Cardiology
What is the mechanism of action of ivabradine in treating heart failure?
Ivabradine selectively inhibits the "funny" current (If) in the sinoatrial node, reducing heart rate without affecting contractility.
What is the diagnostic criterion for ARDS based on the PaO2/FiO2 ratio?
PaO2/FiO2 ratio ≤ 300 mmHg
What is the classic electrolyte abnormality seen in Conn’s syndrome (primary hyperaldosteronism)
Hypokalemia and metabolic alkalosis
Which nephritic syndrome is associated with low C3 complement levels but normal C4 levels
Post-infectious glomerulonephritis
What is the causative organism of infectious endocarditis in IV drug users?
Staphylococcus aureus
What is the significance of electrical alternans on an ECG, and in what condition is it most commonly seen?
Electrical alternans is alternating amplitude of the QRS complexes and is commonly seen in cardiac tamponade
Name a common organism causing pneumonia in a patient with cystic fibrosis
Pseudomonas aeruginosa
What enzyme deficiency is responsible for congenital adrenal hyperplasia in 21-hydroxylase deficiency
21-hydroxylase enzyme deficiency, leading to decreased cortisol and aldosterone production
What is the pathophysiological basis for osmotic demyelination syndrome after rapid correction of chronic hyponatremia
Rapid correction of hyponatremia causes osmotic shifts leading to dehydration and demyelination of brain cells, particularly in the pons
What is the mechanism of action of the antibiotic daptomycin, and why is it contraindicated in pneumonia
Daptomycin disrupts bacterial cell membranes by depolarizing the membrane potential, but it is inactivated by pulmonary surfactant
What is the target blood pressure for patients with chronic kidney disease according to the most recent ACC/AHA guidelines?
< 130/80 mmHg
Which specific receptor does the drug pirfenidone inhibit to treat idiopathic pulmonary fibrosis (IPF)
Pirfenidone inhibits the TGF-β receptor.
In a patient with pheochromocytoma, what preoperative medication is essential to prevent a hypertensive crisis
Alpha-blockade (e.g., phenoxybenzamine) is initiated before beta-blockade
In the context of rhabdomyolysis, what urine test can give a false positive for blood, and why?
A dipstick can show a false positive for blood due to myoglobinuria.
Which virus is known to cause progressive multifocal leukoencephalopathy (PML) in immunocompromised patients?
JC virus
Which congenital heart condition is associated with an increased risk of aortic dissection, particularly in younger patients?
Bicuspid aortic valve
What is the primary difference in the oxygen dissociation curve seen in patients with methemoglobinemia
The oxygen dissociation curve is shifted to the left, indicating decreased oxygen release to tissues, due to increased hemoglobin affinity for oxygen in the presence of methemoglobin
What is the diagnostic test of choice to differentiate between central and nephrogenic diabetes insipidus
The water deprivation test followed by administration of desmopressin
What nephrological condition is commonly associated with HIV and presents with nephrotic-range proteinuria?
Focal segmental glomerulosclerosis (FSGS)
What is the pathophysiology behind Jarisch-Herxheimer reaction, and in which infections is it most commonly seen?
The Jarisch-Herxheimer reaction is caused by the rapid release of endotoxins from lysed spirochetes, triggering a systemic inflammatory response. It is most commonly seen in syphilis, particularly after treatment with penicillin.
Explain the mechanism by which Takotsubo cardiomyopathy mimics an acute myocardial infarction and describe the characteristic echocardiogram finding
Takotsubo cardiomyopathy involves catecholamine surge-induced myocardial stunning, primarily affecting the left ventricular apex. The characteristic finding is apical ballooning with preserved basal contractility
What is the pathophysiological mechanism underlying hypoxic pulmonary vasoconstriction in patients with chronic lung diseases
Hypoxic pulmonary vasoconstriction occurs as a compensatory response to divert blood from poorly ventilated alveoli to better-ventilated areas, thereby optimizing gas exchange
Explain the mechanism by which amiloride treats Liddle syndrome, and how this genetic condition affects renal sodium channels
Liddle syndrome is caused by gain-of-function mutations in the ENaC (epithelial sodium channel), leading to increased sodium reabsorption and hypertension. Amiloride blocks ENaC, reducing sodium reabsorption
In patients with insulinoma, what biochemical feature distinguishes it from factitious hypoglycemia?
Elevated C-peptide levels in insulinoma help distinguish it from factitious hypoglycemia, where exogenous insulin suppresses C-peptide
What genetic mutation is associated with increased susceptibility to mycobacterial infections, and what is the underlying immunological defect?
Mutations in the IFN-γ receptor or IL-12 receptor increase susceptibility to mycobacterial infections by impairing macrophage activation and the TH1 cell-mediated immune response.