a covert combination…

the case.

72 year old male presents to your Emergency Department with a 4-5 hour history of palpitations. He appears well and has no associated symptoms.

BP 146/88, SaO2 99% (RA), chest clear.


  • Atrial fibrillation
  • Automatic implantable cardioverter-defibrillator [AICD]
    • Sick sinus syndrome with inducible VT on electrophysiology study
  • Hypertension

Here is his initial 12-lead ECG… ECG#1

[DDET Describe & interpret his ECG…]

Standard rate & calibration.

  •  Rate:
    • 150 bpm.
  • Rhythm.
    • Regular without obvious P waves.
  • Axis.
    • Rightward axis [+129*].
  • Intervals.
    • PR ~ n/a.
    • QRS ~ 160 msec [RBBB morphology]
    • QTc ~ 580 msec.
  • Segments.
    • QRS:T wave discordance
  • Other.
    • Features suggesting VT.
      • Fusion beats seen below (red & blue circles)
      • Monomorphic R-wave in V1.


Broad complex tachycardia with RBBB appearance and features of AV dissociation, highly concerning for ventricular tachycardia.

DDx: Atrial flutter (2:1) + RBBB.

annotated rhythm strip


[DDET What would you do next ?]

My approach to any dysrhythmia, fast or slow, is to detect and correct;

  • Ischaemia
  • Electrolytes
  • Medications…

Meanwhile, the patient stays connected to a monitor with defibrillator pads placed for good measure. He is advised to stay nil by mouth, pending the need for sedation. You also arrange for his AICD to be interrogated.

We top up his magnesium and obtain this second ECG….

Broad complex tachycardia at a rate of 136 per minute. RAD. Underlined complex (#5) concerning for AV dissociation.
Broad complex tachycardia at a rate of 136 per minute. RAD. Underlined complex (#5) concerning for AV dissociation.


For more information on VT versus SVT with aberrancy see;

  1. Broad, fast & regular… – the blunt dissection
  2. VT versus SVT with aberrancy via LITFL.com


[DDET So you finally get his AICD interrogated….]

A-lead demonstrating fibrillation at a rate of 175-375 bpm. V-lead sensing independent ventricular tachycardia at a rate of 136/min.  There is no associated between the atrial & ventricular rhythms.
A-lead demonstrating fibrillation at a rate of 175-375 bpm. V-lead sensing independent ventricular tachycardia at a rate of 136/min. There is no association between the atrial & ventricular rhythms.


[DDET The diagnosis…?]

Double Tachycardia

ie. ventricular tachycardia with co-existing atrial fibrillation !!

Double tachycardia is a relatively uncommon type of tachycardia. It is classically defined as the simultaneous occurrence of organised atrial and ventricular tachycardias, or junctional and ventricular tachycardias.

Reported causes include;

  • Digitalis toxicity
  • Left ventricular dysfunction
  • Exercise
  • Catecholamine abuse

They can be difficult to diagnose and often require electrophysiology studies for further assessment. Interestingly, the presence of dual-lead ICDs now allow for this non-invasively.

Atrial Fibrillation with AICDs.

Atrial fibrillation is a very common dysrhythmia in patients requiring an AICD.

  • ~20% have AF at time of implantation
  • >50% of patients develop AF during the lifespan of their device.

In the setting of an AICD, AF can result in inappropriate ventricular shocks, ventricular arrhythmia induction & thromboembolism (after ventricular shocks in the presence of unknown AF).

Dual chamber rate-responsive pacing may prevent AF by improving haemodynamics, optimising ventricular filling and preventing retrograde atrial conduction. New overdrive pacing algorithms have been introduced to add incremental anti-arrhythmic benefits to physiological pacing. The aim is that consistent atrial pacing acts to suppress atrial fibrillation.

The PR Logic dual-chamber detection algorithm is widely used in dual-chamber Medtronic ICDs. It discriminates SVTs from ventricular tachycardias using hierarchal rules & timing of atrial and ventricular events.

Double Tachycardia Rules

[DDET Now, lets go back & have a closer look at that interrogation strip….]

annotated interrogation



[DDET The conclusion…]

Interestingly, his AICD was programmed to intervene on VT only at a rate exceeding 170 beats per minute. We attempt to overdrive the VT using his AICD…

Overdrive attempt

Unfortunately this was unsuccessful so an amiodarone bolus was administered and an infusion commenced.

Approximately 45 minutes into his infusion, our patient dropped his blood pressure into the 70’s with associated clamminess and distress. He received some ketamine sedation and was cardioverted to sinus rhythm.

He was discharged home two days later.


[DDET References]

  1. Washizuka, T., Niwano, S., Tsuchida, K., & Aizawa, Y. (1999). AV reentrant and idiopathic ventricular double tachycardias: complicated interactions between two tachycardias. Heart, 81(3), 318–320.
  2. Santini, M., & Ricci, R. (2001). Atrial fibrillation coexisting with ventricular tachycardia: a challenge for dual chamber defibrillators. Heart, 86(3), 253–254.
  3. Weng, K.-P., Chiou, C.-W., Kung, M.-H., Lin, C.-C., & Hsieh, K.-S. (2005). Radiofrequency catheter ablation of coexistent idiopathic left ventricular tachycardia and atrioventricular nodal reentrant tachycardia. Journal of the Chinese Medical Association : JCMA, 68(10), 479–483. doi:10.1016/S1726-4901(09)70078-4
  4. Chowdhry, I. H., Hariman, R. J., Gomes, J. A., & El-Sherif, N. (1983). Transient digitoxic double tachycardia. Chest, 83(4), 686–687.
  5. Brown, M. L., Christensen, J. L., & Gillberg, J. M. (2002). Improved discrimination of VT from SVT in dual-chamber ICDs by combined analysis of dual-chamber intervals and ventricular electrogram morphology, 117–120.
  6. Jason’s Blog: ECG Challenge of the Week for Feb. 24th – March 3rd – another example of a double tachycardia case !!


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