Arrhythmic Risk Assessment of Hypokalaemia Using Human Pluripotent Stem Cell-Derived Cardiac Anisotropic Sheets

Introduction: Hypokalaemia, defined as an extracellular concentration of K+ below 3.5 mM, can cause cardiac arrhythmias by triggered or re-entrant mechanisms. Whilst these effects have been reported in animal and human stem cell-based models, to date there has been no investigation in more complex structures such as the human ventricular cardiac anisotropic sheet (hvCAS). Here, we investigated arrhythmogenicity, electrophysiological, and calcium transient (CaT) changes induced by hypokalaemia using this bioengineered platform.Methods: An optical mapping technique was applied on hvCAS derived from human pluripotent stem cells to visualize electrophysiological and CaT changes under normokalaemic (5 mM KCl) and hypokalaemic (3 mM KCl) conditions.Results: Hypokalaemia significantly increased the proportion of preparations showing spontaneous arrhythmias from 0/14 to 7/14 (Fisher’s exact test, p = 0.003). Hypokalaemia reduced longitudinal conduction velocity (CV) from 7.81 to 7.18 cm⋅s−1 (n = 9, 7; p = 0.036), transverse CV from 5.72 to 4.69 cm⋅s−1 (n = 12, 11; p = 0.030), prolonged action potential at 90% repolarization (APD90) from 83.46 to 97.45 ms (n = 13, 15; p < 0.001), increased action potential amplitude from 0.888 to 1.195 ΔF (n = 12, 14; p < 0.001) and CaT amplitude from 0.76 to 1.37 ΔF (n = 12, 13; p < 0.001), and shortened effective refractory periods from 242 to 165 ms (n = 12, 13; p < 0.001).Conclusion: Hypokalaemia exerts pro-arrhythmic effects on hvCAS, which are associated with alterations in CV, repolarization, refractoriness, and calcium handling. These preparations provide a useful platform for investigating electrophysiological substrates and for conducting arrhythmia screening.

Mechanisms of ventricular arrhythmias elicited by coexistence of multiple electrophysiological remodeling in ischemia: a simulation study

Myocardial ischemia, injury and infarction (MI) are the three stages of acute coronary syndrome (ACS). In the past two decades, a great number of studies focused on myocardial ischemia and MI individually, and showed that the occurrence of reentrant arrhythmias is often associated with myocardial ischemia or MI. However, arrhythmogenic mechanisms in the tissue with various degrees of remodeling in the ischemic heart have not been fully understood. In this study, biophysical detailed single-cell models of ischemia 1a, 1b, and MI were developed to mimic the electrophysiological remodeling at different stages of ACS. 2D tissue models with different distributions of ischemia and MI were constructed to investigate the mechanisms of initiation of reentrant waves during the progression of ischemia. Simulation results in 2D tissues showed that the vulnerable window (VW) in the tissue with multiple pathological conditions were determined by the VWs in the tissues with a single pathological condition. In different pathological conditions, action potential duration (APD) and the conduction velocity (CV) change differently. In the tissue with multiple pathological conditions, when the borders of different pathological conditions were perpendicular to the excitation wavefront, reentrant waves were mainly induced by the spatial heterogeneity of refractory periods due to the interaction of APD and CV along the wavefront. When the borders were parallel to the wavefront, the increased excitation threshold of MI region as well as the impaired excitability of ischemia region were the primary reason for the generation of reentry. Finally, the reentrant wave was observed in a 3D model with a scar reconstructed from MRI images of a MI patient. These comprehensive findings provide novel insights for understanding the arrhythmic risk during the progression of myocardial ischemia and highlight the importance of the multiple pathological stage in designing medical therapies for arrhythmia in ischemia.

Impact of adenosine on mechanisms sustaining persistent atrial fibrillation: Analysis of contact electrograms and non-invasive ECGI mapping data

Background We evaluated the effect of adenosine upon mechanisms sustaining persistent AF through analysis of contact electrograms and ECGI mapping. Methods Persistent AF patients undergoing catheter ablation were included. ECGI maps and cycle length (CL) measurements were recorded in the left and right atrial appendages and repeated following boluses of 18 mg of intravenous adenosine. Potential drivers (PDs) were defined as focal or rotational activations completing ≥ 1.5 revolutions. Distribution of PDs was assessed using an 18 segment biatrial model. Results 46 patients were enrolled. Mean age was 63.4 ± 9.8 years with 33 (72%) being male. There was no significant difference in the number of PDs recorded at baseline compared to adenosine (42.1 ± 15.2 vs 40.4 ± 13.0; p = 0.417), nor in the number of segments harbouring PDs, (13 (11–14) vs 12 (10–14); p = 0.169). There was a significantly higher percentage of PDs that were focal in the adenosine maps (36.2 ± 15.2 vs 32.2 ± 14.4; p < 0.001). There was a significant shortening of CL in the adenosine maps compared to baseline which was more marked in the right atrium than left atrium (176.7 ± 34.7 vs 149.9 ± 27.7 ms; p < 0.001 and 165.6 ± 31.7 vs 148.3 ± 28.4 ms; p = 0.003). Conclusion Adenosine led to a small but significant shortening of CL which was more marked in the right than left atrium and may relate to shortening of refractory periods rather than an increase in driver burden or distribution. Registered on Clinicaltrials.gov: NCT03394404.

Control of colonic motility using electrical stimulation to modulate enteric neural activity

Electrical stimulation of the enteric nervous system (ENS) is an attractive approach to modify gastrointestinal transit. Colonic motor complexes (CMCs) occur with a periodic rhythm, but the ability to elicit a premature CMC depends, at least in part, upon the intrinsic refractory properties of the ENS, which are presently unknown. The objectives of this study were to record myoelectric complexes (MCs, the electrical correlates of CMCs) in the smooth muscle and (i) determine the refractory periods of MCs, (ii) inform and evaluate closed-loop stimulation to repetitively evoke MCs, and (iii) identify stimulation methods to suppress MC propagation. We dissected the colon from male and female C57BL/6 mice, preserving the integrity of intrinsic circuitry while removing the extrinsic nerves, and measured properties of spontaneous and evoked MCs in vitro. Hexamethonium abolished spontaneous and evoked MCs, confirming the necessary involvement of the ENS for electrically-evoked MCs. Electrical stimulation reduced the mean interval between evoked and spontaneous CMCs (24.6 ± 3.5 vs 70.6 ± 15.7 s, p = 0.0002, n = 7). The absolute refractory period was 4.3 s (95% CI = 2.8 - 5.7 s, R2 = 0.7315, n = 8). Electrical stimulation applied during fluid distention-evoked MCs led to an arrest of MC propagation, and following stimulation, MC propagation resumed at an increased velocity (n = 9). The timing parameters of electrical stimulation increased the rate of evoked MCs and the duration of entrainment of MCs, and the refractory period provides insight into timing considerations for designing neuromodulation strategies to treat colonic dysmotility.

Antiarrhythmic effect of ranolazine in combination with selective NCX-inhibition in an experimental model of atrial fibrillation

Background Previous studies showed an antiarrhythmic effect of ranolazine in different clinical and experimental studies. The aim of this study was to investigate the effects of a combination of ranolazine with different selective NCX-inhibitors in an established experimental model of atrial fibrillation. Methods and results 18 hearts of New Zealand white rabbits were retrogradely perfused. Left and right atrial catheters were used to record monophasic action potentials. Hearts were paced at three different cycle lengths (350ms, 250ms, 150ms). Thereby, cycle-length dependent atrial action potential durations (aAPD90), atrial effective refractory periods (aERP) and atrial post-repolarization refractoriness (aPRR=aERP-aAPD90) were obtained. Vulnerability to AF was tested by a standardized protocol employing several trains of burst pacing. After generating baseline data, the hearts were perfused with a combination of acetylcholine (ACh, 1μM) and isoproterenol (Iso, 1μM) to increase occurrence of AF. Afterwards, the hearts were assigned to two groups and additionally perfused with a combination of 10 μM ranolazine and 1 μM of the selective NCX-inhibitor ORM-10103 (group 1: Rano-ORM) or 10 μM ranolazine and 1 μM of another NCX-inhibitor, SEA0400 (group 2: Rano-SEA). Infusion of ACh/Iso led to a shortening of aAPD90 (group 1/2: −27.2ms/−24.5ms p&lt;0.05), aERP (−29.2ms/−35.6ms p&lt;0.05), aPRR (−12.2ms/−13.7ms p=ns) and the occurrence of AF-Episodes was significantly increased (group 1: baseline 6 episodes to 34 episodes under ACh/Iso p&lt;0.05, group 2: baseline 7 episodes to 26 episodes under ACh/Iso p&lt;0.05). Additional perfusion with ranolazine and ORM-10103 did not alter aAPD90 (−0,47ms) while effective refractory periods (+21.4ms, p&lt;0.05) and aPRR (+43ms, p&lt;0.05) were significantly prolonged and AF episodes were effectively reduced to 15 episodes (p&lt;0.05). In group 2, Rano-SEA led to a slight decrease in aAPD90 (−9.5ms) while aERP (+13.3ms, p&lt;0.05) and aPRR (+19.8ms, p&lt;0.05) were prolonged. The occurrence of AF episodes was reduced to 15 episodes (p=0.1). Conclusion To our knowledge this is the first study investigating the effect of ranolazine combined with different selective NCX-inhibitors in an isolated whole-heart model of AF. Atrial repolarization was not significantly changed with either of the combinations. However, both combinations prolonged aERP and aPRR and thereby suppressed induction of AF. Combining novel cellular targets may therefore lead to new potentially interesting options for antiarrhythmic AF therapy that have to be tested in clinical studies. Funding Acknowledgement Type of funding source: None

Antiarrhythmic Effect of Ranolazine in Combination with Selective NCX-Inhibition in an Experimental Model of Atrial Fibrillation

The aim of this study was to investigate the effects of a combination of ranolazine with different selective inhibitors of the Na+/Ca2+-exchanger (NCX) in an established experimental model of atrial fibrillation (AF). Eighteen hearts of New Zealand white rabbits were retrogradely perfused. Atrial catheters were used to record monophasic action potentials (aPRR). Hearts were paced at three different cycle lengths. Thereby, atrial action potential durations (aAPD90), atrial effective refractory periods (aERP) and atrial post-repolarization refractoriness were obtained. Isoproterenol and acetylcholine were employed to increase the occurrence of AF. Thereafter, the hearts were assigned to two groups (n = 9 each group) and additionally perfused with a combination of 10 µM ranolazine and 1 µM of the selective NCX-inhibitor ORM-10103 (group A: Rano-ORM) or 10 µM ranolazine and 1 µM of another NCX-inhibitor, SEA0400 (group B: Rano-SEA). The infusion of Iso/ACh led to a shortening of aAPD90, aERP, aPRR and the occurrence of AF episodes was significantly increased. Additional perfusion with ranolazine and ORM-10103 (group A) significantly prolonged the refractory periods and aPRR and AF episodes were effectively reduced. In group B, Rano-SEA led to a slight decrease in aAPD90 while aERP and aPRR were prolonged. The occurrence of AF episodes was consecutively reduced. To our knowledge, this is the first study investigating the effect of ranolazine combined with different selective NCX-inhibitors in an isolated whole-heart model of AF. Both combinations prolonged aERP and aPRR and thereby suppressed the induction of AF.

P333Left atrial function by echocardiography is independent of degree of left atrial electrical scar

Introduction Assessment of left atrial function via transthoracic echocardiography (TTE) is performed most commonly by measuring the transmitral A wave in sinus rhythm. Left atrial (LA) fibrosis plays an important role in the pathogenesis and perpetuation of Atrial Fibrillation (AF). It may be identified by bipolar voltage (BiV) mapping, which can easily be performed at the beginning of a Pulmonary Vein Isolation (PVI) procedure. The relationship between the degree of LA fibrosis, characterised with mapping, and LA function, determined by echocardiography, has not previously been elucidated. Methods Patients were enrolled in a project to evaluate the degree of fibrosis during PVI procedures. Pre-procedure TTEs of those presenting in sinus rhythm were assessed and the transmitral A wave was measured and compared to the degree of scarring seen. The high density electroanatomic maps (HD-EAMs) created during the PVIs were analysed using a novel VHA algorithm after the procedure. All points with voltages &lt; 0.5mV were defined to have electrical scar. Patients were classified into 4 quartiles based on the levels of scar seen (Figure 1). Results 39 patients were included in the evaluation. Average age was 60.6 +/- 13.2 years. 32 (82.0%) of the patients were male. Mean CHADS2VASc score was 1.5. The mean percentage of scar was calculated as 19.6 +/- 15.9%. The average A wave was 0.62 +/- 0.18 ms-1. Pearson’s correlation coefficient showed no relationship between LA scar and either A wave velocities (r = 0.26, p = 0.11) or E:A ratio (r=-0.02, p = 0.91). A significant correlation between A wave velocity and CHADS2VASc was observed (r = 0.49, p = 0.001). Conclusion Our study demonstrates no relationship between degree of LA scarring and reduced LA function on TTE as assessed by the A wave. It has been established that structural remodelling in AF (such as atrial dilatation) may occur independently of the electrical remodelling. A potential explanation for our findings is that the electrical scarring in AF, which results in alterations in refractory periods, precedes the negative remodelling which ultimately results in reduced atrial function. This hypothesis would need to be further evaluated in larger studies. Abstract Figure 1

P1421Assessment of intraatrial conduction during staged catheter ablation of persistent AF

Goal. To evaluate the electrophysiological changes in the LA myocardium between the stages of sequential RFA of persistent AF. Materials and methods. From 2015 to 2018 43 patients (27 men and 16 women) underwent sequential ablation (second intervention in a period of 3 to 6 months) of persistent AF. The routine isolation was performed in the first stage. During the second stage additional lesions were performed in the areas of the restored conduction and posterior wall isolation. All patients underwent a routine EP before each stage with measurements of the atrial myocardial refractory periods, as well as intraatrial conduction. Results. The EP parameters before the first and second stages had significantly changed: refractory periods in the areas of previously performed RFA had increased from 184 (166; 208) ms to 212 (174; 249) ms, respectively, p &lt;0.001, the dispersion of refractivity decreased from 34 (18; 48) ms to 21 (16; 29) ms, p = 0.017. According to ECG, the duration of intraatrial conduction also decreased by 34 (24; 51) ms, p = 0.034. Conclusion. Electrophysiological markers of intra- and interatrial conduction show a tendency to reverse modeling of atrial functions in patients passing through the staged treatment of persistent AF.