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Biomedical subjects

D Wyn Davies

Publications and source records attributed to D Wyn Davies.

At least 19 recordsLinked to original sources
PubMed2006

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.

OBJECTIVE: To demonstrate that the use of a 20-pole catheter (Halotrade mark) 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 METHODS: Seven 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). RESULTS: AP 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+/-2 min, and 25+/-17 min post Halo deployment without clinical recurrence at 12+/-4 months follow-up. CONCLUSION: A Halo positioned at the TVA can ease the localisation of right-sided AP, facilitate catheter stability during ablation, and guides successful ablation.

Adult↗
PubMed2006

Haemodynamic effects of changes in atrioventricular and interventricular delay in cardiac resynchronisation therapy show a consistent pattern: analysis of shape, magnitude and relative importance of atrioventricular and interventricular delay.

OBJECTIVE: To assess the haemodynamic effect of simultaneously adjusting atrioventricular (AV) and interventricular (VV) delays. METHOD: 35 different combinations of AV and VV delay were tested by using digital photoplethysmography (Finometer) with repeated alternations to measure relative change in systolic blood pressure (SBP(rel)) in 15 patients with cardiac resynchronisation devices for heart failure. RESULTS: Changing AV delay had a larger effect than changing VV delay (range of SBP(rel) 21 v 4.2 mm Hg, p < 0.001). Each had a curvilinear effect. The curve of response to AV delay fitted extremely closely to a parabola (average R2 = 0.99, average residual variance 0.8 mm Hg2). The response to VV delay was significantly less curved (quadratic coefficient 67 v 1194 mm Hg/s2, p = 0.003) and therefore, although the residual variance was equally small (0.8 mm Hg2), the R2 value was 0.7. Reproducibility at two months was good, with the SD of the difference between two measurements of SBP(rel) being 2.5 mm Hg for AV delay (2% of mean systolic blood pressure) and 1.5 mm Hg for VV delay (1% of mean systolic blood pressure). CONCLUSIONS: Changing AV and VV delays results in a curvilinear acute blood pressure response. This shape fits very closely to a parabola, which may be valuable information in developing a streamlined clinical protocol. VV delay adjustment provides an additional, albeit smaller, haemodynamic benefit to AV optimisation.

Aged↗
PubMed2006

Determination of optimal atrioventricular delay for cardiac resynchronization therapy using acute non-invasive blood pressure.

AIMS: In this study, we apply non-invasive blood pressure (BP) monitoring, by continuous finger photoplethysmography (Finometer), to detect directly haemodynamic responses during adjustment of the atrioventricular (AV) delay of cardiac resynchronization therapy (CRT), at different heart rates. METHODS AND RESULTS: Twelve patients were studied with six re-attending for reproducibility assessment. At each AV delay, systolic BP relative to a reference AV delay of 120 ms (SBPrel) was calculated. We found that at higher heart rates, altering the AV delay had a more pronounced effect on BP (average range of SBPrel=17.4 mmHg) compared with resting rates (average range of SBPrel=6.5 mmHg), P<0.0001. Secondly, peak AV delay differed between patients (minimum 120 ms, maximum 200 ms). Thirdly, small changes in AV delay had significant BP effects: programming AV delay 40 ms below the peak AV delay reduced SBPrel by 4.9 mmHg (P<0.003); having it 40 ms above the peak decreased SBPrel by 4.4 mmHg (P<0.0005). Finally, the peak AV delay is highly reproducible both on the same day and at 3 months (Bland-Altman difference: 3+/-8 ms). CONCLUSIONS: Continuous non-invasive arterial pressure monitoring demonstrates that even small changes in AV delay from its haemodynamic peak value have a significant effect on BP. This peak varies between individuals, is highly reproducible, and is more pronounced at higher heart rates than resting rates.

Adult↗
PubMed2006

Age-related changes in human left and right atrial conduction.

INTRODUCTION: Advancing age is an independent risk factor for atrial fibrillation (AF), which is considered to be initiated by ectopic triggers and maintained by an arrhythmogenic substrate. It is not known whether substrate changes produce this age-related increase in propensity toward AF. We addressed the hypothesis that advancing age is associated with changes in biatrial electrophysiology even in patients with no history of atrial arrhythmias. METHODS AND RESULTS: Patients with left-sided accessory pathways and requiring routine electrophysiological studies were recruited. Electroanatomic mapping was performed in the left and right atria of 23 patients (age ranging from 17 to 75 years) with structurally normal hearts and no history of AF during sinus rhythm and pacing. Unlike previous studies, a trigonometric method was used to quantify wavefront propagation velocities (WPV) precisely in the direction of propagation. Refractoriness was measured at 2 cycle lengths, at three different atrial sites. Both right (r =-0.77, P < 0.0001) and left (r =-0.79, P < 0.001) atrial WPV demonstrated strongly inverse correlation with age. Furthermore, left and right WPVs were highly correlated (r = 0.66, P < 0.01), with velocities being 6.4 +/- 2.2 cm/sec higher in the right atria (P < 0.01). Refractoriness was significantly correlated with increasing age only at the septum (r = 0.53, P < 0.01). Left atrial wavelength was inversely correlated with increasing age (r =-0.56, P = 0.03). P wave duration was associated with age (r = 0.42, P = 0.04) and left atrial size (r = 0.44, P = 0.04) but not atrial WPV. CONCLUSION: Aging human atria demonstrate progressive decline in WPV and increase in septal refractoriness. These age-related changes in biatrial electrophysiology are likely to be important factors in the age-related increase in AF prevalence.

Adolescent↗
PubMed2005

Atrial fibrillation management: a prospective survey in ESC member countries: the Euro Heart Survey on Atrial Fibrillation.

AIMS: To describe atrial fibrillation (AF) management in member countries of the European Society of Cardiology (ESC) and to verify cardiology practices against guidelines. METHODS AND RESULTS: Among 182 hospitals in 35 countries, 5333 ambulant and hospitalized AF patients were enrolled, in 2003 and 2004. AF was primary or secondary diagnosis, and was confirmed on ECG in the preceding 12 months. Clinical type of AF was reported to be first detected in 978, paroxysmal in 1517, persistent in 1167, and permanent in 1547 patients. Concomitant diseases were present in 90% of all patients, causing risk factors for stroke to be also highly prevalent (86%). As many as 69% of patients were symptomatic at the time of the survey; among asymptomatic patients, 54% were previously experienced symptoms. Oral anticoagulation was prescribed in 67 and 49% of eligible and ineligible patients, respectively. A rhythm control strategy was applied in 67% of currently symptomatic patients and in 44% of patients who never experienced symptoms. CONCLUSION: This survey provides a unique snapshot of current AF management in ESC member countries. Discordance between guidelines and practice was found regarding several issues on stroke prevention and antiarrhythmic therapy.

Adult↗
PubMed2005

New mapping technologies: an overview with a clinical perspective.

Conventional catheter mapping techniques continue to form the basis of mapping for all arrhythmias. Constantly evolving "advanced" mapping systems can facilitate arrhythmia mapping by allowing reconstruction of three-dimensional models of cardiac chambers, combining electrical and anatomical information at multiple sites, creating voltage and activation maps and reducing the need for fluoroscopy.

Arrhythmias, Cardiac↗
PubMed2005

Long-term results after ablation of infarct-related ventricular tachycardia.

OBJECTIVES: The purpose of this study was to assess the long-term effects of ablation of infarct-related ventricular tachycardia (VT) and the subsequent requirement for implantable cardioverter-defibrillator (ICD) therapy. BACKGROUND: The long-term consequences after initially successful catheter ablation of infarct-related VT remain unclear. METHODS: Forty patients who presented with infarct-related VT were studied using noncontact mapping to guide ablation. RESULTS: One hundred forty VTs were mapped using the noncontact mapping system, including 36 (25.7%) clinical VTs. An endocardial exit site was determined in 100% of VT circuits, diastolic endocardial activity in 77 VTs (55%), and complete circuits in 24 VTs (17.1%). Eighty-one VTs (57.9%) were targeted for ablation, of which 67 (82.7% of targeted) were successfully ablated, including 27 clinical VTs (75% of clinical). Documented recurrence of an ablated VT occurred in 7.5% of patients over 36.3 +/- 21.0 months of follow-up. Episodes of new or recurrent, nontargeted VT or ventricular fibrillation (VF) occurred in 37.5% and VT recurrence without documentation of cycle length in 5%. In patients with ICDs, mean shock frequency was reduced from 6.8 +/- 7.3 per month in the year prior to ablation to 0.05 +/- 0.12 per month after ablation, over 24.7 +/- 18.9 months of follow-up (P < .0001). CONCLUSIONS: In patients with infarct-related VT, noncontact mapping-guided VT ablation is associated with a high procedural success rate, and VT recurrence necessitating ICD therapy delivery is significantly reduced. However, only 42.5% of patients remain free from VT/VF 3 years after ablation. Catheter ablation for infarct-related VT is indicated as an adjunctive therapy in patients with symptomatic VT but cannot substitute for ICDs and antiarrhythmic drugs.

Aged↗
PubMed2004

Mechanism of pacing-induced ventricular fibrillation in the infarcted human heart.

BACKGROUND: The mechanisms by which ventricular fibrillation (VF) is initiated in the infarcted human heart have not been defined. METHODS AND RESULTS: Left ventricular noncontact mapping of 8 episodes of pacing-induced VF in 6 patients (age 64.8+/-7.9 years, with previous myocardial infraction and left ventricular ejection fraction of 36+/-4%) undergoing ventricular tachycardia (VT) ablation revealed a consistent mechanism of VF induction. Whether during VT or sinus rhythm, the first of a train of paced extrastimuli to capture the LV produced an arc or arcs of functional block at regions bordering scar. With subsequent extrastimuli, the arcs elongated to circumscribe an enlarging area of increasingly late activation, with reentry through part of this functional (unidirectional) block leading to wavefront fragmentation and VF. These regions had longer fibrillation intervals (263+/-63 ms) than remote LV regions (209+/-23.4 ms; P<0.0001), implying longer refractory periods, and in 6 of the 8 VF episodes, these regions correlated with VT exit sites. In each of the 2 patients with 2 episodes of VF, both episodes formed arcs of functional block in the same location, despite pacing from different sites. CONCLUSIONS: Pacing-induced VF in the infarcted human heart is initiated by the development of functional lines of block dictated by the properties of a particular region of myocardium characterized by longer refractory periods, at or near VT circuit exit sites. Identification of these characteristic properties may help stratify risk of arrhythmic death and explain the potential for VT ablation to modify risk of VF in the infarcted heart.

Aged↗
PubMed2004

Clinical usefulness of cryomapping for ablation of tachycardias involving perinodal tissue.

OBJECTIVES: 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. METHODS: 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 degrees C) which causes transient electrical dysfunction was performed, and in the absence of AH interval prolongation, a full cryoablation (<or=-70 degrees C) was applied to the same site. RESULTS: 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. CONCLUSION: Cryomapping may help identify sites for safe and effective ablation of pathways and foci located near the AV node.

Adult↗
PubMed2004

Percutaneous pulmonary vein cryoablation to treat atrial fibrillation.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Analysis of Variance↗
PubMed2004

Localization of the isthmus in reentrant circuits by analysis of electrograms derived from clinical noncontact mapping during sinus rhythm and ventricular tachycardia.

INTRODUCTION: New methods for electrogram analysis accurately estimated reentrant circuit isthmus location and shape in a canine model. It was hypothesized that these methods also would locate reentrant circuits causing clinical ventricular tachycardia (VT). METHODS AND RESULTS: Intracardiac electrogram recordings, obtained with a noncontact mapping system, were analyzed retrospectively from 14 patients with reentrant VT who had undergone successful radiofrequency ablation for prevention of VT initiation. Unipolar electrograms from 256 uniformly distributed endocardial sites were reconstructed by mathematical transformation. Twenty-seven tachycardias were mapped; 15 (in 11 patients) had a complete endocardial reentrant circuit with a figure-of-eight conduction pattern. During sinus rhythm, the location and axis of the slowest and most uniform conduction in the region of latest endocardial activation (the primary axis), the limits of which were defined as boundaries with >15 ms difference in electrogram duration between contiguous recordings, identified the location and shape of the reentrant circuit isthmus with a mean sensitivity compared with activation mapping of 79.3% and a mean specificity of 97.6%. The midpoint of a theoretical "estimated best ablation line" drawn perpendicular to the primary axis of activation, spanning the estimated isthmus location was within 1.3 +/- 0.2 cm (mean distance +/- SD) of the actual ablation site that terminated tachycardia. Analysis of VT electrograms, based on time shifts in the far-field component of the local electrogram when cycle length changed (piecewise linear adaptive template matching [PLATM] method) in 5 of the cases, accurately estimated the time interval between activation at the recording site and the circuit isthmus slow conduction zone where the effective ablation lesion had been placed, which is proportional to the distance between the two locations (mean difference compared with activation mapping: +/-37.3 ms). CONCLUSION: In selected patients with VT who have a complete endocardial circuit, isthmus location and shape can be discerned by analysis of sinus rhythm or tachycardia electrograms, and an effective ablation site can be predicted without the need to construct activation maps of reentrant circuits.

Algorithms↗
PubMed2004

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.

Adult↗
PubMed2004

Catheter inversion: a technique to complete isthmus ablation and cure atrial flutter.

Cure of typical atrial flutter (AFL) by catheter ablation to produce bidirectional block across the tricuspid annulus-inferior vena cava isthmus (IS) is highly effective, but failures may occur. We describe a technique that may allow creation of bidirectional block where a conventional strategy has failed. AFL ablation was performed using the conventional approach with a mapping/ablation (ablation) catheter introduced via the right femoral vein (RFV) to create a line of bidirectional block across the IS. If this was not achieved after five passes of the ablation catheter from the tricuspid annulus to the inferior vena cava (IVC) a catheter inversion technique was used. This allowed stable positioning of the ablation catheter at the IVC end of the isthmus. In 11 patients, a mean of 17 (range 3 to 45) radiofrequency (RF) applications was given before the catheter inversion technique was applied. Following catheter inversion a mean of 4 (1 to 14) further RF applications achieved bidirectional isthmus block in every patient. No complications occurred. Catheter inversion provides a simple, safe, and effective means of achieving bidirectional isthmus conduction block in cases where a conventional ablation strategy might have failed.

Aged↗