The Report of Community-Based and Government-Endorsed Screening Program of Atrial Fibrillation in Taiwan.

BACKGROUND: Although international guidelines recommended opportunistic screening for atrial fibrillation (AF), the community-based AF screening program incorporated into the government-endorsed health care system is rarely reported in Asian countries. OBJECTIVES: We aimed to test the feasibility of adding AF screening into the preexistent adult health check program and report the AF detection rate and percentages of OAC prescriptions before and after AF screening with the involvement of public health care systems. METHODS: We performed this program in three counties (Chiayi county, Keelung City, and Yilan county) in Taiwan which have their own official preexistent adult health check programs conducted by public health bureaus for years. However, electrocardiography (ECG) was not included in these programs before. We cooperated with the public health bureaus of the three counties and performed single-lead 30-second ECG recording for every participant. RESULTS: From January to December 2020, AF screening was performed in 199 sessions with 23,572 participants. AF was detected in 278 subjects with a detection rate of 1.19% (age ≥65 years: 2.39%; ≥75 years: 3.73%). The mean CHA2DS2-VASc score of these 278 subjects was 2.36, with 91% of them had a score ≥1 (males) or ≥2 (females). The number needed to screen was 42 and 27 for subjects aged ≥65 and ≥75 years, respectively. The prescription rate of OACs significantly increased from 11.4 to 60.6% in Chiayi county and from 15.8 to 50.0% in Keelung City after screening (both p-values <0.001). CONCLUSION: This community-based and government-endorsed AF screening project in Taiwan demonstrated that incorporation of AF screening into the preexistent adult health check programs through co-operations with the government was feasible. Actions to detect AF, good education, and well-organized transferring plan after AF being detected with the involvement of public health care systems could result in a substantial increase in the prescription rate of OACs.

Levosimendan attenuates electrical alternans and prevents ventricular arrhythmia during therapeutic hypothermia in isolated rabbit hearts.

BACKGROUND: Therapeutic hypothermia (TH) increases the susceptibility to ventricular arrhythmias (VAs) by prolonging action potential duration (APD) and facilitating arrhythmogenic spatially discordant alternans (SDA). Levosimendan, a calcium sensitizer, has been reported to shorten APD by enhancing the adenosine triphosphate (ATP)-sensitive K current. OBJECTIVE: The purpose of this study was to test the hypothesis that, during TH, levosimendan shortens the already prolonged APD, attenuates SDA, and prevents VA. METHODS: Langendorff-perfused isolated rabbit hearts were subjected to TH (30°C) for 15 minutes, followed by treatment with either levosimendan 0.5 µM (n = 9) or vehicle (n = 8) for an additional 30 minutes under TH. Using an optical mapping system, epicardial APD was evaluated by S1 pacing. SDA threshold was defined as the longest pacing cycle length (PCL) that induces the phenomenon of SDA. Ventricular fibrillation (VF) inducibility was evaluated by burst pacing for 30 seconds at the shortest PCL that achieved 1:1 ventricular capture. RESULTS: During TH, levosimendan shortened ventricular APD (PCL 400 ms; from 259 ± 8 ms to 241 ± 18 ms; P = .036) and decreased SDA threshold (from 327 ± 88 ms to 311 ± 68 ms; P = .011). VF inducibility was lowered from 39% ± 30% to 14% ± 12% with levosimendan (P = .018), whereas APD at PCL 400 ms (P = .161), SDA threshold (P = 1), and VF inducibility (P = .173) were not changed by vehicle. CONCLUSION: During TH, levosimendan could protect hearts against VA by shortening APD and decreasing SDA threshold. Enhancing ATP-sensitive K current with levosimendan might be a novel approach to preventing VA during TH.

The Contribution of Tissue Inhibitor of Metalloproteinase-2 Genotypes to Breast Cancer Risk in Taiwan.

Tissue inhibitor of metalloproteinase-2 (TIMP-2) is an endogenous inhibitor of matrix metalloproteinase-2 and is highly expressed in breast cancer (BC) cases at diagnosis. However, the genetic investigations for the association of TIMP-2 genotypes with BC risk are rather limited. In this study, contribution of TIMP-2 rs8179090, rs4789936, rs2009196 and rs7342880 genotypes to BC risk was examined among Taiwan's BC population. TIMP-2 genotypic profiles were revealed among 1232 BC cases and 1232 controls about their contribution to BC using a PCR-based RFLP methodology. The TIMP-2 rs8179090 homozygous variant CC genotype was significantly higher in BC cases than controls (odds ratio (OR) = 2.76, 95% confidence interval (95%CI) = 1.78-4.28, p = 0.0001). Allelic analysis showed that C allele carriers have increased risk for BC (OR = 1.39, 95%CI = 1.20-1.62, p = 0.0001). Genotypic together with allelic analysis showed that TIMP-2 rs4789936, rs2009196 or rs7342880 were not associated with BC risk. Stratification analysis showed that TIMP-2 rs8179090 genotypes were significantly associated with BC risk among younger (≤55) aged women, not among those of an elder (>55) age. Last, rs8179090 genotypes were also associated with triple negative BC. This study sheds light into the etiology of BC in Taiwanese women. Rs8179090 may be incorporated into polygenic risk scores and risk prediction models, which could aid in stratifying individuals for targeted breast cancer screening.

Efficacy of Cryoballoon Ablation for Atrial Fibrillation and Recurrence Predictors in an Asian Cohort.

BACKGROUND: Cryoballoon ablation (CBA) for atrial fibrillation (AF) is a rhythm control procedure used in clinical trials, mostly in Western countries. Its efficacy and the predictors of AF recurrence after CBA remain unclear for Asian populations. We aimed to investigate the efficacy of CBA and the predictors of AF recurrence after CBA in Asian AF patients. METHODS: We included consecutive AF patients undergoing CBA for rhythm control between 2014 and 2020. The baseline characteristics, including AF types, symptom severity, and left atrial diameter (LAD), were analyzed. Holter's monitoring and 12-lead ECG were performed to document AF recurrence. A multivariate Cox hazards regression model was used to evaluate the risk of AF recurrence. RESULTS: A total of 120 AF patients (aged 61.9 ± 9.3 years) were included. The percentage of patients free from AF in the year following CBA was 74.2%. Among the three independent predictors of AF recurrence within one year were the presence of persistent AF (p = 0.025), an LAD ≥ 4.75 cm (p = 0.016), and pre-procedural cardioversion (p = 0.025). All patients survived and none had a stroke after CBA. CONCLUSION: CBA for AF is an effective and safe procedure in Asian populations. The presence of persistent AF, an LAD ≥ 4.75 cm, and severe symptoms are predictors of AF recurrence in the year following CBA.

Rhythm Control Better Prevents Dementia than Rate Control Strategies in Patients with Atrial Fibrillation-A Nationwide Cohort Study.

Background: Atrial fibrillation (AF) increases the risk of dementia. Whether the pharmacological rhythm control of AF can reduce the risk of dementia compared to the rate control strategy remains unclear. We hypothesize that the rhythm control strategy is better than the rate control strategy in preventing dementia. Methods: AF patients aged ≥65 years were identified from the Taiwan National Health Insurance Database. Patients receiving anti-arrhythmic drugs at a cumulative defined daily dose (cDDD) of >30 within the first year of enrollment constituted the rhythm control group. Patients who used rate control medications for a cDDD of >30 constituted the rate control group. A multivariate Cox hazards regression model was used to determine the hazard ratio (HR) for dementia. Results: A total of 3382 AF patients (698 in the rhythm control group; 2684 in the rate control group) were analyzed. During a 4.86 ± 3.38 year follow-up period, 414 dementia events occurred. The rhythm control group had a lower rate of dementia than the rate control group (adjust HR: 0.75, p = 0.031). The rhythm control strategy reduced the risk of dementia particularly in those receiving aspirin (p = 0.03). Conclusions: In patients with AF, pharmacological rhythm control was associated with a lower risk of dementia than rate control over a long-term follow-up period, particularly in patients receiving aspirin treatment.

Detecting supraventricular tachycardia with smartwatches facilitates the decision for catheter ablation: A case series.

Smartwatch allows easy detection of arrhythmia. Such an approach is widely used for detecting atrial fibrillation. However, there has been no consensus on the diagnostic power of smartwatch-detected supraventricular tachycardia (SVT). We reported three patients of SVT presenting with infrequent palpitations. Their SVTs were not documented with single-lead or standard ECG in hospital before, but only recorded by the single-lead ECG on smartwatches. Electrophysiological studies confirmed the mechanisms of these SVTs and led to successful catheter ablations. In conclusion, in patients with recurrent symptomatic tachycardia and a smartwatch-detected SVT, an electrophysiological study is indicated rather than to wait for a standard ECG for clinical decision. This approach might prevent the delay for successful treatment.

Protective Effects of Crocetin on Arsenic Trioxide-induced Oxidative Stress in Human Umbilical Vein Endothelial Cells.

BACKGROUND/AIM: The clinical use of arsenic trioxide (As2O3) is hampered due to its cardiotoxicity. Therefore, it is critical to prevent As2O3-induced loss of endothelial integrity. The purpose of this study was to examine As2O3-induced endothelial dysfunction and evaluate the efficacy of crocetin on reversing As2O3-induced cardiotoxicity. MATERIALS AND METHODS: Cultured human umbilical vein endothelial cells (HUVECs) were used to examine As2O3-induced oxidative stress, apoptosis, production of reactive oxygen species (ROS) and DNA adducts. In addition, the impact of crocetin on As2O3-induced cardiotoxicity was evaluated. RESULTS: As2O3 decreased the viability of HUVEC cells and led to apoptosis. Additionally, As2O3 elevated NADPH oxidase activity, and the levels of intracellular ROS. Furthermore, the formamidopyrimidine DNA-glycosylase- and endonuclease III-digestible adducts were induced by As2O3 Crocetin treatment reversed the As2O3-induced reduction in cell viability, the induction of apoptosis, the activation of NADPH oxidase activity, ROS levels and DNA adducts. CONCLUSION: Crocetin protects from As2O3-induced cardio-toxicity.

Protective Effects of Baicalin on Arsenic Trioxide-induced Oxidative Damage and Apoptosis in Human Umbilical Vein Endothelial Cells.

BACKGROUND/AIM: Arsenic trioxide (As2O3) is an environmental pollutant. However, the detailed mechanisms about As2O3-induced loss of endothelial integrity are unknown. This study aimed at investigating how As2O3 causes endothelial dysfunction and whether baicalin can reverse such dysfunction. MATERIALS AND METHODS: Human umbilical vein endothelial cells (HUVECs) were used to examine As2O3-induced oxidative stress, and apoptosis. The influence of baicalin on As2O3-induced endothelial dysfunction were investigated. RESULTS: The viability of HUVECs was inhibited by As2O3 and cells underwent apoptosis. As2O3 treatment increased NADPH oxidase activity, and elevated the level of reactive oxygen species (ROS). Formamidopyrimidine DNA-glycosylase- and endonuclease III-digestible adducts were accumulated. Baicalin reversed As2O3-induced apoptosis and As2O3-suppressed cell viability. Baicalin caused a decrease in NADPH oxidase activity, and re-balanced the ROS level. As2O3-induced formamidopyrimidine DNA-glycosylase- and endonuclease III-digestible adducts were down-regulated. CONCLUSION: Baicalin was found to have the potential capacity to protect endothelial cells from As2O3-induced cytotoxicity.

Ventricular divergence correlates with epicardial wavebreaks and predicts ventricular arrhythmia in isolated rabbit hearts during therapeutic hypothermia.

INTRODUCTION: High beat-to-beat morphological variation (divergence) on the ventricular electrogram during programmed ventricular stimulation (PVS) is associated with increased risk of ventricular fibrillation (VF), with unclear mechanisms. We hypothesized that ventricular divergence is associated with epicardial wavebreaks during PVS, and that it predicts VF occurrence. METHOD AND RESULTS: Langendorff-perfused rabbit hearts (n = 10) underwent 30-min therapeutic hypothermia (TH, 30°C), followed by a 20-min treatment with rotigaptide (300 nM), a gap junction modifier. VF inducibility was tested using burst ventricular pacing at the shortest pacing cycle length achieving 1:1 ventricular capture. Pseudo-ECG (p-ECG) and epicardial activation maps were simultaneously recorded for divergence and wavebreaks analysis, respectively. A total of 112 optical and p-ECG recordings (62 at TH, 50 at TH treated with rotigaptide) were analyzed. Adding rotigaptide reduced ventricular divergence, from 0.13±0.10 at TH to 0.09±0.07 (p = 0.018). Similarly, rotigaptide reduced the number of epicardial wavebreaks, from 0.59±0.73 at TH to 0.30±0.49 (p = 0.036). VF inducibility decreased, from 48±31% at TH to 22±32% after rotigaptide infusion (p = 0.032). Linear regression models showed that ventricular divergence correlated with epicardial wavebreaks during TH (p<0.001). CONCLUSION: Ventricular divergence correlated with, and might be predictive of epicardial wavebreaks during PVS at TH. Rotigaptide decreased both the ventricular divergence and epicardial wavebreaks, and reduced the probability of pacing-induced VF during TH.

Hypoglycaemic episodes increase the risk of ventricular arrhythmia and sudden cardiac arrest in patients with type 2 diabetes-A nationwide cohort study.

BACKGROUND: The impact of hypoglycaemic episode (HE) on the risk of ventricular arrhythmia (VA) and sudden cardiac arrest (SCA) remains unclear. We hypothesized that HE increases the risk of both VA and SCA and that glucose-lowering agents causing HE also increase the risk of VA/SCA in patients with type 2 diabetes (T2D). METHODS: Patients aged 20 years or older with newly diagnosed T2D were identified using the Taiwan National Health Insurance Database. HE was defined as the presentation of hypoglycaemic coma or specified/unspecified hypoglycaemia. The control group consisted of T2D patients without HE. The primary outcome was the occurrence of VA (including ventricular tachycardia and fibrillation) and SCA during the defined follow-up periods. A multivariate Cox hazards regression model was used to evaluate the hazard ratio (HR) for VA or SCA. RESULTS: A total of 54 303 patients were screened, with 1037 patients with HE assigned to the HE group and 4148 frequency-matched patients without HE constituting the control group. During a mean follow-up period of 3.3 ± 2.5 years, 29 VA/SCA events occurred. Compared with the control group, HE group had a higher incidence of VA/SCA (adjusted HR: 2.42, P = .04). Patients who had used insulin for glycaemic control showed an increased risk of VA/SCA compared with patients who did not receive insulin (adjusted HR: 3.05, P = .01). CONCLUSIONS: The HEs in patients with T2D increased the risk of VA/SCA, compared with those who did not experience HEs. Use of insulin also independently increased the risk of VA/SCA.

Data for rate versus rhythm control strategy on stroke and mortality in patients with atrial fibrillation.

The data relates to the cohort of patients with atrial fibrillation (AF) from the National Health Insurance Research Database of Taiwan, "Rhythm Control Better Prevents Stroke and Mortality than Rate Control Strategies in Patients with Atrial Fibrillation - A Nationwide Cohort Study" (Weng et al., in press). The AF patients might receive either rate or rhythm control strategy according to the medication used. The baseline medication in rate and rhythm control groups was included in this dataset. Multivariate Cox hazards regression model was used to evaluate the hazard ratio (HR) for major adverse cardiovascular events (MACE), including ischemic/hemorrhagic stroke and mortality in AF patients receiving rate or rhythm control. The occurrence of MACE was identified from the ICD-9 CM codes. The data also contains the HR for MACE stratified by the CHA2DS2-VASc score, baseline characteristics, and the duration of strategy employed of the AF patients.

Rhythm control better prevents stroke and mortality than rate control strategies in patients with atrial fibrillation - A nationwide cohort study.

BACKGROUND: Atrial fibrillation (AF) increases the risk of stroke and mortality. However, rhythm control strategy did not reduce cardiovascular risks in short-term studies. We hypothesize that rhythm control better prevents stroke and mortality than rate control in AF patients over a long-term period. METHODS: AF patients aged ≥18 years were identified from Taiwan National Insurance Database. Patients using anti-arrhythmia drugs to control rhythm at a >30 defined daily dose (DDD) were defined as the rhythm control group. Patients who used rate control medications for >30 DDDs constituted the rate control group. Multivariate Cox hazards regression model was used to evaluate the hazard ratio (HR) for major adverse cardiovascular events (MACE), including ischemic/hemorrhagic stroke and mortality. RESULTS: A total of 11,968 AF patients were enrolled, and 2850 of them (654 in rhythm control group; 2196 in rate control group) were analyzed. During a 6.3 ±â€¯3.7 year's follow-up, a total of 1101 MACE occurred. Compared to rate control group, rhythm control group displayed a lower rate of ischemic stroke (adjusted HR: 0.65, p = 0.002) and mortality (adjusted HR: 0.81, p = 0.009). The rhythm control group showed a lower incidence of MACE than that of the rate control group (adjusted HR: 0.82, p = 0.009). The reduction of stroke (p = 0.004), mortality (p = 0.006), and MACE (p = 0.007) risk was observed particularly in rhythm control patients with a CHA2DS2-VASc score of ≥3. CONCLUSIONS: In patients with AF, rhythm control better prevents MACE risk than rate control over a long-term period, particularly in those at high risk (CHA2DS2-VASc score ≥3) for stroke.

Glitazones and alpha-glucosidase inhibitors as the second-line oral anti-diabetic agents added to metformin reduce cardiovascular risk in Type 2 diabetes patients: a nationwide cohort observational study.

OBJECTIVE: Metformin is the standard first-line drug for patients with Type 2 diabetes (T2DM). However, the optimal second-line oral anti-diabetic agent (ADA) remains unclear. We investigated the cardiovascular risk of various ADAs used as add-on medication to metformin in T2DM patients from a nationwide cohort. METHODS: T2DM patients using different add-on oral ADAs after an initial metformin therapy of > 90 days were identified from the Taiwan National Health Insurance Database. Five classes of ADAs, including sulphonylureas (SU), glinides, thiazolidinediones (TZD), alpha-glucosidase inhibitors (AGI), and dipeptidyl peptidase-4 inhibitors (DPP-4I) were selected for analysis. The reference group was the SU added to metformin. Patients were excluded if aged < 20 years, had a history of stroke or acute coronary syndrome (ACS), or were receiving insulin treatment. The primary outcomes included any major adverse cardiovascular event (MACE) including ACS, ischemic/hemorrhagic stroke, and death. A Cox regression model was used to estimate the hazard ratio (HR) for MACE. RESULTS: A total of 26,742 patients receiving their add-on drug to metformin of either SU (n = 24,277), glinides (n = 962), TZD (n = 581), AGI (n = 808), or DPP-4I (n = 114) were analyzed. After a mean follow-up duration of 6.6 ± 3.4 years, a total of 4775 MACEs occurred. Compared with the SU+metformin group (reference), the TZD+metformin (adjusted HR: 0.66; 95% CI 0.50-0.88, p = 0.004) and AGI+metformin (adjusted HR: 0.74; 95% CI 0.59-0.94, p = 0.01) groups showed a significantly lower risk of MACE. CONCLUSION: Both TZD and AGI, when used as an add-on drug to metformin were associated with lower MACE risk when compared with SU added to metformin in this retrospective cohort study. Trial registration CE13152B-3. Registered 7 Mar, 2013, retrospectively registered.

Gap junction modifier rotigaptide decreases the susceptibility to ventricular arrhythmia by enhancing conduction velocity and suppressing discordant alternans during therapeutic hypothermia in isolated rabbit hearts.

BACKGROUND: Therapeutic hypothermia (TH) may increase the susceptibility to ventricular arrhythmias by decreasing ventricular conduction velocity (CV) and facilitating arrhythmogenic spatially discordant alternans (SDA). OBJECTIVE: The purpose of this study was to test the hypothesis that rotigaptide, a gap junction enhancer, can increase ventricular CV, delay the onset of SDA, and decrease the susceptibility to pacing-induced ventricular fibrillation (PIVF) during TH. METHODS: Langendorff-perfused isolated rabbit hearts were subjected to 30-minute moderate hypothermia (33°C) followed by 20-minute treatment with rotigaptide (300 nM, n = 8) or vehicle (n = 5). The same protocol was also performed at severe hypothermia (30°C; n = 8 for rotigaptide, n = 5 for vehicle). Using an optical mapping system, epicardial CV and SDA threshold were evaluated by S1 pacing. Ventricular fibrillation inducibility was evaluated by burst pacing for 30 seconds at the shortest pacing cycle length (PCL) that achieved 1:1 ventricular capture. RESULTS: Rotigaptide increased ventricular CV during 33°C (PCL 300 ms, from 76 ± 6 cm/s to 84 ± 7 cm/s, P = .039) and 30°C (PCL 300 ms, from 62 ± 6 cm/s to 68 ± 4 cm/s, P = .008). Rotigaptide decreased action potential duration dispersion at 33°C (P = .01) and 30°C (P = .035). During 30°C, SDA thresholds (P = .042) and incidence of premature ventricular complexes (P = .025) were decreased by rotigaptide. PIVF inducibility was decreased by rotigaptide at 33°C (P = .039) and 30°C (P = .042). Rotigaptide did not change connexin43 expressions and distributions during hypothermia. CONCLUSION: Rotigaptide protects the hearts against ventricular arrhythmias by increasing ventricular CV, delaying the onset of SDA, and reducing repolarization heterogeneity during TH. Enhancing cell-to-cell coupling by rotigaptide might be a novel approach to prevent ventricular arrhythmias during TH.

Moderate Hypothermia (33 °C) Decreases the Susceptibility to Pacing-Induced Ventricular Fibrillation Compared with Severe Hypothermia (30 °C) by Attenuating Spatially Discordant Alternans in Isolated Rabbit Hearts.

BACKGROUND: Severe hypothermia (SH, 30 °C) increases the risk of pacing-induced ventricular fibrillation (PIVF) by enhancing spatially discordant alternans (SDA). Whether moderate hypothermia (MH, 33 °C), which is clinically used for therapeutic hypothermia, also facilitates SDA remains unclear. We hypothesized that MH attenuates SDA occurrence compared with that achieved by SH, and decreases the susceptibility of PIVF. METHODS: Using an optical mapping system, action potential duration (APD)/conduction velocity restitutions and thresholds of APD alternans were determined by S1 pacing in Langendorff-perfused isolated rabbit hearts. In the MH group (n = 7), S1 pacing was performed at baseline (37 °C), after 5-min MH, and after 5-min rewarming (37 °C). In the SH group (n = 9), pacing was also performed at baseline (37 °C), after 5-min SH, and after 5-min rewarming (37 °C). The thresholds of APD alternans were defined as the longest S1 pacing cycle length at which APD alternans were detected. RESULTS: Although the thresholds of APD alternans were not different between the MH (273 ± 46 ms) and the SH (300 ± 35 ms) (p = 0.281) groups, SDA threshold was shorter (at a faster heart rate) during MH (228 ± 33 ms) than that during SH (289 ± 42 ms) (p = 0.028). At APD alternans threshold, SH hearts showed more SDA than that during MH (SH: 7 hearts, MH: 2 hearts, p = 0.049). SDA could be induced in all 9 SH hearts (100%), while only 4 MH hearts (57%) had SDA (p = 0.029). The PIVF inducibility during SH (44 ± 53%) was higher than that during MH (0%) (p = 0.043). CONCLUSIONS: Compared with SH, the MH group showed greater attenuation of SDA and decreased the susceptibility of PIVF. Therefore, MH is safer as a procedural guideline for use in clinical therapeutic hypothermia than SH. KEY WORDS: Cardiac alternans; Conduction velocity; Hypothermia; Optical mapping.

Pretreatment of BAPTA-AM suppresses the genesis of repetitive endocardial focal discharges and pacing-induced ventricular arrhythmia during global ischemia.

INTRODUCTION: In isolated rabbit hearts, repetitive endocardial focal discharges (REFDs) were consistently observed during ventricular fibrillation (VF) with prolonged (>5 minutes) global ischemia (GI). We hypothesized that BAPTA-AM, a calcium chelator, can suppress these REFDs. METHODS AND RESULTS: Using a two-camera optical mapping system, we simultaneously mapped endocardial (left ventricle, LV) and epicardial (both ventricles) activations during ventricular arrhythmia with GI. In 5 hearts (protocol I), we infused Tyrode's solution (no BAPTA-AM) for ≥30 minutes before the onset of no-flow GI. In 7 additional hearts (protocol II), BAPTA-AM (20 µmol/L) was infused for ≥30 minutes before the initiation of GI. In protocol I, sustained VF (>30 seconds) was successfully induced in all 5 hearts with prolonged GI. REFDs were present in >85 % of recording time. In protocol II, however, ventricular arrhythmia was not inducible and REFDs were not observed after 5-minute GI in 5 hearts. Effects of BAPTA-AM on intracellular calcium (Ca(i) ) at the LV endocardium were also evaluated in 5 hearts (protocol III) using dual Ca(i) /membrane potential mapping. GI, both without and with BAPTA-AM pretreatment, caused a decrease of Ca(i) amplitude during S(1) pacing. However, this effect was more pronounced in the hearts with BAPTA-AM pretreatment (P < 0.001). GI, without BAPTA-AM pretreatment, caused broadening of Ca(i) transient. In contrast, GI, with BAPTA-AM pretreatment, caused narrowing of Ca(i) transient. CONCLUSIONS: BAPTA-AM pretreatment attenuates Ca(i) transient, suppressing the genesis of REFDs and pacing-induced ventricular arrhythmia during GI. These findings support the notion that Ca(i) dynamics is important in the maintenance of REFDs.