Arrhythmias Flashcards
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?
A RARE PQRST
DR III EEE
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?
DR III EEE:
Drugs , e.g. Digoxin, tricyclic antidepressants
Rhythm and rate abnormalities, e.g. AV block of 1,2,3 degree, AFib, SVT? Interval prolongation?
- *Ischemia?**
- *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:
A R A R E P Q R S T
D R I I I E E E
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?
A:
