Tom Wong

Initial Experience Using a Forward Directed, High-Intensity Focused Ultrasound Balloon Catheter for Pulmonary Vein Antrum Isolation in Patients with Atrial Fibrillation

Background: A high‐intensity‐focused ultrasound balloon catheter (HIFU‐BC) is designed to isolate pulmonary veins (PV) outside the ostia (PV antrum). This catheter uses a parabolic CO2 balloon (behind water balloon) to focus a 20‐, 25‐, or 30‐mm diameter ring of ultrasound forward of the balloon (parallel to catheter shaft). The purpose of this study is to test the safety and efficacy of the HIFU‐BC for PV antrum isolation in patients with atrial fibrillation (AF).

Mechano-Electrical Interaction Late After Fontan Operation Relation Between P-Wave Duration and Dispersion, Right Atrial Size, and Atrial Arrhythmias

Background—The growing population with Fontan operation surviving into adulthood has significant morbidity and mortality rates from recurrent atrial tachyarrhythmias. We hypothesized that the structural characteristics and electrical behavior of atria may differ in these patients compared with those without arrhythmias. Methods and Results—We studied 33 consecutive patients (age, 25.4± 9.5 years) with Fontan circulation, of whom 19 had a history of documented sustained atrial tachyarrhythmias. We analyzed their clinical and investigational data, including echocardiographic assessment of atrial dimensions and surface 12-lead ECG measurement of the P-wave duration and its dispersion between leads. Twenty age- and sex-matched healthy control subjects were also studied. First, patients who had the Fontan procedure overall had longer P-wave duration (144±33 versus 100± 7 ms, P < 0.001) and greater P-wave dispersion (74±33 versus 34±9 ms, P < 0.001) than control subjects. Among the patients who had the Fontan procedure, those with atrial tachyarrhythmias had longer P-wave duration (159±28 versus 123±28 ms, P < 0.001) and greater P-wave dispersion (91±30 versus 50±19 ms, P < 0.001) than those without. Second, the patients with atrial tachyarrhythmias who had the Fontan procedure had larger right atrial dimension than those without arrhythmias (6.4±1.4 versus 5.0±1.0 cm, P = 0.01). Third, both P-wave duration and dispersion were significantly correlated to right atrial dimension within the Fontan group (r = 0.55, P = 0.002, and r = 0.56, P = 0.002, respectively). Conclusions—Patients with atrial tachyarrhythmias late after Fontan operation have longer P-wave duration and P-wave dispersion and larger right atrial dimension than those without the arrhythmias; these abnormalities are interrelated. This observation represents an atrial mechano-electrical remodeling phenomenon in parallel to an increase in arrhythmia propensity in this vulnerable population and warrants further investigation.

Spatiotemporal Behavior of High Dominant Frequency During Paroxysmal and Persistent Atrial Fibrillation in the Human Left Atrium

Background— Sites of high dominant frequency (DFpeak) are thought to indicate the location of drivers of atrial fibrillation (AF), but characterization of their spatiotemporal distribution and stability, critical to their relevance as targets for catheter ablation, requires simultaneous global mapping of the left atrium. Methods and Results— Noncontact electrograms recorded simultaneously from 256 left atrial sites during spontaneous AF were analyzed. After subtraction of the ventricular component, fast Fourier transform identified the DF at each site. Focal areas of DFpeak were defined as those having a DF >20% above all neighboring sites. Twenty-four patients with spontaneous AF (11 paroxysmal and 13 persistent) were studied. In paroxysmal AF, sites of DFpeak (mean DF, 11.6±2.9 Hz) were observed in 100% of patients (present during 65% of the mapping period). In contrast, DFpeak was detected in only 31% of patients with persistent AF (P<0.001) and for only 5% of the mapping period (P<0.001). In both groups, locations of DFpeak varied widely in both consecutive and separated segments of AF (&kgr; coefficient range, -0.07–0.22). Activation sequences around sites of DFpeak did not demonstrate centrifugal activation that would be expected from focal drivers. Conclusions— Focal areas of high DF are more frequent in paroxysmal than persistent AF, are spatiotemporally unstable, are not the source of centrifugal activation, and are not, therefore, indicative of fixed drivers of AF. In the absence of spatiotemporal stability, the success of ablation at sites of DFpeak cannot be explained by elimination of fixed drivers.

Clinical Usefulness of Cryomapping for Ablation of Tachycardias Involving Perinodal Tissue

AbstractObjectives: Radiofrequency (RF) ablation near the AV node carries a significant risk of AV block. We report our initial experience of using cryomapping function to aid the safe cryoablation close to the compact atrioventricular (AV) node.nMethods: Five consecutive patients with para-Hisian accessory pathways (AP) (n = 2), or focal atrial tachycardia (AT) originating near the AV node (n = 3) underwent cryoablation using a 7F 4 mm-tipped catheter. At each prospective ablation site, cryo-mapping (−30°C) which causes transient electrical dysfunction was performed, and in the absence of AH interval prolongation, a full cryoablation (≤−70°C) was applied to the same site.nResults: The AT foci, left in 2 patients and right in 1, and the APs were located 1.9 ± 3.0 mm and 4.5 ± 8.1 mm from the catheter recording the His deflection in two orthogonal radiographic projections. A His signal (0.18 ± 0.07 mV) was recorded at the site of successful cryoablation in both patients with AP and 1 with right AT. There was no change in AV nodal function during/after ablation. At each successful cryoablation site, interruption of target pathway/focus function was observed during cryo-mapping after 19.8 ± 12.4 s. Full cryoablation at sites where cryo-mapping had not caused an effect did not then produce any further electrophysiologic effect. All pathways and foci were ablated successfully without complications, using 3.2 ± 3.9 cryothermic applications alone in 4 patients, and after a supplementary RF ablation in 1. All patients remained free of arrhythmia at 15 ± 8 months follow-up.nConclusion: Cryomapping may help identify sites for safe and effective ablation of pathways and foci located near the AV node.

Percutaneous Pulmonary Vein Cryoablation to Treat Atrial Fibrillation

AbstractBackground: Cryothermic tissue injury, unlike hyperthermic tissue injury, preserves tissue architecture and causes less thrombus formation, and thus may prevent venous stenosis and stroke in ablating pulmonary veins (PVs) to treat patients with atrial fibrillation (AF). We investigate the feasibility, efficacy, safety and clinical outcome of using percutaneous cryoablation to treat such patients.nMethods: Thirty-one patients who had drug refractory paroxysmal (20) or persistent (11) AF underwent 37 PV ablative procedures using a 4 mm- or 6 mm-tipped 7F cryoablation catheter (CryoCath Technologies Inc., Quebec, Canada). Segmental isolation at the veno-atrial junction was guided by a distal circumferential mapping catheter.nResults: A total of 47 PV were ablated, of which 35/47 (74%) were electrically isolated and the remaining 12/47 had attenuation of PV electrograms, altered activation sequence, and marked slowing of left atrial-PV conduction. There was no change in PV diameter, either immediately following cryoablation (21 ± 5 versus 22 ± 6, p = 0.69), or at 18 ± 9 months follow-up (22 ± 5 versus 22 ± 5 mm, p = 0.23). There was no clinical thromboembolic event.The duration of cryoablation for each treated PV and procedural duration was 65 ± 39 and 290 ± 101 min, respectively. Following cryoablation, 5/30 (6%) were free from AF and 12/30 (43%) showed improvement from previously ineffective antiarrhythmic drug therapy. 13/30 (43%) patients were unchanged by cryoablation.nConclusions: Cryothermic ablation shows great promise in reducing the risks of PV stenosis and thrombo-embolism associated with PV isolative procedures. However, cryoablation of these veins with linear catheters is time consuming, and the clinical outcomes are disappointing. Alternative catheter designs are required to overcome these difficulties.

A novel algorithm for determining endocardial VT exit site from 12-lead surface ECG characteristics in human, infarct-related ventricular tachycardia.

Introduction: Characteristics of the 12‐lead ECG during VT are used to guide initial placement of mapping catheters in endocardial ventricular tachycardia (VT) ablation. Previously constructed algorithms for guidance in human infarct‐related VT are limited to patients known to have anterior or inferior infarcts only. We hypothesized that 12‐lead ECG characteristics could be used to determine VT exit site in patients with all types of infarction of unknown location.

Percutaneous Isolation of Multiple Pulmonary Veins Using an Expandable Circular Cryoablation Catheter

Although radiofrequency pulmonary vein (PV) ablation is effective in the treatment of atrial fibrillation (AF), it is associated with small but significant risks of PV stenosis and systemic thromboembolism. The characteristics of cryothermic tissue injury may reduce the likelihood of such complications, but using conventionally tipped cryoablation catheters can be time consuming and may, thus, not permit isolation of all PVs during a single procedure. We describe a case of rapid and effective isolation of all electrically connected PVs in a patient with paroxysmal AF, using a percutaneous self‐expanding circular‐tipped cryoablation catheter. (PACE 2004; 27:551–554)

Intra-coronary guidewire mapping–A novel technique to guide ablation of human ventricular tachycardia

HypothesisEndocardial catheter ablation of ventricular tachycardia (VT) may fail if originating from epicardial or intramural locations. We hypothesized that mapping could be achieved using an angioplasty guidewire in the coronary circulation, to guide trans-coronary ablation.Methods and resultsSix patients (2 male), 64u2009±u200914xa0years and previously unsuccessful endocardial VT ablation were studied. Using ECG and existing endocardial mapping data, a coronary artery supplying the predicted VT origin was selected. A 0.014-in angioplasty guidewire was advanced into branches of the artery and connected to an amplifier to record unipolar signals against an indifferent electrode within the inferior vena cava. An uninflated angioplasty balloon was advanced over the wire such that only the distal 5xa0mm was used for mapping. One VT per patient was mapped (CL 348u2009±u2009102.1xa0ms). Diastolic potentials were recorded from all (77.7u2009±u200943.8xa0ms pre-QRS onset) and concealed entrainment demonstrated in 3. Pacemapping during sinus rhythm was used in the remainder due to failure of entrainment (nu2009=u20092) or degeneration to VF (nu2009=u20091). Following branch identification, cold saline injection causing VT termination was used for further confirmation. Five VTs were ablated using intra-coronary ethanol injection via the central lumen of the inflated over the wire balloon. The other was ablated using radiofrequency energy in a coronary vein adjacent to the target artery, which was too small for an angioplasty balloon. No complications or recurrence of ablated VT was seen over 19u2009±u200917xa0months of follow up.ConclusionsIntracoronary guidewire mapping is a novel method of electrophysiological epicardial mapping to help guide trans-coronary VT ablation.

Ablation of difficult right-sided accessory pathways aided by mapping of tricuspid annular activation using a Halo catheter : Halo-mapping of right sided accessory pathways.

ObjectiveTo demonstrate that the use of a 20-pole catheter (Halo™) positioned around the tricuspid valve annulus (TVA) is helpful in rapidly localising right free wall accessory pathways (AP), enhancing catheter stability during ablation, and leading to increased success in ablating these challenging pathways.Patients and methodsSeven consecutive patients who underwent Halo-mapping of right-sided AP were studied. All but one had previously failed ablation. With a Halo catheter deployed at TVA, the accessory pathway location was rapidly identified using the sites of earliest atrial (A) activation during ventricular (V) pacing or orthodromic tachycardia, or earliest V-activation during sinus rhythm or A-pacing were identified. The stability of the ablation catheter was guided fluoroscopically (with reference to the stationary Halo), and electrically (contact artefact between the ablation catheter and Halo poles).ResultsAP locations were identified by the Halo (anterior in one patient, antero-lateral in one, lateral in two, and postero-lateral in three) where similar local VA/AV intervals were recorded at both the ablation catheter and Halo bipoles recording the shortest VA/AV intervals (four of seven patients), contact artefact between the ablation catheter and those Halo bipoles was seen (six of seven patients), or both (three of seven patients). All APs were ablated successfully after a mean RF duration of 5±2xa0min, and 25±17xa0min post Halo deployment without clinical recurrence at 12±4xa0months follow-up.ConclusionA Halo positioned at the TVA can ease the localisation of right-sided AP, facilitate catheter stability during ablation, and guides successful ablation.

Multiple distinct right atrial endocardial origins in a patient with atrial tachycardia: mapping and ablation using noncontact mapping.

Noncontact mapping identified the endocardial origins of four distinct atrial tachycardias in a young patient with drug refractory palpitations and effected successful ablation with no recurrence of symptoms in 5 months of follow‐up. (PACE 2004; 27:541–544)