ECG Flashcards
Why take an ECG?
Limitations?
- Primary tool to evaluate cardiac rhythm
- Recommended to investigate:
- Irregular rhythm
- Bradycardia
- Tachycardia
- Pulse deficits
- Clinical signs of syncope, weakness
<><> - If abnormalities are found, ECG does not tell you the cause
- Not a good tool to identify structural heart disease
normal heart rate for dog
~ 60 – 160/min
normal heart rate for cat
~ 120 – 240/min
how do we position animal for ECG? where do coloured probes go?
Patient in right lateral recumbency (can do other positions depending on scenario eg. fractious cat, but RL is preference)
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Right side: white on right (limb) (+/- green is ground)
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Left side: smoke (black) over fire (red) (black on forelimb, red on hind)
what are unipolar leads? how can they look on ECG? what about augmented? how many ECG formats can we get from 3 leads?
unipolar leads show electrical activity between those two points on the body
> depending on which limbs the leads are placed
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Augmented take sum from two electrodes, and compare the sum to the other lead
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Can get 6 leads from having 3 electrodes on patient - 6 different ECGs
(unipolar I, II, III)
(Augmented aVF, aVL, aVR)
what do positive and negative deflections on the ECG correspond to?
each lead sees electrical activity the moves directly towards or away from that lead - cannot see perpendicular
- positive deflection on ECG moves towards + lead, negative deflection moves away from + lead
Mean Electrical Axis
- what is it, why is it useful
- how to determine
gives us an idea of the direction that electricity moves through the heart on average > take into account all 6 lead orientations from multi-lead ECG
> fairly narrow range of what is normal > if out of range, could be something wrong
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look at most isoelectric lead and consider direction of that lead > mean electrical axis will be perpendicular to this isoelelectric arrangement
> then we need to decide if its going in the + or - direction; look at ECG and see if positive or negative deflection (remember, positive deflection if current moves towards + lead)
mean electrical axis of dog vs cat
dog ~ 30 - 90
cat ~ 0 - 150
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with 0 at the 3 o’clock position
Things to ask yourself when looking at ECG
- What is the heart rate?
> Tachycardic?
> Bradycardic? - Is the rhythm regular or irregular?
- Are there any normal sinus complexes?
> If so, compare any abnormal complexes to the normal ones
how to count HR on ECG
- know paper speed, eg. 25mm/s
- Each big box is 5mm; 5 big boxes = 25mm = 1s
- (If paper speed 50mm/s, 10 big boxes = 50mm = 1s)
regular sinus rhythm vs sinus arrhythmia
Regular sinus rhythm
* P for every QRS
* P wave positive in lead II
* QRS for every P
* Equal R-R interval
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Sinus arrhythmia
* P for every QRS
* P wave positive in lead II
* QRS for every P
* Changing R-R interval
what are the phases of the heartbeat as recorded by the ECG?
- Initiates at SA node
- Depolarizes atria (P wave)
- Delay through AV node (PQ interval)
- Depolarizes ventricles via His-Purkinje system (QRS complex)
- Ventricles repolarize (T wave)
supraventricular tachycardia (SVT) ECG appearance
- if the complexes of the SVT look the same as the sinus QRS-complexes that means they will be supraventricular complexes (arising from the atria).
- The atrial depolarization will be different from the depolarization caused by a sinus complex, therefore there will be no or a different to the ‘normal’ P-wave looking P-wave. The ventricular depolarization from the AV-node onwards will be the same as for the sinus complex. Therefore, the complexes of the SVT look the same as the sinus QRS-complexes.
- As differentiation to a sinus tachycardia, which might look similar: the episode of SVT is of sudden onset and sudden offset, a sinus tachycardia will never be of such sudden onset and offset, and P-waves will be present in front of the QRS-complexes. If this episode would be a sinus tachycardia caused by stress, pain, excitement,.. it would be of slow onset and slow offset.
<><><><> - Spontaneous & premature depolarization originating from ABOVE the ventricles
- Depolarizes ventricle via the His-Purkinje system, therefore QRS complex identical (or nearly identical) to sinus QRS
- Due to cardiac or systemic disease (ie. almost anything!)
ventricular tachycardia ECG pattern, consequences
these complexes arise from the ventricle, their conduction can not use the normal fast conduction pathway. This makes these complexes different in appearance when compared with a sinus QRS-complex. R-on-T phenomenon (red circle) means the complexes get so close to each other that the baseline between them cannot be identified. This is concerning as it is an indication that this patient is at risk of sudden death.
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- Spontaneous & premature depolarization originating from ventricle
- Depolarizes ventricle myocyte to myocyte – slower than HPS therefore wider QRS complex
- Due to cardiac or systemic disease (ie. almost anything!)
first and second degree AV block ECG appearance?
The PR-interval is prolonged (1st degree AVB): the PR interval measures 11 mm (1 mm = 0.02 sec), that is consistent with a PR-interval of 0.22 sec (for dogs 0.06-0.13 sec, and for cats 0.05-0.09 sec, is normal). Additionally, non-conducted P-waves are present (black circles), that means there is no QRS-complex that follows the P-wave. The prolonged PR-interval of the P-waves that are conducted (=followed by a QRS-complexes) is consistent with a first degree AVB, the non-conducted P-waves indicate 2nd degree AVB.
