Arrhythmias Flashcards Preview

Cardiovascular System > Arrhythmias > Flashcards

Flashcards in Arrhythmias Deck (11):

Formula for cardiac output?

CO = SV * HR  




What does stroke volume depend on?

SV depends on

1) IN - efficient diastolic filling

2) OUT - efficient heart pumping

at extremes:

tachycardia is a problem of efficient filling (too little t) 

same is also true for premature beats - not enough time for ventricles to fully fill

bradycardia is a problem of efficient pumping (too slow)



What does P wave, QRS complex and T wave stand for?

P wave = atrial depolarization (activation)

QRS = ventricular depolarization (activation)

T wave = ventricular repolarization (relaxation)


* QT interval = important on wards for one condition - prolonged QT interval (by drugs, genetics), potential for lethal arrhythmias*


* ST segment - between S and T wave, especially important for MIs and ischemia*



Define PR, QRS and ST intervals?

PR - from start of P to start of QRS

PR < 0.2 s (under 5 blocks)


QRS < 0. 1 s (under 2.5 blocks), if < 0.12 s - some widening, if >0.12 s - severe widening, blockage in ventricle (bundle branch block!)


ST - from end to QRS to end of T wave



One more time, lets go through the whole piece of ECG!

Nothing is nothing, it is diastolic filling, if the time is short, there is trouble - CO effect!


What is a rhythm strip?

usually lead II along bottom (b/c it mimics direction of electric flow best)


start each ECG analysis by looking at rhythm strip


Approach to ECG readin'?

1. Rate (300-150-100-75-60-50 rule)

60-100 normal

>100 tachycardia

<60 bradycardia

or count a number of big squares btwn each QRS and divide 300 by # of squares. if 3 boxes, 100 bpm


2. Rhythm 

  • regular
  • regular with extra random beats
  • irregular with pattern
  • irregular without pattern

3. P wave - atrial activation, priming ventricular pump

Present? Same shape and size? more of fewer than QRS complexes? relationship btwn the P wave and QRS complexes?

PR 0.12-0.2 (3-5 boxes)

4. QRS 

normal is <= 3 squares = 0.12 seconds

wider - conduction delay, like bundle branch blocks, ectopic beats (conducted through myocardium and not conducting system, so takes longer), toxic drugs...

5. T wave

ALSO Pacemaker location

determine the location of the pacemaker:

SA, atria, AV, ventricles

and direction: does atrium activate ventricle, etc



Cool mnemonic for ECG approach?



Age, e.g. a 60-yo patient is likely have a different pathology from a 30-yo patient
Rate, e.g. fast or slow?
Axis, e.g. left or right?
Rhythm, e.g. regular or irregular?
Evaluate each EKG element as follows:
P wave, e.g. peaked or absent? PR interval - short or prolonged?
Q wave, e.g. deep Q wave? QT inerval - - short or prolonged?
R wave, e.g. tall? look at QRS complex width for RBBB or LBBB
ST segment, e.g. elevation or depression?
T wave, e.g. peaked or inverted? U wave?


Drugs , e.g. Digoxin, tricyclic antidepressants
Rhythm and rate abnormalities, e.g. AV block of 1,2,3 degree, AFib, SVT? Interval prolongation?

Infarct? Deep Q wave?
Infection, e.g. pericarditis

Enlargement, e.g. LVH, RVH, left or right atrium enlargement?
Electrolyte disturbances, e.g. hyperkalemia, hypokalemia, hypercalcemia,
Endocrine causes, e.g. hypothyroidism

How to use this approach in practice?

Look at the EKG and write down on a piece of paper:


Circle the abnormalities you discover in step 1 -- A RARE PQRST. Then, connect and try to explain these abnormalities by looking at the list of possible etiologies presented in step 2 -- DR III EEE. That's it!


What are the maximum HRs for different pacemakers (SA, atria, AV, ventricle)?

SA- maximum physiological HR is 220-age

therefore if HR>200, SA as pacemaker unlikely

P waves present, since travels to AV ->...

short PR interval unlikely, since signal starts normally and has to travel through all the stops (atria, AV, Bundle of his...); P wave followed by QRS


Atria  - refractory period, HR > 200 unlikely to be in atria

atrial pacemakers have to conduct through the rest of the atria, so they do generate P wave, but it would be a different shape, as atrial pacemaker will be located in a different location from SA node

atrial fibrillation - irregular chaotic rhythm, no pattern, no P waves

atrial flutter - sawtooth


AV node - slow heart rate (normal 45-50), but can generate faster heart rate if part of re-entry circuit

AV node does not have the normal refractory period of SA, so if part of re-entry, can generate > 200 bpm

P wave timing will depend on how far in the AV node the pacemaker is - near the top - very short PR interval, then QRS, near the bottom - P after QRS 

P usually inverted (upside down) because traveling in opposite direction


Ventricles - QRS will be wide because signal would travel slowly

No P wave that goes up to atria, QRS alone is hard,

sometimes there might be something in atria generating P, so P and QRS dissociated completely

shorter refractory periods than in atria, > 200 bpm possible

=> > 200 bpm usually exclude atria and SA






What does an ECG with pacemaker look like?

the first spike before QRS is called a pacing spike - it generates an electrical signal to cause ventricle to contract

pacing spike tells you where pacemaker is located - if before P wave - in atrium, if before QRS and T wave - in ventricle

we pace people normally when heart is too slow, sometimes can also rapidly pace someone out of tachycardias


How would you treat?