Validation of Dipole Density Mapping During Atrial Fibrillation and Sinus Rhythm in Human Left Atrium.

OBJECTIVES: This study sought to validate the accuracy of noncontact electrograms against contact electrograms in the left atrium during sinus rhythm (SR) and atrial fibrillation (AF). BACKGROUND: Noncontact mapping offers the opportunity to assess global cardiac activation in the chamber of interest. A novel noncontact mapping system, which records intracardiac voltage to derive cellular charge sources (dipole density), allows real-time mapping of AF to guide ablation. METHODS: Noncontact and contact unipolar electrogram pairs were recorded simultaneously from multiple locations. Morphology correlation and timing difference of reconstructed electrograms obtained from a noncontact catheter were compared with those from contact electrograms obtained from a contact catheter at the same endocardial locations. RESULTS: A total of 796 electrogram pairs in SR and 969 electrogram pairs in AF were compared from 20 patients with persistent AF. The median morphology correlation and timing difference (ms) in SR was 0.85 (interquartile range [IQR]: 0.71 to 0.94) and 6.4 ms (IQR: 2.6 to 17.1 ms); in AF was 0.79 (IQR: 0.69 to 0.88) and 14.4 ms (IQR: 6.7 to 26.2 ms), respectively. The correlation was stronger and the timing difference was less when the radial distance (r) from the noncontact catheter center to the endocardium was ≤ 40 versus > 40 mm; 0.87 (IQR: 0.72 to 0.94) versus 0.73 (IQR: 0.56 to 0.88) and 5.7 ms (IQR: 2.6 to 15.4 ms) versus 15.1 ms (IQR: 4.1 to 27.7 ms); p < 0.01 when in SR; 0.81 (IQR: 0.69 to 0.89) versus 0.67 (IQR: 0.45 to 0.82) and 12.3 ms (IQR: 5.9 to 21.8 ms) versus 28.3 ms (IQR: 16.2 to 36.0 ms); p < 0.01 when in AF. CONCLUSIONS: This novel noncontact dipole density mapping system provides comparable reconstructed atrial electrogram measurements in SR or AF in human left atrium when the anatomical site of interest is ≤40 mm from the mapping catheter.

Reinserting Physiology into Cardiac Mapping Using Omnipolar Electrograms.

Omnipolar electrograms (EGMs) make use of biophysical electric fields that accompany activation along the surface of the myocardium. A grid-like electrode array provides bipolar signals in orthogonal directions to deliver catheter-orientation-independent assessments of cardiac electrophysiology. Studies with myocyte monolayers, isolated animal and human hearts, and anesthetized animals validated the tenets of omnipolar EGMs. The combination of information from omnipolar-based activation vectors and voltages may aid in localizing areas of scar, lesion gaps, wavefront disorganization, and fractionation or collision during arrhythmias. The goal of omnipolar EGMs is to better characterize myocardium through reintroducing electrogram direction related fundamentals of cardiac electrophysiology.

Determinants of atrial bipolar voltage: Inter electrode distance and wavefront angle.

BACKGROUND: Local bipolar electrogram (EGM) peak-to-peak voltage (Vpp) is currently used to characterise mapped myocardial substrate. However, how interelectrode distance and angle of wavefront incidence affect bipolar, Vpp values, in the current era of multi-electrode mapping is unknown. OBJECTIVES: To elucidate the effects of tissue and electrode geometry on bipolar Vpp measurements, when mapping healthy versus diseased atrial regions. METHODS: A bidomain model of human atrial tissue was used to quantify the influence on Vpp values of various electrode configurations in healthy tissue, and tissue containing an unexcitable region. The orientation angle and interelectrode spacing of a surface bipole, and thickness and depth of the unexcitable core were serially varied. Results were validated with data obtained from isolated porcine hearts. RESULTS: In healthy tissue, bipolar Vpp values increased with increasing interelectrode spacing and plateaued beyond a spacing of approximately 4 mm. The bipolar Vpp values in healthy tissue were relatively less sensitive to wavefront orientation angle with large interelectrode spacing. In diseased tissue, on the contrary, with increasing interelectrode spacing, bipolar Vpp values increased linearly without a plateau and were more sensitive to orientation angle. The bipolar Vpp values decreased with increasing thickness of the scar, with larger relative decrease in small bipoles than larger ones. Bipolar Vpp values increased with a progressively intramural location of fixed-size scar and became less distinguishable from healthy tissue especially for smaller interelectrode spacings. CONCLUSIONS: The scalable relationship established for interelectrode distances favour an electric-field-based assessment as opposed to traditional Vpp values as a tool for physiologically relevant measurement for mapping catheters with interelectrode spacing up to 4 mm. This will allow for universal assessment of myocardial health across catheters with varied spacing.

Quantifying the determinants of decremental response in critical ventricular tachycardia substrate.

BACKGROUND: Decremental response evoked with extrastimulation (DEEP) is a useful tool for determining diastolic return path of ventricular tachycardia (VT). Though a targeted VT ablation is feasible with this approach, determinants of DEEP response have not been studied OBJECTIVES: To elucidate the effects of clinically relevant factors, specifically, the proximity of the stimulation site to the arrhythmogenic scar, stimulation wave direction, number of channels open in the scar, size of the scar and number of extra stimuli on decrement and entropy of DEEP potentials. METHODS: In a 3-dimensional bi-domain simulation of human ventricular tissue (TNNP cell model), an irregular subendocardial myopathic region was generated. An irregular channel of healthy tissue with five potential entry branches was shaped into the myopathic region. A bipolar electrogram was derived from two electrodes positioned in the centre of the myopathic region. Evoked delays between far-field and local Electrogram (EGM) following an extrastimulus (S1-S2, 500-350 ms) were measured as the stimulation site, channel branches, and inexcitable tissue size were altered. RESULTS: Stimulation adjacent to the inexcitable tissue from the side opposite to the point-of-entry produces longest DEEP delay. The DEEP delay shortens when the stimulation point is farther away from the scar, and it decreases maximally when stimulation is done from a site beside a conduction barrier. Entropy increases with S2 when stimulation site is from farther away. An unprotected channel structure with multiple side-branch openings had shorter DEEP delay compared to a protected channel structure with a paucity of additional side-branch openings and a point-of-entry on the side opposite to the pacing source. Addition of a second shorter extrastimulus did not universally lead to higher DEEP delay CONCLUSIONS: Location and direction of the wavefront in relation to scar entry and size of scar determine the degree of evoked response while the number of extrastimuli has a small additional decremental effect.

Characterising the difference in electrophysiological substrate and outcomes between heart failure and non-heart failure patients with persistent atrial fibrillation.

Aims: Characterizing the differences in substrate and clinical outcome between heart failure (HF) and non-heart failure (non-HF) patients undergoing persistent atrial fibrillation (AF) ablation. Methods and results: Using complex fractionated electrograms (CFE) as a surrogate marker of substrate complexity, we compared the bi-atrial substrate in patients with persistent AF with and without HF, at baseline and after ablation, to determine its impact on clinical outcome. In this retrospective analysis of two prospective studies, 60 patients underwent de-novo step-wise left atrial (LA) ablation, 30 with normal left ventricular ejection fraction (LVEF) ≥ 50% (non-HF group) and 30 with LVEF ≤ 35% (HF group). Multiple high-density bi-atrial CFE maps were acquired along with AF cycle length (AFCL) at each procedural stage. Change in bi-atrial CFE areas, AFCL and outcome data were then compared. In the non-HF group, higher CFE-areas were found at baseline and at each step of the procedure in the LA. In both LA and the right atrium (RA), baseline and final CFE area were also higher in the non-HF group. Single procedure, arrhythmia-free survival at 1 year was higher in the HF group compared with the non-HF group (72% vs. 43%, log rank P = 0.04). Final total bi-atrial CFE area was an independent predictor of arrhythmia recurrence. Conclusions: CFE represents an important surrogate marker of atrial substrate complexity. The atrial substrate in persistent AF differs between HF and non-HF with the latter representing a more complex 'primary' bi-atrial myopathy. LA focussed ablation results in more extensive substrate modification in HF and better clinical outcomes as compared with non-HF.

Catheter ablation vs electrophysiologically guided thoracoscopic surgical ablation in long-standing persistent atrial fibrillation: The CASA-AF Study.

BACKGROUND: Catheter ablation (CA) outcomes for long-standing persistent atrial fibrillation (LSPAF) remain suboptimal. Thoracoscopic surgical ablation (SA) provides an alternative approach in this difficult to treat cohort. OBJECTIVE: To compare electrophysiological (EP) guided thoracoscopic SA with percutaneous CA as the first-line strategy in the treatment of LSPAF. METHODS: Fifty-one patients with de novo symptomatic LSPAF were recruited. Twenty-six patients underwent electrophysiologically guided thoracoscopic SA. Conduction block was tested for all lesions intraoperatively by an independent electrophysiologist. In the CA group, 25 consecutive patients underwent stepwise left atrial (LA) ablation. The primary end point was single-procedure freedom from atrial fibrillation (AF) and atrial tachycardia (AT) lasting >30 seconds without antiarrhythmic drugs at 12 months. RESULTS: Single- and multiprocedure freedom from AF/AT was higher in the SA group than in the CA group: 19 of 26 patients (73%) vs 8 of 25 patients (32%) (P = .003) and 20 of 26 patients (77%) vs 15 of 25 patients (60%) (P = .19), respectively. Testing of the SA lesion set by an electrophysiologist increased the success rate in achieving acute conduction block by 19%. In the SA group, complications were experienced by 7 of 26 patients (27%) vs 2 of 25 patients (8%) in the CA group (P = .07). CONCLUSION: In LSPAF, meticulous electrophysiologically guided thoracoscopic SA as a first-line strategy may provide excellent single-procedure success rates as compared with those of CA, but there is an increased up-front risk of nonfatal complications.

Physiological Assessment of Ventricular Myocardial Voltage Using Omnipolar Electrograms.

BACKGROUND: Characterization of myocardial health by bipolar electrograms are critical for ventricular tachycardia therapy. Dependence of bipolar electrograms on electrode orientation may reduce reliability of voltage assessment along the plane of arrhythmic myocardial substrate. Hence, we sought to evaluate voltage assessment from orientation-independent omnipolar electrograms. METHODS AND RESULTS: We mapped the ventricular epicardium of 5 isolated hearts from each species-healthy rabbits, healthy pigs, and diseased humans-under paced conditions. We derived bipolar electrograms and voltage peak-to-peak (Vpps) along 2 bipolar electrode orientations (horizontal and vertical). We derived omnipolar electrograms and Vpps using omnipolar electrogram methodology. Voltage maps were created for both bipoles and omnipole. Electrode orientation affects the bipolar voltage map with an average absolute difference between horizontal and vertical of 0.25±0.18 mV in humans. Vpps provide larger absolute values than horizontal and vertical bipolar Vpps by 1.6 and 1.4 mV, respectively, in humans. Bipolar electrograms with the largest Vpps from either along horizontal or vertical orientation are highly correlated with omnipolar electrograms and with Vpps values (0.97±0.08 and 0.94±0.08, respectively). Vpps values are more consistent than bipoles, in both beat-by-beat (CoV, 0.28±0.19 versus 0.08±0.13 in human hearts) and rhythm changes (0.55±0.21 versus 0.40±0.20 in porcine hearts). CONCLUSIONS: Omnipoles provide physiologically relevant and consistent voltages that are along the maximal bipolar direction on the plane of the myocardium.

When Ventricular Safety Standby Does Not Work.

Dual chamber pacemakers have inbuilt advanced safety systems such as ventricular safety standby (crosstalk detection) to prevent ventricular oversensing resulting in inappropriate pacing inhibition. We describe a case where this safety mechanism does not reliably work and the management required to rectify the situation in an educational format.

Effect of spatial resolution and filtering on mapping cardiac fibrillation.

BACKGROUND: Endocardial mapping tools use variable interelectrode resolution, whereas body surface mapping tools use narrow bandpass filtering (BPF) to map fibrillatory mechanisms established by high-resolution optical imaging. OBJECTIVE: The purpose of this study was to study the effect of resolution and BPF on the underlying mechanism being mapped. METHODS: Hearts from 14 healthy New Zealand white rabbits were Langendorff perfused. We studied the effect of spatial resolution and BPF on the location and characterization of rotors by comparing phase singularities detected by high-resolution unfiltered optical maps and of fibrillating myocardium with decimated and filtered maps with simulated electrode spacing of 2, 5, and 8 mm. RESULTS: As we decimated the maps with 2-mm, 5-mm, and 8-mm interelectrode spacing, the mean ( ± SD) number of rotors detected decreased from 10.2 ± 9.6, 1.6 ± 3.2, and 0.2 ± 0.5, respectively. Lowering the resolution led to synthesized pseudo-rotors that may be inappropriately identified. Applying a BPF led to fewer mean phase singularities detected (248 ± 207 vs 333 ± 130; P<.01), giving the appearance of pseudo-spatial stability measured as translation index (with BPF 3.6 ± 0.4 mm vs 4.0 ± 0.5 mm without BPF; P<.01) and pseudo-temporal stability with longer duration (70.0 ± 17.6 ms in BPF maps vs 44.1 ± 6.6 ms in unfiltered maps; P<.001) than true underlying fibrillating myocardium mapped. CONCLUSION: Electrode resolution and BPF of electrograms can result in distortion of the underlying electrophysiology of fibrillation. Newer mapping techniques need to demonstrate sensitivity analysis to quantify the degree of distortion before clinical use to avoid inaccurate electrophysiologic interpretation.

Evaluation of a novel high-resolution mapping system for catheter ablation of ventricular arrhythmias.

BACKGROUND: The mapping of ventricular arrhythmias in humans using a minibasket 64-electrode catheter paired with a novel automatic mapping system (Rhythmia) has not been evaluated. OBJECTIVE: The purpose of this study was to evaluate the safety and efficacy of mapping ventricular arrhythmias and clinical outcomes after ablation using this system. METHODS: Electroanatomic maps for ventricular arrhythmias were obtained during 20 consecutive procedures in 19 patients (12 with ventricular tachycardia [VT] and 2 with ventricular ectopy [VE]). High-density maps were acquired using automatic beat acceptance and automatic system annotation of electrograms. RESULTS: Forty-seven electroanatomic maps (including 3 right ventricular and 9 epicardial maps) were obtained. Left ventricular endocardial mapping by transseptal (n = 13) and/or transaortic (n = 11) access was safe with no complications related to the minibasket catheter. VT substrate maps (n = 14; median 10,184 points) consistently demonstrated late potentials with high resolution. VT activation maps (n = 25; median 6401 points) obtained by automatic annotation included 7 complete maps (covering ≥90% of the tachycardia cycle length) in 5 patients in whom the entire VT circuit was accurately visualized. VE timing maps (n = 8) successfully localized the origin of VEs in all, with all accepted beats consistent with clinical VEs. Over a median follow-up of 10 months, no arrhythmia recurrence was noted in 75% after VT ablation and 86% after VE ablation. CONCLUSION: In this first human experience for ventricular arrhythmias using this system, ultra-high-density maps were created rapidly and safely, with a reliable automatic annotation of VT and consistent recording of abnormal electrograms. Medium-term outcomes after ablation were encouraging. Further larger studies are needed to validate these findings.

Impact of stepwise ablation on the biatrial substrate in patients with persistent atrial fibrillation and heart failure.

BACKGROUND: Ablation of persistent atrial fibrillation can be challenging, often involving not only pulmonary vein isolation (PVI) but also additional linear lesions and ablation of complex fractionated electrograms (CFE). We examined the impact of stepwise ablation on a human model of advanced atrial substrate of persistent atrial fibrillation in heart failure. METHODS AND RESULTS: In 30 patients with persistent atrial fibrillation and left ventricular ejection fraction ≤35%, high-density CFE maps were recorded biatrially at baseline, in the left atrium (LA) after PVI and linear lesions (roof and mitral isthmus), and biatrially after LA CFE ablation. Surface area of CFE (mean cycle length ≤120 ms) remote to PVI and linear lesions, defined as CFE area, was reduced after PVI (18.3±12.03 to 10.2±7.1 cm(2); P<0.001) and again after linear lesions (7.7±6.5 cm(2); P=0.006). Complete mitral isthmus block predicted greater CFE reduction (P=0.02). Right atrial CFE area was reduced by LA ablation, from 25.9±14.1 to 12.9±11.8 cm(2) (P<0.001). Estimated 1-year arrhythmia-free survival was 72% after a single procedure. Incomplete linear lesion block was an independent predictor of arrhythmia recurrence (hazard ratio, 4.69; 95% confidence interval, 1.05-21.06; P=0.04). CONCLUSIONS: Remote LA CFE area was progressively reduced following PVI and linear lesions, and LA ablation reduced right atrial CFE area. Reduction of CFE area at sites remote from ablation would suggest either regression of the advanced atrial substrate or that these CFE were functional phenomena. Nevertheless, in an advanced atrial fibrillation substrate, linear lesions after PVI diminished the target area for CFE ablation, and complete lesions resulted in a favorable clinical outcome.