Phases of the cardiac cycle US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Phases of the cardiac cycle. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Phases of the cardiac cycle US Medical PG Question 1: A 62-year-old man comes to the physician for decreased exercise tolerance. Over the past four months, he has noticed progressively worsening shortness of breath while walking his dog. He also becomes short of breath when lying in bed at night. His temperature is 36.4°C (97.5°F), pulse is 82/min, respirations are 19/min, and blood pressure is 155/53 mm Hg. Cardiac examination shows a high-pitch, decrescendo murmur that occurs immediately after S2 and is heard best along the left sternal border. There is an S3 gallop. Carotid pulses are strong. Which of the following is the most likely diagnosis?
- A. Aortic valve regurgitation (Correct Answer)
- B. Tricuspid valve regurgitation
- C. Mitral valve prolapse
- D. Mitral valve regurgitation
- E. Mitral valve stenosis
Phases of the cardiac cycle Explanation: ***Aortic valve regurgitation***
- A **high-pitch, decrescendo murmur immediately after S2** and heard best along the **left sternal border** is characteristic of **aortic regurgitation**.
- Symptoms like **dyspnea on exertion** and **orthopnea**, an **S3 gallop**, and a **wide pulse pressure** (155/53 mmHg) further support heart failure due to chronic aortic regurgitation.
*Tricuspid valve regurgitation*
- This typically presents with a **holosystolic murmur** best heard at the **left lower sternal border** that increases with inspiration.
- Clinical signs often include **jugular venous distension** and **peripheral edema**, not primarily a decrescendo diastolic murmur.
*Mitral valve prolapse*
- Characterized by a **mid-systolic click** followed by a **late systolic murmur**, and symptomatically may be asymptomatic or cause palpitations.
- The described diastolic murmur and symptoms of heart failure do not align with mitral valve prolapse.
*Mitral valve regurgitation*
- Typically presents as a **holosystolic murmur** heard best at the **apex** and often radiating to the axilla.
- While it can cause dyspnea and an S3, the character and timing of the murmur reported (decrescendo, immediately after S2) are inconsistent with mitral regurgitation.
*Mitral valve stenosis*
- This condition presents with a **diastolic rumble** heard best at the **apex** with an opening snap.
- The murmur described is a high-pitch decrescendo murmur, which is distinct from the low-pitched rumble of mitral stenosis.
Phases of the cardiac cycle US Medical PG Question 2: A 76-year-old male with a history of chronic uncontrolled hypertension presents to the emergency room following an episode of syncope. He reports that he felt lightheaded and experienced chest pain while walking his dog earlier in the morning. He notes that he has experienced multiple similar episodes over the past year. A trans-esophageal echocardiogram demonstrates a thickened, calcified aortic valve with left ventricular hypertrophy. Which of the following heart sounds would likely be heard on auscultation of this patient?
- A. Crescendo-decrescendo murmur radiating to the carotids that is loudest at the right upper sternal border (Correct Answer)
- B. Diastolic rumble following an opening snap with an accentuated S1
- C. Early diastolic high-pitched blowing decrescendo murmur that is loudest at the left sternal border
- D. Holosystolic murmur radiating to the axilla that is loudest at the apex
- E. Midsystolic click that is loudest at the apex
Phases of the cardiac cycle Explanation: ***Crescendo-decrescendo murmur radiating to the carotids that is loudest at the right upper sternal border***
- The patient's symptoms of **syncope**, **chest pain**, and findings of a **thickened, calcified aortic valve** with **left ventricular hypertrophy** are classic for **aortic stenosis**.
- Aortic stenosis classically presents with a **systolic ejecting crescendo-decrescendo murmur** which is loudest at the **right upper sternal border**, and often **radiates to the carotids**.
*Diastolic rumble following an opening snap with an accentuated S1*
- This description is characteristic of **mitral stenosis**, which is typically caused by **rheumatic fever**.
- Mitral stenosis would present with dyspnea and fatigue, unlike the syncope and chest pain seen in this patient.
*Early diastolic high-pitched blowing decrescendo murmur that is loudest at the left sternal border*
- This murmur describes **aortic regurgitation**, where blood flows back into the left ventricle during diastole.
- While aortic regurgitation can cause heart failure symptoms, the echocardiogram shows a thickened, calcified valve more consistent with stenosis.
*Midsystolic click that is most prominent that is loudest at the apex*
- A **midsystolic click** followed by a **late systolic murmur** is characteristic of **mitral valve prolapse**.
- Symptoms of mitral valve prolapse can include atypical chest pain and palpitations, but not generally exertional syncope or the severe structural changes seen in the aortic valve.
*Holosystolic murmur radiating to the axilla that is loudest at the apex*
- This is the classic description of **mitral regurgitation**, indicating blood flow back into the left atrium during systole.
- Mitral regurgitation is associated with symptoms of heart failure and fatigue, but not usually the anginal chest pain and syncope in a patient with a calcified aortic valve.
Phases of the cardiac cycle US Medical PG Question 3: A 64-year-old man presents to his physician for a scheduled follow-up visit. He has chronic left-sided heart failure with systolic dysfunction. His current regular medications include captopril and digoxin, which were started after his last episode of symptomatic heart failure approximately 3 months ago. His last episode of heart failure was accompanied by atrial fibrillation, which followed an alcohol binge over a weekend. Since then he stopped drinking. He reports that he has no current symptoms at rest and is able to perform regular physical exercise without limitation. On physical examination, mild bipedal edema is noted. The physician suggested to him that he should discontinue digoxin and continue captopril and scheduled him for the next follow-up visit. Which of the following statements best justifies the suggestion made by the physician?
- A. Long-term digoxin therapy produces significant survival benefits in patients with heart failure, but at the cost of increased heart failure-related admissions.
- B. Both captopril and digoxin are likely to improve the long-term survival of the patient with heart failure, but digoxin has more severe side effects.
- C. Captopril is likely to improve the long-term survival of the patient with heart failure, unlike digoxin.
- D. Digoxin does not benefit patients with left-sided heart failure in the absence of atrial fibrillation.
- E. Digoxin is useful to treat atrial fibrillation, but does not benefit patients with systolic dysfunction who are in sinus rhythm. (Correct Answer)
Phases of the cardiac cycle Explanation: ***Digoxin is useful to treat atrial fibrillation, but does not benefit patients with systolic dysfunction who are in sinus rhythm.***
- The patient's **atrial fibrillation** was likely triggered by the alcohol binge and has since resolved, suggesting he is now in **sinus rhythm**.
- Digoxin's primary benefit in heart failure with **systolic dysfunction** (HFrEF) is to control ventricular rate in patients with **atrial fibrillation**, but it does not offer survival benefit in HFrEF patients who are in **sinus rhythm** and well-managed with other therapies.
*Long-term digoxin therapy produces significant survival benefits in patients with heart failure, but at the cost of increased heart failure-related admissions.*
- This statement is incorrect; digoxin has been shown to **reduce hospital admissions** for heart failure, but it does **not provide a significant survival benefit** in patients with HFrEF in sinus rhythm.
- The main benefit of digoxin in HFrEF is to improve symptoms and quality of life, alongside reducing hospitalizations, but not prolonging life.
*Both captopril and digoxin are likely to improve the long-term survival of the patient with heart failure, but digoxin has more severe side effects.*
- **Captopril (an ACE inhibitor)** does improve **long-term survival** in heart failure, but **digoxin does not** demonstrably improve survival.
- While digoxin can have side effects, its lack of survival benefit for HFrEF in sinus rhythm is the primary reason for discontinuation, not just side effect severity.
*Captopril is likely to improve the long-term survival of the patient with heart failure, unlike digoxin.*
- This statement is partially correct that **captopril improves survival**, but it does not fully explain the physician's decision to discontinue digoxin.
- The key missing piece is the patient's current **sinus rhythm** and the lack of benefit of digoxin in that specific context for HFrEF.
*Digoxin does not benefit patients with left-sided heart failure in the absence of atrial fibrillation.*
- This statement is nearly correct, but "left-sided heart failure" is broad. It is specifically in patients with **systolic dysfunction (HFrEF)** who are in **sinus rhythm** that digoxin lacks significant benefit beyond symptom control, and does not provide survival benefit.
Phases of the cardiac cycle US Medical PG Question 4: A 60-year-old male engineer who complains of shortness of breath when walking a few blocks undergoes a cardiac stress test because of concern for coronary artery disease. During the test he asks his cardiologist about what variables are usually used to quantify the functioning of the heart. He learns that one of these variables is stroke volume. Which of the following scenarios would be most likely to lead to a decrease in stroke volume?
- A. Anxiety
- B. Heart failure (Correct Answer)
- C. Exercise
- D. Pregnancy
- E. Digitalis
Phases of the cardiac cycle Explanation: ***Heart failure***
- In **heart failure**, the heart's pumping ability is impaired, leading to a reduced **ejection fraction** and thus a decreased **stroke volume**.
- The weakened myocardium cannot effectively contract to expel the normal volume of blood, resulting in lower blood output per beat.
*Anxiety*
- **Anxiety** typically causes an increase in **sympathetic nervous system** activity, leading to increased heart rate and myocardial contractility.
- This often results in a temporary **increase in stroke volume** due to enhanced cardiac performance, not a decrease.
*Exercise*
- During **exercise**, there is a significant **increase in venous return** and sympathetic stimulation, leading to increased **end-diastolic volume** and contractility.
- This physiological response causes a substantial **increase in stroke volume** to meet the body's higher oxygen demands.
*Pregnancy*
- **Pregnancy** leads to significant **physiological adaptations** to accommodate the growing fetus, including a substantial increase in **blood volume**.
- This increased blood volume and cardiac output result in an **increase in stroke volume** to maintain adequate perfusion for both mother and fetus.
*Digitalis*
- **Digitalis** is a cardiac glycoside that **increases intracellular calcium** in myocardial cells, enhancing the **force of contraction**.
- This positive inotropic effect leads to an **increased stroke volume** by improving the heart's pumping efficiency.
Phases of the cardiac cycle US Medical PG Question 5: A 64-year-old man presents to the emergency department because he has been experiencing increased shortness of breath for the last 2 weeks. Specifically, he says that he can barely walk up the stairs to his apartment before he feels winded. In addition, he has been waking up at night gasping for breath and has only been able to sleep propped up on 2 more pillows than usual. Physical exam reveals jugular venous distention as well as pitting lower extremity edema. Which of the following abnormal sounds will most likely be heard in this patient?
- A. Opening snap
- B. Extra heart sound in early diastole (Correct Answer)
- C. Extra heart sound in late diastole
- D. Fixed splitting
- E. Parasternal holosystolic murmur
Phases of the cardiac cycle Explanation: ***Extra heart sound in early diastole***
- The patient's symptoms (dyspnea, orthopnea, paroxysmal nocturnal dyspnea, jugular venous distention, edema) are classic for **congestive heart failure (CHF)**.
- An **S3 gallop** is an extra heart sound occurring in **early diastole** and is pathognomonic for **volume overload** and **ventricular dysfunction** in CHF.
*Opening snap*
- An **opening snap** is typically heard in **mitral stenosis**, which is not directly indicated by the patient's symptoms of volume overload from heart failure.
- This sound occurs shortly after S2 as the stenotic mitral valve opens.
*Extra heart sound in late diastole*
- An extra heart sound in **late diastole** is often an **S4 gallop**, which indicates **poor ventricular compliance** (e.g., in hypertension or aortic stenosis) rather than the pronounced volume overload suggested by the current presentation.
- An S4 is heard just before S1, as the atria contract to push blood into a stiff ventricle.
*Fixed splitting*
- **Fixed splitting of S2** is characteristic of an **atrial septal defect (ASD)**, where there is a constant delay in pulmonic valve closure, independent of respiration.
- This is not a typical finding in the context of acute decompensated heart failure as described.
*Parasternal holosystolic murmur*
- A **parasternal holosystolic murmur** is typically associated with **ventricular septal defect (VSD)** or **tricuspid regurgitation**.
- While tricuspid regurgitation can occur secondary to right heart failure, the most immediate and common auscultatory finding for overall heart failure with volume overload is an S3.
Phases of the cardiac cycle US Medical PG Question 6: An 80-year-old man presents to the emergency department because of gnawing substernal chest pain that started an hour ago and radiates to his neck and left jaw. A 12-lead ECG is obtained and shows ST-segment elevation with newly developing Q waves. He is admitted for treatment. 4 days after hospitalization he suddenly develops altered mental status, and his blood pressure falls from 115/75 mm Hg to 80/40 mm Hg. Physical examination shows jugular venous distention, pulsus paradoxus, and distant heart sounds. What is the most likely cause of this patient's condition?
- A. Pericardial inflammation
- B. Compression of heart chambers by blood in the pericardial space (Correct Answer)
- C. Arrhythmia caused by ventricular fibrillation
- D. Rupture of papillary muscle
- E. Acute pulmonary edema from left heart failure
Phases of the cardiac cycle Explanation: ***Compression of heart chambers by blood in the pericardial space***
- The patient's initial presentation with ST-elevation myocardial infarction (STEMI) and subsequent development of **hypotension**, **jugular venous distention**, **pulsus paradoxus**, and **distant heart sounds** (Beck's triad) is highly indicative of **cardiac tamponade.**
- In the context of a recent MI, this constellation of symptoms strongly suggests a **cardiac free wall rupture**, leading to blood accumulation in the pericardial sac and compression of the heart.
- Free wall rupture typically occurs **3-7 days post-MI** and is a life-threatening mechanical complication.
*Pericardial inflammation*
- While pericardial inflammation (pericarditis) can occur post-MI, it typically manifests with **pleuritic chest pain** that is relieved by leaning forward and is often associated with a **pericardial friction rub.**
- It does not typically lead to acute, severe hypotension, pulsus paradoxus, or sudden circulatory collapse in this manner without significant effusion and tamponade physiology.
*Arrhythmia caused by ventricular fibrillation*
- **Ventricular fibrillation** would cause immediate cardiac arrest and loss of consciousness, not a gradual development of hypotension, JVD, and pulsus paradoxus.
- While arrhythmias are common post-MI, the specific physical findings point away from isolated VFib as the primary cause of hemodynamic collapse.
*Acute pulmonary edema from left heart failure*
- **Acute pulmonary edema** is a manifestation of **left heart failure**, characterized by severe dyspnea, orthopnea, and crackles on lung auscultation.
- While left heart failure can cause hypotension in cardiogenic shock, it would not typically present with the classic signs of cardiac tamponade such as pulsus paradoxus, distant heart sounds, and prominent JVD without pulmonary congestion findings.
*Rupture of papillary muscle*
- **Papillary muscle rupture** leads to severe **acute mitral regurgitation**, causing acute pulmonary edema, a new holosystolic murmur, and often cardiogenic shock.
- While it can lead to hypotension, it doesn't typically present with the classic signs of cardiac tamponade such as pulsus paradoxus and distant heart sounds; instead, a loud murmur would be prominent.
Phases of the cardiac cycle US Medical PG Question 7: An abnormal wave is noted on a routine ECG. The wave in question represents which of the following electrical events in the cardiac cycle?
- A. Period between ventricular depolarization and repolarization
- B. Atrial repolarization
- C. Ventricular repolarization (Correct Answer)
- D. Ventricular depolarization
- E. Atrial depolarization
Phases of the cardiac cycle Explanation: ***Ventricular repolarization***
- The **T wave** represents ventricular repolarization, which is the electrical recovery phase of the ventricles after contraction
- T wave abnormalities are among the most common ECG findings and include **T wave inversions** (myocardial ischemia, ventricular hypertrophy), **peaked T waves** (hyperkalemia), **flattened T waves** (hypokalemia, ischemia), and **biphasic T waves**
- The T wave corresponds to **phase 3** of the ventricular action potential when potassium channels open and the membrane repolarizes
*Period between ventricular depolarization and repolarization*
- This describes the **ST segment**, which represents the period when ventricles are completely depolarized before repolarization begins
- The **QT interval** encompasses both ventricular depolarization and repolarization (QRS + ST segment + T wave)
- These are intervals or segments, not waves
*Atrial repolarization*
- Atrial repolarization occurs during ventricular depolarization and is represented by the **Ta wave**
- This wave is typically **not visible** on standard ECG because it is **masked by the much larger QRS complex** and has very low amplitude
- It cannot be identified as a distinct wave on routine ECGs
*Ventricular depolarization*
- The **QRS complex** represents ventricular depolarization, the electrical activation that triggers ventricular contraction
- Normal QRS duration is **0.06-0.10 seconds** (3 small boxes or less)
- QRS abnormalities include bundle branch blocks, ventricular hypertrophy patterns, and pre-excitation
*Atrial depolarization*
- The **P wave** represents atrial depolarization, the electrical activation that triggers atrial contraction
- Normal P wave characteristics: **upright in leads I, II, aVF**; duration less than 0.12 seconds; amplitude less than 2.5 mm
- P wave abnormalities include left atrial enlargement (broad, notched P waves) and right atrial enlargement (tall, peaked P waves)
Phases of the cardiac cycle US Medical PG Question 8: A 12-year-old girl is brought to an oncologist, as she was recently diagnosed with a rare form of cancer. Cytogenetic studies reveal that the tumor is responsive to vinblastine, which is a cell-cycle specific anticancer agent. It acts on the M phase of the cell cycle and inhibits the growth of cells. Which of the following statements best describes the regulation of the cell cycle?
- A. Inhibitors of DNA synthesis act in the M phase of the cell cycle.
- B. The G0 phase is the checkpoint before G1.
- C. Cyclin-dependent activation of CDK1 (CDC2) takes place upon the entry of a cell into M phase of the cell cycle. (Correct Answer)
- D. EGF from a blood clot stimulates the growth and proliferation of cells in the healing process.
- E. Replication of the genome occurs in the M phase of the cell cycle.
Phases of the cardiac cycle Explanation: ***Cyclin-dependent activation of CDK1 (CDC2) takes place upon the entry of a cell into M phase of the cell cycle.***
- The **M-phase promoting factor (MPF)**, composed of **CDK1 (CDC2)** and **cyclin B**, is activated at the G2/M transition, driving the cell into mitosis.
- Activation of CDK1 by **cyclin B binding** and subsequent dephosphorylation of threonine 161 is crucial for initiation of mitosis.
*Inhibitors of DNA synthesis act in the M phase of the cell cycle.*
- **Inhibitors of DNA synthesis**, such as **hydroxyurea** and **methotrexate**, primarily act during the **S phase** of the cell cycle, when DNA replication occurs.
- The M phase is characterized by **mitosis** (nuclear division) and **cytokinesis** (cytoplasmic division), not DNA synthesis.
*The G0 phase is the checkpoint before G1.*
- The **G0 phase** is a **resting state** where cells exit the cell cycle and cease to divide, not a checkpoint before G1.
- The main checkpoint before G1 is typically referred to as the **restriction point** or **G1 checkpoint**, which determines if a cell will commit to division.
*EGF from a blood clot stimulates the growth and proliferation of cells in the healing process.*
- While **EGF (Epidermal Growth Factor)** does stimulate cell growth and proliferation in healing, it is not primarily associated with blood clots.
- **Platelets** in blood clots release growth factors like **PDGF (Platelet-Derived Growth Factor)** and **TGF-β (Transforming Growth Factor-beta)**, which are critical for wound healing.
*Replication of the genome occurs in the M phase of the cell cycle.*
- **Replication of the genome** (DNA synthesis) occurs during the **S phase** (synthesis phase) of the cell cycle.
- The **M phase** is dedicated to **mitosis** (separation of duplicated chromosomes) and **cytokinesis**, where the cell divides into two daughter cells.
Phases of the cardiac cycle US Medical PG Question 9: An 8-year-old boy is brought to the physician because of a 1-day history of severe left hand pain. He has had similar painful episodes in the past that required hospitalization. Physical examination shows pale conjunctivae. There is tenderness on palpation of the wrist and the small joints of the left hand. Peripheral blood smear shows crescent-shaped erythrocytes. He is started on a pharmacologic agent that is known to cause macrocytosis. This drug causes an arrest in which of the following cell cycle phases?
- A. S phase (Correct Answer)
- B. G0 phase
- C. G2 phase
- D. M phase
- E. G1 phase
Phases of the cardiac cycle Explanation: ***S phase***
- This patient presents with **sickle cell disease** given the history of recurrent severe pain episodes, pale conjunctivae (suggesting anemia), and **crescent-shaped erythrocytes** on peripheral blood smear.
- The pharmacologic agent that causes **macrocytosis** and is used in sickle cell disease is **hydroxyurea** through increasing **fetal hemoglobin**; it primarily works by inhibiting **ribonucleotide reductase**, an enzyme essential for **DNA synthesis**, thereby arresting cells in the **S phase**.
*G0 phase*
- The **G0 phase** is a resting phase where cells are not actively dividing or preparing to divide.
- Hydroxyurea targets rapidly dividing cells by interfering with DNA replication, so it does not primarily arrest cells in the inactive G0 phase.
*G2 phase*
- The **G2 phase** is the growth phase where the cell checks its DNA and prepares for mitosis.
- While hydroxyurea can indirectly affect the G2/M checkpoint, its direct mechanism of action is primarily in the S phase by preventing proper DNA synthesis.
*M phase*
- The **M phase** is the stage of cell division, including mitosis and cytokinesis.
- Drugs that block the M phase typically interfere with **microtubule formation** (e.g., vinca alkaloids, taxanes), which is not the primary mechanism of hydroxyurea.
*G1 phase*
- The **G1 phase** is the initial growth phase where the cell grows and synthesizes proteins.
- While cells must pass through G1 before entering S phase, hydroxyurea's direct DNA synthesis inhibition occurs during the S phase rather than preventing entry into S from G1.
Phases of the cardiac cycle US Medical PG Question 10: A 52-year-old man presents to the emergency department because of fatigue, abdominal distension, and swelling of both legs for the last 3 weeks. His wife says that he lost some weight recently. He has had type 2 diabetes mellitus for 12 years, for which he takes metformin and sitagliptin. He has a history of Hodgkin’s lymphoma which was successfully treated with mediastinal radiation 20 years ago. He does not smoke or drink alcohol. He has a family history of type 2 diabetes in his father and elder sister. Vital signs include a blood pressure of 100/70 mm Hg, a temperature of 36.9°C (98.4°F), and a regular radial pulse of 90/min. On physical examination, there is jugular venous distension, most prominently when the patient inhales. Bilateral ankle pitting edema is present, and his abdomen is distended with shifting dullness on percussion. An early diastolic knocking sound is audible on the chest. His chest X-ray is shown in the exhibit. Which of the following is the best treatment for this patient?
- A. Pericardiectomy (Correct Answer)
- B. Percutaneous aspiration with high-flow oxygen
- C. Pleurodesis
- D. Ibuprofen, plus colchicine
- E. Pericardiocentesis
Phases of the cardiac cycle Explanation: ***Pericardiectomy***
- This patient presents with signs and symptoms of **constrictive pericarditis**, including **fatigue**, **abdominal distension** (ascites), **bilateral leg swelling** (edema), **jugular venous distension** (Kussmaul sign), and an **early diastolic knocking sound**. The **chest X-ray** demonstrating **pericardial calcification** (arrows) is highly suggestive of this condition.
- As medical therapies are generally ineffective for constrictive pericarditis, **surgical pericardiectomy** (removal of the pericardium) is the definitive treatment to relieve the constriction and improve cardiac function.
*Percutaneous aspiration with high-flow oxygen*
- This treatment is typical for a **tension pneumothorax**, which involves air accumulation in the pleural space, compressing the lung and mediastinum.
- The patient's symptoms and imaging, especially the chest X-ray showing pericardial calcification, are inconsistent with pneumothorax.
*Pleurodesis*
- **Pleurodesis** is a procedure used to prevent recurrent **pleural effusions** or **pneumothorax** by adhering the parietal and visceral pleura.
- This patient's presentation points to pericardial, not pleural, pathology, and there is no mention of recurrent pleural effusions or pneumothorax.
*Ibuprofen, plus colchicine*
- This combination is the standard treatment for **acute pericarditis**, which is characterized by chest pain, pericardial friction rub, and EKG changes.
- The patient's chronic symptoms, signs of fluid overload, and pericardial calcification indicate **constrictive pericarditis**, not acute inflammation, making anti-inflammatory agents ineffective.
*Pericardiocentesis*
- **Pericardiocentesis** is indicated for **pericardial tamponade** or large, symptomatic **pericardial effusions** to relieve pressure.
- While fluid overload is present, the key underlying issue is chronic pericardial constriction due to calcification, not a large acute effusion amenable to simple drainage.
More Phases of the cardiac cycle US Medical PG questions available in the OnCourse app. Practice MCQs, flashcards, and get detailed explanations.
