Case 2- ECG and imaging Flashcards
ECG change in MI
ST elevation if there is a full thickness infarction. If the ST elevation is not present then its not full thickness
What does the ECG record
The electrical depolarisation of the myocardial tissue produces a dipole current which can be detected by an electrode pair on a body surface, the signals are then amplified on a monitor. Measures the potential difference between two different areas on the skin
ECG- P wave
Atrial depolarisation
ECG- QRS complex
Ventricular depolarisation, should be between 80-100ms, over 120 is a wide QRS may be due to a pacemaker or drug toxicity
ECG- PR interval
The time between the onset of the P wave and the QRS complex, should be 120-200ms. Look at its relation to the QRS complex, is each P wave followed by a QRS
ECG- T wave
Ventricular repolarisation
ECG- ST segment
The interval between the S wave and the T wave
ECG- QT interval
From the start of the QRS complex to the end of the T wave. Affected by heart rate so need to adjust it to create the QTc (corrected QT). Should be under 440ms in men and 460ms in women
Wires in an ECG
Positive electrode, negative electrode and earth wire
ECG- lead 1
The negative electrode is attached to your right wrist and the positive electrode is attached to the left wrist. Earth wire on the ankle
ECG- lead 2
Negative electrode is on the right wrist and the positive electrode is on the left ankle, the lead is about the same angle as the heart in the body. Produces bigger spikes on an ECG so is used more commonly.
ECG- lead 3
When the negative electrode is on the left wrist and the positive electrode is on the left ankle.
12 lead ECG
The 12 angles an ECG can be taken from
Working out heart rate
You count the squares, the small squares are 0.04 seconds, the medium squares are 0.2 seconds
ECG changes in left ventricular hypertrophy
More muscle needs to be depolarised so you will have a tall R wave. The S wave will be deeper and there may be an inverted T wave.
ECG first degree heart block
The PR interval is >200ms. Each P wave is followed by a QRS. Due to a delay in the signal reaching the ventricles
ECG second degree heart block (Mobitz 1)
The PRS interval extends till the QRS complex is dropped, the system will then rest itself to start again
ECG second degree heart block (Mobitz 2)
The PR does not extend but the QRS is occasionally dropped. Not every P wave is associated with a QRS complex. A ventricular contraction is skipped due to the signal not conducting through the AV node each time.
ECG third degree heart block
No correlation between the P wave and QRS. They can be regular but they are independent of each other. There is no communication between the atria and ventricles
ECG atrial fibrillation
No P wave and an irregular rhythm