EKG & Cardiac Arrhythmias 2 Flashcards Preview

Term 5 - PathoPhysio > EKG & Cardiac Arrhythmias 2 > Flashcards

Flashcards in EKG & Cardiac Arrhythmias 2 Deck (18):
1

Three basic mechanisms for tachyarrhythmias:

  1. Increased automaticity of pacemaker
  2. Spontaneous depolarizations
  3. Reentrant circuit

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  • Increased automaticity of pacemaker
  • Origin:
  • Examples:

  • Origin: Impulse generating the heart beats are from SA node, but at a faster pace than normal. Occurs in: Exercise, stress, fright, fever
  • Examples: Sinus Tachycardia as in hyperthyroidism, Anxiety, Pheochromocytoma and pulm embolism
  • More rapid phase 4 depolarization of the action potential of SA node leads to faster heart rate

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  • Spontaneous depolarizations
  • Cause

  • If repolarization is delayed (longer plateau period), spontaneous depolarizations (EAD /DAD) can occur in phase 3 or phase 4 of the ventricular/atrial action potential
  • These depolarizations can repetitively reach threshold and cause tachycardia

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  • Examples of tachyarrhythmias from spontaneous depolarizations (EAD/DAD) are:

  • Long QT syndrome
  • Torsades de pointes
  • Reentrant circuit

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Long QT syndrome

  • Due to several specific ion channel defects
  • Reduced function of potassium channels leads to a prolonged plateau period, leading to a prolonged QT interval
  • These patients are prone to triggered activity because of reactivation of sodium and calcium channels (early after depolarizations (EAD)
  • Triggered activity in the ventricles can lead to life-threatening ventricular arrhythmias

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Torsades de pointes

  • A “twisting”, polymorphic ventricular tachyarrhythmia that is observed in situations where the QT interval has been prolonged
  • The phrase "Torsades de Pointes" (French) means "twisting of the spikes", referring to the characteristic appearance of the EKG
  • A triggered arrhythmia, which may cause blackouts or even sudden death.

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  • Reentrant circuit
  • Re-entry requires

  • Re-entry requires
    • (i) an area of slow conduction with unidirectional block, and
    • (ii) an area of fast conduction (two pathways in a region).
  • A - Block at slow tract & fast moves down
  • B - Slow moves retrograde in fast tract and blocks the incoming next fast
  • C - Retrograde fast reenters in the slow tract

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Origin of Re-entrant arrhythmias:

  • From atrium: Known as SupraVentricular Tachycardia (SVT) – Examples, atrial tachycardia, atrial flutter and atrial fibrillation
    • Commonly occurring SVTs:
      • Atrial Tachycardia (atrial rate: 150-250/min; single focus)
      • Atrial Flutter (atrial rate: 250-350/min; single focus)
      • Atrial Fibrillation (atrial rate: 350-600/min & multifoci of origin )
  • From Ventricle: known as Ventricular Tachycardia (VT)
  • Atrio-Ventricular origin: Example, as in WolffParkinson-White syndrome

 

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Differentiating between Supraventricular Tachycardia (SVT) from Ventricular Tachycardia (VT)

  • If the QRS complex is narrow/normal (within normal limits)
    • Indicates that depolarization of the ventricles must be occurring normally over the specialized conduction tissues and the arrhythmia must be originating at or above the AV node. Tachycardia with such QRS are – SVT
  • If the QRS complex is wide
    • Indicates that ventricular depolarization is NOT occurring normally over the specialized conduction tissues. Tachycardia with such QRS are - VT

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Most common complication of AF

  • systemic thromboembolism

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Wolff-Parkinson-White Syndrome

  • Short PR interval; wide QRS with a slurred upstroke
  • Electrophysiological studies confirm presence of a bypass tract (Bundle of Kent)
  • An accessory atrioventricular connection is found in approximately 1 in 1000 persons
  • Part of the ventricle is "pre-excited" by the accessory pathway before the normal conduction via the AV node, the surface ECG shows a short PR interval and a relatively wide QRS with a slurred upstroke, termed a delta wave.
  • If the accessory pathway recovers rapidly, the normal cardiac impulse may travel in retrograde fashion to the atria through this accessory pathway and initiate a reentrant, atrio-ventricular tachycardia (Patient feels palpitations at this moment).

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A quick approach to Arrhythmias:

  • First look at the heart rate:
    • >100 bpm = tachyarrhythmia
    • <60 bpm = bradyarrhythmia
  • Secondly assess the origin of the arrhythmia:
    • If the QRS <120ms, then it is either a sinus arrhythmia, supraventricular tachycardia or a junctional tachycardia.
    • If the QRS >120ms, it is either a ventricular tachycardia or a supraventricular rhythm with additional bundle branch block or an additional accessory AV pathway.
  • Are there extra beats? → Ectopic (QRS without P)