The ECG Flashcards
Describe in general terms and draw a diagram of the pattern of spread of excitation over the heart
Action potential is generated by pacemaker cells in the SA node
This spreads across the surface of the heart and reaches the AV node, where there is a delay of around 120ms
This then spreads through bundle of His and both bundle branches, depolarising from inside to outside (endo to epi)
After around 280 ms they repolarise from outside in.
Explain briefly the upward and downward deflections seen from different leads, and why they appear different
depolarisation towards and electrode = upward
depolarisation moving away = downward
repolarisation toward = downward
repolarisation away = upward
How can you calculate the heart rate from an ECG?
for regular: 300 / large squares in RR interval
for irregular: QRS in 10 seconds times 6
Explain what you would see on an ECG for: ectopic ventricular beats, AF, VF, type I II and III heart block
ectopics: wider and taller QRS which occurs sooner than the regular rhythm of the trace would dictate
AF: irregular QRS with absence of P waves
VF: quivering of the ventricles, seen as waves
I HB: prolonged PR interval
II HB: Mobitz and Wenckebach’s
III: no correlation between P and QRS (AV block)
Describe in outline the changes seen on an ECG during an MI and ischemia during exercise
MI usually gives ST elevation
Ischemia can give T inversion and ST depression
Old MI might show abnormal Q wave depression
