Cardiac cycle

Cardiac cycle US Medical PG Question 1: A 75-year-old man presents to the emergency department after an episode of syncope while walking outside with his wife. His wife states that he suddenly appeared pale and collapsed to the ground. She says he remained unconscious for 1 minute. He says he noticed a fluttering in his chest and excessive sweating before the episode. He has type 2 diabetes mellitus, essential hypertension, and chronic stable angina. He has not started any new medications in the past few months. Vital signs reveal: temperature 37.0°C (98.6°F), blood pressure 135/72 mm Hg, and pulse 72/min. Physical examination is unremarkable. ECG shows an old bifascicular block. Echocardiogram and 24-hour Holter monitoring are normal. Which of the following is the best next step in the evaluation of this patient's condition?

• A. Cardiac enzymes
• B. Continuous loop recorder (Correct Answer)
• C. Valsalva maneuver
• D. Electroencephalography (EEG)
• E. Tilt-table test

Cardiac cycle Explanation: ***Continuous loop recorder*** - This patient's syncope is preceded by **palpitations (fluttering in chest)** and **sweating**, suggesting a cardiac etiology, specifically a **transient arrhythmia** not captured on a standard ECG or 24-hour Holter. - A continuous loop recorder provides prolonged monitoring (months to years), increasing the likelihood of detecting intermittent arrhythmias responsible for syncopal episodes. *Cardiac enzymes* - While cardiac enzymes (e.g., troponin) are crucial for evaluating **acute myocardial ischemia** or infarction, the patient presents with syncope and no new chest pain, and his stable angina suggests chronic disease rather than an acute event leading to syncope in this specific instance. - An **ECG showing an old bifascicular block** and an **unremarkable physical exam** make an acute cardiac event less likely as the primary cause of syncope when an arrhythmia is suspected. *Valsalva maneuver* - The Valsalva maneuver is a diagnostic tool often used to differentiate between certain types of **tachyarrhythmias** or to evaluate for **autonomic dysfunction**, but it is not an evaluative step for a patient presenting with unexplained syncope where an arrhythmia has not yet been documented. - It would not help in identifying the cause of intermittent syncope in a patient whose standard workup has been unremarkable, as it's a test for immediate physiological response, not prolonged cardiac rhythm monitoring. *Electroencephalography (EEG)* - EEG is indicated when **seizure disorder** is suspected as the cause of loss of consciousness, often characterized by tonic-clonic movements, post-ictal confusion, or focal neurologic signs, which are absent in this patient's presentation. - The patient's pre-syncopal symptoms of **palpitations and sweating** point away from a seizure and towards a cardiac cause. *Tilt-table test* - A tilt-table test is used to evaluate for **vasovagal syncope** or **postural orthostatic tachycardia syndrome (POTS)**, often considered when other cardiac causes are ruled out or when syncope is typically triggered by prolonged standing. - Given the patient's pre-syncopal **palpitations**, a **cardiac arrhythmia** remains a higher suspicion than vasovagal syncope at this stage, especially after normal echocardiogram and Holter monitoring, necessitating further arrhythmia investigation.

Cardiac cycle US Medical PG Question 2: 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

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.

Cardiac cycle US Medical PG Question 3: During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?

• A. Decreased blood viscosity
• B. Increased cardiac output (Correct Answer)
• C. Increased hemoglobin affinity
• D. Enhanced oxygen diffusion

Cardiac cycle Explanation: ***Increased cardiac output*** - During exercise, **cardiac output** increases significantly due to both an elevated **heart rate** and increased **stroke volume**, directly pushing more oxygenated blood to the active muscles. - This augmentation in blood flow is the primary factor ensuring a sufficient supply of oxygen and nutrients to meet the heightened metabolic demands of exercising muscles. *Decreased blood viscosity* - While factors like **hemodilution** can decrease blood viscosity during prolonged exercise, this effect is relatively minor and not the primary mechanism for acute increases in oxygen delivery compared to the dramatic increase in cardiac output. - A decrease in blood viscosity can slightly improve flow efficiency, but it doesn't fundamentally change the amount of blood pumped per minute to the muscles. *Increased hemoglobin affinity* - An *increased* hemoglobin affinity for oxygen would actually make it *harder* for oxygen to unload from hemoglobin to the tissues, which is counterproductive for oxygen delivery during exercise. - In fact, during exercise, local conditions like increased temperature, decreased pH (**Bohr effect**), and increased 2,3-BPG tend to *decrease* hemoglobin's affinity for oxygen, facilitating oxygen release to active muscles. *Enhanced oxygen diffusion* - While exercise does improve the efficiency of oxygen extraction at the tissue level due to a steeper partial pressure gradient and increased capillary recruitment, the *rate* of oxygen diffusion across the capillary membrane isn't the primary modulator of overall oxygen delivery. - The main determinant is the *amount* of oxygenated blood reaching the muscle, which is governed by cardiac output and local blood flow regulation.

Cardiac cycle US Medical PG Question 4: A 27-year-old man presents to the clinic for his annual physical examination. He was diagnosed with a rare arrhythmia a couple of years ago following an episode of dizziness. A mutation in the gene encoding for the L-type calcium channel protein was identified by genetic testing. He feels fine today. His vitals include: blood pressure 122/89 mm Hg, pulse 90/min, respiratory rate 14/min, and temperature 36.7°C (98.0°F). The cardiac examination is unremarkable. The patient has been conducting some internet research on how the heart works and specifically asks you about his own “ventricular action potential”. Which of the following would you expect to see in this patient?

• A. Abnormal phase 2 (Correct Answer)
• B. Abnormal phase 4
• C. Abnormal phase 0
• D. Abnormal phase 3
• E. Abnormal phase 1

Cardiac cycle Explanation: ***Abnormal phase 2*** - Phase 2 of the ventricular action potential, also known as the **plateau phase**, is primarily maintained by the influx of **L-type calcium channels** and the efflux of potassium. - A mutation in the gene encoding for the L-type calcium channel protein would directly affect phase 2 and likely **result in an abnormal plateau phase** of the action potential. *Abnormal phase 4* - Phase 4 represents the **resting membrane potential** in ventricular myocytes and is maintained by **inward-rectifier potassium channels**. - Mutations affecting L-type calcium channels would not directly or primarily cause an abnormality in the resting potential. *Abnormal phase 0* - Phase 0, the **depolarization phase**, is driven by the rapid influx of **sodium ions** through fast voltage-gated sodium channels. - While calcium channels play a minor role, their primary impact is not on the initial rapid upstroke of phase 0. *Abnormal phase 3* - Phase 3, the **repolarization phase**, is primarily mediated by the **efflux of potassium ions** through various potassium channels (e.g., delayed rectifier potassium channels). - Although calcium channel inactivation contributes to the end of the plateau, the **dominant ion flux** determining phase 3 is potassium efflux. *Abnormal phase 1* - Phase 1, the **initial repolarization phase**, is characterized by the **inactivation of sodium channels** and a brief efflux of potassium ions through transient outward potassium channels. - L-type calcium channel activity is just beginning during this phase and is not the primary determinant of its shape.

Cardiac cycle US Medical PG Question 5: 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

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.

Cardiac cycle US Medical PG Question 6: A 70-year-old Caucasian male visits your office regularly for treatment of New York Heart association class IV congestive heart failure. Which of the following medications would you add to this man's drug regimen in order to improve his overall survival?

• A. Spironolactone (Correct Answer)
• B. Furosemide
• C. Amiloride
• D. Acetazolamide
• E. Hydrochlorothiazide

Cardiac cycle Explanation: ***Spironolactone*** - **Spironolactone** is an **aldosterone antagonist** that has been shown to reduce mortality and morbidity in patients with **NYHA Class III and IV heart failure**. - It works by blocking the harmful effects of **aldosterone** on the heart, such as **fibrosis** and remodeling, improving cardiac function and survival. *Furosemide* - **Furosemide** is a **loop diuretic** primarily used to relieve **symptoms of congestion** (edema, dyspnea) in heart failure by promoting fluid excretion. - While it improves symptoms, **furosemide** alone does not significantly improve long-term survival in patients with heart failure. *Amiloride* - **Amiloride** is a **potassium-sparing diuretic** that works by blocking sodium channels in the collecting duct, leading to modest diuresis. - It is often used to prevent **hypokalemia** caused by other diuretics but does not have the same proven mortality benefit in heart failure as spironolactone. *Acetazolamide* - **Acetazolamide** is a **carbonic anhydrase inhibitor** primarily used for glaucoma, metabolic alkalosis, and altitude sickness. - It has a weaker diuretic effect and is not a commonly used or recommended medication for improving long-term survival in patients with heart failure. *Hydrochlorothiazide* - **Hydrochlorothiazide** is a **thiazide diuretic** primarily used for hypertension and mild to moderate edema. - While it can help manage fluid retention, it does not offer the same mortality benefit in advanced heart failure as aldosterone antagonists like spironolactone.

Cardiac cycle US Medical PG Question 7: A 21-year-old man presents to his physician for a routine checkup. His doctor asks him if he has had any particular concerns since his last visit and if he has taken any new medications. He says that he has not been ill over the past year, except for one episode of the flu. He has been training excessively for his intercollege football tournament, which is supposed to be a huge event. His blood pressure is 110/70 mm Hg, pulse is 69/min, and respirations are 17/min. He has a heart sound coinciding with the rapid filling of the ventricles and no murmurs. He does not have any other significant physical findings. Which of the following best describes the heart sound heard in this patient?

• A. Fourth heart sound (S4)
• B. Opening snap
• C. Third heart sound (S3) (Correct Answer)
• D. Second heart sound (S2)
• E. Mid-systolic click

Cardiac cycle Explanation: ***Third heart sound (S3)*** - An **S3 heart sound** is a low-pitched sound heard during **rapid ventricular filling** in early diastole, immediately after S2. - In young, healthy individuals, especially athletes, an S3 can be a normal physiological finding, representing rapid filling of a **compliant ventricle**. *Fourth heart sound (S4)* - An **S4 heart sound** occurs during **atrial contraction** against a stiff or non-compliant ventricle, just before S1. - It is typically associated with conditions like **ventricular hypertrophy** or **ischemia** and is less likely to be a normal finding in a young, healthy individual. *Opening snap* - An **opening snap** is a high-pitched, crisp sound heard after S2, caused by the sudden opening of a **stenotic mitral** or **tricuspid valve**. - It indicates valvular pathology, specifically **mitral stenosis**, and is not related to ventricular filling in a healthy heart. *Second heart sound (S2)* - The **S2 heart sound** represents the **closure of the aortic and pulmonary valves** at the end of ventricular systole. - While it marks the beginning of diastole, it does not coincide with the rapid filling of the ventricles itself. *Mid-systolic click* - A **mid-systolic click** is typically associated with **mitral valve prolapse**, caused by the sudden tensing of the chordae tendineae or valve leaflets. - It occurs during systole, not diastole, and is not related to ventricular filling.

Cardiac cycle US Medical PG Question 8: You are interested in studying the etiology of heart failure reduced ejection fraction (HFrEF) and attempt to construct an appropriate design study. Specifically, you wish to look for potential causality between dietary glucose consumption and HFrEF. Which of the following study designs would allow you to assess for and determine this causality?

• A. Cross-sectional study
• B. Case series
• C. Cohort study (Correct Answer)
• D. Case-control study
• E. Randomized controlled trial

Cardiac cycle Explanation: ***Cohort study*** - A **cohort study** observes a group of individuals over time to identify risk factors and outcomes, allowing for the assessment of **temporal relationships** between exposure (dietary glucose) and outcome (HFrEF). - This design is suitable for establishing a potential **causal link** as it tracks participants from exposure to outcome, enabling the calculation of incidence rates and relative risks. *Cross-sectional study* - A **cross-sectional study** measures exposure and outcome simultaneously at a single point in time, making it impossible to determine the **temporal sequence** of events. - This design can only identify **associations** or correlations, not causation, as it cannot establish whether high glucose consumption preceded HFrEF. *Case series* - A **case series** describes characteristics of a group of patients with a particular disease or exposure, often to highlight unusual clinical features, but it lacks a **comparison group**. - It cannot assess causality because it does not provide information on the frequency of exposure in healthy individuals or the incidence of the disease in unexposed individuals. *Case-control study* - A **case-control study** compares individuals with the outcome (cases) to those without the outcome (controls) to determine past exposures, which makes it prone to **recall bias**. - While it can suggest associations, it cannot definitively establish a temporal relationship or causation as the outcome is already known when exposure is assessed. *Randomized controlled trial* - A **randomized controlled trial (RCT)** is the gold standard for establishing causation by randomly assigning participants to an intervention or control group, but it may not be ethical or feasible for studying long-term dietary exposures and chronic diseases like HFrEF due to the long follow-up period and complexity of diet. - While ideal for causality, directly controlling and randomizing dietary glucose intake over decades to observe HFrEF development might be practically challenging or unethical.

Cardiac cycle US Medical PG Question 9: An 83-year-old male presents with dyspnea, orthopnea, and a chest radiograph demonstrating pulmonary edema. A diagnosis of congestive heart failure is considered. The following clinical measurements are obtained: 100 bpm heart rate, 0.2 mL O2/mL systemic blood arterial oxygen content, 0.1 mL O2/mL pulmonary arterial oxygen content, and 400 mL O2/min oxygen consumption. Using the above information, which of the following values represents this patient's cardiac stroke volume?

• A. 30 mL/beat
• B. 70 mL/beat
• C. 40 mL/beat (Correct Answer)
• D. 60 mL/beat
• E. 50 mL/beat

Cardiac cycle Explanation: ***40 mL/beat*** - First, calculate cardiac output (CO) using the **Fick principle**: CO = Oxygen Consumption / (Arterial O2 content - Venous O2 content). Here, CO = 400 mL O2/min / (0.2 mL O2/mL - 0.1 mL O2/mL) = 400 mL O2/min / 0.1 mL O2/mL = **4000 mL/min**. - Next, calculate stroke volume (SV) using the formula: SV = CO / Heart Rate. Given a heart rate of 100 bpm, SV = 4000 mL/min / 100 beats/min = **40 mL/beat**. *30 mL/beat* - This answer would result if there was an error in calculating either the **cardiac output** or if the **arteriovenous oxygen difference** was overestimated. - A stroke volume of 30 mL/beat with a heart rate of 100 bpm would yield a cardiac output of 3 L/min, which is sub-physiologic for an oxygen consumption of 400 mL/min given the provided oxygen content values. *70 mL/beat* - This stroke volume is higher than calculated and would imply either a significantly **lower heart rate** or a much **higher cardiac output** than derived from the Fick principle with the given values. - A stroke volume of 70 mL/beat at a heart rate of 100 bpm would mean a cardiac output of 7 L/min, which is inconsistent with the provided oxygen consumption and arteriovenous oxygen difference. *60 mL/beat* - This value is higher than the correct calculation, suggesting an error in the initial calculation of **cardiac output** or the **avO2 difference**. - To get 60 mL/beat, the cardiac output would need to be 6000 mL/min, which would mean an avO2 difference of 0.067 mL O2/mL, not 0.1 mL O2/mL. *50 mL/beat* - This stroke volume would result from an incorrect calculation of the **cardiac output**, potentially from a slight miscalculation of the **arteriovenous oxygen difference**. - A stroke volume of 50 mL/beat at 100 bpm would mean a cardiac output of 5 L/min, requiring an avO2 difference of 0.08 mL O2/mL, which is not consistent with the given values.

Cardiac cycle US Medical PG Question 10: A 73-year-old woman presents to clinic with a week of fatigue, headache, and swelling of her ankles bilaterally. She reports that she can no longer go on her daily walk around her neighborhood without stopping frequently to catch her breath. At night she gets short of breath and has found that she can only sleep well in her recliner. Her past medical history is significant for hypertension and a myocardial infarction three years ago for which she had a stent placed. She is currently on hydrochlorothiazide, aspirin, and clopidogrel. She smoked 1 pack per day for 30 years before quitting 10 years ago and socially drinks around 1 drink per month. She denies any illicit drug use. Her temperature is 99.0°F (37.2°C), pulse is 115/min, respirations are 18/min, and blood pressure is 108/78 mmHg. On physical exam there is marked elevations of her neck veins, bilateral pitting edema in the lower extremities, and a 3/6 holosystolic ejection murmur over the right sternal border. Echocardiography shows the following findings: End systolic volume (ESV): 100 mL End diastolic volume (EDV): 160 mL How would cardiac output be determined in this patient?

• A. 108/3 + (2 * 78)/3
• B. (160 - 100) / 160
• C. 160 - 100
• D. (160 - 100) * 115 (Correct Answer)
• E. (100 - 160) * 115

Cardiac cycle Explanation: ***(160 - 100) * 115*** - **Cardiac output (CO)** is calculated as **stroke volume (SV) multiplied by heart rate (HR)**. - **Stroke volume** is determined by subtracting the **end-systolic volume (ESV)** from the **end-diastolic volume (EDV)** (SV = EDV - ESV). *(108/3 + (2 * 78)/3)* - This formula represents the calculation for **mean arterial pressure (MAP)**, which is not directly used to determine cardiac output. - **MAP** is approximated as (Systolic BP + 2 * Diastolic BP) / 3. *(160 - 100) / 160* - This formula calculates the **ejection fraction (EF)**, which is the fraction of blood pumped out of the ventricle with each beat. - While **ejection fraction** is a crucial measure of cardiac function, it does not directly determine cardiac output. *160 - 100* - This calculation represents the **stroke volume (SV)** (EDV - ESV), which is the amount of blood ejected from the ventricle per beat. - However, to get the **cardiac output**, stroke volume must be multiplied by the heart rate. *(100 – 160) * 115* - This calculation would result in a **negative stroke volume**, which is physiologically incorrect as stroke volume must be a positive value. - **Stroke volume** is always calculated as the **end-diastolic volume minus the end-systolic volume**.

Cardiac cycle Flashcard 1 of 10

Question: _____ is the fourth phase of a cardiac cycle and represents the period just after mitral valve opening

Answer: Rapid ventricular filling

Cardiac cycle Flashcard 2 of 10

Question: What type of action potential occurs in the ventricles, atria, and Purkinje system?_____

Answer: Myocardial action potentials (phase 0 through phase 4)

Cardiac cycle Flashcard 3 of 10

Question: What phase of the cardiac cycle is most affected by changes in heart rate?_____

Answer: Reduced ventricular filling (diastasis)

Cardiac cycle Flashcard 4 of 10

Question: Cardiac contractility correlates directly with intracellular _____ concentration

Answer: Ca2+

Cardiac cycle Flashcard 5 of 10

Question: Blood flows continuously through the cardiac cycle in all organs except the _____

Answer: heart

Cardiac cycle Flashcard 6 of 10

Question: Where in the heart is conduction velocity the slowest? _____

Answer: AV node

Extra Information:   https://onlinemeded.org/spa/cardiac/arrhythmias/acquire?ref=anki  

Cardiac cycle Flashcard 7 of 10

Question: During rapid ventricular ejection, the ventricular pressure becomes greater than aortic pressure and the _____ valve opens

Answer: aortic

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/cardiology/videos/cardiac-cycle?index=6] https://onlinemeded.org?ref=anki 

Cardiac cycle Flashcard 8 of 10

Question: Inspiration delays closure of the _____ valve which causes splitting of the S2 heart sound

Answer: pulmonic

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/cardiology/videos/cardiac-cycle?index=4] https://onlinemeded.org?ref=anki 

Cardiac cycle Flashcard 9 of 10

Question: What phase of the cardiac cycle begins during the QRS complex on ECG? _____

Answer: Isovolumetric ventricular contraction

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/cardiology/videos/cardiac-cycle?index=6] https://onlinemeded.org?ref=anki 

Cardiac cycle Flashcard 10 of 10

Question: Parasympathetic stimulation decreases atrial contractility via _____ receptors

Answer: M2

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/cardiology/videos/Cardiac%20Conductive%20Physiology?index=8] https://onlinemeded.org/spa/cardiac/arrhythmias/acquire?ref=anki