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Tachyarrhythmias Associated with Preexcitation

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Abstract

Preexcitation can be associated with a variety of tachyarrhythmias. In some cases, accessory path is necessary for the initiation and maintenance of the tachyarrhythmia. In other cases, accessory path allows rapid conduction of a supraventricular tachyarrhythmia to the ventricles. Careful analysis of the electrocardiogram recorded during tachyarrhythmia can give reasonable impression about the presence and location of the accessory path. This is important because preexcitation may not be obvious in electrocardiogram recorded in the absence of tachyarrhythmia (concealed preexcitation). Correct diagnosis is important because catheter ablation of the accessory path can cure the problem. This chapter deals with electrocardiographic differentiation of various tachyarrhythmias that can occur in the presence of an accessory path. Summary and MCQs at the end of the chapter help in quick revision and self-assessment.

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References

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Author information

Authors and Affiliations

  1. Ex Senior professor and head of the department of cardiology, Jawaharlal Nehru Medical College, Ajmer, India

    Sitaram Mittal

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  1. Sitaram Mittal
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Appendices

Summary

Patients with preexcitation can have the following:

  1. (A)

    Narrow QRS regular tachycardia (Fig. 9.18a–e)

    It can occur in the following situations:

    1. 1.

      Orthodromic atrioventricular reciprocating tachycardia (orthodromic AVRT) with retrograde conduction over the Kent bundle (Fig. 9.18a). Tachycardia rate around 250/min, electrical alternans, and a P′ wave coming clearly after completion of the QRS (in the ST segment) support this possibility.

    2. 2.

      Long RP′ tachycardia (Fig. 9.18b).

    3. 3.

      Atrioventricular nodal reentry tachycardia (AVNRT) (Fig. 9.18c).

    4. 4.

      Atrial flutter with regular 2:1 conduction over the atrioventricular node (Fig. 9.18d).

    5. 5.

      Supraventricular tachycardias in patients with a short PR interval but a normal QRS (no delta wave) in sinus rhythm (Fig. 9.18e).

      1. (a)

        Atrioventricular conduction over atrio-Hisian pathway. It is also called Lown-Ganong-Levine (LGL) syndrome.

      2. (b)

        Rapid conduction through the atrioventricular node.

  2. (B)

    Broad QRS regular tachycardia (Fig. 9.19)

    1. 1.

      Orthodromic AVRT with preexisting bundle branch block or aberrant ventricular conduction (Fig. 9.19a, b).

    2. 2.

      Antidromic AVRT involving a Kent bundle (Fig. 9.19c).

      1. (a)

        Left bundle branch block pattern suggests the presence of a right-sided bypass tract.

      2. (b)

        Right bundle branch block pattern suggests the presence of a left-sided bypass tract.

    3. 3.

      Antidromic AVRT involving atriofascicular bypass tract. It has left bundle branch block pattern (Fig. 9.19d).

    4. 4.

      Atrial flutter with 2:1 atrioventricular conduction with preexisting bundle branch block or aberrant ventricular conduction (Fig. 9.19e, f)

    5. 5.

      Atrial flutter with 2:1 conduction over an accessory pathway.

    6. 6.

      Ventricular tachycardia.

    Antidromic AVRT or atrial flutter with conduction over Kent bundle may mimic VT on the surface ECG.

  3. (C)

    Irregular tachycardia (Fig. 9.20)

    It can occur in the following situations:

    1. 1.

      Rate more than 200/min

      1. (a)

        Atrial fibrillation with antegrade conduction over an accessory path. QRS is broad due to the presence of the delta wave (Fig. 9.20a).

      2. (b)

        Atrial fibrillation with rapid conduction over the atrioventricular node. QRS is narrow unless there is aberrant ventricular conduction (Fig. 9.20b).

    2. 2.

      Rate less than 180/min. Atrial fibrillation with antegrade conduction over the atrioventricular node. QRS is usually narrow but can be broad if there is aberrant ventricular conduction or preexisting bundle branch block (Fig. 9.20c).

Fig. 9.18
4 illustrations of A P-A V N impulse routes and their respective waveforms. a and b. orthodromic and long R-P orthodromic A V R T, the impulse circulates between A P and A V N. Their waveforms have short peaks and long dips, respectively, between minimal variation intervals. c and d. In A V N R T, the impulse circulates within A V N and passes through it, and in atrial flutter, it passes directly through A V N. Their waveforms have a cascading trend and a minimal variation between short peaks, respectively.

Showing causes of narrow QRS tachycardias. In a case of preexcitation. AP accessory pathway, AVN atrioventricular node, HB His bundle

Full size image
Fig. 9.19
7 illustrations. a and b. orthodromic A V R T with aberrancy and pre-existing B B B. c and d. antidromic A V R T involving K B and A F A P. e and f. atrial flutter with aberrancy and pre-existing B B B. g. involves A V N, B B and V T.

Showing causes of broad QRS regular tachycardia in a case of preexcitation. KB Kent bundle, AVN atrioventricular node, BB bundle branch, AVRT atrioventricular reciprocating tachycardia

Full size image
Fig. 9.20
3 waveforms labeled V subscript 1 for 3 types of atrial fibrillation: conduction over the accessory pathway, aberrant ventricular conduction, and preexisting B B B. Their waveforms have a series of tall, uniform peaks, short peaks with highly fluctuating intervals, and tall peaks with minimally varying intervals, respectively.

Showing causes of broad QRS irregular tachycardia in the presence of preexcitation

Full size image

When ventricular rate is more than 200/min, it may be difficult to differentiate antegrade conduction over the accessory pathway from rapid conduction over the atrioventricular node with aberrant ventricular conduction. In such cases electric cardioversion is safe. If drugs are to be used, the atrioventricular node-blocking drugs (digoxin, diltiazem, verapamil, beta-blockers) should be used only in combination with drugs blocking the accessory pathway (e.g., amiodarone). Isolated use of the atrioventricular node-blocking drugs may increase antegrade conduction over the Kent bundle resulting in further increase in ventricular rate. In such a situation, some atrial impulse may reach the ventricle in vulnerable period and precipitate ventricular fibrillation.

MCQs

Q1. In patients with atrioventricular reentry tachycardia, ECG during sinus rhythm must show:

  1. (a)

    Short PR interval

  2. (b)

    Delta wave

  3. (c)

    Broad QRS

  4. (d)

    None of the above

Q2. A normal electrocardiogram in sinus rhythm excludes any possibility of occurrence of:

  1. (a)

    AVNRT

  2. (b)

    Antidromic AVRT

  3. (c)

    Orthodromic AVRT

  4. (d)

    None of the above

Q3. Concealed accessory pathway can produce:

  1. (a)

    Atrioventricular reentry tachycardia

  2. (b)

    Fast ventricular rate in atrial flutter

  3. (c)

    Fast ventricular rate in atrial fibrillation

  4. (d)

    All

Q4. In a case of regular narrow QRS tachycardia, atrioventricular reentry tachycardia can be suspected if there is:

  1. (a)

    ST segment depression only during tachycardia

  2. (b)

    P′ wave occurs clearly after the QRS complex

  3. (c)

    Retrograde P′ wave is negative in lead I

  4. (d)

    None of the above

Q5. During tachycardia, development of bundle branch block with reduction in the rate of tachycardia suggests:

  1. (a)

    AVNRT with preexisting bundle branch block

  2. (b)

    Atrial tachycardia with preexisting bundle branch block

  3. (c)

    AVRT with accessory pathway on the side of the bundle branch block

  4. (d)

    AVRT with accessory pathway in the ventricle on the side opposite to that of the bundle branch block

Q6. During tachycardia, which feature suggests retrograde conduction via a septal accessory pathway?

  1. (a)

    P′ wave occurring before the QRS

  2. (b)

    P′ waves occurring in the initial or the terminal portion of the QRS

  3. (c)

    Inverted P′ wave in leads II, III, and aVF following the QRS

  4. (d)

    Inverted P′ wave in lead I following the QRS

Q7. Regular narrow QRS tachycardia with an inverted P wave falling after the completion of the QRS complex suggests:

  1. (a)

    Atrial tachycardia

  2. (b)

    AVNRT

  3. (c)

    Antidromic atrioventricular reciprocating tachycardia

  4. (d)

    Orthodromic atrioventricular reciprocating tachycardia

Q8. Regular wide QRS tachycardia with an inverted P wave falling after the completion of the QRS complex suggests:

  1. (a)

    Atrial tachycardia with preexisting bundle branch block

  2. (b)

    Ventricular tachycardia

  3. (c)

    Antidromic atrioventricular reciprocating tachycardia

  4. (d)

    Orthodromic atrioventricular reciprocating tachycardia

Q9. Irregular wide QRS tachycardia at a rate of 250/min suggests:

  1. (a)

    Atrial fibrillation with aberrant conduction

  2. (b)

    Atrial fibrillation with preexisting bundle branch block

  3. (c)

    Atrial fibrillation with antegrade conduction over an accessory path

  4. (d)

    Atrial fibrillation with ventricular ectopics

Q10. Accessory pathway can precipitate:

  1. (a)

    Atrial flutter

  2. (b)

    Atrial fibrillation

  3. (c)

    AVNRT

  4. (d)

    Atrial tachycardia

Q11. A patient with preexcitation during sinus rhythm can have:

  1. (a)

    Sinus node reentry tachycardia

  2. (b)

    Atrial tachycardia

  3. (c)

    AVNRT

  4. (d)

    None

Answers

(1) d; (2) d; (3) a; (4) a, b, c; (5) c; (6) c; (7) c; (8) d; (9) c; (10) b; (11) a, b, c

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Mittal, S. (2023). Tachyarrhythmias Associated with Preexcitation. In: Insights into Electrocardiograms with MCQs. Springer, Singapore. https://doi.org/10.1007/978-981-99-0127-2_9

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  • DOI: https://doi.org/10.1007/978-981-99-0127-2_9

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  • Publisher Name: Springer, Singapore

  • Print ISBN: 978-981-99-0126-5

  • Online ISBN: 978-981-99-0127-2

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