6. Arrhythmias & Acute Affects Flashcards Preview

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Flashcards in 6. Arrhythmias & Acute Affects Deck (23):

What are the mechanisms of the interval-duration relationship? 

  • Increased Ca2+
  • Increased Na+
  • Sympathetic stimulation


What leads to increased cytosolic Ca2+ and Na+?

More frequent APs


What is an absolute ("effective") refractory period?

Period of time after an AP is fired during which another AP cannot be fired


What dictates the duration of a refractory period?

AP duration


What is a relative refractory period?

Period of time after the absolute refractory period during which another AP can fire, but the resulting membrane potential will be smaller than normal

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What is a supranormal period?

Period of time while membrane is still trying to stabilize during which an AP can trigger again very promptly w/ very little stimulation

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What is heterogeneity in regards to AP characteristics? Significance?

  • Individual cells are in different excitatory states
  • Any spatial or temporal heterogeneity in AP characteristics may be arrhythmogenic


Define tachyarrhythmia.

  • Increased firing rate
  • HR > 100 bpm


Define bradyarrhythmia.

  • Decreased firing rate
  • HR < 60 bpm


What can cause tachyarrhytmias?

  • Increased automaticy of SA node
  • Increased automaticity of latent pacemakers
  • Abnormal automaticity
  • Unidirectional block and re-entry ("circus rhythms")
  • Triggerd activity: "after-depolarizations"


What can cause bradyarrhythmias?

  • Enhanced vagal tone (athletic heart)
  • Decreased automaticity of SA node
  • SA node dysfunction --> latent pacemakers take over
  • AV conduction block


What are after-depolarizations? When do they occur? Consequence?

  • Oscillations of the membrane voltage triggered by a preceding AP
  • Can be self-renewing and lead to a series of abnormal APs
  • Blood is not pumped during this contraction

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What is an early afterdepolarization? When do they occur?

Oscillating pattern of membrane potential that occurs during repolarization phase (refractory period)

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What is a delayed afterdepolarization? When do they occur?

Prematurely triggered contraction that occurs after repolarization phase is complete

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What is a reentrant rhythm?

An electrical impulse that circulates repeatedly, continually depolarizing a circuit of myocardium


What is the critical condition for reentry? In what ways can this condition be met?

The propagating impulse must continue to encounter excitable myocardium

  • Electrically heterogenous myocardium (following ischemia)
  • Anatomically heterogenous myocardium (scar)


What is the Wolff-Parkinson-White Syndrome?

  • Anatomically-fixed reentry condition
  • Conduction is faster in the bypass tract than AV node
  • Conduction moves slower in ventricles b/c electrical signals travel through ventricular muscle (syncytial) rather than through the rapid, purkinje conduction system
  • Sets up a two-circuit route w/ diff refractory periods
  • Reentrant supraventricular tachycardia --> HR stays high after exercise has stopped

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How can we estimate max HR?

220 - age in years


How does the heart respond to the onset of exercise?

Tachycardia: initial HR increase due to withdrawal of vagal tone and increased SNS tone


What are the expected EKG changes during acute exercise?

  • Sinus tachycardia
  • Hemodynamic changes: shortened diastole --> less coronary blood flow to heart


What is the only arrhythmia that exercise should reliably provoke?

Sinus tachycardia


What causes many "trivial" arrhythmias? (PACs, PVCs)

  • Shortened diastolic interval

  • Higher sympathetic stimulation

  • Increased myocardial O2 demand


What is a consequence of ventricular tachycardia?

Not enough time for diastolic filling