Lectures 12 + 13 - ECG Flashcards
what are the parts of the conducting system of the heart ?
and their function
SA node - sets the sinus rhythm - normal - 60-100bpm
fastest rate of depolarisation
AV node - has a longer refractory period, serves to delay the AP giving atria time to contract before sending signal to ventricles - slows conduction
bundle of his - only point to relay signal between atria and ventricles
Fibrous cartilage - insulates between atria and ventricles. also has structural importance for valves
Left and right bundle branches
depolarisation occurs from left to right branch
Pukinje fibers
explain how the viewing of electrical activity from different directions
direction will depend on if singal is towards or away from electrode - and if its repol or depol
the more in line with the depol the larger the signal, as angle grows signal reduces
draw an example ECG
Label all the correct regions (from exact points),
what they represent
how large is normal / abnormal
what each label is doing signal wise in the heart
P QRS T
PR section - between start of P wave and start of QRS complex
check against lecture 12
PR region - 3-5 small boxes - 0.12-0.2 secs
prolonged if > 1 large Box
QRS region <3 small boxes / 0.12 secs
prolonged if > 3 small Boxes
QT Interval - Prolonged if greater than 44 small boxes
what are the leads of an ECG,
what regions are looked at by each electrode ?
limb leads give - I, II, III, aVF, aVR, aVL - vertical plane
inferior surface of the ventricles is viewed by II, III, aVF
Lateral surface of the ventricle is viewed by leads -
I, aVL, V5 and V6
horizontal plane - V1-V6
V1 - V4 are antero-septal leads
V1, V2 show the right ventricle and septum
V3 and V4 show the apex and anterior surface of RV and LV
give two ways to calculate the heart rate
standard is 300/ one R-R interval
if heart rate is irregular then count R-R interval in 30 large squares (6 seconds) and multiply by 10
what does a widened QRS normally represent ?
failure to spread the excitation wave between atria and ventricles
so ventricles depolarise at own far slower (about 30bpm) rate
what is normal sinus rhythm ?
a normal heart beat, ran by the sinus pulse (SA node)
regular rhythm normal heart rate - 60-100 BPM has P waves regular R-R interval PR and QRS are normal in shape and length a QRS follows every P wave
what are the names for Fast and Slow rhythms that are still normal
fast but normal is a sinus tachycardia - more than 100 BPM
slow but normal is a sinus bradycardia - less than 60 BPM
what are the types of heart block
what is heart block
heart block is a delay or failure of conduction of impulses from atria to the ventricles via the AV node and bundle of his
first degree heart block - benign - prolonged PR interval
second degree heart block
type 1 - a slowing of atrial conduction - legnthening PR interval until a QRS drops - benign
type 2 - PR intervals do not lengthen, but sudden drop of QRS
high risk of progression to complete heart block - give a premptitive pacemaker
special - 2:1 - where there are 2 P waves for every QRS, so every other QRS is dropped
Third degree hear block - complete heart block
atria and ventricles depolarise independently
P - P intervals are normal, as atria beats normally
R-R intervals are independent of P waves, normally beat ALOT slower - ie 30 BPM as contractions are at rate of ventricular depolarisation
A wide QRS is seen - as contraction is slower
URGENT pacemaker is needed
Bundle Branch block - one of the two bundles is blocked - gives normal P wave and PR interval but a wide QRS as slower contraction on one side of ventricle
name the terms of abnormal impulse formations
may get a SUPRAventricular rhythm
these will give a normal QRS size
this can be due to the
SA node
AV node
Atrium
or a Ventricular rhythm
abnormal QRS
- due to the ventricle
outline AF
Atrial Fibrillation - a supraventricular rhythm
comes from multiple ectopic beats in the atria
atrial contraction is lost - its just a flutter/quiver - so blood can pool and cause a clot forming, potential stroke cause
ventricles and hence QRS contract normally but at an irregular rate - as not all impulses are conducted by AV node due to a refactory period, but still irregular impulses conduct
NO P waves are seen - wavy baseline
Narrow QRS complex
R-R intervals are irregulary irregular
what are the three issues associated with the ventricles ?
how are they linked ?
what do each look like - check lectures
Ventricular ectopic beats
abnormal impulse
slower depol as via ventricular muscle not AV node
wide QRS
Ventricular tachycardia multiple V.ectopics occuring if more then 3 consecutive gives a VT broad QRS dangerous - risk of VF fast regular broad beats
Ventricular Fibrillation
fast, abnormal V. Depol
many ectopic sites
quivering ventricles gives no contraction
rapid irregular rhythm
there is no cardiac output - so cardiac arrest
how do we determine the location of a MI or Ischemia in the heart ?
look at the leads that correspond to the artery
so
inferior surface - II, III, aVF - Right Coronary Artery
Antero - Septal - V1 - V4 - Left anterior descending (LAD)
Lateral Surface - Lead I, aVL , V5 and V6 - Circumflex Artery
how do we determine between ischemia of the heart and a MI
in ischemia there is no necrosis of heart, in an MI there is necrosis
so we do a blood test for cardiac troponins
-ve for ischemia
+ve for MI - as necrosis is occuring
MI can be
STEMI - ST segment elevation MI
Non STEMI - Non ST Segment elevation MI
what is a STEMI
STEMI - ST segment elevation MI
complete occlusion of a coronary artery
a sub EPICARDIAL injury causes ST segment elevation as earliest sign - seen in leads facing affected area
need urgent reperfusion of area with blood
will also see a Large Q wave appear after some hours
this will be a permanent change for patient - seen on a ECG months after, where as if they survive the ST elevation normalises within days
q wave if pathological will be
> 1 small square wide
> 2 small square deep
deeper than 1/4 of R wave
also get some temporary T wave inversion in the following days
