Cardiac Physiology (Cycle, Output, ECG, Electrophysiology) MCQs

Physiology · 87 free questions with answers & explanations.

1. A 55-year-old man with a resting heart rate of 72 bpm has a stroke volume of 70 mL. His end-diastolic volume is 130 mL. What is his ejection fraction?
2. During the cardiac cycle, the period of isovolumetric contraction ends when which of the following events occurs?
3. On a standard 12-lead ECG, a patient shows a PR interval of 280 ms that remains constant with occasional dropped beats following every third P wave. Which conduction disorder best explains this finding?
4. The resting membrane potential of a ventricular myocyte is approximately −90 mV. This potential is primarily maintained by which ion's equilibrium?
5. A patient is found to have a cardiac output of 4 L/min with a heart rate of 80 bpm. Compared to a healthy individual with cardiac output of 5 L/min at the same heart rate, what is the most likely physiological explanation for the reduced output?
6. A patient is found to have a left ventricular end-diastolic volume of 140 mL and an end-systolic volume of 70 mL. Aortic diastolic pressure is 80 mmHg and left ventricular systolic pressure at peak is 130 mmHg. Which of the following correctly describes the pressure-volume loop of this ventricle?
7. During an exercise stress test, a patient's cardiac output increases from 5 L/min to 20 L/min. Heart rate rises from 70 to 160 bpm. What is the approximate stroke volume at peak exercise?
8. On a 12-lead ECG, the QT interval measures 520 ms at a heart rate of 60 bpm (RR interval = 1000 ms). Using Bazett's formula, what is the corrected QT (QTc) and how should this be interpreted?
9. A ventricular myocyte is held at its resting membrane potential of −90 mV. Tetrodotoxin (TTX) is applied, which blocks fast voltage-gated Na⁺ channels. Which phase of the cardiac action potential will be most directly abolished?
10. A Wiggers diagram shows that left ventricular pressure exceeds aortic pressure during a brief interval of the cardiac cycle. This crossover represents which event?
11. During the plateau phase (phase 2) of the ventricular action potential, the membrane potential is maintained near 0 mV primarily because of a balance between which two ion currents?
12. A 58-year-old man in the ICU has a pulmonary capillary wedge pressure of 24 mmHg and a cardiac output of 3.1 L/min. His systemic vascular resistance is calculated to be elevated. According to the Frank-Starling mechanism, which of the following best describes the state of his left ventricle?
13. In the sinoatrial node action potential, the 'funny current' (If) responsible for spontaneous diastolic depolarisation is carried predominantly by:
14. Which component of the ECG corresponds to the refractory period during which a second ventricular contraction cannot be initiated, and why is a P wave sometimes hidden within this interval?
15. Laplace's law applied to ventricular wall stress states: Wall stress = (Pressure × Radius) / (2 × Wall thickness). In a dilated cardiomyopathy patient with an LV end-diastolic radius of 4 cm and wall thickness of 0.8 cm compared to a normal LV with radius 2.5 cm and wall thickness 1.1 cm, systolic wall stress is markedly elevated because:
16. The rapid upstroke (phase 0) of the ventricular action potential is generated by activation of which channel type, and what is its approximate reversal potential?
17. During a normal cardiac cycle, the 'a' wave of the jugular venous pulse corresponds to which event?
18. A 58-year-old man has a prolonged PR interval of 240 ms. Which ion channel abnormality is most directly responsible for slow conduction through the AV node?
19. At a heart rate of 150 bpm, cardiac output is 9 L/min despite a stroke volume of only 60 mL. Which Frank-Starling mechanism best explains why stroke volume does not rise further despite increased contractile demand?
20. The T wave on a surface ECG represents which phase of the ventricular action potential, and why is it normally upright in leads with a dominant R wave?
21. The rapid upstroke (phase 0) of the ventricular action potential is generated by which ion channel, and what is its approximate reversal potential?
22. A patient presents with a prolonged QT interval and episodes of polymorphic ventricular tachycardia (torsades de pointes). The underlying defect is most likely loss-of-function mutation in which channel?
23. During isovolumetric relaxation, which of the following correctly describes the pressure-volume relationship within the left ventricle?
24. The Bezold-Jarisch reflex, triggered by inferior myocardial ischemia, is characterized by which triad?
25. The force-frequency relationship (Bowditch staircase / Treppe) in the heart occurs due to increased intracellular availability of which ion?
26. A researcher studying ion currents in sinoatrial node pacemaker cells records a slowly depolarizing 'funny current' (If). Which ion channels predominantly carry this current during the diastolic depolarization phase?
27. During the isovolumetric relaxation phase of the cardiac cycle, which of the following pressure relationships is correct?
28. A patient with severe aortic regurgitation has a widened pulse pressure and a low diastolic blood pressure. The primary mechanism causing the reduction in diastolic blood pressure is:
29. On a standard 12-lead ECG, the delta wave and short PR interval characteristic of Wolff-Parkinson-White syndrome result from pre-excitation of the ventricles. The abnormal pathway responsible conducts impulses via:
30. The Bowditch staircase (Treppe) phenomenon in cardiac muscle describes an increase in contractile force with increasing heart rate. The cellular mechanism underlying this phenomenon is:
31. During phase 2 (plateau) of the cardiac ventricular action potential, the net inward current is primarily carried by which channel, and its prolonged opening is responsible for which clinically important property?
32. A patient with hypertrophic obstructive cardiomyopathy (HOCM) undergoes Valsalva maneuver during examination. The dynamic outflow obstruction worsens. Which physiological mechanism best explains the worsening obstruction during forced expiration against a closed glottis?
33. The IKs current (slow delayed rectifier potassium current) is encoded by KCNQ1 (KvLQT1) + KCNE1 (minK). Loss-of-function mutation in KCNQ1 leads to which specific consequence on the cardiac action potential and which syndrome?
34. In a patient with complete heart block, the ventricular escape rhythm originates from Purkinje fibers at ~30 bpm. The slow diastolic depolarization (phase 4) in these cells is driven primarily by which ionic mechanism?
35. A 55-year-old hypertensive man has a stroke volume of 60 mL, ejection fraction of 40%, and heart rate of 80 bpm. His pulse pressure is narrowed. Which hemodynamic parameter is most directly responsible for his reduced pulse pressure?
36. The plateau phase (phase 2) of the cardiac ventricular action potential is primarily maintained by which ionic current balance?
37. A researcher blocks the IKr channel (hERG channel) in cardiac myocytes. Which phase of the ventricular action potential will be most directly prolonged, and what is the principal clinical risk?
38. During isovolumeric contraction in the cardiac cycle, which of the following events accurately describes the pressure–volume relationship of the left ventricle?
39. The hyperpolarization-activated cyclic nucleotide-gated (HCN) channel responsible for the pacemaker 'funny current' (If) in the SA node is activated by which condition?
40. A patient with severe aortic stenosis shows a paradoxically split second heart sound (S2). The physiological basis of this paradoxical splitting is:
41. The funny current (If) in sinoatrial node pacemaker cells is carried primarily by which ion channel, and what is its key gating characteristic?
42. A 45-year-old man with hypertrophic obstructive cardiomyopathy (HOCM) has a systolic murmur that increases with Valsalva maneuver and decreases with squatting. The pathophysiological basis of the Valsalva-induced change is:
43. During an action potential in a ventricular cardiomyocyte, calcium-induced calcium release (CICR) from the sarcoplasmic reticulum is triggered by Ca²⁺ entry through which channel, and the SR release channel involved is:
44. On a 12-lead ECG, an acute posterior myocardial infarction manifests in the standard leads as:
45. The Brugada syndrome pattern on ECG (coved-type ST elevation in V1–V2) results from dysfunction of which molecular channel, and what is the consequence for action potential phase 1?
46. A 52-year-old undergoes cardiac catheterization. His left ventricular end-diastolic pressure (LVEDP) is 18 mmHg and end-systolic pressure 120 mmHg. End-diastolic volume is 150 mL and end-systolic volume is 60 mL. His ventricular stroke work can be calculated as approximately:
47. An electrophysiology study identifies aberrant automaticity in a Purkinje fiber. The ionic current responsible for spontaneous phase 4 depolarization (pacemaker potential) in Purkinje fibers is primarily:
48. A 48-year-old with hypertrophic obstructive cardiomyopathy (HOCM) has dynamic LV outflow tract obstruction. Maneuvers that worsen the obstruction include:
49. During which phase of the cardiac cycle is the velocity of blood flow across the aortic valve the HIGHEST?
50. The PR interval on ECG is prolonged in first-degree AV block. The normal delay at the AV node (rather than His-Purkinje) serves which physiological function?
51. In the Frank-Starling mechanism, which molecular event explains increased force of contraction with increased preload?
52. In the ECG of a patient with hyperkalaemia, which sequence of ECG changes is seen with progressively rising serum potassium?
53. The J-wave (Osborn wave) appearing at the QRS-ST junction on ECG is most characteristically associated with:
54. In a pressure-volume (PV) loop of the left ventricle, end-systolic pressure-volume relationship (ESPVR) is a measure of cardiac contractility. An increase in preload with unchanged contractility produces which change in the PV loop?
55. A prolonged QT interval on ECG predisposes to Torsades de Pointes (TdP). The underlying ionic mechanism of QT prolongation in congenital long QT syndrome type 2 (LQTS2) involves:
56. A patient has the following hemodynamic values: PCWP 22 mmHg, PA systolic/diastolic 45/28 mmHg, CVP 14 mmHg, cardiac output 2.8 L/min. Which cardiac condition is MOST consistent?
57. The QT interval on ECG is measured as 480 ms at a heart rate of 60 bpm (QTc by Bazett formula = QT/√RR interval). This patient is started on haloperidol. What is the PRIMARY mechanism by which haloperidol prolongs the QT interval?
58. During the isovolumetric contraction phase of the cardiac cycle, which of the following is TRUE?
59. The Frank-Starling mechanism is demonstrated experimentally in an isolated heart preparation. At constant contractility and afterload, increasing end-diastolic volume from 120 mL to 150 mL increases stroke volume from 70 to 90 mL. The underlying molecular mechanism at the sarcomere level is BEST explained by:
60. A patient's ECG shows a QT interval of 480 ms with a heart rate of 60 bpm. The corrected QT (QTc) using Bazett's formula is calculated. What is the QTc, and does it indicate prolongation?
61. Which ion channel is responsible for the plateau phase (phase 2) of the ventricular action potential, and what is its physiological significance?
62. A patient with severe aortic stenosis (AVA 0.7 cm²) has maintained normal stroke volume. Which Frank-Starling mechanism explains this preserved function, and what eventual failure mechanism supervenes?
63. On the ECG of a patient with complete right bundle branch block (RBBB), which of the following findings is characteristically seen in lead V1?
64. Which ion current is primarily responsible for the plateau phase (phase 2) of the ventricular action potential, and why is calcium entry during this phase critical?
65. A patient with complete heart block (CHB) has a ventricular rate of 38 bpm and an atrial rate of 80 bpm on ECG, with P waves bearing no consistent relationship to QRS complexes. The QRS is wide (0.14 s). From which pacemaker focus do the QRS complexes most likely originate, and why?
66. The Frank-Starling mechanism is assessed in a patient with isolated left ventricular systolic dysfunction. At a given afterload and contractility, increasing preload from 8 mmHg to 14 mmHg LVEDP increases stroke volume from 60 to 80 mL. Beyond which physiological point does further preload increase stop improving or reduce stroke volume, and what is the mechanism?
67. In the cardiac action potential of ventricular myocytes, the plateau phase (phase 2) is maintained by:
68. A patient has a prolonged QTc interval of 510 ms. Which ion channel defect is most commonly associated with long QT syndrome Type 2 (LQT2)?
69. During early diastole, the rapid filling phase of the ventricle occurs. The sound heard on auscultation that corresponds to this event in pathological states is:
70. A patient develops complete heart block. The ventricular escape rhythm at 35 bpm originates from the Purkinje fibres. This escape rate (35 bpm) reflects the intrinsic automaticity of Purkinje fibres because the SA node (60–100 bpm) and AV node (40–60 bpm) are non-conducting. The mechanism of phase 4 spontaneous depolarization in Purkinje fibres involves which ion current?
71. On a standard ECG, the QTc interval corrects QT for heart rate (Bazett's formula: QTc = QT/√RR). In a patient taking sotalol, QTc is 510 ms (normal <440 ms in men). The electrophysiological risk of this prolonged QTc is:
72. During the cardiac cycle, the mitral valve closes at the START of which phase?
73. A patient's ECG shows QT interval of 480 ms with a heart rate of 64 bpm (RR interval 938 ms). Calculate the corrected QT interval (QTc) using Bazett's formula, and determine if it is prolonged.
74. Which phase of the ventricular action potential is primarily responsible for the plateau phase (phase 2) in ventricular muscle cells, and what distinguishes it from the cardiac pacemaker (SA node) action potential?
75. A 45-year-old hypertensive patient undergoes valsalva maneuver. In phase II of the Valsalva maneuver, which hemodynamic change occurs?
76. A patient's corrected QT interval (QTc) is calculated using Bazett's formula. The measured QT is 480 ms at a heart rate of 60 bpm (RR interval = 1000 ms). What is the QTc, and is it prolonged?
77. During phase 2 (plateau) of the cardiac ventricular action potential, which ionic currents are most responsible for maintaining the prolonged depolarization?
78. The Fick principle states that cardiac output (CO) = oxygen consumption (VO2) ÷ arteriovenous oxygen difference. If VO2 = 250 mL/min, arterial O2 content = 200 mL/L, and mixed venous O2 content = 150 mL/L, what is the cardiac output?
79. In aortic regurgitation, what is the primary adaptive mechanism that allows the ventricle to handle the large regurgitant volume while maintaining forward stroke volume?
80. On the wiggers diagram, the 'c' wave of the central venous pressure (JVP) trace corresponds to which event?
81. A patient has an ECG with a PR interval of 320 ms that is constant, and random non-conducted P waves. This describes:
82. In the Frank-Starling mechanism, the fundamental cellular explanation for increased stroke volume with increased end-diastolic volume is:
83. The corrected QT interval (QTc) using Bazett's formula for a patient with heart rate 100 bpm and QT interval 380 ms is approximately:
84. The dicrotic notch (incisura) seen on the aortic pressure tracing is produced by:
85. During which phase of the cardiac cycle are all four cardiac valves closed while ventricular volume remains constant and ventricular pressure rises sharply?
86. Under normal resting conditions, the single most important chemical stimulus regulating ventilation is:
87. Which of the following changes shifts the oxygen–haemoglobin dissociation curve to the RIGHT, favouring oxygen unloading at the tissues?