MD Cardiovascular System Pathophysiology 4 — Questions and Answers
Question 1: Pulsus paradoxus (>10 mmHg fall in SBP with inspiration) is caused by which mechanism in cardiac tamponade?
- Inspiratory decrease in heart rate via vagal activation
- Exaggerated interventricular dependence as RV filling compromises LV filling (Correct answer)
- Inspiratory increase in systemic vascular resistance
- Paradoxical septal motion causing mitral stenosis
Correct answer: Exaggerated interventricular dependence as RV filling compromises LV filling
Inspiration increases RV filling, but the tamponade-restricted pericardial space forces the interventricular septum to bow into the LV, reducing LV stroke volume and systolic pressure.
Question 2: A 48-year-old woman with systemic lupus erythematosus develops pleuritic chest pain and friction rub. Libman-Sacks endocarditis in SLE most commonly affects which valve?
- Aortic valve (aortic stenosis)
- Tricuspid valve (tricuspid regurgitation)
- Mitral valve (mitral regurgitation) (Correct answer)
- Pulmonary valve (pulmonary stenosis)
Correct answer: Mitral valve (mitral regurgitation)
Libman-Sacks endocarditis produces sterile verrucous vegetations on both surfaces of the mitral valve, causing mitral regurgitation.
Question 3: Which mechanism explains the wide pulse pressure seen in aortic regurgitation?
- Elevated systolic pressure from increased stroke volume and low diastolic pressure from regurgitant runoff (Correct answer)
- Decreased heart rate allowing greater diastolic filling
- Peripheral vasoconstriction raising systolic and diastolic pressure equally
- Increased blood viscosity due to polycythemia
Correct answer: Elevated systolic pressure from increased stroke volume and low diastolic pressure from regurgitant runoff
In AR, the large forward stroke volume raises systolic pressure, while diastolic runoff back into the LV lowers diastolic pressure, widening the pulse pressure.
Question 4: A patient with inferior MI develops complete heart block. The culprit artery and mechanism are most likely:
- LAD occlusion causing His-Purkinje ischemia
- RCA occlusion causing ischemia of the AV node supplied by posterior AV nodal artery (Correct answer)
- LCX occlusion causing sinus node dysfunction
- RCA occlusion causing left bundle branch block
Correct answer: RCA occlusion causing ischemia of the AV node supplied by posterior AV nodal artery
The AV node is supplied by the AV nodal artery, a branch of the RCA in ~90% of patients; inferior MI from RCA occlusion frequently causes AV nodal block.
Question 5: In a patient with severe mitral regurgitation, pulmonary capillary wedge pressure tracing will show:
- Prominent 'a' wave from vigorous atrial contraction
- Large 'v' wave from systolic regurgitant flow into the left atrium (Correct answer)
- Absent 'x' descent due to elevated left atrial pressure
- Low mean PCWP despite pulmonary edema
Correct answer: Large 'v' wave from systolic regurgitant flow into the left atrium
During systole, regurgitant flow from the LV into the LA generates a large 'v' wave on the PCWP tracing, proportional to the severity of regurgitation.
Question 6: Long QT syndrome predisposes to torsades de pointes. Which underlying mechanism is common to both congenital and acquired forms?
- Increased sodium influx shortening the action potential plateau
- Reduced repolarizing current (IKr) prolonging phase 3 of the action potential (Correct answer)
- Increased automaticity in Purkinje fibers
- Enhanced calcium release from the sarcoplasmic reticulum
Correct answer: Reduced repolarizing current (IKr) prolonging phase 3 of the action potential
Both congenital LQTS (e.g., KCNQ1, HERG mutations) and drug-induced forms reduce the rapid delayed rectifier potassium current (IKr), prolonging repolarization and QT interval.
Question 7: A marathon runner collapses and is found to have hypertrophic cardiomyopathy. The mechanism of sudden cardiac death in HCM during exertion is most likely:
- Acute MI from atherosclerotic plaque rupture triggered by exercise
- Exercise-induced ventricular fibrillation from dynamic LVOT obstruction and myocardial ischemia (Correct answer)
- Respiratory failure from pulmonary hypertension
- Aortic dissection from exertional hypertension
Correct answer: Exercise-induced ventricular fibrillation from dynamic LVOT obstruction and myocardial ischemia
Exercise-induced LVOT obstruction and septal ischemia (from small vessel disease and increased oxygen demand) create an arrhythmogenic substrate that can trigger ventricular fibrillation.
MD Cardiovascular System Pathophysiology 4
Pulsus paradoxus (>10 mmHg fall in SBP with inspiration) is caused by which mechanism in cardiac tamponade?