Combined endo- and epicardial pace-mapping to localize ventricular tachycardia isthmus in ischaemic and non-ischaemic cardiomyopathy

Aims A high-density pace-mapping can depict an abrupt transition in paced QRS morphology from a poor to excellent match, unmasking the critical component of ventricular tachycardia (VT) isthmus from the entrance to exit. We sought to assess pace-mapping at multiple sites within the endo- and epicardial scars to identify the VT isthmus in patients with ischaemic (ICM) and non-ischaemic cardiomyopathy (NICM). Methods and results Colour-coded maps correlating to the percentage matches between 12-lead electrocardiograms during VT and pace-mapping [referred to as correlation score maps (CSMs)] were analysed. We studied 115 CSMs (80 endo- and 35 epicardial CSMs) in 37 patients (17 ICM, 20 NICM). The CSM with an abrupt change (AC) in pacemap score (AC-type) on the endocardium was more frequently observed in ICM than in NICM [11/39 (28%) vs. 1/41 (2%); P = 0.001]. Among 35 CSMs that were analysed by the combined endo- and epicardial mapping, 10 (29%) CSMs exhibited non-AC-type on the endocardium; however, AC-type was present on the opposite epicardium. Although 24 (69%) CSMs did not show AC-type on both the endocardium and epicardium, 16 of them had either an excellent (>90%) or poor (<0%) correlation score on either side, associated with isthmus exit or entrance, respectively. However, the remaining eight CSMs had neither excellent nor poor scores. Conclusion The CSM may provide electrophysiological information to localize the endo- and epicardial VT isthmus. The absence of AC-type CSM on the endocardium, which is frequently observed in NICM, appears to indicate the sub-epicardial or intramural course of the critical isthmus.

Epicardial Radiofrequency Ablation: Who, When, and How?

In the past decades, it has been known that reentry circuits for ventricular tachycardia or focal triggers of premature ventricular complexes are not limited to the subendocardial myocardium. Rather, intramural or subepicardial substrates may also give rise to ventricular tachycardia, particularly in those with non-ischemic cardiomyopathy. Besides, some of the idiopathic ventricular tachycardia might be originated from epicardial foci. Percutaneous epicardial mapping and ablation have been successfully introduced to treat this sub-epicardiac ventricular tachycardia. Herein, this chapter reviews the indications for epicardial ablation and the identification of epicardial ventricular tachycardia by disease entity, electrocardiography and imaging modalities. This chapter also described the optimal technique for epicardial access and the potential complication.

Electrocardiographic and Electrophysiological Characteristics of Idiopathic Ventricular Arrhythmias Ablated Through a Percutaneous Trans-pericardial Approach

Aims Idiopathic epicardial ventricular arrhythmias (VAs) are clustered in the areas of the summit and crux. This study was to report a group of idiopathic epicardial VAs remote from the summit and crux areas. Methods In total, 9 patients (6 males, mean age 32±13 years) were enrolled. The locations were identified by epicardial mapping and ablation. The electrocardiographic and electrophysiological characteristics were compared to those of 9 patients who had VAs ablated at the opposite endocardial site. Results VAs were identified at the epicardium, with 4 patients had VAs located at the inferior wall, one at the anterior wall, one at the apex and 3 patients had VAs at the lateral wall. A “QS” type at the location-related leads was the only identified surface electrocardiogram indication suggesting epicardial origin (compared to that of the controls, 100% vs 0%, p<0.001). Endocardial and epicardial mapping revealed pre-maturities of -11±4 ms and -25±8 ms, respectively (VS. -28±8 ms revealed by endocardial mapping in control patients, p<0.001 and p=0.389, respectively). All of the study cases demonstrated an “rS” pattern in the endocardial unipolar electrogram. Acute and long-term successful ablation (a median of 11 months of follow-up) was achieved in all patients without complications. Conclusion A distinct group of idiopathic VAs remote from the summit and crux areas warranting ablation by a subxiphoid approach were identified. Morphological ECG features of a “QS” type among the location-related grouped leads combined with the mapping findings helped in the identification of the epicardial site of origin.

Conduction Disorders during Sinus Rhythm in Relation to Atrial Fibrillation Persistence

Classification of atrial fibrillation (AF) is currently based on clinical characteristics. However, classifying AF using an objective electrophysiological parameter would be more desirable. The aim of this study was to quantify parameters of atrial conduction during sinus rhythm (SR) using an intra-operative high-resolution epicardial mapping approach and to relate these parameters to clinical classifications of AF. Patients were divided according to the standard clinical classification and spontaneous termination of AF episodes. The HATCH score, a score predictive of AF progression, was calculated, and surface ECGs were evaluated for signs of interatrial block. Conduction disorders mainly differed at Bachmann’s bundle (BB). Activation time (AT) at BB was longer in persistent AF patients (AT-BB: 75 (53–92) ms vs. 55 (40–76) ms, p = 0.017), patients without spontaneous termination of AF episodes (AT-BB: 53.5 (39.6–75.8) ms vs. 72.0 (49.6–80.8) ms, p = 0.009) and in patients with a P-wave duration ≥ 120 ms (64.3 (52.3–93.0) ms vs. 50.5 (39.6–56.6) ms, p = 0.014). HATCH scores also correlated positively to AT-BB (rho 0.326, p = 0.029). However, discriminatory values of electrophysiological parameters, as calculated using ROC-curves, were limited. These results may reflect shortcomings of clinical classifications and further research is needed to establish an objective substrate-based classification of AF.

Identification of Low-voltage Areas: A Unipolar, Bipolar and Omnipolar Perspective

Background - Low-voltage areas (LVA) are commonly considered surrogate markers for an arrhythmogenic substrate underlying tachyarrhythmias. It remains challenging to define a proper threshold to classify LVA and it is unknown whether unipolar, bipolar and the recently introduced omnipolar voltage mapping techniques are complementary or contradictory in classifying LVAs. Therefore, this study examined similarities and dissimilarities in unipolar, bipolar and omnipolar voltage mapping and explored the relation between various types of voltages and conduction velocity (CV). Methods - Intra-operative epicardial mapping (interelectrode distance 2mm, ±1900 sites) was performed during sinus rhythm in 21 patients (48±13 years, 9 male) with atrial volume overload. Cliques of 4 electrodes (2x2 mm) were used to calculate the maximal unipolar (V uni,max ), bipolar (V bi,max ) and omnipolar (V omni,max ) voltages and mean CV. Areas with V bi,max or V omni,max ≤0.5 mV were defined as LVA. Results - V uni,max was not only larger than V bi,max but also larger than V omni,max (7.08 [4.22-10.59] mV vs. 5.27 [2.39-9.56] mV and 5.77 [2.58-10.52] mV respectively, P<0.001). In addition, the largest bipolar clique voltage was on average 1.66 (range: 1.0 - 59.0) times larger to the corresponding perpendicular bipolar voltage pair. LVAs identified by a bipolar or omnipolar threshold corresponded to a broad spectrum of unipolar voltages and, even though CV was generally decreased, still high CVs and large unipolar voltages were found in these LVAs. Conclusions - In patients with atrial volume overload, there were considerable discrepancies in the different types of LVAs. Additionally, identification of LVAs was hampered by considerable directional differences in bipolar voltages. Even using directional independent omnipolar voltage to identify LVAs, high CVs and large unipolar voltages are present within these areas. Therefore, a combination of low unipolar and low omnipolar voltage may be more indicative of 'true' LVAs.

Reduction of Conduction Velocity in Patients with Atrial Fibrillation

It is unknown to what extent atrial fibrillation (AF) episodes affect intra-atrial conduction velocity (CV) and whether regional differences in local CV heterogeneities exist during sinus rhythm. This case-control study aims to compare CV assessed throughout both atria between patients with and without AF. Patients (n = 34) underwent intra-operative epicardial mapping of the right atrium (RA), Bachmann’s bundle (BB), left atrium (LA) and pulmonary vein area (PVA). CV vectors were constructed to calculate median CV in addition to total activation times (TAT) and unipolar voltages. Biatrial median CV did not differ between patients with and without AF (90 ± 8 cm/s vs. 92 ± 6 cm/s, p = 0.56); only BB showed a CV reduction in the AF group (79 ± 12 cm/s vs. 88 ± 11 cm/s, p = 0.02). In patients without AF, there was no predilection site for the lowest CV (P5) (RA: 12%; BB: 29%; LA: 29%; PVA: 29%). In patients with AF, lowest CV was most often measured at BB (53%) and ranged between 15 to 22 cm/s (median: 20 cm/s). Lowest CVs were also measured at the LA (18%) and PVA (29%), but not at the RA. AF was associated with a prolonged TAT (p = 0.03) and decreased voltages (P5) at BB (p = 0.02). BB was a predilection site for slowing of conduction in patients with AF. Prolonged TAT and decreased voltages were also found at this site. The next step will be to determine the relevance of a reduced CV at BB in relation to AF development and maintenance.