Introduction to the ECG Flashcards
Complete the diagram of the heart


Draw a coronal section of the heart showing the conduction system.
You do not need to include the valves or the vena cava

What is a functional syncytium?
Functional syncytium = many cells acting as one
What is a precordial lead?
There are six precordial (or chest) unipolar leads: V1, V2, V3, V4, V5, V6.
A “chest” lead. It is a configuration in an ECG of electrodes such that one electrode in placed on the chest and the negative “electrode” being Wilson’s central terminal.
Wilson’s central terminal is a combination of electrodes that act together as if they were a reference electrode positioned in the centre of the heart.
Precordial leads make measurements of electrical activity in the transverse plane
What are the approximate conduction velocities (including units) for: the fastest neurons/axons, His-Purkinje system, contractile cardiomyocytes, the AV node?
- Purkinje fibres up to 5 m/s
- fastest neurons ~100 m/s
- AV node 0.05 m/s
- ventricular myocytes 0.3-0.5 m/s
How and why does the AV node delay conduction of waves of depolarisation?
30 ms to AV node
90 ms delay before enters penetrating portion of AV bundle
40 ms delay in penetrating bundle
•Total of 160 ms delay in AV network.
Mostly due to increased resistance
•(i) diminished numbers of gap junctions between modified myocytes per cross sectional area, (ii) smaller fibres, (iii) more cell junctions per length distance travelled
Draw what a single lead of a normal ECG should look like (for 2 heart beats), and label the following on it: T wave, QRS complex, P wave, PR interval, ST segment, QT interval.

List four different forms of heart block, and how they are differentiated.
1st Degree Block - PR interval > 5 little boxes (200 ms), Asymptomatic, Often young people (adolescents), Delayed AV node transmission, Rarely treated
2nd Degree Block Type I – é PR interval, AV damage, no treatment
2nd Degree Block Type II – PR interval stable, Bundle of His, high risk, leads to third degree heart block, implant pacemaker
•3rd Degree Block – atrial signals do not arrive at ventricles, ventricles beat at their own pace: 30-40 bpm
What is the normal range (or a normal value) for QT interval?
From start of P-wave to start of QRS complex (name is misleading)
300-460 milliseconds
What is the normal range (or a normal value) for PR interval?
Under 200 ms ( 5 boxes)
Usually over 120 ms
What is the normal range (or a normal value) for RR interval?
RR interval is the reciprocal of heart rate per second
For 60 bpm, RR = 1000 milliseconds, for
Normal = 75 bpm RR = 800 milliseconds
Accept 50 -90 bpm = 1200 ms to 667 ms
What is the normal range (or a normal value) for PP interval?
PP interval is the reciprocal of atrial heart rate per second
For 60 bpm, PP = 1000 milliseconds, for
Normal sinus rhythm = 75 bpm PP = 800 milliseconds
Accept 50 - 90 bpm = 1200 ms to 667 ms
Draw an ECG showing the end of the PR interval clearly?

Draw an ECG showing both ends of the Q interval clearly?

What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

The P waves are not coordinated with the QRS complexes. The atria and ventricles are beating independently of one another. Note that the ventricular rate is less than half of the atrial rate; there are 11 big boxes between QRS complexes (the ventricular rate is less than 30 beats per minute). This is complete (third degree) heart block. It is usually symptomatic. The patient will not be exercise tolerant, may be haemodynamically unstable, and may be unconscious due to low cardiac output. This patient will be treated with a pacemaker.
What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

PR interval lasts too long. It should last for less than 5 little boxes. This is First degree heart block. Often there is no treatment except to monitor the patient for problems.
What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

There are no P waves, except before the the second QRS complex from left. These are fibrillatory waves instead of a P wave. This is atrial fibrillation. Note the highly irregular RR intervals (ie not consistent ventricular rate, but the ventricular rate is definitely fast).
This is likely to be treated with anticoagulants to prevent stroke
It may also be treated (depending on other aspects of history) with electrical cardioversion, digoxin, etc
What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

Skipped QRS complexes, varying PR interval. This is Mobitz type I second degree heart block (Wenckebach), it might not be treated.
What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

ST segment is elevated. This is an acute myocardial infarct.
This is most likely to be treated with immediate revascularisation using PCI or clot busting drugs (tPA)
The patient would also be treated with morphine, oxygen, nitrates, and aspirin
What is clinically relevant about this rhythm, and what is the mostly likely form of treatment?

Missed QRS complex. Consistent PR interval. This is Mobitz type II second degree heart block (Hay). It is potentially very dangerous, as it could degenerate into 3rd degree heart block. This may be treated with an implantable pacemaker.
What is clinically relevant about this rhythm, and how might it come about?

It is very slow. The RR interval is ~ 9 big boxes, so the rate is about ~ 33 beats per minute. However, there are normal QRS complexes, and normal P and T waves. This is Sinus bradycardia
Causes include: high doses of beta blockers or calcium channel blockers, as well as sick sinus syndrome, hypothermia and sleep apnoea
What is the cellular basis of the P wave, the QRS complex, and the T wave
P wave: depolarisation of atria as wave travels from SA node inferiorly to rest of atria.
QRS complex: depolarisation of ventricles – note that this masks the signal of the atria repolarising.
T wave: repolarisation of the ventricles starting from the apex and going superiorly.
Describe the progression of electrical activity through the heart during a single beat.
Impulse begins in SA node. 4 internodal bundles relay depolarisation from SA node. 3 (anterior, middle, and posterior tracts) go to AV node; Bachmann’s bundle goes to the left atrium. By the time it has emerged from the AV node impulse has been delayed ~ 160 ms. Impulse exits AV node and enters ventricles at bundle of His. This splits into the left bundle branch and right bundle branch (which also continue to have smaller branches), which travel down the septum. At the septum the two branching systems go in opposite directions, superiorly to the right ventricle and superiorly to the left ventricle.
In ECGs, what is a lead?
A lead is one of the twelve configurations of electrodes used for detecting the heart’s electrical activity. Sometimes the word “lead” is used to refer to one of the wires connecting to an electrode