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BIOC34H3 (46)

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6 Pages
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Department
Biological Sciences
Course Code
BIOC34H3
Professor
Stephen Reid

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Lecture 2 Study Notes
Bipolar ECG limb leads record the voltage b/n electrodes placed on the wrists and the
arms
This forms an equilateral triangle around the heart, referred to as Einhovens
Triangle
There are 3 standard bipolar limb leads: slide 3
oLead I:Right arm (always negative) to left arm
oLead I I: Right arm to left leg (always positive)
oLead I II: Left arm (in this case -) to left leg
Applying these leads to the axial reference system:
oLead I (RA LA): corresponds to 0 degrees
oLead II (RA LL): corresponds to 60 degrees
oLead III (LA LL): corresponds to 120 degrees
So if you were to apply these bipolar limb leads to an ECG trace, it would be
straightforward
oDepolarisation
Any depolarisation in the direction of the Left Leg (always +)
will give a positive inflection on the trace
Any depolarisation in direction of Right Arm (always -) will
give negative inflection on the trace
www.notesolution.com
Apply it this way
oRepolarisation
Opposite of depolarisation patterns
ECG waves
P wave: Atrial depolarisation (small cause of less muscle mass than ventricles)
QRS complex: Depolarisation of ventricles and repolarisation of atrium (silent
atrium repolarisation). Blip sound you hear
T wave: ventricular repolarisation
Important ECG Wave and Conduction co-ordination pathway: slide 8 15
Augmented Unipolar limb leads: use exactly the same type of leads as bipolar limb
leads, with exception of all destinations being positive. This changes the reference degrees:
www.notesolution.com

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Description
Lecture 2 Study Notes Bipolar ECG limb leads record the voltage b/n electrodes placed on the wrists and the arms • This forms an equilateral triangle around the heart, referred to as Einhoven’s Triangle • There are 3 standard bipolar limb leads: slide 3 o Lead I:Right arm (always negative) to left arm o Lead II: Right arm to left leg (always positive) o Lead III: Left arm (in this case -) to left leg • Applying these leads to the axial reference system: o Lead I (RA – LA): corresponds to 0 degrees o Lead II (RA – LL): corresponds to 60 degrees o Lead III (LA – LL): corresponds to 120 degrees • So if you were to apply these bipolar limb leads to an ECG trace, it would be straightforward o Depolarisation Any depolarisation in the direction of the Left Leg (always +) will give a positive inflection on the trace Any depolarisation in direction of Right Arm (always -) will give negative inflection on the trace www.notesolution.com Apply it this way o Repolarisation Opposite of depolarisation patterns ECG waves • P wave: Atrial depolarisation (small cause of less muscle mass than ventricles) • QRS complex: Depolarisation of ventricles and repolarisation of atrium (silent atrium repolarisation). Blip sound you hear • T wave: ventricular repolarisation Important ECG Wave and Conduction co-ordination pathway: slide 8 – 15 Augmented Unipolar limb leads: use exactly the same type of leads as bipolar limb leads, with exception of all destinations being positive. This changes the reference degrees: www.notesolution.com • aVL: Left arm positive lead -30 degrees from Lead I (RA to LA) of bipolar limb lead • aVR: Right arm positive lead -150 degrees from Lead I • aVF: Left leg positive +90 degrees from Lead I • if going in opposite directions e.g. Lead II and aVR, the inflections on ECG will be opposite to each other Unipolar chest leads: • Just a series of six leads V1 – V6 placed all over upper body ECG segments • R – R segment: represents the distance/time interval b/n two heart beats • P – Q/P – R segment: time of conduction from AV node down through the purkinje fibres • T – Q segment: represents time period ventricles are relaxing (diastole period) • Q – T segment: represents ventricular contraction (systole period) Arrhythmias: Irregular heart rhythms • Sinus Arrhythmia: slide 23 o QRS complex not evenly spaced, total irregularity of beat (R-R) o P-R distance, however, remains the same o Disappears with holding breath www.notesolution.com (irregular R-R distance) • Wandering Atrial pacemaker: slide 24 o Pacemaker activity originates from differ
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