Module 3 4201

Conduction sequence

Conduction sequence

electrical impulse travels from the SA node to the AV node then down the bundle of His. The electrical impulse will then go down the L and R BB and then the purkinje fibers

what allows the ventricles time to fill?

The AV node slows the impulse down to allow the atria to fill the ventricles with blood

why is coordination of ventricle contraction important?

in order to have enough pressure within the chambers to eject blood

Name two important processes for the heart to pump properly

Impulse generation and impulse conduction

examples of abnormal SA node impulse generation

paroxysmal atrial contraction and atrial tachycardia

What sort of foci can occur during coronary ischemia? How does it happen?

PVCs in the ventricles, the foci must have high excitability to cause ectopic impulses

Default gain standard for ECGs

1mV/10mm or 0.1mV/1mm

what should be noted about heart rhythm in holter scanning?

• the underlying rhythm

• any alternate rhythms

• variations in conduction like AV block or intermittent nocturnal wenckebach block

how can you determine the origin of an impulse?

by looking at its polarity, patterns and time intervals compared to other waves

the first step in determining abnormalities in heart beats

try to find the P waves

QRS origin of impulse

• AV: normal QRS, either inverted or no P wave

• Ventricles: Wide QRS, no P, inverted polarity

• pacemaker: pacer spike

difference between sinus pause and SA block

sinus pause is a delay in impulse conduction and SA block is cause by a conduction defect

SA impulse generation defects

• aging

• ischemia

• inflammation

• drug effects

where is afib often generated?

in cells within the opening of the pulmonary veins

aflutter atrial rate

300-500bpm

Idioventricular rate

30-45bpm

what is ventricular pre-excitation?

when the AV delay is shorter which allows the ventricles to be stimulated earlier than normal

what may be the cause of a shift in AV delay?

overstimulation of SNS or a decrease in PNS

how is a delta wave created?

when the impulse travels down the bundle of Kent and partially depolarizes the ventricles before another impulse travels down the AV node

there is an increased incidence for WPW in:

• MVP

• tricuspid malformation

• cardiomyopathy

WPW and other pre-excitation syndromes are at increased risk of developing what?

a re-entrant circuit that can initiate paroxysmal tachycardia

when is 2nd and 3rd degree AV block considered more serious?

when its caused by degenerate or acute conditions like

• MI

• direct ischemia of AV node

• sclerosis or fibrosis of AV node or bundle of His

where may wenckebach occur?

in the AV node or SA node as a form of exit block

what is Stokes-Adams syndrome?

when someone experiences syncope before the escape rhythm is initiated

when does the RBB branch off?

when it reaches the distal portion of the septum and apex of right V

what are the two branches of the LBB called?

the anterior-superior and posterior-inferior

normal depolarization is completed in how many seconds?

less than 0.12sec

lesions in His-purkinje system causing delays may be caused by:

• ischemia

• inflammation

• hypoxia

• drugs

conduction defects may occur in what 5 sites of the bundle branches?

• common bundle

• right bundle

• left main branch

• anterior-superior branch

• posterior-inferior branch

ECG characteristics of RBBB

• tall and wide QRS in V6 and lead I

• prolonged QRS

• slurred S in V6 and lead I

• prominent S in V1 and AVR

ECG characteristics in LBBB

• polarization the opposite of normal

• slurred R in V6, lead I

• Q wave or small R with deep S wave in V1, AVR

• wide QRS >0.12 sec

• T wave and ST segment deviations

anterior hemiblock characteristics

• normal QRS

• Large positive R wave in Lead I, negative S wave in Lead III

• QRS axis -45 or more (left axis deviation)

posterior hemiblock characteristics

• normal QRS

• large positive R wave in lead III, negative S wave in Lead I

• QRS axis +120 or more (right axis deviation)