Case study: AT ablation in a patient with complex congenital heart disease
Ms Holly Daw, Chief Cardiac Physiologist, Barts Heart Centre, London.
With improvements to treatment and corrective surgery over the years the number of adults living with congenital heart disease now outnumbers the amount of children living with these heart defects. Arrhythmias are a common issue for these patients and depending on the specific nature of the congenital abnormality and repair may range from relatively benign to life threatening. When cardiac morphology is particularly abnormal even atrial arrhythmias can quickly lead to extremely symptomatic or even life threatening episodes. As such the treatment of arrhythmias in the Congenital Heart Disease population has seen a dramatic increase in recent years and is expected to continue to do so for some time to come. These patients provide many additional challenges when performing ablation procedures in comparison to the normal heart population.
Ms KC is a 38 year old female with complex congenital heart disease under regular follow-up with the GUCH (Grown-Ups with Congenital Heart disease) team at Barts Heart Centre and had remained relatively stable and well over a number of years. Palpitations had been reported since 2011 and hence she was referred to the specialist GUCH arrhythmia team. The palpitations were at this point short lived and largely un-troublesome and so it was decided after much discussion not to proceed to ablation at this time. However by December 2015 two more severe episodes had occurred, both requiring eventual DCCV and the patient was now keen to proceed to catheter ablation. Medical history included:
1. Tricuspid atresia
2. Large ASD (almost common atria)
3. Large unrestrictive VSD
4. Transposition of the great arteries
5. Pulmonary hypertension and cyanosis
6. Mitral valve regurgitation
7. Mitral valve annuloplasty and pulmonary artery banding – 1986
In addition to:
1. Severe kyphoscoliosis – 3 surgeries
2. Recurrent severe iron depletion anaemia
3. Recurrent chest infections
Two ECGs were available documenting what appeared to be two distinct tachyarrhythmias. Both showed a LBBB morphology with left axis deviation with a somewhat irregular ventricular rate at 150 – 170 bpm, however one ECG appeared to have a ‘sawtooth’ like appearance to the baseline often described as a ‘typical’ re-entry-like pattern. This occurs because in a re-entry arrhythmia a part of the atrium is always undergoing depolarisation as the wavefront travels around the tachycardia circuit. There is therefore no isoelectric line between atrial activations and the ‘flutter waves’ show distinct positive and negative deflections as the electrical activity propagates towards then away from the point of reference (e.g. Lead II). In contrast in the other ECG it was much more difficult to visualise distinct P waves or organised atrial activity although the overall impression was not of atrial fibrillation with probable small negative atrial deflections seen in inferior leads.
ECG 1: Showing showing ‘sawtooth’ like baseline commonly associated with re-entry arrhythmias.
ECG 2: Showing irregular ventricular response and indistinct P waves.
In preparation for the ablation procedure a CT scan was requested with the aim of clarifying cardiac anatomy and associated structures and to assist in navigation of catheters in the heart. The CT scan was then imported into the Biosense Webster Carto electroanatomical mapping system and the various cardiac structures segmented. Figures 1 – 3 show the CT scan after segmentation, the atrial, ventricles, and great vessels were all identified. The IVC was not easily discernible on the CT which it eventually emerged was due to an unusual folded appearance and a sharp angulation at the junction with the right atrium which was identified eventually by venogram. The SVC however was clearly defined. The ascending and descending aorta were also of abnormal appearance, best seen in the RAO projection (figure 3).
Figure 1: An A-P projection showing the segmented CT scan with structures visible – red = aorta and left coronary artery, purple = right ventricle, yellow = left ventricle, green = atria (left and right atrial appendages visible in this view), blue = pulmonary artery, purple = SVC.
Figure 2: A P-A projection showing the segmented CT scan with structures visible – red = aorta, purple = right ventricle, yellow = left ventricle, green = atria, blue = pulmonary artery, dark green = pulmonary veins, gold = coronary sinus.
Figure 3: An LAO projection showing the segmented CT scan with structures visible – red = aorta, purple = right ventricle, yellow = left ventricle, green = atria, blue = pulmonary artery, dark green = pulmonary veins, gold = coronary sinus, purple = SVC.
The patient was placed under general anaesthetic and ultrasound guided access obtained to the right femoral vein. Heparin was administered at various points during the procedure to maintain an ACT greater than 300. The CT was used as a guide to the anatomy and a decapolar catheter was advanced with difficulty into the right atrium. It was not possible to advance the ablation catheter to the RA due to a sharp angulation at the IVC – RA junction, even with the use of a steerable Agilis sheath. Therefore a secondary access point was created at the right internal jugular vein through which the mapping and ablation catheter (Biosense Webster STSF F curve) was advanced to the atria. The MAP catheter was then used to create an anatomical shell of the atria with identification of the SVC, left sided pulmonary veins and mitral annulus. The CARTO geometry was then merged with the CT and these were displayed side by side in synchronised views throughout the rest of the procedure.
Figure 4: A P-A caudal projection showing CT (left) and Carto geometry (right). The anatomical landmarks such as left common pulmonary vein (centre – marked with blue dot) and SVC (far right heading superiorly) can clearly be seen on both.
Tachycardia was easily induced by burst pacing from the decapolar catheter which was in a stable position in the high right atrium / roof area. An initial tachycardia cycle length of 220ms was seen and mapping commenced with an ‘early-meets-late’ propagation pattern suggestive of mitral dependent flutter. Early-meets-late refers to the pattern of activation occurring in re-entry circuits as the circuit is mapped and identified. Compared to a reference signal (in this case from the decapolar catheter) the timing of electrograms seen on the mapping catheter will become increasingly ‘early’ as the mapping catheter travels around the path of electrical propagation, until eventually the next signals are so ‘early’ as to be ‘late’ in comparison to the preceding reference signal, often described as like the Ouroboros symbol of a serpent trying to eat its own tail. Entrainment was performed from the septal and lateral sides of the mitral valve and returned values supportive of a mitral valve dependant re-entry circuit.
Figure 5: Entrainment performed at lateral MV annulus with a PPI (post pacing interval) – TCL 14ms, consistant with a mitral dependant flutter. (N.B catheter labelled as ‘CS’ actually placed in a superior atrial position).
Figure 6: An LAO caudal projection showing CT (left) and Carto geometry (right), as if looking en-face at the mitral valve annulus. Although the Carto geometry created is at this point limited an ‘early-meets-late’ pattern appears to be emerging around the mitral valve consistent with mitral dependant flutter. ‘Early’ signals are red changing through green to blue / purple signals representing ‘late’.
It was therefore decided to isolate the left common pulmonary vein with circumferential ablation and a linear lesion set from the inferior aspect of the LPV to the mitral valve. The pulmonary vein was noted to be very small in calibre and so it was not deemed appropriate to attempt to place a Lasso catheter, instead the ablation catheter was advanced into the vein ostium and used to confirm isolation. The line was completed with some slowing of the tachycardia but not termination. Catheter stability in this region was difficult and delivery of sufficient energy to the tissue appeared hampered by poor contact with the endocardial surface. A more anterior position was investigated with improved stability and a widening of the ablation line to include the more anterior aspect of the pulmonary vein and mitral isthmus resulted in profound slowing of the tachycardia over several beats and finally termination to sinus rhythm. A number of consolidation lesions were applied in this area to complete the line. The catheter was then moved along the line with either electrical silence suggestive of fully ablated tissue or double potentials seen, representative of activity either side of a line of block. Differential pacing was attempted but was inconclusive due to difficulty in catheter placement (no coronary sinus access obtained) and extensive areas of scar resulting in failure to capture and / or lack of signals.
The decision was taken to end the procedure without attempting to induce further tachycardia as the procedure time was already well in excess of 6 hours. The patient was extubated on ITU before being taken to the cardiac ward and was discharged the following day feeling well and in sinus rhythm. Three month follow-up in the GUCH arrhythmia clinic was arranged and this is anticipated in the near future.
Figure 7: This projection, showing CT (left) and Carto geometry (right) shows the ‘mitral line’ ablated, with circumferential ablation around the Left Common PV and extending down to the mitral valve.
This case is presented as a demonstration of the additional processes often involved when planning and performing electrophysiology and / or ablation procedures in patients with complex congenital heart malformations. The congenital patient will often bring together several challenging aspects within a single procedure. These technical considerations often result in general anaesthesia being necessary, and this in turn is often challenging and may require specialist anaesthetic support and the ready availability of ITU care if required. Appropriate pre-procedure planning, above and beyond that required prior to ablation procedures in the ‘normal heart’ population can help to alleviate some of these issues, reducing procedure times and improving success rates. In this case the availability of the CT as a guide to the complex anatomy, along with standard techniques such as use of venograms and deflectable catheters and sheaths as well the willingness to adapt (for example to use somewhat less conventional access points), all helped to keep this case from being any longer than it might otherwise have been whilst maintaining a reasonable expectation of success in an extremely complex patient.
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