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Richard K Shepard

Publications and source records attributed to Richard K Shepard.

15 recordsLinked to original sources
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

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↗
PubMed2004

An algorithm to predict implantable cardioverter-defibrillator lead failure.

OBJECTIVES: The goal of this analysis was to test an algorithm that identifies implantable cardioverter-defibrillator (ICD) lead problems before clinical failure and/or inappropriate therapy. BACKGROUND: The ICD lead failures typically present as inappropriate shock therapy. Identifying lead failures before their clinical presentation may prevent patient discomfort, improve device longevity, and avoid device-induced proarrhythmia. METHODS: We tested an algorithm that uses two measures of oversensing and one measure of abnormal impedance to detect a lead failure. The oversensing measures consisted of a counter for RR intervals <140 ms and nonsustained ventricular tachycardia episodes with mean RR interval <200 ms. The impedance measure tracked lead impedances every day and each week. Abnormal impedance was defined as a decrease in impedances or an outlier value compared with baseline. Lead failures were identified when both oversensing measures were met or abnormal impedance and one oversensing measure occurred. The stored data from 696 patients with an ICD were analyzed to determine the sensitivity and specificity of the algorithm to detect lead failures. RESULTS: Twenty-nine patients demonstrated clinical lead failures with an average of 6 +/- 9 inappropriate shocks per patient. The two oversensing measures used in the algorithm predicted 72% (21 of 29) of the lead failures. Fulfilling at least two of the three impedance and oversensing measures, the sensitivity of our algorithm was 83% (24 of 29) with a 100% (667 of 667) specificity. CONCLUSION: Oversensing combined with abnormal impedance trends may be used to identify ICD lead failures with high sensitivity and very high specificity.

Algorithms↗
PubMed2004

A comparison of pulmonary vein ostial anatomy by computerized tomography, echocardiography, and venography in patients with atrial fibrillation having radiofrequency catheter ablation.

Accurate assessment of pulmonary vein anatomy is important to procedures that isolate these structures in patients with atrial fibrillation. Various modalities of pulmonary vein (PV) imaging are employed in clinical practice; however, the consistency of findings among the different modalities is unknown. The purpose of this study is to compare PV ostial anatomy by 4 common imaging techniques. Twenty-four patients undergoing catheter-based PV isolation procedures for atrial fibrillation had their PV ostial anatomy determined by cardiac computerized tomography (CT) and transesophageal echocardiography (TEE) before ablation and by intracardiac echocardiography (ICE) and venography during the ablation procedure. The number and maximal dimension of the PV ostia were determined by each imaging modality. In the 24 patients, 98 PV ostia were visualized by CT, 93 by ICE, 81 by TEE, and 71 by venography. The average ostial diameters were similar between CT (1.45 +/- 0.29 cm) and ICE (1.51 +/- 0.22 cm, p = 0.066). Compared with CT or ICE, the ostial diameters were larger with venography (1.67 +/- 0.32 cm) and smaller with TEE (1.16 +/- 0.28 cm, all p <0.001). PV ostial diameters as determined by ICE were significantly correlated with CT measurements (r = 0.57, p <0.001) and venography (r = 0.52, p <0.001). Venography measures of PV diameter were correlated with measures by CT (r = 0.33, p = 0.03). TEE measures were not correlated with any other modality (all p >/=0.43). CT identifies the greatest number of PV ostia followed by ICE. Venography overestimates and TEE underestimates ostial diameters compared with CT or ICE. The PV ostial dimensions obtained by ICE, CT, and venography are all significantly correlated.

Atrial Fibrillation↗
PubMed2004

Use of a non-fluoroscopic catheter navigation system for pulmonary vein isolation.

INTRODUCTION: Pulmonary vein (PV) isolation is commonly performed by using separate mapping and ablating catheters. Steering the ablation catheter to the target electrodes on the mapping catheter can be difficult and time consuming under fluoroscopic guidance. We investigated the use of a non-fluoroscopic catheter navigation system to facilitate radiofrequency pulmonary vein isolation. METHODS: The LocaLisa non-fluoroscopic catheter navigation system was used during PV isolation in 21 patients. Eleven control patients underwent the procedure under fluoroscopic guidance alone. PV isolation was performed by mapping the veins with a 10 or 20 pole circular mapping catheter and ablating at targeted mapping bipoles with a separate ablation catheter. RESULTS: The electrodes of both catheters were visualized in 3 dimensional virtual space by LocaLisa. There were no clinical differences between the LocaLisa and control patients. During mapping, electrical artifacts were produced on specific mapping electrodes by contact with the ablation catheter. A blinded observer using LocaLisa correctly identified the mapping electrodes being contacted by the ablation catheter in 368 of 398 (92%) of cases. Total fluoroscopic time was reduced in the LocaLisa group (72 +/- 29 minutes) compared to the control group (102 +/- 37 minutes, p = 0.02). There were no differences between the groups in total procedure times, number of lesions given, complications or long term procedural success (all p > 0.45). CONCLUSIONS: The LocaLisa catheter navigation system accurately identifies the position of an ablation catheter relative to the target electrodes on a circular mapping catheter. The system also significantly reduces total fluoroscopic time for PV isolation.

Atrial Fibrillation↗
PubMed2004

Response of pulmonary vein potentials to burst pacing.

BACKGROUND: Pulmonary vein potentials recorded at the ostia of pulmonary veins (PV) are a useful guide for segmental isolation of the PV in patients with atrial fibrillation (AF). Even during coronary sinus pacing at 600 ms, atrial (A) and PV potentials can overlap in 50-60% of patients making the accurate identification of PV potentials very difficult. METHODS: Nineteen patients (M:F 15:4) with paroxysmal AF underwent segmental isolation of one or more PV. Coronary sinus (CS) pacing was performed at cycle lengths of 600/550/500/450/400/350/300 ms and bipolar electrograms were recorded from the 10 or 20 pole Lasso catheter placed at the atrial-PV junction in 27 pulmonary veins. Stimulus (S) to A, S-PVP and A-PVP intervals were measured during CS pacing at the different cycle lengths at sweep speed of 200 mm/sec. RESULTS: During CS pacing at 600 ms the A and PV potentials were significantly overlapped (A-PVP < or = 25 ms) in 15 of 27 (55%) veins. During pacing at 300 ms, the A and PV potentials were significantly separated (A-PVP > or = 25 ms) in 9 of the 15 veins where A and PV potentials overlapped and 21 of all 27 (78%) veins. In two patients pacing at 300 ms was associated with 2:1 conduction block from atrial to PV fascicle. CONCLUSIONS: Coronary sinus pacing at cycle length of 300 ms demonstrated better separation of A and PV potentials compared to pacing at 600 ms. This strategy is easier and less time consuming compared to extrastimuli testing. It also confirms that the electrophysiological properties of PV fascicles are different from that of the adjacent atrial musculature.

Atrial Fibrillation↗
PubMed2003

Detection and management of an implantable cardioverter defibrillator lead failure: incidence and clinical implications.

OBJECTIVES: This study evaluated the long-term reliability of an implantable cardioverter defibrillator (ICD) lead to determine the incidence, clinical presentation, and management of lead failure. BACKGROUND: Despite recent advances in ICD technology, the long-term reliability of ICD leads remains a significant problem. METHODS: Concern about long-term reliability of coaxial polyurethane ICD leads caused us to systematically study all patients implanted with Medtronic (Minneapolis, Minnesota) 6936 lead at our institution. We performed follow-up of 74 patients with 76 ICD leads that were implanted from February 28, 1995 to September 8, 1997. Thirty-seven patients underwent routine clinical ICD follow-up testing and ventricular fibrillation induction to determine the status of their ICD lead after a mean follow-up of 68.6 +/- 8.2 months. RESULTS: The lead survival analysis shows a cumulative failure probability of 37% (confidence interval, 24% to 54%) at 68.6 months. Six patients demonstrated a previously undescribed mode of ICD lead failure: prolonged oversensing immediately after shock therapy. The use of short interval counters to monitor nonphysiologic R-R intervals and the measurement of ring-to-coil impedance detected early lead failures in five patients. CONCLUSIONS: This analysis shows: 1) problems with ICD leads may not become apparent until late during follow-up and may become a significant late problem, 2) a "signature" mode of lead failure for the 6936 consisting of oversensing of electrical noise following shocks, 3) early detection of lead failure with a short interval counter algorithm or measurement of ring-to-coil impedance may be clinically useful.

Aged↗
PubMed2003

Prospective randomized comparison of 65%/65% versus 42%/42% tilt biphasic waveform on defibrillation thresholds in humans.

BACKGROUND: The waveform tilt of biphasic shocks yielding the lowest defibrillation threshold (DFT) is not well defined. Some evidence indicates that tilts less than 65% may improve DFTs. METHODS: In 57 patients undergoing ICD implantation, DFTs were determined with truncated exponential biphasic waveform tilts at 65%/65% and at 42%/42%. An external defibrillator with custom software was used for testing. The effective capacitance of the defibrillator was 132-microF for both waveforms. DFTs were determined using a binary search method starting with 12 Joules (J). Patients were randomly assigned to initial testing with either one of the two tilts. Thirty patients (Group 1) were tested with a two electrode (active can to RV coil, or SVC coil to RV coil) and 27 patients (Group 2) were tested with a three electrode system (subcutaneous patch or active can + SVC coil to RV coil). RESULTS: Groups 1 and 2 did not differ in age, ejection fraction or antiarrhythmic medications. Group 1 delivered energy DFTs were 10.1 +/- 5.5 J with the 65%/65% tilt and 10.1 +/- 5.9 J for the 42%/42% tilt (p = 0.92). In group 2 the average DFT for the 65%/65% tilt was 8.4 +/- 5.7 J and for the 42%/42% tilt was 8.1 +/- 5.3 J (p = 0.70). There were no significant differences in DFTs for either group. The system impedance for Group 1 was 64 +/- 12 ohms and for Group 2 was 39 +/- 6 ohms (p < 0.0001). CONCLUSIONS: We found no differences in DFTs between 65%/65% tilt and 42%/42% tilt using either 2- or 3-electrode defibrillation systems. Further research is needed to optimize waveforms in order to minimize DFTs, which will result in smaller ICDs and/or greater safety margins for defibrillation.

Aged↗
PubMed2003

Long-term outcome of patients after successful radiofrequency ablation for typical atrial flutter.

The aim of the study was to determine the long-term freedom from atrial arrhythmias after radiofrequency ablation of atrial flutter and to determine the factors associated with recurrent arrhythmias. Radiofrequency ablation has emerged as the preferred treatment for recurrent, typical atrial flutter. Although the short-term results after radiofrequency ablation of atrial flutter have been widely reported, there is insufficient data on long-term outcome with respect to the occurrence of atrial arrhythmias in patients after successful ablation. The first 108 patients to undergo successful ablation for typical atrial flutter at the authors' institutions were followed prospectively until the occurrence of typical atrial flutter, atrial fibrillation, atypical atrial flutter, or death. Several prespecified clinical and procedural factors were tested using univariate and multivariate analysis as predictors of arrhythmia recurrence. Patients were followed for a minimum of 3 years and a maximum of 8 years, or until the first arrhythmia recurrence (average duration 17 +/- 17 months). Recurrences of typical atrial flutter were usually observed within the first 6 months (73%, n = 16), with the remainder (27%, n = 6) occurring between 6 months and 2 years, and none were observed later. Freedom from recurrence of typical atrial flutter was 80% at 1 year (95% CIs 72-89%), 73% at 2 years (CIs 63-83%), and 73% at 5 years (CIs 63-83%). By contrast, freedom from occurrence of atrial fibrillation or atypical atrial flutter progressively declined over time; 80% at 1 year (CIs 71-88%), 59% at 2 years (CIs 48-70%), and 33% at 5 years (CIs 19-48%). A history of atrial fibrillation or atypical atrial flutter prior to ablation was associated with an increased risk of occurrence during follow-up (relative risk 3.4, CIs 1.5-8.1, P < 0.05). Freedom from occurrence of any atrial arrhythmia was only 27% at 5 years (CIs 15-40%). After successful ablation of typical atrial flutter, recurrence of typical flutter is relatively uncommon and usually occurs early. However, there is a progressive occurrence of atrial fibrillation and/or atypical flutter during follow-up so that many patients require further antiarrhythmic or additional ablative therapy. Radiofrequency ablation of typical atrial flutter should be considered a palliative procedure for most patients and only one component of the long-term care of the patient with atrial tachyarrhythmias.

Aged↗
PubMed2003

Characterization of sustained atrial tachycardia in dogs with rapid ventricular pacing-induced heart failure.

INTRODUCTION: Atrial arrhythmias often complicate congestive heart failure (CHF). We characterized inducible atrial tachyarrhythmias and electrophysiologic alterations in dogs with CHF and atrial enlargement produced by rapid ventricular pacing. METHODS AND RESULTS: Endocardial pacing leads were implanted in the right ventricle, right atrium, and coronary sinus in 18 dogs. The right ventricular lead was connected to an implanted pacemaker capable of rapid ventricular pacing. The atrial leads were used to perform electrophysiologic studies in conscious animals at baseline in all dogs, during CHF induced by rapid ventricular pacing at 235 beats/min in 15 dogs, and during recovery from CHF in 6 dogs. After 20 +/- 7 days of rapid ventricular pacing, inducibility of sustained atrial tachycardia (cycle length 120 +/- 12 msec) was enhanced in dogs with CHF. Atrial tachycardia required a critical decrease in atrial burst pacing cycle length (< or = 130 msec) for induction and often could be terminated by overdrive pacing. Calcium antagonists (verapamil, flunarizine, ryanodine) terminated atrial tachycardia and suppressed inducibility. Effective refractory periods at 400- and 300-msec cycle lengths in the right atrium and coronary sinus were prolonged in dogs with CHF. Atrial cells from dogs with CHF had prolonged action potential durations and reduced resting potentials and delayed afterdepolarizations (DADs). Mitochondria from atrial tissue from dogs with CHF were enlarged and had internal cristae disorganization. CONCLUSIONS: CHF promotes inducibility of sustained atrial tachycardia. Based on the mode of tachycardia induction, responses to pacing and calcium antagonists, and presence of DADs, atrial tachycardia in this CHF model has a mechanism most consistent with DAD-induced triggered activity resulting from intracellular calcium overload.

Action Potentials↗
PubMed2003

Focal origin of atrial tachycardia in dogs with rapid ventricular pacing-induced heart failure.

UNLABELLED: Mapping and Ablation of Atrial Tachycardia in Heart Failure. INTRODUCTION: Dogs with rapid ventricular pacing-induced congestive heart failure (CHF) have inducible atrial tachycardia (AT), with a mechanism consistent with delayed afterdepolarization-mediated triggered activity. We assessed the hypothesis that AT has a focal origin. METHODS AND RESULTS: Twenty-one CHF dogs undergoing 3 to 4 weeks of ventricular pacing at 235 beats/min were studied. Biatrial epicardial mapping of 20 sustained AT episodes (cycle length [CL], 175 +/- 53 msec) in 5 dogs revealed an area of earliest activation in the right atrial (RA) free wall (13 episodes), RA appendage (4 episodes), or between the pulmonary veins (3 episodes). Total epicardial activation time during AT (73 +/- 19 msec) was similar to that during sinus rhythm (72 +/- 13 msec) and on average was <50% of the AT CL. Higher-density mapping of the RA free wall during 30 sustained AT episodes (163 +/- 55 msec) in 9 dogs identified a site of earliest activation along the sulcus terminalis most frequently as a stable, focal activation pattern from a single site. Endocardial mapping of 49 sustained AT episodes (156 +/- 27 msec) in 10 dogs revealed multiple sites of AT origin arising along the crista terminalis and pulmonary veins. Right and left ATs were terminated with discrete radiofrequency ablation, but other ATs remained inducible. A rapid, left AT generating an ECG pattern of atrial fibrillation was ablated inside the pulmonary vein. CONCLUSION: AT induced in this CHF model after 3 to 4 weeks of rapid ventricular pacing has an activation pattern consistent with a focal origin. Sites of earliest activation are distributed predominately along the crista terminalis and within or near the pulmonary veins.

Animals↗
PubMed2002

Delayed complications following pacemaker implantation.

Acute complications resulting from permanent pacemaker implantation are well known and include perforation of the right atrium or right ventricle. Recently, several reports have described the occurrence of perforation and pericarditis as late complications following pacemaker implantation. These complications may occur days to weeks following uncomplicated pacemaker implantation and may lead to death if they are not recognized early. Five patients with late complications caused by active-fixation leads are reported and the clinical features of their presentation and management are reviewed. Late perforation of the right atrium or right ventricle is an uncommon complication after pacemaker implantation but should be suspected by the general cardiologist in a patient who has a device implanted within a week to several months prior to the development of chest pain.

Adult↗
PubMed2002

Phased-array intracardiac echocardiography during pulmonary vein isolation and linear ablation for atrial fibrillation.

INTRODUCTION: Fluoroscopic imaging provides limited anatomic guidance for left atrial structures. The aim of this study was to determine the utility of real-time, phased-array intracardiac echocardiography during radiofrequency ablation for atrial fibrillation. METHODS AND RESULTS: In 29 patients undergoing pulmonary vein isolation (n = 16) or linear (n = 13) left atrial radiofrequency ablation for atrial fibrillation, intracardiac phased-array echocardiography was used to visualize left atrial anatomy and the pulmonary veins, as well as ablation and mapping catheters during ablation procedures. In the 16 pulmonary vein isolation patients, the mean pulmonary vein ostial diameters measured by venography and intracardiac echocardiography were similar for all veins positions, except that left common pulmonary vein diameters were larger as measured by echocardiography (2.50 +/- 0.29 cm) than by venography (1.79 +/- 0.50 cm, P = 0.001). The ostial diameters measured by echocardiography and venography were not correlated, however (r = 0.23, P = 0.19). As directed by echocardiography, only 1 of 25 circular mapping catheters (4%) used in 16 patients was replaced due to inappropriate sizing of the pulmonary veins. Mean pulmonary vein Doppler flow velocities increased after ablation for left-sided veins but ostial diameters were unchanged. In the linear ablation patients, the entire extent of the linear electrode array could be visualized in only 3 of 52 of catheter positions (6%) in the 13 patients. A portion of the catheter could be seen in only 50% of all target catheter positions. CONCLUSION: Phased-array intracardiac echocardiography (1) allows sizing and positioning of pulmonary vein mapping catheters, (2) provides measures of pulmonary vein ostial diameters, (3) continuously monitors pulmonary vein Doppler flow velocities, and (4) has limited use in positioning linear ablation catheters in the left atrium.

Alabama↗