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Biomedical subjects

Mark A Wood

Publications and source records attributed to Mark A Wood.

At least 19 recordsLinked to original sources
PubMed2006

Accuracy of intracardiac echocardiography for assessing the esophageal course along the posterior left atrium: a comparison to magnetic resonance imaging.

BACKGROUND: Atrioesophageal fistula is a potentially fatal complication of ablation in the left atrium (LA) to treat atrial fibrillation. OBJECTIVE: The objective of our study was to systematically evaluate the diagnostic potential of intracardiac echocardiography (ICE) for accurately assessing the esophageal course along the posterior LA. METHODS: Thirty-five patients underwent magnetic resonance imaging (MRI) before and ICE during pulmonary vein (PV) isolation to visualize the esophagus. The location of the esophagus was determined in relation to the PVs and anatomic regions of the LA by both ICE and MRI. Using the MRI images as a reference, the accuracy of ICE localization was assessed. RESULTS: The most common location for the esophagus to appear was the mid-posterior wall (80% of patients by ICE, 71% of patients by MRI), followed by the left posterior wall (71% of patients by ICE, 63% of patients by MRI) and the right posterior wall (60% of patients by ICE, 51% of patients by MRI). The esophagus was seen to course near the left PV antrums (left superior PV antrum 34% of patients by ICE and MRI; left inferior PV antrum 34% of patients by ICE, 37% of patients by MRI), left superior PV (17% of patients by ICE, 20% of patients by MRI), left inferior PV (17% of patients by ICE and MRI), right inferior PV antrum (29% of patients by ICE, 37% of patients by MRI) and the right inferior PV (3% of patients by ICE, 17% of patients by MRI). The sensitivity for esophageal location by ICE compared to that by MRI ranged between 33% (right inferior PV) and 92% (left superior PV antrum, left inferior PV antrum, and mid-posterior wall). The specificity for esophageal location by ICE compared to that by MRI ranged between 60% (mid-posterior wall) and 100% (right inferior PV). The positive predictive value ranged between 80% (left inferior PV) and 100% (right inferior PV). The negative predictive value ranged between 84% (right inferior PV antrum) and 96% (left superior PV antrum). CONCLUSION: Phased array ICE provides rapid, real-time localization of the esophagus during LA ablation that is comparable to MRI.

Atrial Fibrillation↗
PubMed2006

Atrial arrhythmias following ostial or circumferential pulmonary vein ablation.

AIMS: The incidence, clinical significance and optimum treatment of AF ablation-induced proarrhythmia is not entirely known. This report describes the incidence and management of atrial arrhythmias occurring after various techniques for the ablative therapy of atrial fibrillation (AF). METHODS: Five hundred and forty-four patients with paroxysmal atrial fibrillation were subjected to ostial pulmonary vein (PV) (n = 204), antral (n = 300), or circumferential (n = 40) ablation around the PV ostia. RESULTS: Atrial tachycardia or flutter during the first 6 months after AF ablation was detected in 14 patients and was more common among patients subjected to circumferential or circumferential and linear ablation (18% and 22%, respectively) than to other techniques (p < 0.001). The risk of atrial tachycardia or flutter among patients who underwent ostial, ostial with lines and antral ablation was 1%, 8% and 1%, respectively. No difference was observed in the risk of atrial arrhythmia between patients who underwent ablation with or without additional lines, either ostial (p = 0.17) or circumferential (p = 0.99). Re-ablation was performed in patients with sustained atrial arrhythmia (11 out of 14 patients). At 6 months, no recurrence was seen in 10 of these patients as well as in 3 patients with non-sustained atrial tachycardia or flutter. CONCLUSIONS: The incidence of atrial tachycardia or flutter following AF ablation is lower for ostial than circumferential ablation. The addition of lines along the mitral isthmus and between the superior PVs does not significantly affect the risk of ablation-induced arrhythmia. Non-sustained atrial tachycardia or flutter following AF ablation procedures does not always require additional ablation.

Adult↗
PubMed2006

Paradoxical undersensing during atrial flutter: what is the mechanism?

A patient with congenital complete heart block underwent implantation of a dual-chamber pacemaker. He presented to the emergency room with fatigue and was found to be in atrial flutter. Device interrogation revealed undersensing of 5 mV flutter waves at a programmed sensitivity of 0.5 mV. Due to undersensing, mode switch did not occur. This case illustrates apparently paradoxical undersensing of atrial flutter waves by a dual-chamber pacemaker and can be explained by a phenomenon known as "quiet timer blanking."

Adult↗
PubMed2006

Management of recalled pacemakers and implantable cardioverter-defibrillators: a decision analysis model.

CONTEXT: Limited information exists to direct clinical management after an implantable device has been put under advisory. A better understanding of the risks and benefits of device replacement compared with continued clinical follow-up would be helpful to clinicians. OBJECTIVE: Using the tools of decision analysis, to determine the best management approach (immediate device replacement vs continued monitoring) in the setting of a device advisory. DESIGN: A decision model was constructed to evaluate the risks and benefits associated with immediate device replacement compared with continued monitoring. MAIN OUTCOME MEASURES: Variables considered included indications for device implantation, anticipated course following device failure, device failure rates from the advisory ranging from 0.0001% to 1.0% per year, and device replacement mortality rates ranging from 0.10% to 1.00% per procedure. Device replacement was preferred to continued follow-up when replacement led to greater patient survival. RESULTS: The decision to replace a recalled device depends primarily on the advisory's estimated device failure rate and the likely effects of device failure on mortality. Procedural mortality is an important secondary factor, while patient age and remaining generator life have the least influence on the decision. For pacemaker-dependent patients, advisory device failure rates exceeding 0.3% warrant device replacement in most situations. In patients with implantable cardioverter-defibrillators for primary or secondary prevention, a failure rate associated with an advisory of 3.0% is needed to favor replacement in most cases, decreasing to close to 1.0% as procedural mortality rates decrease to 0.1% or risk of fatal arrhythmias increase to near 20% per year. In cases of pacemaker implantation for non-life-threatening situations (eg, carotid sinus hypersensitivity), most device advisories do not warrant device replacement. CONCLUSIONS: The decision to replace a device under advisory is determined primarily by the incidence of device malfunction and the likely effects of device failure. This analysis provides a framework for managing recalled devices in the context of device, patient, and institutional characteristics.

Decision Support Techniques↗
PubMed2006

Effects of gap geometry on conduction through discontinuous radiofrequency lesions.

BACKGROUND: Gaps of sufficient cross-sectional dimensions within linear radiofrequency (RF) lesions may allow conduction through the lesion. The purpose of this study was to examine the effects of different gap geometries on conduction through discontinuous RF lesions. METHODS AND RESULTS: Radiofrequency lesions were created in isolated, perfused rabbit right ventricular (RV) free wall preparations to produce gaps with 3 different lesion geometries: straight, bifurcated, and angled (n=10 each group). Angled preparations contained 2 right angles within the conduction path. Optical mapping was used to assess bidirectional conduction through the myocardium before and after gap formation during pacing at 1000-, 400-, and 200-ms cycle lengths. Histological analysis was performed on each preparation after optical mapping. After lesion formation, 9 of 10 straight gap preparations and 1 of 10 angled gap preparations demonstrated bidirectional conduction (P<0.001) at all cycle lengths. Nine of 10 bifurcated gap preparations demonstrated bidirectional conduction and 1 demonstrated unidirectional conduction at all cycle lengths. Two bifurcated gap preparations showed rate-dependent unidirectional 2:1 conduction. All unidirectional and rate-dependent block occurred during impulse propagation in the direction of diverging arms of the bifurcation. The occurrence of bidirectional conduction in the gaps was associated with the gap geometry (P<0.0001). Histological analysis confirmed the continuity of viable myocardium transmurally throughout the length of the gap in each preparation. The sites of conduction block were demonstrated to be just after the first angle in the conduction path for angled gaps and at the branch point of a bifurcated gap. The predominant myofiber orientation was changed relative to the conduction path at angulations of the gaps. Flecainide (0.1 micromol/L) produced bidirectional conduction block in straight and bifurcated gap preparations with bidirectional conduction at baseline. CONCLUSIONS: Conduction through discontinuities in RF lesions is associated with gap geometry. Complex gap geometry may allow for unidirectional and/or rate-dependent block. Gaps within RF lesions are susceptible to pharmacological blockade.

Animals↗
PubMed2006

Is time to first recurrence of atrial fibrillation correlated with atrial fibrillation burden?

The time to the first recurrence of atrial fibrillation (AF) and the AF burden have commonly been used as end points for AF therapy. We conducted a retrospective analysis of data from a large pacemaker registry to assess the relation between the time to the first recurrence and the AF burden. Although a statistical association exists, the small correlation coefficients limit the clinical value of the time to first recurrence as an indicator of AF burden.

Aged↗
PubMed2006

Development and testing of an algorithm to detect implantable cardioverter-defibrillator lead failure.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) lead failures often present as inappropriate shock therapy. An algorithm that can reliably discriminate between ventricular tachyarrhythmias and noise due to lead failure may prevent patient discomfort and anxiety and avoid device-induced proarrhythmia by preventing inappropriate ICD shocks. OBJECTIVES: The goal of this analysis was to test an ICD tachycardia detection algorithm that differentiates noise due to lead failure from ventricular tachyarrhythmias. METHODS: We tested an algorithm that uses a measure of the ventricular intracardiac electrogram baseline to discriminate the sinus rhythm isoelectric line from the right ventricular coil-can (i.e., far-field) electrogram during oversensing of noise caused by a lead failure. The baseline measure was defined as the product of the sum (mV) and standard deviation (mV) of the voltage samples for a 188-ms window centered on each sensed electrogram. If the minimum baseline measure of the last 12 beats was <0.35 mV-mV, then the detected rhythm was considered noise due to a lead failure. The first ICD-detected episode of lead failure and inappropriate detection from 24 ICD patients with a pace/sense lead failure and all ventricular arrhythmias from 56 ICD patients without a lead failure were selected. The stored data were analyzed to determine the sensitivity and specificity of the algorithm to detect lead failures. RESULTS: The minimum baseline measure for the 24 lead failure episodes (0.28 +/- 0.34 mV-mV) was smaller than the 135 ventricular tachycardia (40.8 +/- 43.0 mV-mV, P <.0001) and 55 ventricular fibrillation episodes (19.1 +/- 22.8 mV-mV, P <.05). A minimum baseline <0.35 mV-mV threshold had a sensitivity of 83% (20/24) with a 100% (190/190) specificity. CONCLUSION: A baseline measure of the far-field electrogram had a high sensitivity and specificity to detect lead failure noise compared with ventricular tachycardia or fibrillation.

Aged↗
PubMed2006

Right ventricular pacing to assess transisthmus conduction in patients undergoing isthmus-dependent atrial flutter ablation: a new useful technique?

BACKGROUND: Successful radiofrequency (RF) ablation of typical, isthmus-dependent atrial flutter requires establishment and confirmation of bidirectional conduction block across the cavotricuspid isthmus. Low atrial pacing usually is performed from the bipoles of the 20-pole Halo catheter, septal and lateral to the cavotricuspid isthmus ablation line. However, occasionally this is difficult because of high pacing thresholds and/or saturation of the atrial electrograms recorded near the pacing catheter. OBJECTIVES: The purpose of this study was to assess if right ventricular (RV) pacing and resulting retrograde atrial activation can be used to assess conduction block from the septum to the lateral wall in a clockwise direction. METHODS: Thirty-five consecutive male patients (mean age 64 +/- 10 years; mean ejection fraction 42 +/- 13%; mean left atrial dimension 44 +/- 6 mm) with typical isthmus-dependent atrial flutter were studied. The following electrophysiology catheters were used: 20-pole catheter along the tricuspid annulus, quadripolar catheters at the His and/or RV apex, and 8-mm ablation catheter. Following RF ablation of the cavotricuspid isthmus, bidirectional conduction block was confirmed in all 35 patients by pacing at a cycle length of 600 ms from bipoles septal and lateral to the cavotricuspid isthmus ablation line. Conduction times from pacing artifact to adjacent bipolar atrial electrograms and reversal of atrial activation pattern were analyzed. RV pacing was performed and retrograde atrial activation pattern assessed. If retrograde AV nodal conduction was absent, isoproterenol was infused intravenously at 2 microg/min, and RV pacing was repeated. The conduction time between the double potentials across the cavotricuspid isthmus ablation line was measured. RESULTS: Mean conduction times across the isthmus during septal (S), lateral (L), and RV pacing were 145 +/- 21 ms, 144 +/- 24 ms, and 129 +/- 20 ms, respectively. Retrograde AV nodal conduction was present in 34 of 35 patients (isoproterenol 8 patients). Evidence of conduction block by a clear change in activation pattern across the isthmus was seen during RV pacing in 33 of 35 patients with bidirectional conduction block. CONCLUSION: RV pacing is a simple and easy maneuver that can be performed to assess isthmus conduction in most patients.

Atrial Flutter↗
PubMed2006

Detection of microbubble formation during radiofrequency ablation using phonocardiography.

AIMS: To detect and characterize the acoustic energy generated by microbubble (MB) formation in an isolated tissue preparation. MB formation during radiofrequency (RF) ablation indicates excessive tissue heating and may precede explosive 'pops'. Currently, MB formation can only be detected with echocardiography. We hypothesized that MB formation can be detected with high-sensitivity phonocardiography. METHODS AND RESULTS: In a saline bath, RF lesions were created in sections of porcine left ventricle, using a 4 mm tip irrigated catheter. MB formation was visualized with an echocardiography probe. In 20 preparations, RF energy was begun at 25 W and increased by 5 W every 20 s until a pop occurred. A high-sensitivity computerized phonocardiography transducer with frequency bandwidth of 2 kHz and system noise -90 dB (SonoMedica, Inc., Vienna, VA, USA) was coupled to the external glass wall of the bath. In 15 of 20 (75%) preparations, a characteristic acoustic signature corresponding to MB formation was noted before the pop. These signals were within the 600-2000 Hz range and had an intensity range of 10-40 dB. The earliest MB and acoustic signals occurred 51.3+/-51.5 s before the pop. The acoustic signals continued intermittently up to 10.3+/-12.9 s before the pop. CONCLUSION: The acoustic energy created by MB formation can be detected in an isolated tissue preparation, using a computer-based phonocardiography system. Characteristic acoustic signatures are present before pops and correspond to MB formation. Acoustic monitoring for MB formation may allow for the titration of cooled RF ablation without echocardiography.

Animals↗
PubMed2006

Incidence, time course, and characteristics of microbubble formation during radiofrequency ablation of pulmonary veins with an 8-mm ablation catheter.

BACKGROUND: Microbubble formation during pulmonary vein (PV) radiofrequency (RF) ablation of atrial fibrillation (AF) occurs relatively frequently. Prior studies have shown that microbubble formation may be associated with an increased risk of complications. However, the incidence, time course, and temperature characteristics of microbubble formation during AF ablation with an 8-mm catheter have not been prospectively described in humans. METHODS: We studied 46 (30 men, age 56+/-10 years) patients with AF who underwent RF ablation of PVs between January 2005 and December 2005 using an 8F, 8-mm Biosensetrade mark ablation catheter (Biosense-Webster, Diamond Bar, CA, USA). All patients underwent continuous intracardiac echocardiography (ICE). Microbubble patterns were classified as either type 1 (intermittent, scattered microbubble formation) or type 2 (explosive shower of dense microbubbles). Formation of any microbubbles was detected by ICE and the time, PV location, and electrode temperature were recorded. RESULT: A total of 1,479 (32+/-13, range 12-73) RF lesions were delivered to 167 veins. Twenty (2%) lesions were classified as type 2. Since the number of lesions resulting in type 2 bubbles was very small, only type 1 lesions were included in the final analysis. Thirty-nine (85%) patients had at least one lesion associated with bubble formation during ablation (mean: 7+/-7 lesions, range 1-28 lesions). Twenty-three percent (327) of the RF lesions resulted in bubble formation. RF generator power setting during lesions resulting in bubble formation was lower than lesions which did not result in bubble formation (47.9+/-7.4 W vs 49.7+/-7.1 W, P<0.001). Logistic regression analysis revealed a significant negative correlation (P<0.001) between RF generator power settings and a positive correlation between the generator temperature settings and formation of bubbles (both P<0.02). However, the maximum temperature attained was not different between lesions resulting in bubble formation (n=327) and those which did not result in bubble formation (n=1,139). Fifty-three (16%) of the lesions associated with bubble formation occurred within 2-10 seconds after RF was begun. Bubble formation was significantly more frequent in left superior PVs compared to the other PVs (left superior PV 27.3% left inferior PV 18.6%, right superior PV 20.5%, and right inferior PV 18.8%, P=0.005, left superior PV vs other PVs, P<0.001) even after adjustment for the other factors including generator power settings and the temperature setting. CONCLUSION: Bubble formation is common during RF ablation of PV with 8-mm tip catheter and can occur as early as 2 seconds after starting RF. RF generator power is negatively correlated with bubble formation while generator temperature settings are positively correlated with formation of bubbles. Microbubble formation is also more frequent with ablation of the left superior PV probably due to better catheter contact in that area.

Atrial Fibrillation↗
PubMed2006

Reanalysis of the "pseudo A-A-V" response to ventricular entrainment of supraventricular tachycardia: importance of his-bundle timing.

BACKGROUND: The sequence of atrial and ventricular electrograms following termination of ventricular pacing during supraventricular tachycardia has been shown to reliably differentiate atrial tachycardia from atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT). However in patients with long HV intervals, this may be misleading due to a pseudo "A-A-V" response. The aim of the present study is to see if inclusion of the timing of the His-bundle in the electrogram response (ER) following ventricular pacing would reliably identify the mechanism of tachycardia in patients with long HV intervals. METHODS: Eight patients (7 men) with AVNRT and underlying bundle branch block and long HV (>55 msec) intervals underwent ventricular pacing at 10-40 msec shorter than the tachycardia cycle length during SVT. The ER was classified as "A-A-H" or "A-H" depending on the number of atrial electrograms (A) prior to His deflection following VEP. RESULTS: The ER following ventricular pacing was classified as A-H in all 8 patients. However, using conventional classification the response was A-A-V in 5 of 8 patients due to delayed ventricular activation secondary to long HV intervals and would erroneously suggest atrial tachycardia. The ER was A-V in only 1 of 8 patients. In the remaining 2 patients the A and V electrograms were simultaneous. CONCLUSIONS: Incorporating the His-bundle in the ER following ventricular pacing would eliminate the pseudo "A-A-V" response in patients with AVNRT and long HV intervals. Labeling the response to ventricular pacing as "A-H" or "A-A-H" is simple and more accurate.

Aged↗
PubMed2005

Why should we care about CARE-HF?

Previous trials of cardiac resynchronization therapy (CRT) have suggested that this therapy can significantly improve functional class and exercise capacity during short-term follow-up. The impact of this therapy on morbidity and mortality has only recently been reported. The Cardiac Resynchronization-Heart Failure (CARE-HF) study has definitively shown that CRT significantly reduces mortality (36%, p < 0.002) in patients with NYHA functional class III and IV heart failure and ventricular dyssynchrony. This study also shows that CRT reverses ventricular remodeling and improves myocardial performance progressively for at least 18 months. In heart failure patients, the CARE-HF and Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) (the earlier major morbidity/mortality trial) studies together show the unequivocal benefit for CRT therapy and CRT therapy with back-up defibrillation to significantly reduce mortality and hospitalization compared with optimal medical therapy. Both studies suggest the benefit of adding the implantable cardiac defibrillator to CRT devices, as over one-third of deaths in the CRT-pacemaker arm of both the COMPANION and CARE-HF studies were sudden.

Cardiac Output, Low↗
PubMed2005

Influence of the randomized trials, AFFIRM and RACE, on the management of atrial fibrillation in two University Medical Centers.

The results of the Atrial Fibrillation Follow-Up Investigation of Rhythm Management (AFFIRM) and the Rate Control Versus Electrical Cardioversion for Persistent Atrial Fibrillation (RACE) study were presented in March 2002. These large studies showed no benefit of a rhythm-control strategy over a rate-control strategy in managing atrial fibrillation (AF). Cardioversion and atrioventricular junctional ablation are forms of rhythm control and rate control, respectively. The numbers of cardioversions and atrioventricular junctional ablations performed at the University of Virginia and the Medical College of Virginia during the 52 months before AFFIRM and RACE results were released and the 21 months afterward were compared. From January 1998 to March 2002, monthly averages of 31 +/- 8 elective cardioversions and 6 +/- 3 atrioventricular junctional ablations were performed; from April 2002 to December 2003, the monthly averages were 21 +/- 6 cardioversions (p = 0.001) and 9 +/- 3 ablations (p = 0.001). AF management changed at these institutions shortly after the RACE and AFFIRM results were released.

Atrial Fibrillation↗