Michael Koa-Wing

Outcomes of elderly patients aged 80 and over with symptomatic, severe aortic stenosis: impact of patient's choice of refusing aortic valve replacement on survival

BACKGROUND Aortic valve replacement (AVR) can be performed safely in selected elderly patients with aortic stenosis (AS). However, the survival benefits of AVR over conservative treatment have not been convincingly demonstrated in AS patients aged above 80. AIM To investigate the outcomes of patients aged 80 and over with symptomatic, severe AS and by analyzing the effects of patients choice in either agreeing or refusing to undergo AVR, determine the survival benefits afforded by AVR. DESIGN Cohort study. METHODS Subjects aged 80 and over with severe symptomatic AS, diagnosed between 2001 and 2006 were segregated into three groups: subjects who underwent AVR (Group A); patients who were fit for AVR but declined surgery due to personal choice (Group B) and those who were not fit for surgery and were managed conservatively (Group C). Follow-up was conducted by out-patient attendances, review of medical records and telephone interviews. The primary endpoint was all-cause mortality. RESULTS A total of 103 patients (86.0 +/- 4.2 years, 41% male) were identified and no patient was lost during follow-up. In Group A (n = 17), all 15 patients who underwent AVR were alive after 3.6 +/- 1.4 years follow-up and 2 died whilst awaiting AVR. Seventy-four percent of Group B (n = 24) and 76% of Group C (n = 62) died during follow-up. Group A had significantly better survival than B and C. (P < 0.01) Amongst patients fit for AVR with similar operative risks (Groups A and B), refusal to undergo surgery (hazard ratio 12.61, P = 0.001) was the only predictor of mortality in a multivariate model. CONCLUSION For elderly AS patients fit for surgery, the patients decision to refuse AVR is associated with a >12-fold increase in mortality risk. These findings have significant implications for informed decision-making when managing the fit, elderly patient with AS.

Implantable Cardioverter-Defibrillator Recipient Attitudes towards Device Deactivation: How Much do Patients Want to Know?

Background:  Patients receiving implantable cardioverter‐defibrillators (ICDs) often have severely impaired left ventricular function and a poor prognosis. Having an ICD in situ effectively denies them the possibility of a quick, arrhythmic death. It is still unclear if and when the end of life and device deactivation should be discussed with patients and how much patients want to know prior to ICD implantation.

Noninvasive electrocardiographic mapping to guide ablation of outflow tract ventricular arrhythmias

Background Localizing the origin of outflow tract ventricular tachycardias (OTVT) is hindered by lack of accuracy of electrocardiographic (ECG) algorithms and infrequent spontaneous premature ventricular complexes (PVCs) during electrophysiological studies. Objectives To prospectively assess the performance of noninvasive electrocardiographic mapping (ECM) in the pre-/periprocedural localization of OTVT origin to guide ablation and to compare the accuracy of ECM with that of published ECG algorithms. Methods Patients with symptomatic OTVT/PVCs undergoing clinically indicated ablation were recruited. The OTVT/PVC origin was mapped preprocedurally by using ECM, and 3 published ECG algorithms were applied to the 12-lead ECG by 3 blinded electrophysiologists. Ablation was guided by using ECM. The OTVT/PVC origin was defined as the site where ablation caused arrhythmia suppression. Acute success was defined as abolition of ectopy after ablation. Medium-term success was defined as the abolition of symptoms and reduction of PVC to less than 1000 per day documented on Holter monitoring within 6 months. Results In 24 patients (mean age 50 ± 18 years) recruited ECM successfully identified OTVT/PVC origin in 23/24 (96%) (right ventricular outflow tract, 18; left ventricular outflow tract, 6), sublocalizing correctly in 100% of this cohort. Acute ablation success was achieved in 100% of the cases with medium-term success in 22 of 24 patients. PVC burden reduced from 21,837 ± 23,241 to 1143 ± 4039 (P < .0001). ECG algorithms identified the correct chamber of origin in 50%–88% of the patients and sublocalized within the right ventricular outflow tract (septum vs free-wall) in 37%–58%. Conclusions ECM can accurately identify OTVT/PVC origin in the left and the right ventricle pre- and periprocedurally to guide catheter ablation with an accuracy superior to that of published ECG algorithms.

Characterization of the Left Atrial Neural Network and its Impact on Autonomic Modification Procedures

Background—Left atrial (LA) ganglionated plexi (GP) are part of the intrinsic cardiac autonomic nervous system and implicated in the pathogenesis of atrial fibrillation. High frequency stimulation is used to identify GP sites in humans. The effect of ablation on neural pathways connecting GPs in humans is unknown. Methods and Results—Thirty patients undergoing LA ablation with autonomic modification were recruited. In patients with persistent atrial fibrillation, endocardial continuous high frequency stimulation identified GP sites producing AV block. After right lower GP ablation (N=5), 2 of 15 sites remained positive, whereas after ablation of other GPs (N=5), leaving right lower GP intact, all 19 sites remained positive (right lower GP versus other GP, P<0.005), indicating that neural pathways between LAGPs and the AV node are via the right lower GP. In 20 patients with paroxysmal atrial fibrillation, synchronized high frequency stimulation identified sites initiating pulmonary vein (PV) ectopy. After PV isolation (N=8), no sites remained positive. After local GP ablation (N=9), 3 of 14 sites remained positive, suggesting neural connections to the PV were disrupted by both PV isolation and GP ablation. Heart rate variability indices reduced significantly after right upper GP ablation alone, suggesting that neural pathways from the LA to the SA node travel via the right upper GP. Conclusions—We have demonstrated neural pathways connecting LA GPs with the PVs, AV node, and SA node. The effects of high frequency stimulation at GP sites can be prevented by ablating the GP site or the neural pathway. This further delineates the mechanism via which PV isolation prevents atrial fibrillation and highlights important caveats for autonomic modification end points.

Cardiac ripple mapping: A novel three-dimensional visualization method for use with electroanatomic mapping of cardiac arrhythmias

BACKGROUND Mapping of regular cardiac arrhythmias is frequently performed using sequential point-by-point annotation of local activation relative to a fixed timing reference. Assigning a single activation for each electrogram is unreliable for fragmented, continuous, or double potentials. Furthermore, these informative electrogram characteristics are lost when only a single timing point is assigned to generate activation maps. OBJECTIVE The purpose of this study was to develop a novel method of electrogram visualization conveying both timing and morphology as well as location of each point within the chamber being studied. METHODS Data were used from six patients who had undergone electrophysiological study with the Carto electroanatomic mapping system. Software was written to construct a three-dimensional surface from the imported electrogram locations. Electrograms were time gated and displayed as dynamic bars that extend out from this surface, changing in length and color according to the local electrogram voltage-time relationship to create a ripple map of cardiac activation. RESULTS Ripple maps were successfully constructed for sinus rhythm (n = 1), atrial tachycardia (n = 3), and ventricular tachycardia (n = 2), simultaneously demonstrating voltage and timing information for all six patients. They showed low-amplitude continuous activity in four of five tachycardias at the site of successful ablation, consistent with a reentrant mechanism. CONCLUSION Ripple mapping allows activation of the myocardium to be tracked visually without prior assignment of local activation times and without interpolation into unmapped regions. It assists the identification of tachycardia mechanism and optimal ablation site, without the need for an experienced computer-operating assistant.

Application of Ripple Mapping to Visualize Slow Conduction Channels Within the Infarct-Related Left Ventricular Scar

Background—Ripple mapping (RM) displays each electrogram at its 3-dimensional coordinate as a bar changing in length according to its voltage–time relationship with a fiduciary reference. We applied RM to left ventricular ischemic scar for evidence of slow-conducting channels that may act as ventricular tachycardia (VT) substrate. Methods and Results—CARTO-3© (Biosense Webster Inc, Diamond Bar, CA) maps in patient undergoing VT ablation were analyzed on an offline MatLab RM system. Scar was assessed for sequential movement of ripple bars, during sinus rhythm or pacing, which were distinct from surrounding tissue and termed RM conduction channels (RMCC). Conduction velocity was measured within RMCCs and compared with the healthy myocardium (>1.5 mV). In 21 maps, 77 RMCCs were identified. Conduction velocity in RMCCs was slower when compared with normal left ventricular myocardium (median, 54 [interquartile range, 40–86] versus 150 [interquartile range, 120–160] cm/s; P<0.001). All 7 sites meeting conventional criteria for diastolic pathways coincided with an RMCC. Seven patients had ablation colocating to all identified RMCCs with no VT recurrence during follow-up (median, 480 [interquartile range, 438–841] days). Fourteen patients had ≥1 RMCC with no ablation lesions. Five had recurrence during follow-up (median, 466 [interquartile range, 395–694] days). One of the 2 patients with no RMCC locations ablated had VT recurrence at 605 days post procedure. RMCCs were sensitive (100%; negative predictive value, 100%) for VT recurrence but the specificity (43%; positive predictive value, 35.7%) may be limited by blind alleys channels. Conclusions—RM identifies slow conduction channels within ischemic scar and needs further prospective investigation to understand the role of RMCCs in determining the VT substrate.

Robotic assistance and general anaesthesia improve catheter stability and increase signal attenuation during atrial fibrillation ablation.

AIMS Recurrent arrhythmias after ablation procedures are often caused by recovery of ablated tissue. Robotic catheter manipulation systems increase catheter tip stability which improves energy delivery and could produce more transmural lesions. We tested this assertion using bipolar voltage attenuation as a marker of lesion quality comparing robotic and manual circumferential pulmonary vein ablation for atrial fibrillation (AF). METHODS AND RESULTS Twenty patients were randomly assigned to robotic or manual AF ablation at standard radiofrequency (RF) settings for our institution (30 W 60 s manual, 25 W 30 s robotic, R30). A separate group of 10 consecutive patients underwent robotic ablation at increased RF duration, 25 W for 60 s (R60). Lesions were marked on an electroanatomic map before and after ablation to measure distance moved and change in bipolar electrogram amplitude during RF. A total of 1108 lesions were studied (761 robotic, 347 manual). A correlation was identified between voltage attenuation and catheter movement during RF (Spearmans rho -0.929, P < 0.001). The ablation catheter was more stable during robotic RF; 2.9 ± 2.3 mm (R30) and 2.6 ± 2.2 mm (R60), both significantly less than the manual group (4.3 ± 3.0 mm, P < 0.001). Despite improved stability, there was no difference in signal attenuation between the manual and R30 group. However, there was increased signal attenuation in the R60 group (52.4 ± 19.4%) compared with manual (47.7 ± 25.4%, P = 0.01). When procedures under general anaesthesia (GA) and conscious sedation were analysed separately, the improvement in signal attenuation in the R60 group was only significant in the procedures under GA. CONCLUSIONS Robotically assisted ablation has the capability to deliver greater bipolar voltage attenuation compared with manual ablation with appropriate selection of RF parameters. General anaesthesia confers additional benefits of catheter stability and greater signal attenuation. These findings may have a significant impact on outcomes from AF ablation procedures.

Application of Ripple Mapping with an Electroanatomic Mapping System for Diagnosis of Atrial Tachycardias

Three‐dimensional (3D) mapping is often used to guide ablation in atrial tachycardia (AT), but maps can be susceptible to annotation and interpolation errors. Ripple Mapping (RM) is a technique that displays electrogram time–voltage data simultaneously as dynamic bars on the surface shell to overcome these limitations.

Robotically assisted ablation produces more rapid and greater signal attenuation than manual ablation

Introduction: Robotic remote catheter ablation potentially provides improved catheter‐tip stability, which should improve the efficiency of radiofrequency energy delivery. Percentage reduction in electrogram peak‐to‐peak voltage has been used as a measure of effectiveness of ablation. We tested the hypothesis that improved catheter‐tip stability of robotic ablation can diminish signals to a greater degree than manual ablation.

Radiofrequency Ablation of Infarct Scar‐Related Ventricular Tachycardia: Correlation of Electroanatomical Data with Post‐Mortem Histology

Introduction: Histological data after VT ablation in humans is rare. We present a case of a patient who had ablation for VT storm and who died remotely from non‐arrhythmic causes.