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PHGY 312 > ECG / arrhythmias > Flashcards

ECG / arrhythmias Flashcards

1
Q

What is the isoelectric line?

A

Line of 0 potential recorded

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2
Q

What is the P wave?

A

Depolarization of the atria

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3
Q

What is the QRS complex?

A

Depolarization of the ventricles
70-100 msec

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4
Q

What is the T wave?

A

Repolarization of the ventricles

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5
Q

How long is the R-R interval?

A

~ 1.0 sec (duration of a complete cycle)

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6
Q

What is the PR-interval?

A

from start of P wave → Start of QRS complex
140-200 msec

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7
Q

What is the Q-T interval?

A

From start of Q-wave → end of T-wave
330-430 msec
Reflexes time it takes for the heart to contract and refill with blood before it beats again

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8
Q

What is the ST segment?

A

End of S-wave → start of T wave
*Time between depolarization and repolarization of ventricles → Plateau phase of AP

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9
Q
A
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10
Q

What is the average amplitude of a heart AP?

A

1 mV

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11
Q

What is the amplitude of an ECG wave related to?

A

Amplitude is related to mass of the heart (qty of tissues) being depolarized or repolarized

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12
Q

What situations show positive and negative deflection on the ECG?

A

Depolarizing → +ive terminal = +
Depolarizing → -ive terminal = -
Repolarizing → +ive terminal = -
Repolarizing → -ive terminal = +

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13
Q

What are the standard limb leads?

A

Lead 1: RA(-) → LA(+) = 0˚
Lead 2: RA(-) → LL(+) = 60˚
Lead 3: LA(-) → LL(+) = 120˚
*Show positive deflection, normal AP ECG

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14
Q

What are the augmented limb leads?

A

Lead aVR: LA+LL (-) → RA (+) Negative deflection = -150˚
Lead aVL: RA+LL (-) → LA (+) Biphasic/perpendicular = -30˚
Lead aVF: LA+RA (-) → LL (+) Positive deflection = +90˚

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15
Q

What are the precordial chest leads?

A

V1 (anterior) - V6 (left lateral)

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16
Q

What does a full ECG read look like?

A

Top 12 ECG traces = short segments of each leads (3 standard, 3 augmented, 3 precordial)
Last 3 strips = rythme strips → give you a longer trace to look for an abnormality in the base rythme

17
Q

What is the mean electrical axis?

A

Mean electrical axis = average of all instantaneous mean electrical vectors during depolarization of the ventricles ~40˚

18
Q

How can we calculate the QRS complex mean electrical axis?

A
  1. Need 2 leads
  2. Sum Q + R + S to have length
  3. From specific lead axis, draw perpendicular line
  4. Axis is angle to where the cross from center
19
Q

What is a 1st, 2nd and 3rd degree heart block?

A

1st degree: delay in propagation through AV node (slower than normal)

2nd degree: Wenckeback Rhythms - Drop beats → 3:2, 4:2, etc.

3rd degree: dissociation between P waves and QRS complex, Long R-R intervals, complete block of AV node (atria and ventricles beat at independent rates)

20
Q

What are 4 different causes of abnormal ECG?

A
  • Heart Block
  • Lyme’s Syndrome
  • Hypertrophy, old infract
  • Long QT-Syndrome (Iks, Ikr, Ina, Ica)
21
Q

Wht is the sick sinus syndrome?

A

Heart rythme disorder which affects heart’s natural pacemaker
Cessation of discharge from SA node (absence of P wave)→ no contraction → ventricle beats to compensate so still see QRS complex → when SA node starts again, sinus rhythm comes back

22
Q

What is an Ectopic Foci?

A

An extopic focus is a site of electrical impulse initiation other than the SA node.

  • If more rapid than SA node, ectopic focus becomes the pacemaker
  • May arise in tria, AV node, Purkinje fibres, ventricular muscles
  • Can be induced by hypoxia, ischemia or hypokalemia
    ex: Multifocal atrial tachycardia
23
Q

What is Delayed Afterpolarization (DAD) ?

A

DAD → after full repolarization → transient inward current → result of Na/Ca exchange mechanism
1. Drive tissue with small DAD at higher rate → increase in amplitude
2. Have triggered response → overdrive for short time → stop triggered AP → Incx goes down after stop of trigger, Na-K keeps going → stops DAD

24
Q

What is EAD?

A

Early after depolarization (during depolarization phase) → reactivation of L-type Ca current (surpass Ik)
*Can get it by prolonging APD

25
Q

What are the 4 conditions for re-entry?

A
  • Unidirectional block in conduction around a ring
  • Slow enough conduction velocity
  • Brief refractory period
  • Long enough pathway (mice heart = too small)
26
Q

What is the effect of caffeine on the heart muscle contraction?

A

Depletes Ca from the SR → used to study the effect of an increase in intracellular calcium from low levels to steady-state

27
Q

Explain the effect of Sympathetic activation on the heart AP?

A
  1. B-Adregenic receptor stimulation activated GS (GTP binding protein)
  2. GS stimulates adenyly cyclase (AC) → produces cAMP
  3. cAMP activates PKA (protein kinase A) → phosphorylates L-type Ca2+ channel RyR2, PLB and troponin
  4. Increase in force of contraction + accelerates relaxation
28
Q

What is the effect of PKA phosphorylation?

A

Ionotropic: Ca2+ channel phosphorylation → increase in I caL → increase in SR Ca release → increase force of contraction

Lusitropic: Phosphorylation of troponin I speeds up Ca dissociation from m’y-filaments → accelerates relaxation

29
Q

What are the 2 elements of the muscle that act in contraction?

A
  1. Contractile Element
  2. Series Elastic Element
30
Q

What is the WPW syndrome?

A
  • Reentry at the level of the whole heart →presence of Bundle of Kent (embryonic pathway)
31
Q

What is the effect of an increase in intracellular Calcium?

A
  1. Causes more rapid Ica inactivation
  2. Increases Incx
    *Homeostatic feedback system in the heart
32
Q

What are the differences in sizes between nodal cells and ventricular cells?

A

Nodal cells → smaller in diameter (slower conductance)
Conducting cells → Bundle cells, ventricular cells, purkinje → larger diameter (lower resistance to conductance)

33
Q

What is conduction related to?

A
  1. Upstroke velocity
  2. gap junction density

PHGY 312 (14 decks)

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