A 67-year-old woman was referred for investigation of repetitive syncope. Her significant past medical history included diabetes mellitus, arterial hypertension, chronic kidney disease and left bundle branch block, and a week before admission, she had undergone percutaneous transluminal coronary angioplasty and stenting. Continuous cardiac monitoring revealed episodes of sustained polymorphic ventricular tachycardia initiated by a unifocal ventricular extrasystole. Idiopathic polymorphic ventricular tachycardia of fascicular origin was diagnosed and a radiofrequency catheter ablation procedure was arranged. The patient has provided written consent for publication of this case report.
The procedure was performed under general anaesthesia with sevoflurane and remifentanil, and the trachea was intubated to enable mechanical ventilation. A radial artery catheter was inserted for continuous blood pressure monitoring. Noninvasive cerebral oxygen saturation (SctO2) was monitored bilaterally using near-infrared spectroscopy (NIRS) (FORE-SIGHT cerebral oximetry by CAS Medical Systems, Inc.44 East Industrial RoadBranford, CT 06405 U.S.A) to guide the duration of ventricular tachycardia (VT) mapping. Before induction (breathing room air), baseline SctO2 levels were 64 and 67% for the left and right sides of the brain, respectively. An FiO2 of 0.50 was maintained during the procedure. Low-dose norepinephrine was infused to maintain mean arterial pressure (MAP) above 65 mmHg. Electrophysiological testing and radiofrequency catheter ablation were performed using standard techniques. Mapping and ablation catheters were placed in the right ventricle via the right femoral vein and in the left ventricle using a retrograde aortic approach via the right femoral artery. Paced mapping in sinus rhythm and activation mapping during spontaneous extrasystoles showed an optimal target region in the proximal anterior fascicle. Six applications of radiofrequency energy were delivered. During the mapping and ablation, no specific impact of ventricular pacing was noted on SctO2, although the blood pressure fell mildly while pacing. Gradually, the SctO2 declined to around 60% bilaterally, but with no change in MAP, no specific action was undertaken. After 3 h, the SctO2 suddenly decreased further to 55 and 57% for left and right sides, respectively. Blood pressure remained unchanged at 130/70 mmHg and pulsus paradoxus was not present. Because of the low SctO2 values, FiO2 was increased to 1.0 and several boluses of ephedrine and phenylephrine were given to increase SBP to 150 mmHg: no rise in SctO2 was observed. Fluoroscopy in the left anterior oblique view showed a barely moving heart contour. Urgent transthoracic echocardiography demonstrated a collection of pericardial fluid with a maximum width of 17 mm around the right atrium and ventricle and 7 mm around the apex. The pericardium was drained percutaneously using the subxyphoid approach and 220 ml blood was removed. Immediately, SctO2 recovered to normal values (Fig. 1) and vasopressors were stopped. The pericardial drain was removed after 2 days. The postoperative course was complicated by a mild acute chronic kidney injury and urinary tract infection.
Cardiac tamponade is a known complication of ventricular ablation procedures with an incidence of 1%.1 Several monitoring modalities have been proposed for early recognition of this life-threatening complication: clinical, radiologic and echocardiographic assessments are important.2 Fluoroscopy of the cardiac contour is useful during interventional cardiological procedures,3 and trans-thoracic echocardiography is of value. The latter is the gold standard for diagnosis and should be performed as soon as there is a suspicion of pericardial effusion or tamponade.2 In our patient, the fall in SctO2 was the first warning sign of possible cardiac tamponade. Miller et al.4 have validated the use of a SctO2 threshold of 55% during VT mapping and catheter ablation procedures. They concluded that the MAP necessary to maintain cerebral perfusion during VT is unknown and SctO2 values below 55% were a more clinically relevant indicator for deciding when to terminate the VT.4
Trends in SctO2 have been shown to be a valuable tool in surgical procedures such as coronary artery bypass graft, aortic arch surgery and carotid endarterectomy.5 We are aware of only one previous case report (paediatric) wherein changes in SctO2, as measured by NIRS, correlated with the early diagnosis of cardiac tamponade.6 However, the use of SctO2 monitoring with NIRS has some limitations. Murkin and Arango5 have described several factors that might affect SctO2: the heterogeneity of the transcutaneous NIRS measurements, the fact that SctO2 reflects mostly cortical cerebral tissue and not the deeper brain tissue, the haemoglobin concentration and factors such as oedema or haematoma.
In conclusion, monitoring of SctO2 during catheter ablation procedures for ventricular arrhythmias has two benefits. First, the desaturation threshold of 55% is useful to determine the time that can be spent safely in mapping ventricular tachycardia, and second, in the rare cases of acute perforation with pericardial tamponade, SctO2 desaturation may help expedite the diagnosis and treatment.
Acknowledgements relating to this article
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Conflicts of interest: none.
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