ECG / arrhythmias Flashcards
What is the isoelectric line?
Line of 0 potential recorded
What is the P wave?
Depolarization of the atria
What is the QRS complex?
Depolarization of the ventricles
70-100 msec
What is the T wave?
Repolarization of the ventricles
How long is the R-R interval?
~ 1.0 sec (duration of a complete cycle)
What is the PR-interval?
from start of P wave → Start of QRS complex
140-200 msec
What is the Q-T interval?
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
What is the ST segment?
End of S-wave → start of T wave
*Time between depolarization and repolarization of ventricles → Plateau phase of AP
What is the average amplitude of a heart AP?
1 mV
What is the amplitude of an ECG wave related to?
Amplitude is related to mass of the heart (qty of tissues) being depolarized or repolarized
What situations show positive and negative deflection on the ECG?
Depolarizing → +ive terminal = +
Depolarizing → -ive terminal = -
Repolarizing → +ive terminal = -
Repolarizing → -ive terminal = +
What are the standard limb leads?
Lead 1: RA(-) → LA(+) = 0˚
Lead 2: RA(-) → LL(+) = 60˚
Lead 3: LA(-) → LL(+) = 120˚
*Show positive deflection, normal AP ECG
What are the augmented limb leads?
Lead aVR: LA+LL (-) → RA (+) Negative deflection = -150˚
Lead aVL: RA+LL (-) → LA (+) Biphasic/perpendicular = -30˚
Lead aVF: LA+RA (-) → LL (+) Positive deflection = +90˚
What are the precordial chest leads?
V1 (anterior) - V6 (left lateral)
What does a full ECG read look like?
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
What is the mean electrical axis?
Mean electrical axis = average of all instantaneous mean electrical vectors during depolarization of the ventricles ~40˚
How can we calculate the QRS complex mean electrical axis?
- Need 2 leads
- Sum Q + R + S to have length
- From specific lead axis, draw perpendicular line
- Axis is angle to where the cross from center
What is a 1st, 2nd and 3rd degree heart block?
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)
What are 4 different causes of abnormal ECG?
- Heart Block
- Lyme’s Syndrome
- Hypertrophy, old infract
- Long QT-Syndrome (Iks, Ikr, Ina, Ica)
Wht is the sick sinus syndrome?
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
What is an Ectopic Foci?
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
What is Delayed Afterpolarization (DAD) ?
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
What is EAD?
Early after depolarization (during depolarization phase) → reactivation of L-type Ca current (surpass Ik)
*Can get it by prolonging APD
What are the 4 conditions for re-entry?
- Unidirectional block in conduction around a ring
- Slow enough conduction velocity
- Brief refractory period
- Long enough pathway (mice heart = too small)
What is the effect of caffeine on the heart muscle contraction?
Depletes Ca from the SR → used to study the effect of an increase in intracellular calcium from low levels to steady-state
Explain the effect of Sympathetic activation on the heart AP?
- B-Adregenic receptor stimulation activated GS (GTP binding protein)
- GS stimulates adenyly cyclase (AC) → produces cAMP
- cAMP activates PKA (protein kinase A) → phosphorylates L-type Ca2+ channel RyR2, PLB and troponin
- Increase in force of contraction + accelerates relaxation
What is the effect of PKA phosphorylation?
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
What are the 2 elements of the muscle that act in contraction?
- Contractile Element
- Series Elastic Element
What is the WPW syndrome?
- Reentry at the level of the whole heart →presence of Bundle of Kent (embryonic pathway)
What is the effect of an increase in intracellular Calcium?
- Causes more rapid Ica inactivation
- Increases Incx
*Homeostatic feedback system in the heart
What are the differences in sizes between nodal cells and ventricular cells?
Nodal cells → smaller in diameter (slower conductance)
Conducting cells → Bundle cells, ventricular cells, purkinje → larger diameter (lower resistance to conductance)
What is conduction related to?
- Upstroke velocity
- gap junction density
