Peter S. Spector

Characterization of Reentrant Circuit in Macroreentrant Right Atrial Tachycardia After Surgical Repair of Congenital Heart Disease Isolated Channels Between Scars Allow “Focal” Ablation

Background —The purpose of this study was to characterize the circuit of macroreentrant right atrial tachycardia (MacroAT) in patients after surgical repair of congenital heart disease (SR-CHD). Methods and Results —Sixteen patients with atrial tachycardia (AT) after SR-CHD were studied (atrial septal defect in 6, tetralogy of Fallot in 4, and Fontan procedure in 6). Electroanatomic right atrial maps were obtained during 15 MacroATs in 13 patients, focal AT in 1 patient, and atrial pacing in 2 patients without stable AT. A large area of low bipolar voltage (≤0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width ≤2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified during MacroAT (5 patients) and in 5 channels identified during atrial pacing (2 patients). Conduction block was obtained across 28 of 29 channels. After ablation, reproducible sustained right AT was not induced in any patient. During follow-up (median 13.5 months), new MacroATs, atrial fibrillation, or palpitations occurred in 3 of 16 patients. Conclusions —MacroAT after SR-CHD requires a large area of low voltage containing ≥2 scars forming narrow channels. Ablation within the channels eliminates MacroAT.

Characterization of Reentrant Circuit in Macroreentrant Right Atrial Tachycardia After Surgical Repair of Congenital Heart Disease

Background—The purpose of this study was to characterize the circuit of macroreentrant right atrial tachycardia (MacroAT) in patients after surgical repair of congenital heart disease (SR-CHD). Methods and Results—Sixteen patients with atrial tachycardia (AT) after SR-CHD were studied (atrial septal defect in 6, tetralogy of Fallot in 4, and Fontan procedure in 6). Electroanatomic right atrial maps were obtained during 15 MacroATs in 13 patients, focal AT in 1 patient, and atrial pacing in 2 patients without stable AT. A large area of low bipolar voltage (≤0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width ≤2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified ...

Coronary Sinus-Ventricular Accessory Connections Producing Posteroseptal and Left Posterior Accessory Pathways Incidence and Electrophysiological Identification

Background—The coronary sinus (CS) has a myocardial coat (CSMC) with extensive connections to the left and right atria. We postulated that some posteroseptal and left posterior accessory pathways (CSAPs) result from connections between a cuff of CSMC extending along the middle cardiac vein (MCV) or posterior coronary vein (PCV) and the ventricle. The purpose of the present study was to use CS angiography and mapping to define and determine the incidence of CSAPs and determine the relationship to CS anatomy. Methods and Results—CSAP was defined by accessory pathway (AP) potential or earliest activation in the MCV or PCV and late activation at anular endocardial sites. A CSAP was identified in 171 of 480 patients undergoing ablation of a posteroseptal or left posterior AP. CS angiography revealed a CS diverticulum in 36 (21%) and fusiform or bulbous enlargement of the small cardiac vein, MCV, or CS in 15 (9%) patients. The remaining 120 (70%) patients had an angiographically normal CS. A CSMC extension potential (CSE), like an AP potential, was recorded in the MCV in 98 (82%), in the PCV in 13 (11%), in both the MCV and PCV in 6 (5%), and in the CS in 3 (2%) of 120 patients. CSMC potentials were recorded between the timing of atrial and CSE potentials. Conclusions—CSAPs result from a connection between a CSMC extension (along the MCV or PCV) and the ventricle. The CS is angiographically normal in most patients.

Electrical resynchronization induced by direct His-bundle pacing

BACKGROUND Biventricular pacing (BiV) to effect cardiac resynchronization therapy can be technically difficult and fails to elicit a clinical response in 30% to 40% of patients. Direct His-bundle pacing (DHBP) theoretically could obviate some of these problems. Although DHBP is capable of narrowing the QRS in some patients, the consistency with which this can be achieved has not been characterized. OBJECTIVE The purpose of this study was to restore His-Purkinje functionality in consecutive patients undergoing de novo clinically mandated cardiac resynchronization therapy. METHODS DHBP was temporarily implemented at the time of implantation of a permanent BiV system in patients referred for cardiac resynchronization therapy. Native conduction, DHBP, and BiV QRS duration were compared. All patients presenting for BiV cardiac resynchronization therapy were eligible for the study. Ten patients were studied. RESULTS DHBP was successfully implemented in all 10 patients. In 7 of 10 patients, DHBP narrowed the QRS significantly compared with native conduction and BiV (mean QRS duration: native 171 +/- 13 ms, DHBP 148 +/- 11 ms, BiV 158 +/- 21, P <.0001). QRS narrowing with DHBP was specifically attributable to capture of latent His-Purkinje tissue. DHBP lead implantation time (16 minutes) was shorter than standard left ventricular lead implantation time (42 minutes). CONCLUSION DHBP was readily implemented in patients with standard indications for BiV cardiac resynchronization therapy. In most patients studied, DHBP resulted in a significantly narrower QRS compared with native conduction. DHBP may offer a physiologic alternative to BiV for cardiac resynchronization therapy.

Electrogram Fractionation The Relationship Between Spatiotemporal Variation of Tissue Excitation and Electrode Spatial Resolution

Background— Fractionated electrograms are used by some as targets for ablation in atrial and ventricular arrhythmias. Fractionation has been demonstrated to result when there is repetitive or asynchronous activation of separate groups of cells within the recording region of a mapping electrode(s). Methods and Results— Using a computer model, we generated tissue activation patterns with increasing spatiotemporal variation and calculated virtual electrograms from electrodes with decreasing resolution. We then quantified electrogram fractionation. In addition, we recorded unipolar electrograms during atrial fibrillation in 20 patients undergoing atrial fibrillation ablation. From these we constructed bipolar electrograms with increasing interelectrode spacing and quantified fractionation. During modeling of spatiotemporal variation, fractionation varied directly with electrode length, diameter, height, and interelectrode spacing. When resolution was held constant, fractionation increased with increasing spatiotemporal variation. In the absence of spatial variation, fractionation was independent of resolution and proportional to excitation frequency. In patients with atrial fibrillation, fractionation increased as interelectrode spacing increased. Conclusions— We created a model for distinguishing the roles of spatial and temporal electric variation and electrode resolution in producing electrogram fractionation. Spatial resolution affects fractionation attributable to spatiotemporal variation but not temporal variation alone. Electrogram fractionation was directly proportional to spatiotemporal variation and inversely proportional to spatial resolution. Spatial resolution limits the ability to distinguish high-frequency excitation from overcounting. In patients with atrial fibrillation, complex fractionated atrial electrogram detection varies with spatial resolution. Electrode resolution must therefore be considered when interpreting and comparing studies of fractionation.Background— Fractionated electrograms are used by some as targets for ablation in atrial and ventricular arrhythmias. Fractionation has been demonstrated to result when there is repetitive or asynchronous activation of separate groups of cells within the recording region of a mapping electrode(s). Methods and Results— Using a computer model, we generated tissue activation patterns with increasing spatiotemporal variation and calculated virtual electrograms from electrodes with decreasing resolution. We then quantified electrogram fractionation. In addition, we recorded unipolar electrograms during atrial fibrillation in 20 patients undergoing atrial fibrillation ablation. From these we constructed bipolar electrograms with increasing interelectrode spacing and quantified fractionation. During modeling of spatiotemporal variation, fractionation varied directly with electrode length, diameter, height, and interelectrode spacing. When resolution was held constant, fractionation increased with increasing spatiotemporal variation. In the absence of spatial variation, fractionation was independent of resolution and proportional to excitation frequency. In patients with atrial fibrillation, fractionation increased as interelectrode spacing increased. Conclusions— We created a model for distinguishing the roles of spatial and temporal electric variation and electrode resolution in producing electrogram fractionation. Spatial resolution affects fractionation attributable to spatiotemporal variation but not temporal variation alone. Electrogram fractionation was directly proportional to spatiotemporal variation and inversely proportional to spatial resolution. Spatial resolution limits the ability to distinguish high-frequency excitation from overcounting. In patients with atrial fibrillation, complex fractionated atrial electrogram detection varies with spatial resolution. Electrode resolution must therefore be considered when interpreting and comparing studies of fractionation.

Relation Between Pulmonary Vein Firing and Extent of Left Atrial–Pulmonary Vein Connection in Patients With Atrial Fibrillation

Background—The purpose of this study was to measure the extent of left atrial–pulmonary vein (LA-PV) connections and determine the relation to PV firing in patients with atrial fibrillation (AF). Methods and Results—Ten close-bipolar (1 mm-spacing) Lasso electrograms were recorded circumferentially around 210 PVs (excluding 2 right middle PVs and 4 left common trunks) in 62 patients with AF. PV firing was provoked by isoproterenol (4 &mgr;g/min) and cardioversion of pacing-induced AF. The width of each LA-PV connection was measured in tenths of PV circumference, based on number of continuous close-bipolar Lasso electrode sites required for ablation (10% for each close-bipolar electrode site). One, 2, or 3 to 4 discrete LA-PV connections (discrete connection defined by ablation along 10% to 30% of PV circumference) were present in 18 (9%), 31 (14%), and 32 (15%) of 210 PVs, respectively: 1 broad connection (ablation along continuous 40% to 80% circumference) in 46 (22%) PVs; 1 broad plus other broad or discrete connections in 54 (26%) PVs; and a circumferential connection (ablation along 90% to 100%) in 29 (14%) PVs. Circumferential LA-PV connections were more common in superior than in inferior PVs (20% versus 7%, P <0.01). There was no major difference in distribution of the other types of LA-PV connections between the four PVs. PV firing occurred in 27%, 47%, and 72% of PVs with discrete only, broad and circumferential connections, respectively (P <0.01). Dissociated PV potentials after isolation were more common in arrhythmogenic (firing) PVs (32% versus 8%, P <0.01). Conclusions—The extent of LA-PV connections corresponds with arrhythmognesis. The incidence of PV firing increases with progressively wider LA-PV connections (discrete versus broad versus circumferential).

Effects of electrode size and spacing on the resolution of intracardiac electrograms.

BackgroundElectrogram fractionation can result when multiple groups of cardiac cells are excited asynchronously within the recording region of a mapping electrode. The spatial resolution of an electrode thus plays an important role in mapping complex rhythms. MethodsWe used a computational model, validated against experimental measurements in vitro, to determine how spatial resolution is affected by electrode diameter, electrode length, interelectrode distance (in the case of bipolar recordings), and height of the electrode above a dipole current source. ResultsWe found that increases in all these quantities caused progressive degradation in two independent measures of spatial resolution, with the strongest effect being due to changes in height above the tissue. ConclusionOur calculations suggest that if electrodes could be constructed to have negligible dimensions compared with those in use today, we would increase resolution by about one order of magnitude at most.

The Relationship between Surface Temperature, Tissue Temperature, Microbubble Formation, and Steam Pops

Background: It has been proposed that microbubble (MB) monitoring can be used to safely titrate radiofrequency (RF) power. However, MB formation has been found to be an insensitive indicator of tissue temperature during RF delivery. We hypothesized that MB formation corresponds to surface—not tissue—temperature, and therefore would be an insensitive predictor of steam pops.

Prospective, Tissue-Specific Optimization of Ablation for Multiwavelet Reentry: Predicting the Required Amount, Location, and Configuration of Lesions.

Background—Treatment of multiwavelet reentry (MWR) remains difficult. We previously developed a metric, the fibrillogenicity index, to assess the propensity of homogeneous, 2-dimensional tissues to support MWR. In this study, we demonstrate a method by which fibrillogenicity index can be generalized to heterogeneous tissues and validate an algorithm for prospective, tissue-specific optimization of ablation to reduce MWR burden. Methods and Results—We used a computational model to simulate and measure the duration of MWR in tissues with heterogeneously distributed action potential durations and then assessed the relative efficacy of a variety of ablation strategies for reducing tissues’ ability to support MWR. We then derived and tested a strategy in which multiple linear lesions partially divided a fibrillogenic tissue into functionally equivalent subsections. The composite action potential duration of heterogeneous tissue was well approximated by an inverse sum of cellular action potential durations (R2=0.82). Linear ablation more efficiently reduced MWR duration than branching ablation patterns and optimally reduced disease burden when positioned at a tissue’s functional (rather than geometric) center. The duration of MWR after application of prospective, individually optimized ablation sets fell within 4.4% (95% confidence interval, 3–5.8) of the predicted target. Conclusions—We think that this study presents a novel approach for (1) quantifying the extent of a tissue’s electric derangement, (2) prospectively determining the amount of ablation required to minimize the burden of MWR, and (3) predicting the most efficient distribution of these ablation lesions in tissue refractory to standard ablation strategies.

Multidetector computed tomography guidance in complex cardiac ablations.

Radiofrequency ablation of complex cardiac arrhythmias has undergone significant evolution in the past decade, with the development of technology enabling better anatomic and electrophysiologic mapping of abnormal cardiac tissue. In this paper, we will discuss the role of pre-procedural and post-procedural multidetector computed tomography, with specific focus on the anatomic assessment of pulmonary vein and left atrial anatomy in the ablation of atrial fibrillation. We will also consider how the integration of both multidetector computed tomography and electroanatomic computer-based imaging may contribute more broadly to the management of a variety of complex ablation procedures.