USMLE Step 1 Review/Cardiovascular

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Contents 1 Basic science 1.1 Heart anatomy 1.2 Cardiac cycle 1.3 Heart sounds 1.4 Heart electrophysiology 1.4.1 Conducting system of heart 1.4.2 Myocardial action potentials 2 Cardiovascular pathology 2.1 Arrhythmias 2.2 Endocarditis 2.3 Rheumatic fever 3 References

[edit] Basic science

[edit] Heart anatomy

[edit] Cardiac cycle

[edit] Heart sounds

• S1: MV/TV closure
• S2: AV/PV closure
  • Physiologic splitting of S2 on inspiration (see inset)

[edit] Heart electrophysiology

[edit] Conducting system of heart

Sinoatrial (SA) node in right atrium → atrioventricular (AV) node → His bundle → Purkinje fibers → ventricular myocardium

[edit] Myocardial action potentials

Ventricular action potential

Phase 4

outward potassium leak (resting membrane potential)

Phase 0

inward sodium (rapid depolarization)

Phase 1

outward potassium (partial repolarization)

Phase 2

balance of inward sodium/calcium and outward potassium (plateau)

Phase 3

outward potassium (repolarization)

Pacemaker potential

Phase 4

inward sodium/calcium (slow depolarization; SA/AV cells have no resting membrane potential)

Phase 0

inward calcium (rapid depolarization)

Phase 3

outward potassium (repolarization)

[edit] Cardiovascular pathology

[edit] Arrhythmias

• Atrial fibrillation: irregularly irregular rhythm (no p waves), rate often >100 (a type of supraventricular tachycardia), can result in heart failure, thrombus formation; treat with rate control (beta-blockers, non-DHP calcium channel blockers) or rhythm control (dofetilide, sotalol, amiodarone), and anticoagulation (warfarin).
• Atrial flutter: p waves present in "sawtooth" pattern, often at rate of 300 and ventricular rate of 150 (often 2:1 conduction, but can vary); often resistant to rate control; treat refractory cases with ablation (maze procedure).
• Wolff-Parkinson-White syndrome: supraventricular impulses conducted along accessory pathway leading to early and nonuniform depolarization of ventricles, causing QRS widening with a delta wave.

[edit] Endocarditis

Fever, malaise, embolic phenomena (eg, stroke), new murmur; vegetation on echocardiography, positive blood cultures, elevated ESR/CRP. Treat with empiric antibiotics, using clues to guide antibiotic selection:

IV drug user

Staphylococcus aureus. Often right-sided.

Prosthetic heart valve

Staphylococcus epidermidis.

Gastrointestinal malignancy

Streptococcus bovis.

No structural disease

Streptococcus viridans.

[edit] Rheumatic fever

Diagnosis^[1]

• J♥NES
  • Joints (migratory polyarthritis)
  • ♥ (pancarditis)
  • Subcutaneous Nodules
  • Erythema marginatum
  • Syndenham's Chorea - face, tongue, upper-limb chorea

[edit] References