ECG II Flashcards
What cardiac functions do ECGs provide info on?
Electrical rhythm
Cardiac chamber mass
Cardiac conduction disorders
How is heart rate calculated off an ECG recording?
Calculated from time between peaks of successive R waves
How many beats is bradycardic?
less than 60bpm
How many beats is tachycardic?
More than 100bpm
What is a normal sinus rhythm?
each P wave is followed by a QRS complex
relatively constant intervals
What is the PR interval?
Time taken for electrical signal to reach AV node
What is the QRS interval?
Time for complete depolarization of ventricles
What is the QT interval?
Time for complete depolarization and repolarization of ventricles
What is a second degree heart block?
QRS complexes missing from ECG recording
ventricular depolarization missing
failure of excitation to pass to ventricles
What is third degree heart block?
Wave of excitation does not reach ventricles
QRS not shaped properly and dissociation from p wave
Extra P wave
What are the 2 types of blocks?
Atrioventricular block
Bundle block
What is the Wolff-Parkinson-White syndrome?
Excitation of ventricles is not delayed by AV node
Delta waves reflects early excitation - PR interval reduced
What pathway is involved in Wolff-Parkinson White Syndrome
Accessory pathway between atrium and ventricle (bundle of kent)
What is the electrical axis of the heart?
Average direction of the wave of depolarization through the ventricles
How is the electrical axis calculated?
magnitude of the R wave in leads I,II,II
magnitude of R wave in lead I and aVf (Einhoven’s triangle)
What is the normal axis?
-30 to 90 degrees
What is extreme axis deviation?
+180 -> -90 degrees
What is cardiac ischaemia?
Blood supply is not sufficient to meet metabolic requirements of cardiac tissues
What is cardiac infarction?
Necrosis arising from ischemia
Heart muscle can’t regenerate
What influence does ischemia have on the ECG?
Spread of excitation disrupted
damaged cells undergo depolarization
Myocytes don’t have a longer action potential so they start repolarizing earlier
What determines the depression or elevation of the ST segment?
The location and extent of the damage
What happens in Atrial fibrillation to the ECG?
Can’t locate T/P waves
Irregular baseline
Causes clotting - ventricular filling is insufficient
What happens in ventricular fibrillation?
Can’t recognize any waves
Complete loss of coordination
Pumping quickly without letting heart fill
Brain no longer supplied with blood
