Cardiac Conduction System & ECG Flashcards

1
Q

Action potentials of myocytes –> surface ECG (summary)

A
  • R wave = phase 0
  • isoelectric ST segment = phase 2
  • T wave = phase 3
  • isoelectric segment (after T wave) = phase 4
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2
Q

R wave =

A

The initial rapid upward deflection of the R wave corresponds to phase 0 (fast sodium current)

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3
Q

ST segment =

A

isoelectric ST segment (links the QRS to the T wave) = phase 2 (plateau=calcium influx and potassium efflux are balanced).

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4
Q

T wave =

A

T wave (in which repolarization is occurring) = phase 3 (rapid decrease in voltage as potassium efflux continues).

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5
Q

Isoelectric segment

A

isoelectric segment after T wave = phase 4

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6
Q

Sequence of cardiac electrical system acrtivation

A
  1. pacemaker cells @ SA node generate electrical impulse –> spread via gap jxns
  2. depolarization –> R&L atria = P wave
  3. depolarization –> AV node –> delay: ensures end of atrial contraction before ventricle depolarization
  4. AV node –> R&L bundle of His branches –> fibers of Purkinje cells
  5. Purkinje fibers –> ventricular cardiac myocytes –> contraction
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7
Q

Right bundle of His –> ______

A

single entity that primarily supplies electrical stimulation to R ventricle

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8
Q

Left bundle of His –> ____

A

divides into anterior and posterior branches and supplies those regions of the L ventricle w/electrical stimulation

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9
Q

P wave =

A

small depolarization (reflecting the depolarization of the atria) prior to the larger depolarization of the ventricles (QRS complex).

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10
Q

QRS complex=

A

a large wave reflecting the depolarization of the ventricles after the P wave (depolarization of the atria) and before the T wave (repolarization of the ventricles).

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11
Q

T wave =

A

a small wave after the QRS complex that reflects the repolarization of the ventricles (should always be in same direction as QRS complex).

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12
Q

PR interval =

A
  • the plateau between the P wave and the initiation of the QRS complex, where depolarization pauses at the bundle of His after depolarization of the atria and before depolarization of the ventricles.
  • index of conduction time across the AV node
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13
Q

QT interval =

A
  • The plateau after the QRS complex and the T wave, reflecting the period of time between depolarization and repolarization of the ventricles.
  • QT time: total duration of depolarization and repolarization
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14
Q

First degree atrioventricular block =

A

conduction delayed but all P waves conduct to the ventricles.

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15
Q

Second degree atrioventricular block =

A

some P waves conduct, others do not.

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16
Q

Third degree atrioventricular block =

A

none of the P waves conduct and a ventricular pacemaker takes over.

17
Q

Major mechanisms of disturbance in cardiac conduction –> tachyarrhythmias (3)

A
  1. abnormal reentry pathways
  2. ectopic foci
  3. triggered activity
18
Q

Characteristics of abnormal reentry pathways tachyarrhythmias

A
  • present in the atria, ventricles or the junctional tissue.
  • occurs when there is a unidirectional block and slowed conduction through the reentry pathway.
  • After the slow reentry the previously depolarized tissue has recovered and reentry into it will occur.
  • most common mechanism of serious tachycardias
19
Q

Characteristics of ectopic foci tachyarrhythmias

A
  • myocardium outside the conduction system acquires automaticity
  • rate of depolarization exceeds SA node –> abnormal rhythm occurs.
  • can be isolated ectopic beats or sustained tachyarrhythmias.
20
Q

Characteristics of triggered activity tachyarrhythmias

A
  • abnormal “afterpolarizations” may be triggered by the preceding action potential.
  • early afterpolarization before the action potential has fully repolarized triggers tachyarrhythmia
  • Delayed afterpolarizations appearing after an action potential is complete can also trigger arrhythmias.
21
Q

Effects of left bundle branch block

A
  • QRS widening on ECG
  • delayed conduction to left ventricle
22
Q

Effects of right bundle branch block

A
  • QRS widening on ECG
  • delayed conduction to right ventricle
23
Q

Effects of block of left bundle fascicles

24
Q

Sizable Q wave =

A

transmural infarction/necrosis

25
Q waves @ inferior leads (II, III, aVF) =
inferior infarts
26
Q waves @ V1-V4 =
anterior wall infarcts
27
Q waves @ I, aVL, V5, V6 =
lateral wall infarcts
28
Evolving EKG of transmural myocardial infarct
1. giant T wave 2. t-wave inversion (ischemia) 3. ST elevation (current of injury) 4. Q waves + T inversion
29
Causes of prolonged QT interval
* congenital long-QT syndrome * hypocalcemia * Class 1A or 3 anti-arrhytmic drugs * hypothermia * hypokalemia
30
EKG findings in hypokalemia
* QT generally prolonged * prominent U waves * T waves may be inverted * hypokalemia = common cause of arrhythmias
31
EKG findings in hyperkalemia
* mild --\> peaked high T voltages * moderate --\> P waves flatten, QRS & T broaden * very high --\> sinusoidal w/out P or R
32
EKG changes in L ventricular hypertrophy
* increased voltage of R peak @ L-sided leads * L leads = I, aVL, V5, V6
33
EKG changes in right ventricular hypertrophy
* increased voltage peak in R wave @ R-sided leads * R leads = V1, V2