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The value of the ECG in the diagnosis of supraventricular tachycardias

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European Heart Journal (1996) 17 (Supplement Q, 10-20
The value of the ECG in the diagnosis of supraventricular tachycardias
H. J. J. Wellens
Academic Hospital, Maastricht, The Netherlands
By combining the 12 lead ECG with information from (Eur Heart J 1996; 17 (Suppl C): 10-20) intracardiac activation studies, it has become possible to correctly diagnose the type of supraventricular tachycardia Key Words: Supraventricular tachycardia, electrocardio- on the 12 lead ECG. In this article the typical ECG features gram. allowing that diagnosis are discussed and illustrated.
Introduction ablation of the tachycardia substrate, or interruption of the tachycardia pathway and a better understanding
Information from programmed electrical stimulation o f h o w a n d w h e r e a n t i a r r h y t h m i c drugs exert their of the heart combined with excitation mapping has ^e&aal effects. Last but not least, in the past two led to a much better understanding of the site of the d e c a d e s w e h a v e ^ m a j o r a d v a n c e s i n o u r a b i I i t y
ongin and the mechanism of supraventncular tachy- t 0 comctiy i n t e r p r e t the 12-lead electrocardiogram cardias1 -*. It has also resulted in the development of ( E C G ) o f s u p r a v e n t r i c u i a r tachycardias™. This has new treatment modalities, such as surgical or electncal m a d e t h e E C G a r e H a b l e a n d inexpensive tool with
which to diagnose the site of origin and frequently the Correspondence: Dr H. J. J. Weliens, Academic Hospital mechanism of a supraventricular arrhythmia, thus Maastricht, Department of Cardiology, PO Box 5800, 6202 AZ providing the first Step in guiding our therapeutic Maastricht, The Netherlands. approach.
Table 1 Classification of supraventricular tachycardia according to their site of origin and mechanism
Re-entry DAD AbnAuto
Common form (slow-fast) + Uncommon form (fast-slow) +
AV junctional accelerated rhythm Digitalis induced ? Post cardiac surgery + Infectious + Ischaemic +
AV junctional circus movement tachycardia Paroxysmal
V-A conduction over a rapidly conducting AP +
Non-paroxysmal V-A conduction over a
slowly conducting AP +
D ow
The ECG in supraventricular tachycardias 11
JwA/JW Figure 1 Schematic drawing of the three mechanisms of atrial tachycardia. As indicated, atrial tachycardia in- cludes sinus node re-entrant tachycardia which is based upon re-entry between the sinus node and adjacent atrial tissue (1). Atrial tachycardia can be caused by abnormal automaticity (usually leading to incessant tachycardia) reentry (2) and triggered activity (both resulting in paroxysmal tachycardia (3).
Classification of a supraventricular tachycardias
Arrhythmias can be classified according to their site of origin, their mechanism and their electrocardiographic features. Table 1 lists the different types of supraven- tricular tachycardias according to site of origin and mechanism. Since emphasis in this article will be on the electrocardiographic features, the investigation of the tachycardia mechanism will not be discussed in detail.
Atrial tachycardia
Typically, during atrial tachycardia the P wave precedes the QRS complex on the ECG (Fig. 1). The polarity of the P wave, the P-R interval and the ratio between P waves and QRS complexes depend on the site of origin in the atrium, the rate of abnormal impulse formation, and atrioventricular (AV) nodal transmission character- istics. As indicated in Table 1, there are different forms of atrial tachycardia. The paroxysmal form is the most common type, characterized by sudden onset and ces- sation of the arrhythmia151. An example is shown in Fig. 2. The behaviour of this arrhythmia during programmed electrical stimulation of the heart and its response to different antiarrhythmic drugs suggests that paroxysmal atrial tachycardia is either based upon re-entry (80% of cases) or on triggered activity (20%). Triggered activity is an arrythmogenic mechanism resulting from delayed after depolarization161.
A relatively rare but serious arrhythmia is incessant (or permanent) atrial tachycardia (Fig. 3). In patients suffering from this rhythm disturbance, the arrhythmia is present for more than 50% of the day. As pointed out elsewhere'51, the rate of atrial impulse formation, which is probably caused by ab- normal automaticity, frequently increases during exer- cise. The persistent nature of the tachycardia and the inability to control the ventricular rate by failing to prevent the rate increase of the arrhythmia and 1 to 1 AV conduction, may result in dilated (tachycardia induced) cardiomyopathy171. Recognition that the arrhythmia is the cause rather than the consequence of the cardiomyopathy is important. Destruction or isolation of the atrial area that led to abnormal impulse formation should cure the arrhythmia and improve pump function.
"ilL 800 L. ms - .
Figure 2 Example of a paroxysmal atrial tachycardia. Note the onset of the arrhythmia after three conducted sinus beats with a P wave that precedes the QRS complex but has a different configuration from the sinus P waves.
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12 H. J. J. Wellens
L "*-
; ; t ; i : 4 i I • | ' - i f - ^ - - ••• i I • ' i i - i < ; : < i - i — - — — —
- w. rv. ^« ~w T ^w» ^-r ^r- ^ r ^ ^ ^™v * fi ^ ^ 1 s t 79326
5 Example of an incessant atrial tachycardia. This patient, initially showing 2:1 and later 1:1 AV conduction, has been continuously in tachycardia for 12 years and presented with a picture of a dilated cardiomyopathy.
400 ms
Figure 4 Carotid sinus massage reveals that atrial flutter is the underlying rhythm at the atrial level.
Atrial flutter
Observations both in the tissue bath and in patients[6~l2]
suggest that re-entry is the basis for atrial flutter. The classical sawtooth pattern of atrial activity is the ECG hallmark of the arrhythmia. Carotid sinus massage-induced AV block facilitates recognition of the arrhythmia (Fig. 4).
Atrial fibrillation Typically, the ECG shows rapid, irregular atrial activity, with, in the case of normal atrioventricular conduction a rapid, irregular rhythm.
Experimental work in animals and mapping studies during surgery suggest that multiple re-entrant wavelets are the basis for atrial fibrillation'13'141.
It is important to be aware of two types of paroxysmal atrial fibrillation that can occur in patients
without apparent heart disease. Coumel et al.ll5], have indicated the so-called vagally induced and the catecholamine-sensitive types. Characteristically, the former arrhythmia is found in middle-aged men and begins at night, during rest, or after a meal. Catecholamine-sensitive atrial fibrillation is less com- monly encountered in clinical practice. The arrhythmia is most often observed in young women. It is related to stress and exercise, and can be provoked by caffeine and alcohol. Holter recordings show the occurrence of the arrhythmia in the daytime, usually in the morning, and preceded by an increase in sinus rate.
Atrioventricular nodal tachycardia
Programmed stimulation of the heart resulting in repro- ducible initiation and termination of paroxysmal AV
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The ECG in supraventricular tachycardias 13
Figure 5 Schematic drawing of the mechanism of the common form of AV nodal reentrant tachycardia. Antero- grade conduction in the reentry circuit goes over a slow pathway, retrograde conduction over a fast pathway. The fast pathway may lie within the AV node (left panel) or may be partly outside the AV node (right panel).
Ill
Figure 7 The three types of supraventricular tachy- cardia resulting in a negative P wave in front of the QRS complex in lead II of the electrocardiogram. Statistically the most probable occurrence is a circus movement tachycardia with atrioventricular conduction over the atrioventricular node and ventriculo-atrial con- duction over a slowly conducting accessory pathway (1). The other two possibilities are an atrioventricular nodal tachycardia of the unusual (fast-slow) form (2) or a low atrial tachycardia in the vicinity of the AV node (3).
TrffTTTTT
800 ms
Figure 6 Example of the common form of AV nodal tachycardia. Note the pseudo S wave in leads II and III and the pseudo incomplete right bundle branch block pattern in lead V,, caused by the P wave during tachy- cardia.
JJL Figure 8 Schematic representation of a circus movement tachycardia using a 'concealed' fast-conducting (left panel) or slow-conducting (right panel) accessory AV pathway. The corresponding ECGs during tachycardia with their characteristic R-P/P-R ratio are shown in Fig. 9.
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14 H. J. J. Wellens
Figure 9 Two types of circus movement tachycardia. Cir- cus movement tachycardia due to a rapid (A) and slow (B) conducting accessory pathway (AP). The rapidly conduct- ing AP (A) is associated with a short R-P, the slow conduct- ing AP (B) with a long R-P. In (A) and (B), the P waves are relatively narrow, inverted in the inferior leads, and isoelec- tric in lead I, suggesting a septal or paraseptal location.
nodal tachycardia suggests that re-entry is the under- lying mechanism. This is supported by finding 'dual' AV nodal conduction in many patients'151. The common
type of paroxysmal AV nodal tachycardia typically shows simultaneous activation of the atrium and the ventricle during the arrhythmia'171. Anterograde conduc- tion in the AV node during tachycardia is considered to occur over a slowly conducting pathway and retrograde conduction over a rapidly conducting pathway (Fig. 5). On the ECG during tachycardia, this results in the P wave being either completely hidden in the QRS com- plex or distorting the terminal portion of the QRS complex151. This pattern is graphically represented in Fig. 5, and an ECG of the arrhythmia is shown in Fig. 6. The common type of AV nodal tachycardia occurs twice as often in women as men.
The uncommon type of paroxysmal AV nodal tachycardia is characterized by a P wave following the QRS complex, the mechanism being anterograde AV nodal conduction over a rapid pathway and retrograde conduction over a slow pathway. The R-P interval is long, and the P wave becomes located in front of the subsequent QRS complex. This is a rare, seldom sus- tained, arrhythmia, and has to be differentiated from a low atrial tachycardia or a circus movement tachycardia using a slowly conducting accessory pathway for ventriculo-atrial conduction (Fig. 7).
Circus movement tachycardia
An interesting subgroup of patients with supra- ventricular tachycardia are those with a so-called 'concealed' accessory pathway*20'2'1. These connections conduct the impulse in a ventriculoatrial direction only.
Table 2 Findings on carotid sinus massage in different types of tachycardia
Tachycardia
Circus movement tachycardia (using overt or concealed accessory pathway)
a. b. a. b. a. b. c. a. b. a. b. a. b.
Effect of carotid sinus massage
Gradual and temporary slowing in heart rate.
Cessation of tachycardia No effect Temporary slowing because of increase in AV block No effect Temporary slowing because of increase in AV block Transformation into atrial fibrillation No effect Temporary slowing because of increase in AV block No effect Cessation of tachycardia No effect Cessation of tachycardia No effect
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The ECG in supraventricular tachycardias 15
(A)
932080 400 ms
Figure 10 Example of electrical alternans of the QRS com- plex during a circus movement tachycardia using a 'concealed' accessory AV pathway. Note that QRS alternation is seen in many leads.
Figure 11 Presence of a slower heart rate during supraventricular tachycar- dia, in a case of right bundle branch block. As explained in Fig. 10, this indicates a circus movement tachycardia using an accessory atrioventricular pathway on the same side as the blocked bundle branch. In this example therefore, the accessory pathway is between the right atrium and the right ventricle.
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16 H. J. J. Wellens
They are often present in patients referred for evaluation of a supraventricular tachycardia. Two groups of patients have concealed accessory pathways (Figs 8 and 9), and the smaller group is formed by those with a slowly conducting accessory pathway. In the latter type, atrial activation typically follows the QRS complex with an R-P interval longer than the P-R interval. This type of supraventricular tachycardia must be differentiated from low atrial tachycardia and the uncommon type of AV nodal tachycardia (Fig. 7).
Circus movement tachycardia via an accessory atrioventricular pathway is twice as common in men as in women. Concealed accessory pathways are about half as common as overt anterogradely conducting accessory pathways (ventricular pre-excitation). Age at onset of first tachycardia attack in patients with accessory path- ways is a mean of 10 years younger than patients with AV nodal tachycardia'221.
Additional ECG findings
Carotid sinus massage
Carotid sinus massage-induced changes in the ECG during tachycardia can be helpful in differentiating between the different types of supraventricular tachy- cardia (Table 2).
Electrical alternans of the QRS complex
Alternating changes in the QRS complex during narrow QRS tachycardia are highly suggestive of a circus move- ment tachycardia using an accessory pathway for ven- triculoatrial conduction1231. It is important to stress that QRS alternations as a clue to circus movement tachy- cardia can only be used when present more than 5 s after the start of the tachycardia. Changes in QRS configur- ation are common at the start of a supraventricular tachycardia because the sudden acceleration in ventricu- lar rate leads to different degrees of changes in refrac- toriness and conduction velocity in the conduction system during the first beats of the tachycardia. In patients with circus movement tachycardia and a narrow QRS, the incidence of electrical alternans increases with increasing heart rates during tachycardia'231. An example of electrical alternans is given in Fig. 10.
ace. pathway
His bundle
vrrrcrrrn r280
Figure 12 Increase in the length of the reentry circuit when bundle branch block develops during circus move- ment tachycardia using an accessory pathway on the same side as the bundle branch block. In {A) there is a right-sided accessory pathway. In (B) the tachycardia circuit is confined to the AV node. When right bundle branch block (RBB) develops in the patient with a right-sided accessory pathway, the circuit becomes longer and the tachycardia rate slows (compare V, before and after right bundle branch block on the left). In contrast (shown in (B)), nothing happens with the tachycardia rate when bundle branch block develops during AV nodal re-entrant tachycardia (measurements are in ms).
presence of a circus movement tachycardia. This uses an accessory AV pathway for ventriculoatrial conduction, inserting into the free wall of the ventricle on the same side as the blocked bundle branch.
Slowing in heart rate during tachycardia when bundle branch block
develops
Figures 11 and 12 illustrate the importance of carefully measuring the rate of a tachycardia when bundle branch block develops and disappears during supraventricular tachycardia'2'1. As shown in Fig. 12, slowing in tachy- cardia rate during bundle branch block indicates the
Mode of initiation
Initiation of a supraventricular tachycardia by a single atrial premature beat during sinus rhythm after marked prolongation of the P-R interval suggests the presence of dual AV nodal pathways'161 and AV nodal reentrant tachycardia as the mechanism of the arrhythmia (Fig. 13). In contrast, initiation of a supraventricular tachycardia during sinus rhythm without prolongation of the P-R interval suggests a circus movement tachycardia using an
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The ECG in supraventricular tachycardias 17
400 ms
Figure 13 Clinical example of initiation of the common form of AV nodal tachycardia. After two sinus beats conducted to the ventricle, an atrial premature beat is conducted to the ventricle with marked P-R prolongation, indicating conduction over the slow AV nodal pathway. This is followed by perpetuation of re-entry in the AV node and AV nodal tachycardia. Six precordial leads were recorded simultaneously.
II
Figure 14 Initiation of a supraventricular tachycardia during sinus rhythm. Note that an acceleration in rate during sinus rhythm is followed by a tachycardia with a narrow QRS complex. The R-P interval exceeds the P-R interval during tachycardia with negative P waves in leads II, II, V s and V6. These findings indicate the presence of a circus movement tachycardia using a slowly conducting accessory pathway for ventriculo-atrial conduction.
accessory AV pathway for ventriculoatrial conduction Mode Of termination (Fig. 14). Initiation of a supraventricular tachycardia by a single ventricular premature beat argues in favour of a As explained in Fig. 16, it is extremely unlikely that an circus movement tachycardia, incorporating an accessory AV nodal tachycardia will be terminated by a single atrioventricular pathway (Fig. 15). ventricular premature beat, whereas this is common in a
Eur Heart J, Vol. 17, Suppl C 19%
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18 H. J. J. Wellens
AVnode AVnode
ace. pathway
VPB VPB
Figure 15 During sinus rhythm, a circus movement tachycardia using an accessory AV pathway can easily be initiated by a single ventricular prema- ture beat (VPB) because the VPB finds the distal conduction system refrac- tory and is retrogradely conducted to the atrium over the accessory pathway. In contrast, because of refractoriness of the distal conduction system, a VPB cannot gain access to tbe AV node to initiate AV nodal reentry.
(B)
ace. pathway
VPB VPB
Figure 16 Different ways for a ventricular premature beat (VPB) to gain access to the tachycardia circuit (and to terminate tachycardia) in AV nodal tachycardia and in circus movement tachycardia using an accessory path- way for ventriculo-atrial conduction. As shown in panel (B), the VPB in AV nodal tachycardia will be blocked distal to the reentry circuit, whereas, as shown in panel (A), the VPB easily invades the reentry circuit during circus movement tachycardia.
circus movement tachycardia using an accessory AV pathway for ventriculo-atrial conduction.
The practical approach
When analysing the 12 lead ECG of a supra ventricular tachycardia a stepped approach is used (Fig. 17).
The steps include the relationship between atrial and ventricular events during supraventricular tachycardia; presence or absence of electrical alternans, and the location and configuration of the P wave. If that analysis does not allow a definite diagnosis, an electrophysiologi- cal study is indicated, especially when the tachycardia is symptomatic, leads to myocardial dysfunction or because of its frequent occurrence is annoying and socially incapacitating for the patient.
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The ECG in supraventricular tachycardias 19
(1) 2nd degree AV block? (spontaneous or after CSM) I 1
No Yes
Atrial rate
>250.min I
Atr flutter
(2) QRS alternation?
(4a) P axis (frontal plane)
Inferior-Superior
Other ,—-' ——
(4b) P axis (horizontal plane)
Right -•Left Left Right
Atrial T CMT with slow AP Atrial T
Figure 17 Four steps to be taken when analysing the 12-lead ECG of a regular supraventricular tachycardia. As shown, information should be obtained on the relationship between atrial and ventricular events during supraventricular tachycardia (spontaneously and after carotid sinus massage (CSM)) followed by a search for electrical alternans of the QRS complex. Thereafter the location of the P wave in relation to the QRS complex and the polarity of the P wave in the frontal and horizontal plane should be studied. Atr=atrial; T=tachycardia; AVN=atrioventricular nodal; CMT=circus movement tachycardia; AP=accessory pathway.
References
[1] Wellens HJJ. Electrical stimulation of the heart in the study and treatment of tachycardias. Baltimore: University Park Press, 1971.
[2] Josephson ME, Wellens HJJ. Differential diagnosis of supra- ventricular tachycardia. In: Scheinman MM, ed. Cardiology Clinics. Philadelphia: W. B. Saunders, 1990: 411-42.
[3] Zipes DP. Cardiac electrophysiology. Promises and contri- butions. J…