QRS and ventricles

QRS - Ventricular depolarization

  • If the QRS is narrow

    • The signal came from up top

  • If the QRS is wide (> 2-3 small boxes)

    • The signal came from below

    • Or aberrancy (something below messed with the signal)

Aberrant Conduction (diverging from the normal)

    • Picture the signal from SA node makes it to AV node

    • But damage to the heart limits the fast acting conduction system (bundle branches, Purkinje fibers)

    • Instead, depolarization slowly occurs from one myocyte to another

    • This slower depolarization βž” wider QRS

Premature ventricular contraction (PVC)

  • An ectopic focus depolarizes early that conducts to the rest of the ventricle βž” premature contraction

  • Can be from normal or from damage, medications, hypoxia (to name a few)

  • Some say a triplet is a short run of V-tach

V-tach

Accelerated Idioventricular rhythm

  • Regular at rate of 50-110 with > 3 ventricular beats (wide QRS)

  • Ectopic ventricular foci takes over rate

  • Usually benign, but if hypotensive you would give atropine

    • Hopefully kicks up SA enough to get some AV conduction

Polymorphic V-tach (Torsades de pointes)

  • When the QT is prolonged (hypomag, hypoK, meds) βž” ↑ risk of R on T

  • Depolarization during the relative refractory period can bring on Torsades

  • TX with MgSO4

Ventricular Fibrillation

Ventricular Hypertrophy

Remember the way V1 & V6 "look" at the heart

The positive wave of depolarization is heading toward the LV

    • V6 has a more positive inflection

    • V1 more negative deflection

Normal V1 & V6 QRS

  • When the vector (yellow arrow) changes βž” EKG changes

    • Left ventricular hypertrophy βž” more negative in V1, more positive in V6

      • More of the vector is going away from V1 and toward V6

    • Right ventricular hypertrophy βž” more positive in V1, less positive in V6

      • Less of the vector is going toward V6

Causes of hypertrophy

LVH: HTN, aortic stenosis βž” ↑ afterload; regurgitation βž” ↑ volume to pump out

RVH: Chronic lung DZ (COPD), pulmonary HTN, pulmonary stenosis βž” RV pumping against resistance