Sinus Rhythm Activation Signature Indicates Reentrant Ventricular Tachycardia Inducibility and Approximate Isthmus Location.

BACKGROUND: Sinus rhythm activation time is useful to assess infarct border zone substrate. OBJECTIVE: To further investigate sinus activation in ventricular tachycardia (VT). METHODS: Canine postinfarction data was analyzed retrospectively. In each experiment, an infarct was created in the left ventricular wall by LAD coronary artery ligation. Three-to-five days following ligation, 196-312 bipolar electrograms were recorded from the anterior left ventricular epicardium overlapping the infarct border zone. Sustained monomorphic VT was induced via premature electrical stimulation in 50 experiments and was non-inducible in 43 experiments. Acquired sinus rhythm and VT electrograms were marked for electrical activation time, and activation maps of representative sinus rhythm and VT cycles were constructed. The sinus rhythm activation signature was defined as the cumulative number of multielectrode recording sites that had activated per time epoch, and its derivative was used to predict VT inducibility, and to define the sinus rhythm slow/late activation sequence. RESULTS: Plotting mean activation signature derivative, a best cutoff value was useful to separate experiments with reentrant VT inducibility (sensitivity: 42/50) versus non-inducibility (specificity: 39/43), with an accuracy of 81/93. For the 50 experiments with inducible VT, recording sites overlying a segment of isochrone encompassing the sinus rhythm slow/late activation sequence, spanned the VT isthmus location in 32 cases (64%), partially spanned it in 15 cases (30%), but did not span in 3 cases (6%). CONCLUSION: The sinus rhythm activation signature derivative is assistive to differentiate substrate supporting reentrant VT inducibility versus non-inducibility, and to identify slow/late activation for targeting isthmus location.

Correlation relationships of the reentrant ventricular tachycardia circuit.

INTRODUCTION: A quantitative analysis of the components of reentrant ventricular tachycardia (VT) circuitry could improve understanding of its onset and perpetuation. METHOD: In 19 canine experiments, the left anterior descending coronary artery was ligated to generate a subepicardial infarct. The border zone resided at the epicardial surface of the anterior left ventricle and was mapped 3-5 days postinfarction with a 196-312 bipolar multielectrode array. Monomorphic VT was inducible by extrastimulation. Activation maps revealed an epicardial double-loop reentrant circuit and isthmus, causing VT. Several circuit parameters were analyzed: the coupling interval for VT induction, VT cycle length, the lateral isthmus boundary (LIB) lengths, and isthmus width and angle. RESULTS: The extrastimulus interval for VT induction and the VT cycle length were strongly correlated (p < 0.001). Both the extrastimulus interval and VT cycle length were correlated to the shortest LIB (p < 0.005). A derivation was developed to suggest that when conduction block at the shorter LIB is functional, the VT cycle length may depend on the local refractory period and the delay from wavefront pivot around the LIB. Isthmus width and angle were uncorrelated to other parameters. CONCLUSIONS: The shorter LIB is correlated to VT cycle length, hence its circuit loop may drive reentrant VT. The extrastimulation interval, VT cycle length, and shorter LIB are intertwined, and may depend upon the local refractory period. Isthmus width and angle are less correlated, perhaps being more related to electrical discontinuity caused by alterations in infarct shape at depth.

Lateral Boundaries of the Ventricular Tachycardia Circuit Align With Sinus Rhythm Discontinuities.

BACKGROUND: Sinus rhythm electrical activation mapping can provide information regarding the ischemic re-entrant ventricular tachycardia (VT) circuit. The information gleaned may include the localization of sinus rhythm electrical discontinuities, which can be defined as arcs of disrupted electrical conduction with large activation time differences across the arc. OBJECTIVES: This study sought to detect and localize sinus rhythm electrical discontinuities that might be present in activation maps constructed from infarct border zone electrograms. METHODS: Monomorphic re-entrant VT with a double-loop circuit and central isthmus was repeatedly inducible by programmed electrical stimulation in the epicardial border zone of 23 postinfarction canine hearts. Sinus rhythm and VT activation maps were constructed from 196 to 312 bipolar electrograms acquired surgically at the epicardial surface and analyzed computationally. A complete re-entrant circuit was mappable from the epicardial electrograms of VT, and isthmus lateral boundary (ILB) locations were ascertained. The difference in sinus rhythm activation time across ILB locations, vs the central isthmus and vs the circuit periphery, was determined. RESULTS: Sinus rhythm activation time differences averaged 14.4 milliseconds across the ILB vs 6.5 milliseconds at the central isthmus and 6.4 milliseconds at the periphery (ie, the outer circuit loop) (P ≤ 0.001). Locations with large sinus rhythm activation difference tended to overlap ILB (60.3% ± 23.2%) compared with their overlap with the entire grid (27.5% ± 18.5%) (P < 0.001). CONCLUSIONS: Disrupted electrical conduction is evident as discontinuity in sinus rhythm activation maps, particularly at ILB locations. These areas may represent permanent fixtures relating to spatial differences in border zone electrical properties, caused in part by alterations in underlying infarct depth. The tissue properties producing sinus rhythm discontinuity at ILB may contribute to functional conduction block formation at VT onset.

An Unusual Cause of AV Dyssynchrony: Dual AV Node Physiology With Retrograde Decremental Conduction.

A 71-year-old male with persistent atrial fibrillation and a dual chamber permanent pacemaker presented complaining of dyspnea on exertion, easy fatiguability, and intermittent cough. A 12-lead electrocardiogram revealed ventricular paced complexes, native QRS complexes, and irregular atrial activity. Herein we present an unusual mechanism of atrioventricular dyssynchrony. (Level of Difficulty: Intermediate.).

Improving Time to Defibrillation Following Ventricular Tachycardia (VTach) and Ventricular Fibrillation (VFib) Cardiac Arrest: A Multicenter Retrospective and Prospective Quality Improvement Study.

The goal of this study was to identify how often 2 independent centers defibrillated patients within the American Heart Association recommended 2-minute time interval following ventricular fibrillation/ventricular tachycardia arrest. A retrospective chart review revealed significant delays in defibrillation. Simulation sessions and modules were implemented to train nursing staff in a single nursing unit at a Philadelphia teaching hospital. Recruited nurses completed a code blue simulation session to establish a baseline time to defibrillation. They were then given 2 weeks to complete an online educational module. Upon completion, they participated in a second set of simulation sessions to assess improvement. First round simulations resulted in 33% with delayed defibrillation and 27% no defibrillation. Following the module, 77% of the second round of simulations ended in timely defibrillation, a statistically significant improvement ( P < 0.00001). Next steps involve prospective collection of the code blue data to analyze improvement in real code blue events.

A Survey of Antibiotic Use During Insertion of Cardiovascular Implantable Devices Among United States Implanters.

Antibiotic use for cardiovascular implantable devices (CIED) prophylaxis is well-accepted despite a paucity of data. Pre-procedural prophylaxis lowers the rate of CIED infections; however, data is lacking for intra- or post-procedural antibiotic use. Antibiotic-eluting envelopes (ENVELOPE) [TYRX®TM] have been shown to reduce post-procedural infections. Understanding implanter practices may provide insight as to the need for antibiotic stewardship. The purpose of this survey was to assess the practices of implanters nationally. A survey was completed by 150 implanters across the US. Participants were board certificated, implanters of CIEDs, with varying experience (1-25 years), in various hospital settings. Of the respondents, 97% reported routine use of systemic antibiotics pre-operatively. About two-thirds of implanters continue systemic antibiotics post-operatively, with half continuing antibiotics for >24 h; 83% of implanters add antibiotic to saline for the purpose of irrigating the wound; 55% routinely use ENVELOPE on approximately 38% of patients. Common reasons cited for ENVELOPE use were infection concerns, significant risk factors, prior device infection, and immunosuppressed status. Two-thirds of respondents use systemic antibiotics during generator changes, with >50% continuing antibiotics for >24 h. This study suggests wide variations in practice among implanters. Additional attention to existing guidelines and evidence regarding appropriate use of ENVELOPE is still needed.

Structure and function of the ventricular tachycardia isthmus.

Catheter ablation of postinfarction reentrant ventricular tachycardia (VT) has received renewed interest owing to the increased availability of high-resolution electroanatomic mapping systems that can describe the VT circuits in greater detail, and the emergence and need to target noninvasive external beam radioablation. These recent advancements provide optimism for improving the clinical outcome of VT ablation in patients with postinfarction and potentially other scar-related VTs. The combination of analyses gleaned from studies in swine and canine models of postinfarction reentrant VT, and in human studies, suggests the existence of common electroanatomic properties for reentrant VT circuits. Characterizing these properties may be useful for increasing the specificity of substrate mapping techniques and for noninvasive identification to guide ablation. Herein, we describe properties of reentrant VT circuits that may assist in elucidating the mechanisms of onset and maintenance, as well as a means to localize and delineate optimal catheter ablation targets.

Utilizing ambulatory electrocardiogram monitoring to reduce conduction related death after transcatheter aortic valve replacement.

OBJECTIVE: The purpose of this study is to assess the utility of ambulatory cardiac monitoring (ACM) in detecting delayed advanced conduction abnormalities (DACA) and associated 30-day mortality. BACKGROUND: DACA are well-known complications of TAVR and may be associated with post-discharge mortality within 30-days. METHODS: Between October 2019 and October 2020, TAVR patients who were discharged home without a permanent pacemaker (PPM) were monitored with an ACM device for 14-days. The incidence of DACA at follow up, mortality and readmission within 30-days were investigated. The risk of DACA was assessed in three patient categories based on a composite of their 12-lead electrocardiogram (ECG) data. Group I: Normal pre-TAVR, periprocedural, and discharge ECGs. Group II: Normal pre-TAVR and abnormal subsequent ECGs. Group III. Abnormal baseline and abnormal subsequent ECGs. RESULTS: Among 340 TAVR patients, 248 were discharged home with an ACM device. The overall incidence of DACA was 7% (n = 17), of whom 4% (n = 10) required a PPM. Mortality and readmission between discharge and 30 days was 0% and 8.3%, respectively. Stratification of patients identified 96 (38.7%) patients in Group I: 50 (20%) in Group II, and 102 (41%) in Group III. The incidence of DACA requiring a PPM was 0% in Group I, 4% (n = 2) in Group II, and 8.5% (n = 8) in Group III (p < 0.004). CONCLUSIONS: In TAVR patients who were discharged home with ACM, none died between discharge and 30-days. For those with normal baseline, perioperative and discharge ECG, there were no events of DACA at 14-days.

Ambulatory Electrocardiographic Monitoring Following Minimalist Transcatheter Aortic Valve Replacement.

OBJECTIVES: The aim of this study was to determine the impact of delayed high-degree atrioventricular block (HAVB) or complete heart block (CHB) after transcatheter aortic valve replacement (TAVR) using a minimalist approach followed by ambulatory electrocardiographic (AECG) monitoring. BACKGROUND: Little is known regarding the clinical impact of HAVB or CHB in the early period after discharge following TAVR. METHODS: A prospective, multicenter study was conducted, including 459 consecutive TAVR patients without permanent pacemaker who underwent continuous AECG monitoring for 14 days (median length of hospital stay 2 days; IQR: 1-3 days), using 2 devices (CardioSTAT and Zio AT). The primary endpoint was the occurrence of HAVB or CHB. Patients were divided into 3 groups: 1) no right bundle branch block (RBBB) and no electrocardiographic (ECG) changes; 2) baseline RBBB with no further changes; and 3) new-onset ECG conduction disturbances. RESULTS: Delayed HAVB or CHB episodes occurred in 21 patients (4.6%) (median 5 days postprocedure; IQR: 4-6 days), leading to PPM in 17 (81.0%). HAVB or CHB events were rare in group 1 (7 of 315 [2.2%]), and the incidence increased in group 2 (5 of 38 [13.2%]; P < 0.001 vs group 1) and group 3 (9 of 106 [8.5%]; P = 0.007 vs group 1; P = 0.523 vs group 2). No episodes of sudden or all-cause death occurred at 30-day follow-up. CONCLUSIONS: Systematic 2-week AECG monitoring following minimalist TAVR detected HAVB and CHB episodes in about 5% of cases, with no mortality at 1 month. Whereas HAVB or CHB was rare in patients without ECG changes post-TAVR, baseline RBBB and new-onset conduction disturbances determined an increased risk. These results would support tailored management using AECG monitoring and the possibility of longer hospitalization periods in patients at higher risk for delayed HAVB or CHB.

The Rapid Prediction of Focal Wavefront Origins: Integration With a 3-Dimensional Mapping System.

OBJECTIVES: This study assessed the accuracy of an algorithm that predicts the origin of focal arrhythmias using a limited number of data points. BACKGROUND: Despite advances in technology, ablations can be time-consuming, and activation mapping continues to have inherent limitations. The authors developed an algorithm that can predict the origin of a focal wavefront using the location and activation timing information in 2 pairs of sampled points. This algorithm was incorporated into an electroanatomic mapping (EAM) system to assess its accuracy in a 3-dimensional clinical environment. METHODS: EAM data from patients who underwent successful ablation of a focal wavefront using the CARTO3 system were loaded onto an offline version of the software modified to contain the algorithm. Prediction curves were retrospectively generated. Predictive accuracy, defined as the distance between true and predicted origin wavefront origins, was measured. RESULTS: Seventeen wavefronts in as many patients (2 with atrial tachycardia, 3 with orthodromic re-entrant tachycardia, 8 with premature ventricular complex and/or ventricular tachycardia, 4 with focal pulmonary vein isolation breakthroughs) were studied. Thirty-three origin predictions were attempted (1.9 ± 0.4 per patient) using 132 points. Predictions were successfully calculated in 31 of 33 (93.9%) attempts and were accurate to within 5.7 ± 6.9 mm. Individual prediction curves were accurate to within 3.0 ± 4.7 mm. CONCLUSIONS: Focal wavefront origins may be accurately predicted in 3 dimensions using a novel algorithm incorporated into an EAM system.

Is isolated ST segment elevation in Lead aVR associated with high grade coronary artery disease?

BACKGROUND: The diagnostic accuracy of lead aVR ST-segment elevation for left main or triple vessel disease (LM/3VD) has not been universally accepted. In the present analysis we sought to evaluate the diagnostic accuracy of STEaVR in patients presenting with an acute coronary syndrome (ACS). METHODS: Pooled sensitivity, specificity, positive, and negative likelihood ratios were calculated using a random effects model (DerSimonian-Laird Method) for computing summary estimates and receiver operator curve (ROC) analysis for evaluating overall diagnostic accuracy. RESULTS: This meta-analysis included 14 studies. The pooled sensitivity of STEaVR for LM/3VD was 0.40 (95% CI; 0.38 0.43, p < 0.001), specificity 0.82 (95% CI; 0.81-0.83, p < 0.001). Pooled positive likelihood ratio 2.49 (95% CI; 1.62-3.81, p < 0.001) and negative likelihood 0.54 (95% CI; 0.39-0.76, p < 0.001). The pooled sensitivity of STEaVR for LM was 0.39 (95% CI; 0.34-0.45, p < 0.001) specificity was 0.86 (95% CI; 0.85-0.87, p < 0.001) with an AUC of 0.79. The pooled positive likelihood ratio (LR) for LM was 2.78 (95% CI, 2.28-3.39, p < 0.001) negative likelihood ratio 0.51 (95% CI, 0.33-0.78, p < 0.001). CONCLUSION: Our study shows that in patients presenting with an ACS, presence of STEaVR may indicate the presence of LM or 3VD. STEaVR has a high specificity for both LM and 3VD, with a high pooled LR.

Slow uniform electrical activation during sinus rhythm is an indicator of reentrant VT isthmus location and orientation in an experimental model of myocardial infarction.

BACKGROUND: To validate the predictability of reentrant circuit isthmus locations without ventricular tachycardia (VT) induction during high-definition mapping, we used computer methods to analyse sinus rhythm activation in experiments where isthmus location was subsequently verified by mapping reentrant VT circuits. METHOD: In 21 experiments using a canine postinfarction model, bipolar electrograms were obtained from 196-312 recordings with 4mm spacing in the epicardial border zone during sinus rhythm and during VT. From computerized electrical activation maps of the reentrant circuit, areas of conduction block were determined and the isthmus was localized. A linear regression was computed at three different locations about the reentry isthmus using sinus rhythm electrogram activation data. From the regression analysis, the uniformity, a measure of the constancy at which the wavefront propagates, and the activation gradient, a measure that may approximate wavefront speed, were computed. The purpose was to test the hypothesis that the isthmus locates in a region of slow uniform activation bounded by areas of electrical discontinuity. RESULTS: Based on the regression parameters, sinus rhythm activation along the isthmus near its exit proceeded uniformly (mean r2= 0.95±0.05) and with a low magnitude gradient (mean 0.37±0.10mm/ms). Perpendicular to the isthmus long-axis across its boundaries, the activation wavefront propagated much less uniformly (mean r2= 0.76±0.24) although of similar gradient (mean 0.38±0.23mm/ms). In the opposite direction from the exit, at the isthmus entrance, there was also less uniformity (mean r2= 0.80±0.22) but a larger magnitude gradient (mean 0.50±0.25mm/ms). A theoretical ablation line drawn perpendicular to the last sinus rhythm activation site along the isthmus long-axis was predicted to prevent VT reinduction. Anatomical conduction block occurred in 7/21 experiments, but comprised only small portions of the isthmus lateral boundaries; thus detection of sinus rhythm conduction block alone was insufficient to entirely define the VT isthmus. CONCLUSIONS: Uniform activation with a low magnitude gradient during sinus rhythm is present at the VT isthmus exit location but there is less uniformity across the isthmus lateral boundaries and at isthmus entrance locations. These factors may be useful to verify any proposed VT isthmus location, reducing the need for VT induction to ablate the isthmus. Measured computerized values similar to those determined herein could therefore be assistive to sharpen specificity when applying sinus rhythm mapping to localize EP catheter ablation sites.

Surgical and endoscopic management of a pericardioesophageal fistula after radiofrequency pulmonary vein isolation.

INTRODUCTION: The most feared complication of pulmonary vein isolation (PVI) is an atrioesophageal fistula (AEF). While rare (0.1-0.25%), primary surgical closure (as opposed to esophageal stenting) is associated with lower mortality. Pericardioesophageal fistula (PEF) may present prior to fistulization into the atrium. Unfortunately, data on the optimal management of PEFs are lacking. CASE REPORT: Seventy-one-year-old male with AF presented with chest pain 3 weeks after radiofrequency PVI. Computed tomography angiography (CTA) chest and echocardiogram showed pneumopericardium. Barium esophagram showed extravasation from esophagus into the pericardium without connection to the left atrium. Sternotomy with mediastinal exploration exposed the pericardial defect, over which a CorMatrix patch was placed. The fistula was then stented endoscopically with endosuture fixation. Poststent esophagram did not show barium leak, and the patient was discharged home. One week later, the patient returned with enterococcal and candida bacteremia and an acute right parietal/occipital lobe infarct. Barium esophagram showed contrast extravasation into the pericardium. The patient rapidly succumbed to his illness and died. Autopsy revealed pericardial abscess posterior to the LA in communication with the esophagus. Extension to the LA was not seen. CONCLUSION: While the surgical treatment of AEF is relatively well established, there is no consensus in the management of PEF. While prior small series have suggested PEF may be managed with esophageal stenting, our case illustrates the limitations of this approach.

Does the Presence of Significant Mitral Regurgitation prior to Transcatheter Aortic Valve Implantation for Aortic Stenosis Impact Mortality? - Meta-Analysis and Systematic Review.

BACKGROUND: Mitral regurgitation (MR) is commonly encountered in patients with severe aortic stenosis (AS). However, its independent impact on mortality in patients undergoing transcatheter aortic valve implantation (TAVI) has not been established. METHODS: We performed a systematic search for studies reporting characteristics and outcome of patients with and without significant MR and/or adjusted mortality associated with MR post-TAVI. We conducted a meta-analysis of quantitative data. RESULTS: Seventeen studies with 20,717 patients compared outcomes and group characteristics. Twenty-one studies with 32,257 patients reported adjusted odds of mortality associated with MR. Patients with MR were older, had a higher Society of Thoracic Surgeons score, lower left ventricular ejection fraction, a higher incidence of prior myocardial infarction, atrial fibrillation, and a trend towards higher NYHA class III/IV, but had similar mean gradient, gender, and chronic kidney disease. The MR patients had a higher unadjusted short-term (RR = 1.46, 95% CI 1.30-1.65) and long-term mortality (RR = 1.40, 95% CI 1.18-1.65). However, 16 of 21 studies with 27,777 patients found no association between MR and mortality after adjusting for baseline variables. In greater than half of the patients (0.56, 95% CI 0.45-0.66) MR improved by at least one grade following TAVI. CONCLUSION: The patients with MR undergoing TAVI have a higher burden of risk factors which can independently impact mortality. There is a lack of robust evidence supporting an increased mortality in MR patients, after adjusting for other compounding variables. MR tends to improve in the majority of patients post-TAVI.

Irrigated vs. Non-irrigated Catheters in the Ablation of Accessory Pathways.

There is a paucity of data comparing irrigated to non-irrigated catheters in the ablation of accessory pathways (AP) in adult patients. Retrospective analysis of first-time AP ablations performed at our institution from May 2010 to June 2017. A total of 69 AP ablations were studied; irrigated catheters were used in 78.3% cases. Mean age was 40.9 ± 14.3 years and 56.7% were male. Among APs, 63.8% were left sided and 56.5% were concealed. The total procedure time was 232.0 ± 89.0 min, ablation time was 3.1 ± 5.1 min, and fluoroscopy time was 13.9 ± 15.4 min. The overall acute success rate of ablation was 62/69 (89%). Success rates trended higher with irrigated catheters in both groups and were significant for the population as a whole (94.4% vs. 73.3%, p = 0.04). Analyzing the entire cohort, success rates were significantly higher in ablations using irrigated catheters.

Pulmonary vein antral isolation causes depolarization of vein sleeves: Implications for the assessment of isolation.

PURPOSE: Pulmonary vein isolation (PVI) for atrial fibrillation has been shown to result in inexcitability of a large fraction of pulmonary veins (PVs), but the mechanism is unknown. We investigated the mechanism of PV inexcitability by assessing the effects of PVI on the electrophysiology of PV sleeves. METHODS: Patients undergoing first-time radiofrequency PVI were studied. Capture threshold, effective refractory period (ERP), and excitability were measured in PVs and the left atrial appendage (LAA) before and after ablation. Adenosine was used to assess both transient reconnection and transient venous re-excitability. RESULTS: We assessed 248 veins among 67 patients. Mean PV ERP (249.7 ± 54.0 ms) and capture threshold (1.4 ± 1.6 mA) increased to 300.5 ± 67.1 and 5.7 ± 5.6 mA, respectively (P < .0001 for both) in the 26.9% PVs that remained excitable, but no change was noted in either measure in the LAA. In 16.3% of the 73.1% inexcitable veins, transient PV re-excitability (as opposed to reconnection) was seen with adenosine administration. CONCLUSIONS: Antral PVI causes inexcitability in a majority of the PVs, which can transiently be restored in some with adenosine. Among PVs that remain excitable, ERP and capture threshold increase significantly. These data imply resting membrane potential depolarization of the of PV myocardial sleeves. As PV inexcitability hampers the assessment of entrance and exit block, demonstrating transient PV re-excitability during adenosine administration helps ensure true isolation.

A novel method for the prediction of focal wavefront origins in cardiac arrhythmias.

BACKGROUND: Current techniques for mapping and ablating cardiac arrhythmias are valuable, but have limitations. We devised a novel method of predicting the origin of a focal arrhythmia wavefront that utilizes conduction velocity (CV), the difference in electrogram timing during arrhythmia (t), and the distance between two points (z) to generate prediction curves which can be applied to an electroanatomic map. The intersection of two such curves predicts the origin of the wavefront. OBJECTIVE: To describe the rationale behind a novel method of arrhythmia mapping and assess its feasibility in a retrospective study of focal arrhythmias. METHODS: We retrospectively studied 12 patients with arrhythmias with focal chamber activation that were successfully mapped and treated with ablation. CV during arrhythmia was measured using electroanatomic mapping software. Values for z and t were calculated for two pairs of points. Two prediction curves were generated and superimposed onto the electroanatomic maps. The distance between the intersection of the two curves and the wavefront origin was recorded. The shortest distance between individual curves and the wavefront origin was also measured. RESULTS: Twenty-four curves were successfully generated in 12 patients. The distance from the intersection of two curves and the wavefront origin was 9.2 ±â€¯7.7 mm. The shortest distance between individual prediction curves and the wavefront origin was 5.2 ±â€¯5.2 mm. CONCLUSIONS: Wavefront origins may be predicted by a novel method utilizing a limited number of measurements. Further study of this method requires its integration with an electroanatomical mapping system.

Source-Sink Mismatch Causing Functional Conduction Block in Re-Entrant Ventricular Tachycardia.

Ventricular tachycardia (VT) caused by a re-entrant circuit is a life-threatening arrhythmia that at present cannot always be treated adequately. A realistic model of re-entry would be helpful to accurately guide catheter ablation for interruption of the circuit. In this review, models of electrical activation wavefront propagation during onset and maintenance of re-entrant VT are discussed. In particular, the relationship between activation mapping and maps of transition in infarct border zone thickness, which results in source-sink mismatch, is considered in detail and supplemented with additional data. Based on source-sink mismatch, the re-entry isthmus can be modeled from its boundary properties. Isthmus boundary segments with large transitions in infarct border zone thickness have large source-sink mismatch, and functional block forms there during VT. These alternate with segments having lesser thickness change and therefore lesser source-sink mismatch, which act as gaps, or entrance and exit points, to the isthmus during VT. Besides post-infarction substrates, the source-sink model is likely applicable to other types of volumetric changes in the myocardial conducting medium, such as when there is presence of fibrosis or dissociation of muscle fibers.