Case presentation
A 14-year-old boy was referred for persistent atrial tachycardia after tricuspid valve surgery for severe tricuspid valve regurgitation. He had congenital multivalvular heart disease and had undergone initial mitral valve replacement (Carbomedics 16 mm) at age 2 and mitral valve replacement (Hemodynamic Plus 21 mm) and aortic valve replacement (Regent 17 mm) at age 9. The previous two surgeries could be performed using only a septal superior approach. However, when he underwent mitral valve replacement (Regent 25 mm) and aortic valve replacement (Regent 21 mm) at the age of 14 years, he required a Manouguian line incision from the aorto-mitral curtain to the mitral ring in addition to a septal superior approach because of severe tissue adhesion and small left atrium. After this procedure, atrial tachycardia developed, but no antiarrhythmic surgery was performed, including the most recent tricuspid valve surgery with Contour 28 mm suture and patch augmentation performed 4 months later. His electrocardiogram showed a long RP’ narrow QRS regular tachycardia with a heart rate of 150 beats per min (Figure 1(a)). The supraventricular tachycardia had 1:1 atrioventricular conduction with 398 ms of tachycardia cycle length. The overdrive pacing from right ventricle during the tachycardia revealed atrioventricular dissociation, suggesting the diagnosis of supraventricular tachycardia was atrial tachycardia. The activation map created by OCTARAY® (Biosense Webster, Diamond Bar, California, USA) during the atrial tachycardia showed a pathway towards the atrial septum via cavo-tricuspid isthmus with an earliest site in the middle of the anterior wall of the right atrium (Figure 1(b)). However, local activation time was obtained for only 56% of the tachycardia cycle length. In the substrate map, all right atrium regions except the above were less than 0.1 mV (Figure 1(c)). The activation maps during sinus rhythm and the atrial tachycardia were almost the same. Therefore, the mechanism diagnosis of the atrial tachycardia was essential to perform ablation safely. For focal atrial tachycardia, the ablation for the earliest excitation site may cause sinus node injury, and for macroreentrant atrial tachycardia, the ablation for the pathway to atrioventricular node, including cavo-tricuspid isthmus, may cause isolation of sinus node. Hence, the atrial entrainment pacing was performed from the three sites, such as the earliest site near sinus node, cavo-tricuspid isthmus, and coronary sinus orifice with pacing cycle lengths of 380, 360, and 340 ms for the mechanism diagnosis of the atrial tachycardia (Figure 2). Constant fusion could not be demonstrated because the position of the reference catheter placed at the anterior wall of the right atrium in relation to the pacing sites did not allow for a clear change in atrial sequence by entrainment pacing from the earliest site and cavo-tricuspid isthmus. However, the entrainment pacing from coronary sinus ostium showed constant fusion at 380 ms, progressive fusion, and the termination of the atrial tachycardia at 340 ms. The post pacing interval indicated that all three sites were in tachycardia circuit, suggesting the mechanism of the atrial tachycardia was macroreentry, including the pathway in the order of the anterior wall of right atrium, cavo-tricuspid isthmus, coronary sinus ostium, and the latest site (light blue in Figure 2(a)). There is an invisible circuit for 210 [74-(-136)] ms from the latest site to the earliest site in the activation map that could be created. The invisible circuit was expected to be the circuit that would turn around the left atrium or epicardial side of the right atrium at this latest site as a breakthrough point and return to the earliest site on the current activation map. A region with a slight potential was identified at the anterior wall of the high right atrium (red dot in Figure 2(a)). Although the entrainment pacing was not possible from this site, the atrial tachycardia was terminated with prolonged tachycardia cycle length by application of radiofrequency energy (30W) for this site using a 4 mm-tip catheter (Thermocool smarttouch®, Biosense Webster, Diamond Bar, California, USA). After linear ablation from the site to superior caval vein, the atrial tachycardia was no longer inducible.
The 12-lead electrograms of the supraventricular tachycardia. ( a ) The tachycardia was a long RP’ narrow QRS regular tachycardia with a heart rate of 150 beats per min. The activation map ( b ) of the right atrium during the atrial tachycardia obtained from the anterior view and left lateral view. Only 56% (222/398 ms) were recorded because of surrounding impaired right atrial wall as shown in Figure 1(c). The voltage map ( c ) obtained from the anterior view and left lateral view showed that the myocardium was impaired less than 0.1 mV except for the pathway from the anterior wall to the atrioventricular node. AP = anterior view; LL = left lateral view; orange dot: the site His potential captured.
( a ) The activation map of atrial tachycardia showed three entrainment pacing site (yellow dot) and the reference catheter site. red dot: success site of ablation. ( b ) Surface and intracardiac electrocardiograms during atrial entrainment pacing with 380 ms pacing cycle length from the coronary sinus for the atrial tachycardia. ( c ) The atrial sequences of reference catheter during atrial tachycardia and atrial entrainment pacing from coronary sinus with pacing cycle length of 380 ms, 360 ms, and 340 ms. The entrainment pacing with pacing cycle length of 380 ms showed a steady state of atrial sequences with a mixture of antidromic and orthodromic capture, which indicated the constant fusion. The entrainment pacing with pacing cycle length of 340 ms showed the progressive fusion and tachycardia termination. PPI indicated that all three sites were the on the circuit of the tachycardia. ( d–g ) Illustration of entrainment pacing methos. In the case of a focal AT ( d ): Since entrainment pacing does not entrain the circuit, the sequence of the reference catheter does not change. ( e ) Assumed macroreentrant circuit. ( f ) When entrainment pacing was performed from the coronary sinus ostium at a pacing cycle length of 380 ms and 360 ms during the atrial tachycardia, 1–3 electrodes of the reference catheter were orthodromic captured, 4 and 5 electrodes were antidromic captured, and a steady state was achieved (constant fusion). ( g ) When the pacing cycle length was shortened to 340 ms, 1 and 2 electrodes of the reference catheter were captured in orthodromic, 3–5 electrodes were captured in antidromic (progressive fusion), and the tachycardia was terminated. The electrophysiological findings in Figure. 2(f) and 2(g) proved that the atrial tachycardia mechanism was macroreentry. ABL = ablation catheter placed at the entrainment pacing site; AP = anterior view; AT = atrial tachycardia; CS = coronary sinus; PCL = pacing cycle length; RVA = right ventricular apex; STIM = stimulation; anti: antidromic capture; d: distal; orange dot: atrioventricular node; ortho: orthodromic capture; p: proximal; ref: reference catheter.
Discussion
The invisible circuit from the atrioventricular node to the earliest site was unknown, but it was expected to traverse the left atrium or right atrial epicardium. Transseptal left atrial mapping was not performed in this case because the left atrial pressure was known to be highly elevated due to impaired left ventricular diastolic function by prior haemodynamic catheterisation. Considering that the atrial tachycardia was terminated at the location of the Bachman bundle, i.e., at the breakthrough point for the left atrium, suggesting the atrial tachycardia was likely the bi-atrial tachycardia. The formation of the complex bi-atrial circuit in this case was probably caused by the presence of a large incision line extending from the right atrium to the left atrial roof and aorto-mitral curtain during repeated previous surgeries, as well as the presence of a non-compliant left atrium.
Although the usefulness of the entrainment pacing for ventricular tachycardia had been reported, Reference Deo and Berger1 there are no reports of atrial tachycardia circuit estimation by demonstration of orthodromic and antidromic capture by reference catheter. Reports of atrial entrainment pacing method are limited to the classical atrial flutter diagnosis and differential diagnosis of supraventricular tachycardia via atrioventricular node. Reference Park, Ha and Kim2 Interpretation of entrainment pacing results is often confusing because the positional relationship between the atrial tachycardia circuit, the pacing site, and the reference catheter site determines the direction of potentials captured by the reference catheter, which is the most important factor. Reference Triedman, Alexander and Berul3 If a part of the atrial tachycardia circuit is known, as in this case, the placement of the reference catheter at that known pathway makes the interpretation of the entrainment pacing results easier and to be the effective electrophysiological testing. It is necessary to accumulate the electrophysiological findings of increasingly complex tachyarrhythmia of CHD.
Acknowledgements
None.
Financial support
This research received no specific grants from any funding agency or from commercial or not-for-profit sectors.
Competing interests
None.
Ethical standard
The authors assert that all procedures contributing to this study comply with the ethical standards of relevant guidelines on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008. Our Institutional Review Board has confirmed that no ethical approval is required because this is a case report.
