent pacemaker (intrinsic rate 40–60 bpm). Because the impulse originates at the AV junction, it travels down the normal ventricular conduction system (Bundle of His → Purkinje fibers), resulting in a **normal (narrow) QRS complex**. However, the atria are either not depolarized or are depolarized via retrograde conduction (hidden within or occurring after the QRS), leading to the **absence of a visible P wave**. 2. **Why other options are incorrect:** * **SA Node:** If the SA node were the pacemaker, a normal P wave would precede every QRS complex. * **Bundle of His & Purkinje System:** These are "ventricular" pacemakers. If the impulse originated here (Idioventricular rhythm), the conduction would not follow the physiological pathway, resulting in a **wide, bizarre QRS complex** and a much slower heart rate (20–40 bpm). **High-Yield NEET-PG Pearls:** * **Hierarchy of Pacemakers:** SA node (60–100 bpm) > AV node (40–60 bpm) > Purkinje system (20–40 bpm). The fastest driver suppresses the others (Overdrive Suppression). * **P-wave morphology in Junctional Rhythm:** It may be absent, inverted (retrograde), or appear after the QRS. * **Narrow QRS (<0.12s):** Indicates the rhythm originates at or above the Bundle of His (Supraventricular). * **Wide QRS (>0.12s):** Indicates the rhythm originates within the ventricles.

Question 656: In humans, where does depolarization of cardiac ventricular muscle start?

A. Posterobasal part of ventricle
B. Left side of interventricular septum (Correct Answer)
C. Uppermost part of interventricular septum
D. Basal portion of ventricle

Explanation: ### Explanation **Concept Overview:** The cardiac conduction system is designed to ensure an efficient, coordinated contraction of the ventricles. After the impulse passes through the AV node and the Bundle of His, it enters the left and right bundle branches. In humans, the **left bundle branch** depolarizes slightly before the right. Specifically, the impulse first enters the **left side of the interventricular septum** via the septal fascicle of the left bundle branch. **Why Option B is Correct:** Depolarization begins at the **middle of the left side of the interventricular septum** and moves across the septum to the right. This is why the initial vector of ventricular depolarization (the 'Q' wave on an ECG) is directed from left to right. **Analysis of Incorrect Options:** * **Options A & D (Posterobasal and Basal portions):** These are the **last** parts of the heart to depolarize. The impulse travels from the septum to the apex and then sweeps upwards toward the base of the heart. * **Option C (Uppermost part of the septum):** While the septum is the starting point, the depolarization begins in the middle third of the left septal surface, not the most superior (uppermost) portion. **NEET-PG High-Yield Pearls:** * **Sequence of Depolarization:** Septum (Left to Right) → Apex/Subendocardium → Ventricular Walls → Base of the Heart. * **Direction of Spread:** Ventricular depolarization spreads from the **endocardium to the epicardium**, whereas repolarization typically occurs from the **epicardium to the endocardium**. * **ECG Correlation:** The left-to-right septal depolarization is responsible for the small, physiological 'q' waves seen in lateral leads (V5, V6, I, aVL). * **Conduction Velocity:** The **Purkinje fibers** have the fastest conduction velocity (2.0–4.0 m/s) in the heart, ensuring rapid ventricular activation.

Question 657: Preload is increased by which of the following factors?

A. Increased blood volume (Correct Answer)
B. Increased total peripheral resistance
C. Standing
D. Sitting

Explanation: ### Explanation **Concept Overview** Preload is defined as the initial stretching of the cardiac myocytes prior to contraction. According to the **Frank-Starling Law**, as preload increases, the force of ventricular contraction increases. Clinically, preload is equivalent to the **End-Diastolic Volume (EDV)**, which is primarily determined by venous return to the heart. **Why Option A is Correct** **Increased blood volume** directly increases the volume of blood returning to the right atrium (venous return). This leads to greater filling of the ventricles during diastole, increasing the End-Diastolic Volume and, consequently, the preload. **Why Other Options are Incorrect** * **Option B (Increased Total Peripheral Resistance):** TPR is a primary determinant of **Afterload**, not preload. High TPR increases the resistance against which the heart must pump, which can actually decrease stroke volume and potentially lead to a secondary increase in ESV, but it does not acutely "increase" preload in the physiological sense. * **Options C & D (Standing and Sitting):** Both positions involve a change from supine to upright. Gravity causes **venous pooling** in the lower extremities, which decreases venous return to the heart. This reduction in venous return leads to a **decrease** in preload. **High-Yield NEET-PG Pearls** * **Factors increasing Preload:** Hypervolemia, regurgitant valvular lesions (Mitral/Aortic regurgitation), and horizontal position (supine). * **Factors decreasing Preload:** Hemorrhage, dehydration, diuretics, nitrates (venodilators), and the Valsalva maneuver. * **Clinical Correlation:** In heart failure management, diuretics are used specifically to **reduce preload** to relieve pulmonary congestion. * **Key Formula:** Stroke Volume = EDV (Preload) – ESV (Afterload/Contractility).

Question 658: The SA node acts as the pacemaker of the heart because:

A. It is capable of generating impulses spontaneously.
B. It has rich sympathetic innervation.
C. It has poor cholinergic innervation.
D. It generates impulses at the highest rate. (Correct Answer)

Explanation: ### Explanation The SA node is the primary pacemaker of the heart due to the principle of **Overdrive Suppression**. While multiple tissues in the cardiac conduction system possess intrinsic automaticity, the SA node has the **highest intrinsic firing rate** (typically 60–100 bpm). By generating impulses faster than other latent pacemakers (like the AV node or Purkinje fibers), it depolarizes these tissues before they can reach their own threshold, effectively suppressing their independent activity. **Analysis of Options:** * **Option D (Correct):** The hierarchy of the conduction system is determined by the rate of discharge. Since the SA node is the fastest, it dictates the heart rate. * **Option A (Incorrect):** While the SA node is capable of spontaneous impulse generation (automaticity), so are the AV node (40–60 bpm) and Purkinje fibers (25–40 bpm). Automaticity alone does not make it the *dominant* pacemaker; its superior rate does. * **Option B & C (Incorrect):** Autonomic innervation modulates the heart rate (Sympathetic increases it; Parasympathetic/Cholinergic decreases it), but it is not the reason the SA node is the pacemaker. In fact, the SA node is richly supplied by both divisions, with vagal tone normally predominating at rest. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** The SA node is located at the junction of the superior vena cava and the right atrium (subepicardial). * **Ionic Basis:** The "pacemaker potential" (Phase 4) is primarily due to **funny currents ($I_f$)** through HCN channels (sodium influx) and T-type calcium channels. * **Ectopic Pacemaker:** If the SA node fails, the AV node takes over (Nodal rhythm). If all higher centers fail, a ventricular escape rhythm occurs. * **Stokes-Adams Syndrome:** A sudden transition from SA to a slower latent pacemaker can cause a delay in impulse generation, leading to transient cerebral ischemia and fainting.

Question 659: Incisura is absent in which of the following conditions?

A. Aortic valve replacement
B. Aortic stenosis (Correct Answer)
C. Cardiac tamponade
D. Hypovolemic shock

Explanation: ### Explanation **Underlying Concept:** The **incisura** (or dicrotic notch) on an aortic pressure tracing represents the brief interruption of blood flow caused by the **closure of the aortic valve** at the beginning of ventricular diastole. For an incisura to be visible, there must be a rapid, sharp closure of the valve leaflets and a subsequent rebound of blood against them. **Why Aortic Stenosis is Correct:** In **Aortic Stenosis (AS)**, the valve leaflets are thickened, calcified, and rigid. This leads to two main changes in the pressure pulse: 1. **Pulsus Tardus et Parvus:** The upstroke is slow (tardus) and the peak is low (parvus). 2. **Loss of Incisura:** Because the valve is stiff and does not snap shut or open freely, the sharp pressure drop and rebound (incisura) are smoothed out or entirely absent. The pressure tracing appears "rounded." **Analysis of Incorrect Options:** * **Aortic Valve Replacement:** If a mechanical or functional bioprosthetic valve is placed, it is designed to snap shut effectively, often maintaining a visible (though sometimes altered) notch. * **Cardiac Tamponade:** This affects ventricular filling (diastolic dysfunction). While it causes *Pulsus Paradoxus* (a drop in systolic BP >10 mmHg during inspiration), the aortic valve mechanism remains intact, so the incisura is generally preserved. * **Hypovolemic Shock:** This leads to a narrow pulse pressure and low stroke volume, but the aortic valve still closes mechanically, preserving the dicrotic notch (though it may be positioned lower on the downstroke). **High-Yield Clinical Pearls for NEET-PG:** * **Anacrotic Notch:** A notch on the *ascending* limb of the pulse, also characteristic of Aortic Stenosis. * **Dicrotic Notch vs. Dicrotic Wave:** The *notch* is the pressure dip (aortic tracing); the *wave* is the secondary peak seen in the peripheral pulse (especially in states of low systemic vascular resistance like sepsis). * **Bisferiens Pulse:** A "double-peaked" pulse seen in AR (Aortic Regurgitation) or HOCM.

Question 660: Maximum pressure in the left ventricle is observed during which phase of the cardiac cycle?

A. Isovolumetric contraction
B. Ventricular ejection (Correct Answer)
C. Protodiastole
D. Rapid ventricular filling

Explanation: **Explanation:** The cardiac cycle consists of distinct phases characterized by changes in pressure and volume. The correct answer is **Ventricular Ejection** because this phase encompasses the period when the left ventricle (LV) actively pumps blood into the aorta. 1. **Why Ventricular Ejection is correct:** After the aortic valve opens, the LV continues to contract to overcome afterload. The pressure rises to its absolute peak (approximately **120 mmHg** in a healthy adult) during the **maximum ejection phase**. This is necessary to drive the stroke volume into the systemic circulation. 2. **Why other options are incorrect:** * **Isovolumetric contraction:** This is the phase where pressure rises most *rapidly*, but it ends the moment the aortic valve opens. The pressure here is still lower than the peak pressure reached during active ejection. * **Protodiastole:** This is the very brief initial phase of ventricular relaxation before the aortic valve closes. Pressure is already beginning to fall during this stage. * **Rapid ventricular filling:** This occurs during diastole when the ventricle is relaxed and pressure is at its lowest (near 0–8 mmHg) to allow blood to flow from the atria. **High-Yield NEET-PG Pearls:** * **Maximum Pressure:** Reached during the first half of ventricular ejection. * **Maximum Rate of Pressure Rise ($dP/dt$ max):** Occurs during **Isovolumetric Contraction**; it is a key clinical indicator of ventricular contractility (inotropy). * **Aortic Valve Closure:** Marks the end of ventricular systole and the beginning of isovolumetric relaxation. * **Incisura (Dicrotic Notch):** Seen on the aortic pressure curve due to the backflow of blood hitting the closed aortic valve.

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