A new type of atypical atrial flutter was diagnosed in a patient with previous multiple ineffective surgeries. A patient with impaired pumping function of the heart and a history of repeated ablations of atrial fibrillation and atrial flutter was admitted for treatment of another heart rhythm disturbance – she was diagnosed with ventricular tachycardia. However, the specialists of the Research and Clinical Department of Arrhythmology of Almazov Centre determined that the recurrent atrial flutter with wide QRS complexes due to the left bundle branch block mimics ventricular tachycardia, and the treatment should be completely different.
Electrocardiogram during wide QRS tachycardia. Blue arrows indicate visible F waves of atypical atrial flutter, red arrows indicate QRS cycles with a gradual increase in RR intervals, followed by the loss of the next complex and transient restoration of conduction along the left bundle branch (narrow QRS). Then the atrioventricular conduction 1:1 is restored and the conduction along the left leg of the His bundle is blocked again.
Electrophysiological study identified a very unusual mechanism of tachycardia – reentry (reentrant excitation) with the involvement of the Bachmann’s bundle (a muscular structure connecting the right and left atrial appendages) and of both atria.
“This is a variant of biatrial reentrant tachycardia, which is very difficult to correctly determine, since the Bachmann’s bundle is located outside the heart, outside its cavities, and is not available for traditional mapping,” explains Deputy Director for Research of the Institute of Heart and Vessels Dr. Evgeny Mikhailov. “Our research team first described the mechanisms of biatrial tachycardia involving the Bachmann’s bundle back in 2014 [1], and also proposed approaches to effective catheter ablation of such tachycardia. Since then, the diagnosis and treatment of biatrial reentry have been cited many times, and their imaging has been improved.
Today, we managed to identify another type of biatrial reentrant tachycardia, which has not previously been described anywhere. The peculiarity lies in the fact that the cycle of electrical excitation takes place «in two layers» on the atrial anterior surface. From left to right along the Bachmann’s bundle (upper reentry loop), and from right to left along the short interatrial muscular connections in the upper part of the interatrial septum (lower reentry loop). The upper part of the tachycardia loop drops out of the mapping field and its involvement can be suggested only by indirect signs. In most cases, this can lead to confusion and misinterpretation of the mapping results. The diagnosis of such an arrhythmia mechanism is extremely difficult, but the treatment is surprisingly simple – one application of radiofrequency current on a small area of the left atrial anterior wall is enough. We believe that such tachycardia may be much more common than it seems, especially in patients with previous open heart surgery and procedures for extended catheter ablation of the atrial fibrillation substrate. The larger the area of the altered atrial muscle layer, the higher the likelihood of Bachmann's bundle involvement in tachycardia. Thanks to the well-coordinated work of specialists from the Research and Clinical Department of Arrhythmology and Neuromodulation Research Laboratory, doctors from Department of Cardiology No. 7, intensivists from Intensive Care Department No. 6, we were able to quickly understand the case and help the patient.”
It should be noted that the substrate for this type of tachycardia was described by specialist of Almazov Centre – Head of Pathology Unit Lyubov Mitrofanova in the early 2000s (Fig. A, B). Variants of muscular connections of the right and left atria were demonstrated and a theoretical assumption was made that the identified muscular bundles may be involved in some types of tachyarrhythmia; but there has been no direct evidence of their involvement in reentry cycles so far [2, 3].
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| А | В |
| A — Atrial specimen with removed endocardium. Blue arrows indicate muscular bundles connecting the myocardium of the right and left atria. In the current clinical case, these muscular bundles are involved in the reentry tachycardia cycle (conduction from the right atrium to the left atrial anterior wall). B — Bachmann's bundle (indicated by blue arrows) on the outer surface of the atria |
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Head of Arrhythmology Research Department Prof. Dmitry Lebedev further explains:
“Modern tachyarrhythmia mapping technologies allow diagnosing the most complex cardiac arrhythmias. Today we can see the nature of the conduction of electrical signals in each structure of the heart, accurately localize the critical zone of tachycardia. The 3D arrhythmia mapping systems we use are extremely advanced technologies, previously unimaginable to the most daring doctor. However, even in the 21st century, there remains room for discovering new mechanisms of arrhythmias, when only fundamental knowledge, experience and a desire to help the most difficult patients allow a medical team to succeed.”
[1] Mikhaylov EN, Mitrofanova LB, Vander MA, Tatarskiy RB, Kamenev AV, Abramov ML, Szili-Torok T, Lebedev DS. Biatrial tachycardia following linear anterior wall ablation for the perimitral reentry: incidence and electrophysiological evaluations. J Cardiovasc Electrophysiol. 2015 Jan;26 (1):28-35. doi: 10.1111/jce.12543.
[2] Mitrofanova LB, Gorshkov AN, Lebedev DS, Mikhaylov EN. Evidence of specialized tissue in human interatrial septum: histological, immunohistochemical and ultrastructural findings. PLoS ONE. 2014;9 (11):1-11.
[3] Platonov PG, Mitrofanova L, Ivanov V, Ho SY. Substrates for intra-atrial and interatrial conduction in the atrial septum: anatomical study on 84 human hearts. Heart Rhythm. 2008 Aug;5 (8):1189-95. doi: 10.1016/j.hrthm.2008.04.025.