2. What is arrhythmia?
• Arrhythmias are disorders of cardiac impulse
formation and impulse propagation
• Broadly divided into tachyarrhythmias and
bradyarrhythmias
4. The cardiac conduction system. Depolarisation starts in the sinoatrial node and spreads
through the atria (blue arrows), and then through the AV node (black arrows). Depolarisation
then spreads through the bundle of His and the bundle branches to reach the ventricular
muscle (red arrows). Repolarisation is in the opposite direction (green arrows).
PQRST - The upper limit of the normal range for each interval is given in brackets.
5. The sequence of activation of the ventricles. Activation of the septum occurs first (red
arrows), followed by spreading of the impulse through the left ventricle (blue arrows) and
then the right ventricle (green arrows).
6. The sequence of activation of the ventricles. Activation of the septum occurs first
(red arrows), followed by spreading of the impulse through the left ventricle (blue
arrows) and then the right ventricle (green arrows).
9. Premature complexes (ectopic beats)
• Supraventricular ectopics
– Does not originate in sinoatrial node
– Originates either in left atrium or right atrium,
then transmits to AV node and down to
ventricles – QRST is normal
• Ventricular ectopics
– Originate in left or right ventricle and spread to
ventricles – QRST is broad
10. Atrial ectopic beats. The first, second and fifth
complexes are normal sinus beats. The third, fourth and sixth
complexes are atrial ectopic beats with identical QRS
complexes and abnormal (sometimes barely visible) P waves.
15. Atrial fibrillation
• Common arrhythmia
• Seen in conditions with atrial dilatation
• Worsens heart failure
• Predisposes to thromboembolism
• Indication for anticoagulation
• P wave absent, varying R-R intervals and QRS
voltage
19. Two examples of atrial fibrillation. The QRS complexes are
irregular and there are no P waves. There is usually a fast
ventricular rate, often between 120 and 160/min, at the
onset of atrial fibrillation. In chronic atrial fibrillation the
ventricular rate may be much slower due to the effects of
medication and AV nodal fatigue.
20. Atrial flutter. Simultaneous recording showing
atrial flutter with 3:1 atrioventricular block;
flutter waves are only visible in leads II and III.
21. Paroxysmal SVT
• Reentry in vast majority of cases
• AV nodal reentrant tachycardia (AVNRT) and
atrioventricular reentrant tachycardia (AVRT)
• Regular, narrow QRS complexes (120-250/min).
Initiated by atrial ectopic beat
• Carotid sinus massage may terminate an episode
• Adenosine IV, radiofrequency ablation
• Multifocal atrial tachycardia (MAT)
23. Mechanism of re-entry. Re-entry can occur when there are two alternative pathways with
different conducting properties (e.g. the AV node and an accessory pathway, or an area of
normal tissue and an area of ischaemic tissue). In this example, pathway A conducts slowly
and recovers quickly while pathway B conducts rapidly and recovers slowly. (1) In sinus
rhythm each impulse passes down both pathways before entering a common distal
pathway. (2) As the pathways recover at different rates a premature impulse may find
pathway A open and B closed. (3) Pathway B may recover while the premature impulse
travels selectively down pathway A. The impulse may then travel retrogradely up pathway
B, setting up a closed loop or re-entry circuit. (4) This may initiate a tachycardia that will
continue until the circuit is interrupted by a change in conduction rates or electrical
depolarisation.
24. Wolff-Parkinson-White (WPW)
syndrome
• AV bypass tract present, leading to recurrent
arrhythmias
• Preexcitation – delta waves, short PR interval
with broad QRS on ECG during sinus rhythm
• Risk of SVT, VF, VT
• Radiofrequency ablation of abnormal tracts
25. Wolff-Parkinson-White syndrome. In this condition there is a strip of accessory conducting tissue that allows
electricity to bypass the AV node and spread from the atria to the ventricles rapidly and without delay. When the
ventricles are depolarised through the AV node (1) the ECG is normal, but when the ventricles are depolarised
through the accessory conducting tissue (2) the ECG shows a very short PR interval and a broad QRS complex. Sinus
rhythm. In sinus rhythm the ventricles are partly depolarised through the AV node, and partly through the accessory
pathway, producing an ECG with a short PR interval and broadened QRS complexes; the characteristic slurring of the
upstroke of the QRS complex is known as a delta wave. The degree of pre-excitation (the proportion of electricity
passing down the accessory pathway) and therefore the ECG appearances may vary a lot, and at times the ECG can
look normal. Orthodromic tachycardia. This is the most common form of tachycardia in WPW. The re-entry circuit
passes antegradely through the AV node and retrogradely through the accessory pathway. The ventricles are
therefore depolarised in the normal way, producing a narrow-complex tachycardia that is indistinguishable from
other forms of SVT. Antidromic tachycardia. Occasionally, the re-entry circuit passes antegradely through the
accessory pathway and retrogradely through the AV node. The ventricles are then depolarised through the accessory
pathway, producing a broad-complex tachycardia. Atrial fibrillation. In this rhythm the ventricles are largely
depolarised through the accessory pathway, producing an irregular broad-complex tachycardia which is often more
rapid than the example shown.
28. Ablative therapy for arrhythmias
• Non-surgical approach to map the abnormal
tract and destroy it using radiofrequency
energy
• Usually used in WPW syndrome with SVT
29. Ventricular ectopic beats. There are broad bizarre
QRS complexes (arrows) with no preceding P wave in
between normal sinus beats. Their configuration
varies, so these are multifocal ectopics.
30. Ventricular tachycardia
• Structural heart disease, MI, cardiomyopathy,
long QT
• Most episodes of VF begins with VT
• Wide-complex QRS, regular
• Paroxysmal VT is usually initiated by a VPC
• Cardioversion, ICD implantation, RFA
32. Ventricular tachycardia: fusion beat (arrow). In ventricular
tachycardia there is independent atrial and ventricular
activity. Occasionally a P wave is conducted to the ventricles
through the AV node. This may produce a normal sinus beat
in the middle of the tachycardia (a capture beat); however,
more commonly the conducted impulse fuses with an
impulse from the tachycardia (a fusion beat). This
phenomenon can only occur when there is AV dissociation
and is therefore diagnostic of ventricular tachycardia.
33. Torsades de pointes
• VT with polymorphic QRS
• Associated with QT prolongation
• Hypokalaemia, hypomagnesaemia
• Quinidine, phenothiazines, tricyclics, III
degree AV block, congenital
34. Torsades de pointes. A bradycardia with a long QT
interval is followed by polymorphic ventricular
tachycardia that is triggered by an R on T ectopic.
36. Ventricular fibrillation
• Most common after acute MI
• Side effect of antiarrhythmia drugs
• Long QT and Tdp
• WPW syndrome with AF
• Electric shock
• Treat with
– DC defibrillation
– Implanted cardioverter/defibrillator
37. Ventricular fibrillation. A bizarre chaotic rhythm initiated in this case by
two ectopic beats in rapid succession.
39. Heart blocks (AV blocks)
• Escape rhythm – when SA node does not fire
• His bundle has a rate of 40-60/min
• His-Purkinje system rate 25-45/min, wide QRS
and unstable
• First-degree AV block – PR >0.20 s
• Second-degree – Mobitz type I (Wenckebach
phenomenon) in inferior MI, digoxin, -blockers
• Mobitz type II – His-Purkinje system disease
44. Second-degree atrioventricular block (Mobitz type I-
Wenckebach's phenomenon). The PR interval progressively
increases until a P wave is not conducted. The cycle then
repeats itself. In this example, conduction is at a ratio of 4:3,
leading to groupings of three ventricular complexes in a row.
45. Second-degree atrioventricular block (Mobitz type II). The PR interval of
conducted beats is normal but some P waves are not conducted. The
constant PR interval distinguishes this from Wenckebach's phenomenon.
46. Complete heart block
• III degree AV block – congenital in AVN, lower
blocks require pacing
• AV dissociation
• Atropine and isoprenaline IV
• Cardiac pacemaker: temporary and
permanent
48. Complete (third-degree) atrioventricular block. There
is complete dissociation of atrial and ventricular
complexes. The atrial rate is 80/min and the
ventricular rate is 38/min.
49. Right bundle branch block. Note the wide QRS
complexes with 'M'-shaped configuration in leads V1
and V2 and a wide S wave in lead I.
50. Left bundle branch block. Note the wide QRS
complexes with the loss of the Q wave or
septal vector in lead I and 'M'-shaped QRS
complexes in V5 and V6.