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