Download Electrocardiography ECG A pen recorded paper trace

Electrocardiography
ECG



A pen recorded paper trace of the electrical activity of the heart
When a myocardial cell contracts it de-polarises and after contraction re-polarises
The sum of total myocardial de-polarisation during contraction and re-polarisation after
contraction produces an electromagnetic field which can be detected around the body and within
the heart itself
Types of ECG Machine




Monitors
Portable or Fixed ECG Machines for classic ECG recording
Holter Monitors
Event Recorders
Einthoven’s Limb Leads
 Lead I - Compares Right Forelimb with Left Forelimb
 Lead II - Compares Right Forelimb with Left Hindlimb
 Lead III - Compares Left Forelimb with Left Hindlimb
 Earth -Right Hindlimb
Wilson’s Central Terminal
 Uses Unipolar Leads & Compares 3 Limb Leads with the average of the other 2
 AVR
 AVL
 AVF
Hexaxial Reference






Chest Leads
(Unipolar Leads on Thorax) Give information outside horizontal plane
Nearer the heart so larger tracings compared with Hexaxial Leads
CV5RL (V1 or C1) placed at right costo-chondral junction rib space 4-5
CV6LL (V2 or C2) placed at left 5/6 below costo-chondral junction
CV6LU (V3 or C3)- Above CV6LL
V10 Over 7th Thoracic Vertebra
Recording an ECG







Single or Multichannel
Portable or Fixed
Auto System or Manual
Paper Speed 25mm/sec but 50mm/sec best
Sensitivity .5cm1cm & 2cm/millivolt
Z Fold Paper
No Sedatives


Rhythm




Crocodile Clips No Clipping Surgical Spirit
Filters
Sinus Rhythm- PQRST
Sinus Tachycardia-Faster than normal rate
Sinus Bradycardia- Slower than normal rate
Sinus Arrythmia- Irregular rhythm due to vagal effects of respiration
Calculate Heart Rate





Automatic
Number of beats in 1 seconds x 60
If paper speed 50mm/sec
Instantaneous Ht rate = 3000/R-R Interval
If paper speed 25mm/sec
Instantaneous Ht rate = 1500/R-R Interval
Calibrated Ruler
Evaluate Rhythm




Is there a P for every QRS?
Is the rhythm regular or irregular
Evaluate for normal relationship between P wave and QRS complex
Is the rhythm regularly irregular
Evaluate PQRST
P Wave




Is there a P for every QRS?
Is the rhythm regular or irregular
Evaluate for normal relationship between P wave and QRS complex
Is the rhythm regularly irregular




If tall R wave ventricular dilatation or hypertrophy.
If wide R wave then ventricular dilatation or hypertrophy or conduction defect.
If small R could be obesity, pneumothorax or pericardial effusion.
If varying R waves so called Electrical Alternans due to obesity, pneumothorax or pericardial
effusion, myocardial hypoxia or necrosis.
Notching of R could represent Myocardial Hypoxia, Necrosis, Infarct or Electrolyte disturbance.
QRS

ST





QT
T wave may be +ve -ve or biphasic.
If tall T may be hyperkalaemia or anoxia. T may look tall if R reduced due to obesity,
pneumothorax or pericardial effusion.
If small T and biphasic may indicate hypokalaemia.
Non specific T changes with hypoglycaemia and drug toxicity.
ST coving (depression) or elevation above or below baseline due to myocardial anoxia or drug
toxicity esp. Digoxin


QT interval may be prolonged in toxicity, hypothermia, hypocalcaemia, hypokalaemia and some
CNS disorders.
QT interval may be shortened in hyperkalemia, hypercalcaemia,and digitalis toxicity
Mean Electrical Axis






EA is 90 Degrees to Isoelectric Lead
EA is in direction of largest +ve QRS
EA is 180 Degrees to largest -ve QRS
Algebraic Sum of Lead I & III using Tables
Geometric Construction using algebraic sum of any two leads and drawing perpendicular line on
axis chart. EA is point of interception
Automatic
Report Form
To save repeated interpretation of the same ECG fill in a report form
Supraventricular rhythm Disturbances









Normal QRST
Abnormal or Absent P if non sinus beat
Sinus Arrest- R-R interval more than 2x normal
Atrial Premature Contractions
Atrial Tachycardia- Three or more consecutive APCs
Atrial Flutter saw tooth waves
Atrial Fibrillation
Atrioventricular Junctional Premature Complexes -ve P And not quite same voltage QRS
Junctional Tachycardia- Three or more consecutive AVJPCs
Ventricular Arrhythmias






Ventricular Premature Complexes
Ventricular Tachycardia- 4 or more VPC’s
Ventricular Flutter- QRST just undulating baseline
Ventricular Fibrillation Jagged irregular baseline. No QRST
Ventricular Asystole - Complete Ventricular arrest
Ventricular Escape -A lifesaving depolarisation of ventricle
Abnormalities of Conduction






AV Block First Degree - Prolonged P-R interval
Second Degree - P sometimes not followed by normal QRS
Third Degree - P never followed by normal QRS
Pre- Excitation - Atrial activity shortcuts into ventricle Gets short P-R and unusual QRS
Bundle Branch Blocks- Right or Left
Fasicular Blocks- Left anterior or left posterior
Second Degree AV Block



Mobitz Type I(Wenckebach)
There is a P wave for every QRS
But some P waves without a QRS






P-R Interval becomes progressively longer until P wave blocked or P-R varies with the longest
before the block
Mobitz Type II
There is a P wave for every QRS
But some P waves without a QRS
P-R Interval constant
Usually a fixed ratio of P to QRS 2:1,3:1,4:1 etc
Bundle & Fasicular Blocks




Rt Bundle Branch Block Wide QRS deep S Right Axis Shift
Lt Bundle Branch Block Wide QRS Deep Q Wide QRS Left axis shift
Lt Ant. Fasicular Block- Normal duration QRS but deep S and left axis deviation
Lt Posterior Fasicular Block-Normal duration QRS but deep Q and right axis deviation
Sick Sinus Syndrome



Most common in small breeds esp Min Schnauzers
Bradycardia/Tachycardia Syndrome
Syncopal