Cardiovascular System Medicine: What to Understand and How to Approach It

1. Cardiac Anatomy and Structure

• Chambers: right and left atria (thin-walled, low-pressure receivers) and ventricles (left is thick, right is thinner)
• Valves: mitral, tricuspid, aortic, pulmonary - their positions, attachments via chordae tendineae and papillary muscles, and how pressure gradients open/close them
• Coronary arteries: arising from the aorta directly above the aortic valve; epicardial course, endocardial supply predominantly during diastole
• The interventricular septum and interatrial septum

• Use anatomical atlases alongside cross-sectional echocardiography images - the two together solidify 3D orientation
• Trace blood flow through the heart step by step (right atrium → tricuspid → right ventricle → pulmonary valve → lungs → left atrium → mitral → left ventricle → aortic valve → aorta)
• Study cardiac development (linear heart tube forms at day 21-23; looping at day 26; complete by week 7) to understand congenital anomalies

2. Cardiac Electrophysiology and the Action Potential

• Five phases of the cardiac action potential: Phase 0 (rapid Na+ influx), Phase 1 (early K+ repolarization), Phase 2 (Ca2+ plateau), Phase 3 (K+ repolarization), Phase 4 (resting potential at ~-90 mV)
• Ion channels: sodium, potassium, and calcium channels open and close in a choreographed sequence
• Conduction system: SA node (pacemaker) → AV node → Bundle of His → Purkinje fibers
• SA node cells have less negative resting potentials and undergo spontaneous depolarization (automaticity) via HCN (hyperpolarization-activated cyclic nucleotide-gated) channels
• Genetic mutations in ion channel genes cause inherited arrhythmias (long QT, Brugada syndrome, CPVT)

• Draw the action potential waveform and annotate each phase with the responsible ion and drug targets
• Link each phase to the ECG waveform: P wave (atrial depolarization), QRS (ventricular depolarization), T wave (ventricular repolarization)
• Use a table matching drugs (beta-blockers, calcium channel blockers, class I/III antiarrhythmics) to their ion channel targets

3. Excitation-Contraction Coupling

• Membrane depolarization → L-type Ca2+ channel (LTCC) opens → small Ca2+ influx → triggers ryanodine receptors (RyR2) on the sarcoplasmic reticulum (SR) → massive Ca2+ release (calcium-induced calcium release)
• Ca2+ binds troponin C → conformational change in tropomyosin → actin-myosin cross-bridge formation → contraction
• Relaxation: SERCA pump returns Ca2+ to SR; NCX (sodium-calcium exchanger) extrudes Ca2+ from cell
• Beta-adrenergic signaling: catecholamines bind β-receptors → Gs → adenylyl cyclase → cAMP → PKA → phosphorylates LTCC, RyR2, phospholamban (releases SERCA inhibition) → increased contractility

• Sketch the sarcomere diagram with SR, LTCC, RyR2, SERCA, NCX labeled
• Understand how heart failure drugs intervene: digoxin inhibits Na+/K+-ATPase (raises intracellular Na+ → less Ca2+ extrusion via NCX → more Ca2+ → more contractility); dobutamine activates β1 receptors; sacubitril inhibits neprilysin
• Calcium leak from RyR2 is an emerging mechanism for triggered arrhythmias

4. Cardiac Physiology and Hemodynamics

• Frank-Starling mechanism: increased preload → increased stroke volume
• Preload, afterload, contractility as the three determinants of cardiac output
• Cardiac output = heart rate × stroke volume
• The pressure-volume loop - the cornerstone for understanding systolic and diastolic function
• Coronary blood flow: regulated by nitric oxide, adenosine, bradykinins, prostaglandins, CO2; can increase up to 6-fold during exercise
• Diastolic filling: early passive filling (E wave) and late active filling from atrial contraction (A wave) - the E/A ratio is key in echocardiography
• With aging: diastolic early filling declines by 50%, LV gradually thickens, systolic function is preserved until late

• Practice drawing pressure-volume loops under different conditions (volume overload, pressure overload, heart failure, vasodilator therapy)
• Use Doppler echocardiography images to map these physiological concepts onto real measurements
• Study Starling curves: on one axis cardiac output, on the other filling pressure - understand how the curve shifts with positive inotropes vs. heart failure

5. Electrocardiography (ECG)

• Standard lead system: 12-lead ECG, frontal plane (limb leads) and horizontal plane (precordial leads)
• Normal ECG waveforms: P, PR interval, QRS complex, ST segment, T wave, QT interval
• Systematic reading: rate, rhythm, axis, hypertrophy, ischemia/infarction, intervals
• Patterns: STEMI (ST elevation by territory - anterior, inferior, lateral), NSTEMI, LBBB/RBBB, LVH, RVH, atrial fibrillation, ventricular tachycardia
• Ambulatory monitoring (Holter, event monitors) for paroxysmal arrhythmias

• Practice the 5-step systematic approach on every ECG: rate → rhythm → axis → hypertrophy → ischemia
• Use ECG atlases with 100+ cases - volume of practice is key
• Always correlate ECG findings with anatomy: ST elevation in V1-V4 = LAD territory; II, III, aVF = RCA territory

6. Cardiac Imaging

• Echocardiography: transthoracic (TTE) and transesophageal (TEE) - assesses structure, function (EF), valvular disease, pericardium, hemodynamics
• Coronary angiography (catheterization): gold standard for coronary artery disease (CAD) assessment; enables PCI
• CT angiography (CCTA): non-invasive; coronary calcium scoring; anatomical stenosis assessment
• Nuclear imaging (SPECT/PET): myocardial perfusion, viability
• Cardiac MRI: gold standard for myocardial viability, cardiomyopathy characterization, congenital disease

• Learn the standard echocardiographic views (parasternal long axis, short axis, apical 4-chamber, etc.) and what each shows
• For each imaging modality, know: what it measures, its strengths, its limitations, and when to use it
• Correlate images with anatomy learned in Step 1

7. Heart Failure

• HFrEF (reduced EF, <40%): dilated cardiomyopathy pattern, systolic dysfunction
• HFpEF (preserved EF, >50%): diastolic dysfunction, hypertensive heart disease, elderly; increasingly common especially with aging
• HFmrEF (mildly reduced EF, 40-49%)
• Compensatory mechanisms: RAAS activation, SNS activation, cardiac remodeling - and why they eventually cause harm
• Classification: NYHA functional class I-IV
• Acute vs. chronic heart failure; cardiogenic shock
• Causes: ischemic, hypertensive, valvular, dilated, restrictive, hypertrophic cardiomyopathy

• Master the neurohormonal model: understand why ACE inhibitors, ARBs, beta-blockers, MRAs, and SGLT2 inhibitors improve outcomes
• The "4 pillars" of HFrEF therapy: ACEi/ARB/ARNI + beta-blocker + MRA + SGLT2 inhibitor
• Learn the Forrester classification for acute heart failure (warm/wet, cold/wet, cold/dry, warm/dry) for hemodynamic management

8. Coronary Artery Disease (CAD) and Acute Coronary Syndromes (ACS)

• Atherosclerosis: foam cells, fatty streaks, fibrous plaques, vulnerable plaque rupture → thrombosis
• Risk factors: hypertension, hyperlipidemia, diabetes, smoking, obesity, family history
• Stable angina vs. unstable angina vs. NSTEMI vs. STEMI (the ACS spectrum)
• TIMI and GRACE risk scores
• Management: reperfusion (primary PCI within 90 minutes for STEMI), antiplatelet therapy (aspirin + P2Y12 inhibitor), anticoagulation, beta-blockers, statins

• Learn the pathophysiology of plaque rupture and understand why stable plaques are not always the most obstructive ones
• Use the ACS algorithm: presentation → ECG → troponin → risk stratification → revascularization decision
• Study the major trials: PLATO (ticagrelor), TRITON (prasugrel), COURAGE (PCI vs. medical therapy), ISCHEMIA

9. Arrhythmias

• Supraventricular tachycardias (SVT): sinus tachycardia, atrial fibrillation (AF), atrial flutter, AVNRT, AVRT, WPW
• Ventricular arrhythmias: PVCs, VT, VF (the lethal ones)
• Bradyarrhythmias: sinus node dysfunction, AV blocks (1st, 2nd Mobitz I and II, 3rd degree/complete)
• Atrial fibrillation: most common sustained arrhythmia; risks stroke - CHA2DS2-VASc score; anticoagulation; rate vs. rhythm control; ablation
• Sudden cardiac death: VF is the most common mechanism; ICD indications

• For each arrhythmia: know the mechanism (re-entry vs. automaticity vs. triggered activity), the ECG pattern, and the treatment
• Learn the Vaughan Williams antiarrhythmic drug classification (Class I-IV) and understand which drug targets which mechanism
• Practice rhythm strip interpretation systematically

10. Valvular Heart Disease

• Stenosis (obstruction) vs. regurgitation (incompetence) of each valve
• Most common: aortic stenosis (calcific, age-related), mitral regurgitation, aortic regurgitation, mitral stenosis (rheumatic)
• Hemodynamic consequences: pressure overload (stenosis → concentric hypertrophy), volume overload (regurgitation → eccentric hypertrophy/dilation)
• TAVR (transcatheter aortic valve replacement) has transformed management of aortic stenosis in high-surgical-risk patients
• Rheumatic heart disease remains a major cause in low-income countries

• For each valve lesion: know the etiology, murmur characteristics (location, radiation, timing, maneuvers that change it), hemodynamic consequences, and when to intervene
• Practice auscultation using digital tools or clinical audio recordings
• Study echocardiographic criteria for severity (e.g., AVA <1.0 cm2 for severe AS)

11. Cardiomyopathies

• Dilated (DCM): most common; reduced EF; many causes (ischemic, viral, genetic, alcoholic, peripartum)
• Hypertrophic (HCM): asymmetric septal hypertrophy, often genetic (sarcomere mutations); risk of sudden death; dynamic outflow obstruction
• Restrictive: impaired filling; causes include amyloidosis, hemochromatosis, sarcoidosis
• Arrhythmogenic right ventricular cardiomyopathy (ARVC)
• Stress cardiomyopathy (Takotsubo)

• Use cardiac MRI as the unifying learning tool - it differentiates cardiomyopathy types better than any other modality
• Learn the genetic basis: HCM = sarcomere genes (MYH7, MYBPC3); ARVC = desmosomal genes; Marfan = FBN1
• Understand when sudden death risk warrants ICD implantation

12. Hypertension

• Definition (ACC/AHA 2017: ≥130/80 mmHg; JNC7: ≥140/90 mmHg)
• Primary (essential) vs. secondary hypertension (renal artery stenosis, primary aldosteronism, pheochromocytoma, coarctation)
• Target organ damage: LVH, chronic kidney disease, retinopathy, stroke, MI
• CVD risk estimation: use Pooled Cohort Equations (PCE) for 10-year ASCVD risk
• Hypertensive urgency vs. emergency
• Drug classes: thiazide diuretics, ACE inhibitors, ARBs, CCBs, beta-blockers, MRAs

• Memorize the first-line drug classes for different patient phenotypes (e.g., ACEi/ARB for diabetics with proteinuria; CCB for elderly Black patients)
• Study the major outcomes trials: SPRINT (SBP target <120 vs <140), ALLHAT, HOT
• Learn secondary hypertension workup algorithms: serum aldosterone/renin ratio, renal Doppler, 24h urine catecholamines

13. Pericardial Disease

• Acute pericarditis: viral most common (~80% idiopathic); chest pain, friction rub, saddle-shaped ST elevation, PR depression
• Pericardial effusion and cardiac tamponade: Beck's triad (hypotension, muffled heart sounds, raised JVP); pulsus paradoxus >10 mmHg; emergency pericardiocentesis
• Constrictive pericarditis: fibrous scarring after chronic inflammation; Kussmaul sign; distinguished from restrictive cardiomyopathy by equalization of diastolic pressures

• Practice recognizing tamponade physiology on echocardiography (RA and RV diastolic collapse, respiratory variation in mitral/tricuspid inflow)
• Know the causes that need specific treatment beyond NSAIDs: tuberculosis, malignancy, uremia

14. Pulmonary Hypertension

• WHO groups I-V: Group I (PAH - idiopathic, connective tissue, HIV, drugs), Group II (left heart disease - most common), Group III (hypoxic lung disease), Group IV (chronic thromboembolic), Group V (miscellaneous)
• Definition: mean PAP >20 mmHg at rest on right heart catheterization
• Vasoreactivity testing (for Group I) determines eligibility for CCBs
• Targeted therapy for PAH: prostacyclin analogues, endothelin receptor antagonists (bosentan), PDE5 inhibitors (sildenafil) - note: sildenafil must not be coadministered with protease inhibitors

• The key is correctly classifying the WHO group before initiating therapy - left heart disease (Group II) must be treated by optimizing left heart failure, not with PAH-specific drugs
• Use right heart catheterization findings (PVR, PCWP, transpulmonary gradient) to classify

15. Vascular Medicine

• Peripheral arterial disease (PAD): ankle-brachial index (ABI) <0.9; claudication; critical limb ischemia
• Aortic aneurysm: abdominal (AAA) - risk of rupture; thoracic (TAA) - associated with connective tissue diseases; screening with ultrasound in men >65 who ever smoked
• Aortic dissection: type A (ascending) = surgical emergency; type B (descending) = medical management; classic "tearing" chest pain radiating to back; widened mediastinum on CXR; CT angiography is diagnostic
• Venous thromboembolic disease: DVT and PE; Wells score; D-dimer; anticoagulation; fibrinolysis for massive PE

• Learn ABI interpretation: 1.0-1.4 normal; <0.9 = PAD; >1.4 = non-compressible (calcified) vessels (diabetes, CKD)
• Stanford vs. DeBakey classification of aortic dissection
• Master PESI score for PE risk stratification

16. Congenital Heart Disease

• Shunts: VSD (most common CHD), ASD, PDA - left-to-right shunts; if uncorrected → Eisenmenger syndrome (reversal to right-to-left)
• Cyanotic CHD: Tetralogy of Fallot (VSD + pulmonic stenosis + overriding aorta + RVH), Transposition of Great Arteries (TGA), Truncus arteriosus
• Coarctation of the aorta: hypertension in upper limbs, weak femoral pulses, rib notching on CXR

• Use embryology (heart tube looping, septation events) to understand how each defect arises
• Learn echocardiographic assessment; know which defects can be closed percutaneously vs. surgically

17. Cardiovascular Risk Factor Management

• Primary prevention: 10-year ASCVD risk calculation (age, sex, BP, lipids, diabetes, smoking) using Pooled Cohort Equations
• Lipid management: LDL-C lowering with statins; PCSK9 inhibitors for high-risk/statin-intolerant; targets vary by guideline (ACC/AHA vs. ESC)
• Diabetes and the heart: SGLT2 inhibitors and GLP-1 agonists reduce cardiovascular events independently of glycemic control
• Smoking cessation: largest modifiable risk factor reduction
• Of note: low-dose aspirin is no longer recommended for primary prevention in healthy elderly - harms outweigh benefits

• Use online ASCVD calculators in practice and understand what each variable contributes
• Study the landmark trials: FOURIER (evolocumab), EMPA-REG (empagliflozin), LEADER (liraglutide), REDUCE-IT (icosapentaenoic acid)

18. Cardiac Pharmacology

• Antiarrhythmics (Vaughan Williams Classes I-IV)
• Heart failure drugs: ACEi, ARBs, ARNIs (sacubitril/valsartan), beta-blockers, MRAs, SGLT2 inhibitors, ivabradine, digoxin, diuretics
• Anticoagulants: VKAs (warfarin), DOACs (apixaban, rivaroxaban, edoxaban, dabigatran) - understanding renal dosing, reversal agents
• Antiplatelet agents: aspirin, P2Y12 inhibitors (clopidogrel, ticagrelor, prasugrel)
• Vasodilators and inotropes for acute heart failure: dobutamine, dopamine, milrinone, norepinephrine, nitroprusside, nitroglycerin

• Build drug tables organized by mechanism, indication, contraindications, and key monitoring parameters
• Understand drug interactions specific to cardiology (e.g., amiodarone + warfarin, statins + fibrates, protease inhibitors + sildenafil)

Overarching Study Approach