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PH4.1-11 | Cardiovascular and Blood Pharmacology — PBL Case

CLINICAL SETTING

Suresh, a 58-year-old cotton farmer from rural Vidarbha, is brought to the district hospital by his son at 2 AM with a 3-day history of worsening breathlessness. His son reports that Suresh had to prop himself up on three pillows to sleep and has barely eaten in two days. He has had high blood pressure for the past five years and takes 'some tablet' irregularly. He has never been told about any heart problem. On examination: he appears distressed, sitting upright. BP 162/104 mmHg, HR 126 bpm (irregular), RR 28/min, SpO2 88% on room air. JVP elevated 5 cm above angle. Bilateral coarse crepitations to the mid-zones. Pitting pedal oedema to the knees. Apex beat displaced to the 6th intercostal space, anterior axillary line.

Trigger 1: Initial Presentation

The casualty officer orders an ECG. It shows: rate 126 bpm, no discernible P waves, irregularly irregular rhythm, no ST changes. CXR reveals cardiomegaly, upper lobe venous diversion, and bilateral perihilar haze ('bat-wing' pattern). The following results arrive: Na+ 136 mEq/L, K+ 3.8 mEq/L, Creatinine 1.4 mg/dL (eGFR ~52 mL/min/1.73 m²), BNP 820 pg/mL (elevated). Troponin I negative.

DISCUSSION POINTS

  • What is the most likely primary diagnosis? What does the rhythm finding on ECG tell you?
  • What is causing Suresh's breathlessness — frame your answer around the haemodynamic mechanism, not just the diagnosis.
  • Identify TWO immediate pharmacological priorities for the casualty officer. What class of drug would you use for each? Do not write brand names — explain the mechanism of the first-line agent.
Click to reveal Trigger 2: Treatment Initiation and Complications (discuss previous trigger first!)

Trigger 2: Treatment Initiation and Complications

The physician starts IV furosemide 40 mg and gives oral bisoprolol 2.5 mg for rate control. Over 4 hours, Suresh loses 1.8 L of urine. His HR reduces to 88 bpm. However, at the 6-hour mark, Suresh reports severe muscle cramps and tingling in both hands. Repeat bloods: K+ 2.9 mEq/L, Na+ 132 mEq/L, Creatinine 1.7 mg/dL. ECG shows flattened T-waves with prominent U-waves. The trainee doctor proposes starting digoxin 0.25 mg for 'additional rate control'.

DISCUSSION POINTS

  • Explain the mechanism by which furosemide caused this electrolyte disturbance. What is the clinical significance of this ECG finding?
  • What is the safest immediate management of Suresh's electrolyte imbalance before continuing furosemide?
  • Critically evaluate the trainee's proposal to start digoxin in this setting. Under what conditions would digoxin be safe, and what parameter must be corrected first?
Click to reveal Trigger 3: Discharge Planning and Long-term Management (discuss previous trigger first!)

Trigger 3: Discharge Planning and Long-term Management

After 72 hours, Suresh is euvolaemic, rate-controlled at 78 bpm, and SpO2 is 97% on room air. Echocardiogram shows: LVEF 30%, dilated left ventricle, moderate mitral regurgitation. Diagnosis: Hypertension-related heart failure with reduced ejection fraction (HFrEF) + permanent atrial fibrillation. The treating cardiologist plans discharge. She asks the junior doctor to plan evidence-based discharge medications covering: HFrEF management, AF rate control, stroke prevention, and electrolyte replacement.

DISCUSSION POINTS

  • List the complete discharge drug regimen for Suresh with the mechanism and evidence rationale for each drug. Include at least one drug for each of the four GDMT pillars for HFrEF.
  • Suresh has AF with LVEF 30%: is anticoagulation indicated? Which agent would you choose, considering his eGFR of 52 mL/min/1.73 m²? What is the stroke risk mechanism in AF with HF?
  • Suresh lives 80 km from the nearest hospital. What counselling will you give him about his medications — specifically around: the importance of not stopping beta-blockers, recognising digoxin toxicity (if started), and when to seek emergency care?

Group Task Assignments

Group 1: Pathophysiology of decompensated HFrEF

  • Draw and explain the neurohormonal cascade activated in HFrEF (RAAS, SNS, aldosterone).
  • Explain how each of the four GDMT pillars interrupts a specific step in this maladaptive cascade.
  • Explain why cardiac output falls in HFrEF despite compensatory mechanisms (Frank-Starling, neurohormonal activation).

Competencies: PH4.9

Group 2: Diuretics: mechanism, electrolyte consequences, and clinical use

  • Trace the nephron sites of action of loop diuretics, thiazides, and potassium-sparing diuretics.
  • Prepare a table comparing the electrolyte effects of each diuretic class on Na+, K+, Ca2+, Mg2+, and HCO3−.
  • Explain why furosemide is preferred over hydrochlorothiazide in decompensated HF with CKD.

Competencies: PH4.5

Group 3: RAAS modulators — mechanism, adverse effects, and clinical selection

  • Explain the full RAAS cascade from renin release to aldosterone secretion.
  • Contrast ACEi and ARBs: mechanism, ADR profile, and clinical scenarios where you would choose one over the other.
  • Explain the mechanism of ACEi-induced hyperkalaemia and its clinical implications in a patient already on spironolactone.

Competencies: PH4.6

Group 4: Antiarrhythmic drugs and rate control in AF

  • Classify antiarrhythmic drugs by the Vaughan-Williams system. For each class, give one example and one key clinical indication.
  • Explain the mechanism by which bisoprolol controls ventricular rate in AF. Why are rate-control targets different from rhythm-control targets?
  • Identify the Vaughan-Williams class of amiodarone and explain why it is the preferred agent for ventricular arrhythmias in structural heart disease.

Competencies: PH4.10

Group 5: Anticoagulation in AF with HFrEF: choice, monitoring, and reversal

  • Explain the mechanism by which AF with low ejection fraction increases stroke risk (endothelial + stasis + platelet activation).
  • Compare UFH, warfarin, and DOACs for stroke prevention in AF. Create a comparison table covering mechanism, monitoring, reversal, and renal dose adjustment.
  • Suresh's K+ is 2.9 mEq/L and the trainee proposes starting digoxin. Prepare a 3-minute educational briefing for the trainee explaining why this is dangerous and what must be corrected first.

Competencies: PH4.2

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PH4.9] What is the neurohormonal hypothesis of HFrEF, and how does each of the four GDMT drug classes interrupt it to reduce mortality?
  2. [PH4.5] How do loop diuretics act on the nephron, and what are the predictable electrolyte consequences of their use? Why does hypokalaemia potentiate arrhythmia risk?
  3. [PH4.6] What is the full RAAS cascade, and how do ACEi and ARBs differ in their mechanism of action, adverse effect profile, and clinical indications?
  4. [PH4.10] What are the four Vaughan-Williams classes, and which antiarrhythmic agents are safe for rate control or rhythm control in patients with structural heart disease?
  5. [PH4.2] How do anticoagulants (UFH, warfarin, DOACs) differ in mechanism, monitoring, and reversal? Which requires dose adjustment in CKD?