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Biomedical subjects

Gregory K Feld

Publications and source records attributed to Gregory K Feld.

At least 19 recordsLinked to original sources
PubMed2006

Diagnostic accuracy of irregularly irregular RR intervals in separating atrial fibrillation from atrial flutter.

Periodic electrocardiographic RR intervals are often used to separate atrial flutter (AFl) from atrial fibrillation (AF), but have not yet been validated. We hypothesized that irregularly irregular electrocardiographic RR intervals poorly identify AF from AFl, and that atrial wavefront regularity affects variability in atrioventricular conduction. We studied the electrocardiographic RR intervals in 66 patients referred for ablation of AFl (21 atypical and 21 typical) and AF (n=24) in relation to intracardiac activation. Receiver-operating characteristics showed that periodicity in 60% of RR intervals provided only 66% sensitivity and 86% specificity for typical AFl and failed to separate atypical AFl from AF. Fewer RR intervals were integer atrial/ventricular ratios in atypical than in typical AFl (50% vs 83%, p=0.005), reflecting greater SDs in atrial cycles (6.98+/-7.02 vs 3.10+/-1.62 ms, p=0.023), more variable AH intervals (56+/-28 vs 18+/-21 ms, p=0.002), longer AH intervals (185+/-65 vs 118+/-31 ms, p=0.01), and greater AH variability for any atrial cycle length (p=0.026). In conclusion, irregularly irregular RR intervals are not specific for AF, are common in AFl, and should not be used to conclusively separate AF from AFl in the absence of sawtooth flutter waves. Future studies should explore the relation among AFl circuit location, cycle variability, and atrioventricular nodal conduction.

Atrial Fibrillation↗
PubMed2005

Separating atrial flutter from atrial fibrillation with apparent electrocardiographic organization using dominant and narrow F-wave spectra.

OBJECTIVES: The purpose of this study was to separate atrial flutter (AFL) with atypical F waves from fibrillation (AF) with "apparent organization." BACKGROUND: We hypothesized that F-wave spectra should reveal a dominant and narrow peak in AFL, reflecting its single macro-re-entrant wave front, but broad spectra in AF, reflecting multiple wave fronts. METHODS: We identified 39 patients with electrocardiograms (ECGs) of "AFL/AF" or "coarse AF" from 134 consecutive patients referred for ablation: 21 had AFL (18 atypical, 3 typical), 18 had AF, and all were successfully ablated. Filtered atrial ECGs were created by cross-correlating F waves to successive ECG time points. Dominant peaks between 3 and 10 Hz were identified from power spectra of X (lead V5), Y (aVF), and Z (V1) axes, and for each, we calculated height (relative to two adjacent spectral points) and area ratio to envelopes of bandwidth 0.625, 1.25, 2.5, 3.75, and 5 Hz (range 0 to 1, where higher ratios reflect narrower peaks). RESULTS: Dominant peaks had greater relative height for AFL than AF (three-axis mean: 14.2 +/- 6.4 dB vs. 6.6 +/- 2.1 dB; p < 0.001). Peak area ratios were also higher for AFL than AF for all envelopes (p < 0.001). For the 2.5-Hz envelope, the separation (0.61 +/- 0.14 vs. 0.35 +/- 0.05, respectively; p < 0.001) enabled a ratio > or =0.44 to identify all cases of AFL from AF (p < 0.001). A panel of seven cardiologists blinded to clinical data provided lower diagnostic accuracy (82.1%; p < 0.01). CONCLUSIONS: In ambiguous ECGs with atypical F waves, spectral evidence for a solitary activation cycle separates AFL from AF with "apparent organization." This approach might improve bedside ECG diagnosis and shed light on intra-atrial organization of both rhythms.

Algorithms↗
PubMed2005

Separating non-isthmus- from isthmus-dependent atrial flutter using wavefront variability.

OBJECTIVES: The aim of this study was to separate isthmus-dependent atrial flutter (IDAFL) from non-isthmus-dependent atrial flutter (NIDAFL) from the electrocardiogram (ECG) based on functional differences. BACKGROUND: The ECG analyses of F-wave shape suboptimally separate NIDAFL from IDAFL. The authors hypothesized that anatomic and functional differences may result in greater wavefront variability in NIDAFL than IDAFL, allowing their separation. The authors tested this hypothesis in patients undergoing ablation for atrial flutter using a novel ECG algorithm to detect subtle F-wave variability, validated by intracardiac measurements. METHODS: In 62 patients (23 NIDAFL, 39 IDAFL) ECG atrial wavefronts were represented as correlations of an F-wave template to the ECG over time. Correlations in orthogonal ECG lead-pairs were plotted at each time point to yield loops reflecting temporal and spatial regularity in each plane. The ECG analyses were compared with intracardiac standard deviations of: 1) atrial electrograms (temporal variability), and 2) bi-atrial activation time differences (spatial variability). RESULTS: Atrial ECG temporospatial loops were reproducible in IDAFL, but varied in NIDAFL (p < 0.01) suggesting greater variability that correctly classified IDAFL (39 of 39 cases) from NIDAFL (22 of 23 cases; p < 0.001). Intra-atrial mapping confirmed greater temporal variability for NIDAFL versus IDAFL, in lateral (p < 0.01) and septal (p = 0.03) right atrium, and proximal (p = 0.02) and distal (p < 0.01) coronary sinus. Spatial variability was greater in NIDAFL than IDAFL (p = 0.02). CONCLUSIONS: Greater cycle-to-cycle atrial wavefront variability separates NIDAFL from IDAFL and is detectable from the ECG using temporospatial analyses. These results have implications for guiding ablation and support the concept that IDAFL and NIDAFL lie along a spectrum of intracardiac organization.

Algorithms↗
PubMed2005

Relation of initial resting ventricular rate to the ability to achieve and maintain normal sinus rhythm in patients with atrial fibrillation.

Rate-control and rhythm-control strategies in the management of atrial fibrillation (AF) have been shown to have similar effects on morbidity and mortality. Data are lacking as to whether specific electrocardiographic features of AF affect the ability to achieve rate or rhythm control. This study evaluated the relation between initial resting ventricular rate (IRVR) during AF and the subsequent achievement of rate control and rhythm control in the AFFIRM Study. The independent relations between IRVR and the achievement of rate and rhythm control were assessed using multivariate Cox's proportional hazards modeling. In addition, we evaluated whether IRVR was associated with major cardiovascular end points. IRVR was analyzed in 4,059 patients. IRVR was higher in women, smokers, patients who had a first episode of AF, and in patients who had preserved left ventricular systolic function but lower in patients who had coronary artery disease, hypertension, left atrial enlargement, and a qualifying episode of AF that lasted >48 hours. A higher IRVR was independently associated with the achievement (p <0.0001) and maintenance (p = 0.0002) of sinus rhythm, whereas the ability to achieve adequate rate control was independent of IRVR. A higher IRVR was associated with an increased risk of cardiovascular hospitalization (p <0.0001). In the appropriate clinical setting, a rhythm-control strategy should be considered for patients who have a higher IRVR.

Aged↗
PubMed2004

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study: approaches to control rate in atrial fibrillation.

OBJECTIVES: We sought to evaluate approaches used to control rate, the effectiveness of rate control, and switches from one drug class to another in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study. BACKGROUND: The AFFIRM study showed that atrial fibrillation (AF) can be treated effectively with rate control and anticoagulation, but drug efficacy to control rate remains uncertain. METHODS: Patients (n = 2,027) randomized to rate control in the AFFIRM study were given rate-controlling drugs by their treating physicians. Standardized rate-control efficacy criteria developed a priori included resting heart rate and 6-min walk tests and/or ambulatory electrocardiographic results. RESULTS: Average follow-up was 3.5 +/- 1.3 years. Initial treatment included a beta-adrenergic blocker (beta-blocker) alone in 24%, a calcium channel blocker alone in 17%, digoxin alone in 16%, a beta-blocker and digoxin in 14%, or a calcium channel blocker and digoxin in 14% of patients. Overall rate control was achieved in 70% of patients given beta-blockers as the first drug (with or without digoxin), 54% with calcium channel blockers (with or without digoxin), and 58% with digoxin alone. Adequate overall rate control was achieved in 58% of patients with the first drug or combination. Multivariate analysis revealed an association between first drug class and several clinical variables. There were more changes to beta-blockers than to the other two-drug classes (p < 0.0001). CONCLUSIONS: Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Adrenergic beta-Antagonists↗
PubMed2004

Efficacy of a microwave antenna for ablation of the tricuspid valve--inferior vena cava isthmus in dogs as a treatment for type 1 atrial flutter.

INTRODUCTION: Radiofrequency catheter ablation of the tricuspid valve-inferior vena cava (TV-IVC) isthmus for treatment of atrial flutter (AFL), may in some cases require a large number of energy applications and a long procedure and fluoroscopy time. AIMS OF STUDY: Therefore, we studied the safety and efficacy of a 4 cm long microwave antenna mounted on a steerable 9Fr catheter for linear ablation of the TV-IVC isthmus. METHODS: In 6 anesthetized dogs, multi-electrode catheters were positioned in the coronary sinus (decapolar), at the His bundle (quadripolar) and around the TV annulus (decapolar) for pacing and recording atrial activation sequences before and after ablation. The microwave antenna was then positioned across the TV-IVC isthmus from the TV annulus (identified by equal A and V potentials) to the inferior vena cava with slight traction on the catheter to ensure adequate endocardial contact. Microwave energy was then applied at a fixed power for 120 seconds during each ablation attempt. Ablation was repeated until bi-directional isthmus block was demonstrated during pacing from the coronary sinus ostium and low lateral right atrium, respectively. RESULTS: Linear microwave ablation of the TV-IVC isthmus was completed in all ten dogs using a total of 2.6 +/- 1.17 energy applications per dog. Power was applied in a range of 45-50 watts. There were no acute procedural complications. Bi-directional TV-IVC isthmus block was achieved in all ten dogs, as demonstrated by a strictly descending activation wavefront in the ipsilateral atrial wall, during pacing from the CSO and LLRA respectively. In addition, after ablation conduction time to the LLRA during pacing from the CSO increased from 52 +/- 16.62 before to 87 +/- 12.74 msec (p <.05), and to the CSO during pacing from the LLRA from 51 +/- 12.43 before to 79.50 +/- 9.85 msec (p <.05). Gross and histological examination of the TV-IVC isthmus after ablation revealed continuous transmural lesions, ranging from 3-5 mm in width, spanning the entire TV-IVC isthmus in all ten dogs. CONCLUSIONS: (1) Microwave ablation of the TV-IVC isthmus was safe and effective in this study. (2) Ablation of the entire width and thickness of the TV-IVC isthmus can be rapidly achieved using a long microwave antenna in a fixed trans-isthmus position.

Animals↗
PubMed2004

Radiofrequency ablation of atrial flutter using large-tip electrode catheters.

The use of large-tip ablation catheters in both animal and clinical studies has been documented in work conducted over the last 10 years. These studies have demonstrated the safety and efficacy of the use of 8- and 10-mm tip ablation catheters in the treatment of type I isthmus-dependent atrial flutter. Shorter procedure times are reported with the larger-tip ablation catheters compared to standard 4- or 5-mm tip ablation catheters, with comparable or greater efficacy, no significant increase in complications, and an improved quality of life. Larger-tip ablation electrodes do require the use of higher-power radiofrequency generators up to 100 W. The benefits of large-tip ablation catheters are thus well documented for the treatment of type I isthmus-dependent atrial flutter.

Animals↗
PubMed2004

Radiofrequency catheter ablation of Type 1 atrial flutter using a large-tip electrode catheter and high-power radiofrequency energy generator.

Recent studies have demonstrated a high degree of efficacy of 8 mm electrode-tipped or saline-irrigated-tip catheters for ablation of atrial flutter (AFL). These catheters have a theoretical advantage as they produce a large ablation lesion. However, large-tip ablation catheters have a larger surface area and require a higher power radiofrequency (RF) generator with up to 100 W capacity to produce adequate ablation temperatures (50-60 degrees C). The potential advantages of a large-tip ablation catheter and high-power RF generator include the need for fewer energy applications, shorter procedure and fluoroscopy times, and greater efficacy. Therefore, the safety and efficacy of AFL ablation using 8 or 10 mm electrode catheters and a 100-W RF generator was studied using the Boston Scientific, Inc., EPT-1000 XP cardiac ablation system. There were 169 patients, aged 61 +/- 12 years involved. Acute end points were bidirectional isthmus block and no inducible AFL. Following ablation, patients were seen at 1, 3 and 6 months, with event monitoring performed weekly and for any symptoms. Three quality of life surveys were completed during follow-up. Acute success was achieved in 158 patients (93%), with 12 +/- 11 RF energy applications. The efficacy of 8 and 10 mm electrodes did not differ significantly. The number of RF energy applications (10 +/- 8 vs. 14 +/- 8) and ablation time (0.5 +/- 0.4 vs. 0.8 +/- 0.6 h) were less with 10 mm compared with 8 mm electrodes (p < 0.01). Of 158 patients with acute success, 42 were not evaluated at 6 months due to study exclusions. Of the 116 patients evaluated at 6 months, 112 (97%) had no AFL recurrence. Of those without AFL recurrence at 6 months, 95 and 93% were free of symptoms at 12 and 24 months, respectively. Ablation of AFL improved quality of life scores (p < 0.05) and reduced anti-arrhythmic and rate control drug use (p < 0.05). Complications occurred in six out of 169 patients (3.6%) but there were no deaths. It was concluded that ablation of AFL with 8 or 10 mm electrode catheters and a high-power RF generator was safe, effective and improved quality of life. The number and duration of RF applications was lower with 10 mm compared with 8 mm electrode catheters.

Atrial Flutter↗
PubMed2003

Successful implantation of cardiac defibrillators without induction of ventricular fibrillation using upper limit of vulnerability testing.

INTRODUCTION: Conventionally, the implantable cardioverter-defibrillator (ICD) is tested at implantation by measurement of defibrillation threshold (DFT), which involves repeated induction of ventricular fibrillation (VF). We report our data on successful ICD implantation without VF induction using a modified upper limit of vulnerability (ULV) testing method, compared to standard DFT testing. METHODS: Fourteen patients underwent ICD implantation using a modified ULV testing method by delivering a 15 J shock during the vulnerable period on the peak of the T wave, and if VF was not induced 15 J shocks were repeated at -20 and -40 msec before the peak of T wave. Failure to induce VF, indicating a ULV <15 joules (J), suggested a DFT < or =20 J based on previous studies demonstrating a close correlation (+/-5 J) between ULV and DFT. If VF was induced, a 20 J rescue shock was delivered. ICD therapy was then programmed on the basis of ULV testing. All patients underwent pre-discharge DFT testing to confirm adequate DFT. RESULTS: Using a modified ULV testing method, ICD implantation was completed without induction of VF in 8 patients and only a single episode of VF in 6 patients. The mean number of VF episodes (0.42 +/- 0.5) induced with ULV testing was significantly lower (p <.001) than the number induced during DFT testing (3.9 +/- 0.8). Pre-discharge DFT testing did not alter ICD programming in any patient. During follow-up of 14.85 +/- 12.31 months, three patients had seven episodes of VT/VF, six of whom were converted with the programmed first-shock strength, while one required a second high-energy shock to convert. This patient had a pre-discharge DFT of 10 joules. CONCLUSIONS: Successful ICD implantation can be safely performed with no or fewer episodes of VF induction using a modified ULV testing method.

Aged↗
PubMed2003

Conduction velocity around the tricuspid valve annulus during type 1 atrial flutter: defining the location of areas of slow conduction by three-dimensional electroanatomical mapping.

BACKGROUND: Conduction velocity (CV) around the tricuspid valve annulus (TVA) during type 1 atrial flutter (AFL) has been shown to be slowest in the tricuspid valve-inferior vena cava (TV-IVC) isthmus, compared to the septal or free wall segments of the TVA. However, fiber orientation in the triangle-of-Koch suggests that the inferior septum and medial TV-IVC isthmus should be the most slowly conducting segments around the TVA. METHODS: To test this hypothesis we evaluated CV around the TVA during type 1 atrial flutter in 11 patients, using an electro-anatomical mapping system (Carto). CV was first calculated in 4 segments around the TVA including the TV-IVC isthmus, lateral free wall, superior free wall and septum, and then calculated in 8 segments around the TVA including medial (MI) and lateral isthmus (LI), inferior (IL) and superior lateral (SL) free wall, lateral (LS) and medial superior (MS) free wall, and superior (SS) and inferior septum (IS). Statistical comparison of CV from these multiple segments was made by one-way analysis of variance. RESULTS: Measured in 4 segments around the TVA, mean CV (m/sec) in the TV-IVC isthmus (0.81 +/- 0.23) and the septum (0.93 +/- 0.18) was significantly slower than CV in the lateral free wall (1.16 +/- 0.23) and superior free wall (1.10 +/- 0.20), and CV in the TV-IVC isthmus was significantly slower than in the septum (p < 0.05). However, when analyzed in 8 segments, mean CV in the MI (0.56 +/- 0.16) and IS (0.59 +/- 0.24) was significantly (p < 0.05) slower than in all other segments including the LI (1.06 +/- 0.46), IL (1.17 +/- 0.40), SL (1.15 +/- 0.40), LS (1.04 +/- 0.25), MS (1.15 +/- 0.28), and SS (1.26 +/- 0.36) segments. CONCLUSIONS: Consistent with previous reports, CV around the TVA during type 1 AFL was slowest in the TV-IVC isthmus, compared to the septum, superior and lateral free wall regions. However, when the TVA was further subdivided into 8 segments, CV in the MI and IS segments was significantly slower than in all other segments around the TVA. These observations more precisely define the regions of slow conduction in human type 1 AFL, and are consistent with the known anisotropy and slow conduction in the Triangle of Koch.

Anisotropy↗
PubMed2003

Acute and chronic effects of cryoablation of the pulmonary veins in the dog as a potential treatment for focal atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) may be triggered by premature atrial depolarizations originating in the pulmonary veins (PV). Radiofrequency catheter ablation of PV foci may prevent recurrence of AF, but may cause PV stenosis. Therefore, a safer method for ablation of PV foci is needed. This study evaluated the acute and chronic effects of PV ablation using a cryocatheter ablation (CCA) system, which may be less likely to cause PV stenosis. METHODS: CCA was performed by freezing for 5 minutes or more in one or more PVs in 10 anesthetized dogs. Pacing threshold and vessel diameter were measured before and after PV cryoablation. All dogs were restudied at 4.0 +/- 1.64 months (range 2-7) in a manner identical to baseline. RESULTS: CCA was performed in 27 PVs (range 1-4/dog), with a mean freeze time of 8.62 +/- 5.42 minutes per vein (range 5.23-22.06). Mean temperature for all freezes was -65 +/- 5.3 degrees C. Mean PV diameter was 6.49 +/- 1.73 vs 6.24 +/- 1.83 mm (p = NS) and mean pacing threshold 1.32 +/- 0.75 vs 9.36 +/- 5.93 mA (p <.01), before vs. acutely after ablation. At followup, at the ablation sites PV diameter (7.02 +/- 1.88 mm) was unchanged from baseline, whereas pacing threshold remained elevated (2.54 +/- 1.44 mA, p <.05 vs baseline). There were no acute or long-term complications. CONCLUSIONS; (1) CCA of PVs produced a significant rise in acute and chronic pacing threshold indicating loss of atrial conductivity. (2) CCA of PVs did not cause PV stenosis or other complications. (3) The data suggest that CCA of PVs may be a safe and effective method for treating focal AF.

Animals↗
PubMed2003

Identification of pulmonary vein potentials by differential site atrial pacing in patients with paroxysmal atrial fibrillation: enhanced detection by pulmonary vein pacing.

INTRODUCTION: Pulmonary vein (PV) isolation may cure paroxysmal atrial fibrillation (PAF); however, identification of PV potentials may be difficult in sinus rhythm. Studies have suggested that atrial pacing may improve the identification of PV potentials. METHODS AND RESULTS: In 25 consecutive patients who underwent PV isolation for PAF, the results of pacing from the distal PV, distal and proximal coronary sinus, and high right atrium compared to sinus rhythm were analyzed to determine the most effective pacing site for identification of PV potentials. The percentage of confirmed PV potentials and the longest interval between atrial and PV potentials in each PV were compared during differential site pacing and sinus rhythm. PV potentials were confirmed in 63 (82%) of 77 PVs that could be mapped during the complete pacing protocol and during sinus rhythm. Distal PV pacing identified significantly more PV potentials (left upper pulmonary vein [LUPV] 100%, left lower pulmonary vein [LLPV] 84%, right upper pulmonary vein [RUPV] 80%, right lower pulmonary vein [RLPV] 53%) compared to other pacing sites and sinus rhythm. Among atrial pacing sites, those ipsilateral to the PV being mapped were the most effective for identifying PV potentials. The intervals between atrial and PV potentials were significantly longer during distal PV pacing than pacing at other sites (LUPV 81.6 +/- 26.2 ms, LLPV 61.4 +/- 26.1 ms, RUPV 59.7 +/- 33.2 ms, RLPV 39.7 +/- 26.7 ms). CONCLUSION: (1) Distal PV pacing was most effective for identifying PV potentials. (2) The interval between atrial and PV potentials was longest during distal PV pacing.

Atrial Fibrillation↗
PubMed2003

Quantifying intracardiac organization of atrial arrhythmias using temporospatial phase of the electrocardiogram.

INTRODUCTION: Separating nonisthmus-dependent atrial flutter (AFL) from "organized" atrial fibrillation (AF), or isthmus-dependent AFL, may be difficult using ECG characteristics alone. We hypothesized that temporal and spatial phase analysis of ECG atrial waveforms could effectively separate these rhythms by quantifying subtle variations in ECG atrial activation during supraventricular tachycardias (SVT). METHODS AND RESULTS: We studied 52 patients at electrophysiologic study (EPS) who demonstrated isthmus-dependent (n = 15) and nonisthmus-dependent (n = 9) AFL, atrial tachycardia (n = 6), AV nodal reentry (n = 9), orthodromic reciprocating tachycardia (n = 6), and AF (n = 7). Atrial activity was represented as a series of correlations of an atrial template to successive time samples of the arrhythmia ECG. Spatial phase was analyzed as a reproducible relationship of this atrial activity between leads over time; temporal regularity was measured from power spectra. Spatial phase was maintained (coherent) in lead planes V5/aVF (XY), V5/V1 (XZ), and aVF/V1 (YZ) in 15 of 15 cases of isthmus-dependent AFL, but in only 1 of 9 cases of nonisthmus-dependent AFL (P < 0.01; chi2). Temporally, all cases of AFL showed one dominant peak on correlation spectra (magnitude >6 dB), suggesting one activation wavefront, although this was smeared in nonisthmus-dependent cases. In contrast, AF showed inconsistent spatial phase in all planes and broad band spectra, consistent with multiple and/or variable activation paths. All other SVTs showed spatial coherence and one dominant spectral peak. CONCLUSION: Coherence of temporal and spatial phase is a powerful approach to measure the spatial organization of intracardiac activation from the ECG that reveals a spectrum from SVT to isthmus-dependent and nonisthmus-dependent AFL, to AF.

Adult↗