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Background: The mechanism underlying the sex differences in atrial fibrillation (AF) recurrence following pulmonary vein (PV) isolation is not fully understood. We hypothesized that non-PV foci and epicardial adipose tissue (EAT) play a key role. Methods and Results: Data from 304 consecutive patients (75% males) who underwent contrast-enhanced computed tomography and catheter ablation of AF were reviewed. The EAT around the atrium was measured separately in 4 parts of the atrium. All patients underwent high-dose isoproterenol infusions to assess the non-PV foci. Significantly more non-PV foci and less EAT around the atrium were observed in female patients than in male patients. In males, those with non-PV foci on the left atrial (LA) anterior wall had significantly greater EAT for the same lesions than those without non-PV foci. During a median follow-up of 27 months, the predictors of AF recurrence after first catheter ablation were female sex, presence of non-PV foci, LA diameter, and septal EAT index. A sex-specific analysis revealed that LA diameter was a predictor only in males and that the presence of non-PV foci in the septal region was a strong predictor in males (hazard ratio [HR]: 2.24) and females (HR: 3.65). Conclusions: Sex-specific differences were observed in non-PV foci sites and local EAT and in regard to the predictors of AF recurrence.

Background: Ventricular tachycardia (VT) non-inducibility at the end of ablation is associated with a less likely VT recurrence. However, it is not clear whether we should use VT non-inducibility as a routine end point of VT ablation. The aim of this study was to evaluate VT recurrence in patients in whom VT non-inducibility was not achieved at the end of the RF ablation and the factors attributing to the VT recurrence.Methods: We analyzed 62 patients in whom VT non-inducibility was not achieved at the end of the RF ablation were studied.Results: Over 2 years, 22 (35%) of the cases had VT recurrences. A multivariate analysis showed that an LVEF≥35% (HR:0.19; 95% CI:0.06- 0.49; PConclusion: Even if VT non-inducibility was not achieved, patients with an LVEF≥35% or in whom partial success could be achieved might be prevented from having VT recurrences. The validity of the VT non-inducibility of any VT should be evaluated considering each patient’s background and the results of the procedure.

The skin overlying cardiovascular implantable electronic devices (CIEDs) sometimes becomes very thin after implantations, which could cause a device erosion. The factors related to the skin thickness of device pockets have not been elucidated. This study aimed to evaluate the skin thickness of CIED pockets and search for the factors associated with the thickness.Seventeen skin thickness points around the CIED pocket were measured through ultrasonography in each patient.A total of 101 patients (76 ± 11 years, 26 female) were enrolled. The median duration from the implantation to the examination was 95 months (quartile: 52.5-147.5). The median skin thickness overlying the device was 4.1 mm (3.3-5.9). Patients with heart failure and malignancy had thinner skin overlying the CIED than those without. A significant correlation existed between skin thickness and body mass index (BMI), hemoglobin, serum creatinine, estimated glomerular filtration rate (eGFR), and left ventricular ejection fraction. In contrast, age, gender, and device size did not exhibit a significant correlation with skin thickness. A multivariate logistic regression analysis revealed that chronic heart failure and a decrease in the eGFR and BMI were independent predictive factors of "very thin (≦3.3 mm)" skin of the CIED pocket late after an implantation.Aside from a low BMI, the comorbidities (low hemoglobin, heart failure, and renal dysfunction) had a stronger impact on the skin thickness overlying the device than the device size. A careful observation of the device pocket should be performed in patients with those risk factors.

Background: Demand is growing for remote electrocardiogram (ECG) monitoring systems in the COVID-19 era in Japan. This study describes initial experiences with a small wireless ECG monitoring device and the utility of delivery via the postal service for outpatient care in Japan. Methods and Results: Long-term ECG monitoring following postal delivery of the small ECG device was evaluated in 25 patients. The patients had no difficulties with either the postal delivery or self-fitting and wearing the devices. A median of 57 h monitoring per patient was performed. Arrhythmic events were detected in 8 patients. Most patients were satisfied with both the ECG devices and postal delivery. Conclusions: Postal delivery of ECG devices could be used in clinical practice to achieve less or no in-person contact during the COVID-19 era.

Background A computational model demonstrated that atrial fibrillation (AF) rotors could be distributed in patchy late-gadolinium enhancement (LGE) areas and play an important role in AF drivers. However, this was not validated in humans. Objective The purpose of this study was to evaluate the LGE area properties of AF rotors in patients with persistent AF. Methods A total of 287 segments in 15 patients with persistent AF (longstanding persistent AF in 9 patients) that underwent AF ablation were assessed. Non-passively activated areas (NPAs), where rotational activation (AF rotor) was frequently observed, were detected by the novel real-time phase mapping (ExTRa Mapping). The properties of the LGE areas were assessed using the LGE heterogeneity, and the density was assessed by the entropy (LGE-entropy) and volume ratio of the enhancement voxel (LGE-volume ratio), respectively. Results NPAs were found in 61 (21%) of 287 segments and were mostly found around the pulmonary vein antrum. A receiver operating characteristic curve analysis yielded an optimal cutoff value of 5.7 and 10% for the LGE-entropy and LGE-volume ratio, respectively. The incidence of NPAs was significantly higher at segments with an LGE-entropy of >5.7 and LGE-volume ratio of >10% than at the other segments (38 [30%] of 126 vs. 23 [14%] of 161 segments, p = 0.001). No NPAs were found at segments with an LGE-volume ratio of >50% regardless of the LGE-entropy. Of 5 patients with AF recurrence, NPAs outside the PV antrum were not ablated in 3 patients and the remaining NPAs were ablated, but their LGE-entropy and LGE-volume ratio were low. Conclusion AF rotors are mostly distributed in relatively weak and much more heterogenous LGE areas. This article is protected by copyright. All rights reserved.

Background Inflammation, such as that associated with intermediate CD14++ CD16+ monocytes and atrial structural remodeling (SRM), may be important in the recurrence of atrial fibrillation (AF) after catheter ablation. However, the relationship between the intermediate CD14++ CD16+ monocytes, SRM, and AF recurrence is unclear. Methods Twenty-four patients with AF were enrolled. The proportion of intermediate monocytes (PIM) was assessed before ablation by flow cytometry. As a surrogate marker of SRM, the volume ratio (VR) of signal intensity greater than 1 standard deviation on late-gadolinium enhancement magnetic resonance imaging (LGE-MRI) was calculated. We investigated whether PIM correlated with SRM on LGE-MRI and determined the optimal cutoff value for predicting AF recurrence. Results Univariate analysis revealed positive correlations between PIM and BNP with SRM (PIM: r = .593, p = .002; BNP: r = .567, p = .004). Multivariable analysis revealed that PIM was independently associated with VR on LGE-MRI (β = .522; p = .033). The finding of an area under the receiver operating characteristic curve of 0.750 revealed that a VR ≥ 13.3% on LGE-MRI as the optimal cutoff value to predict AF recurrence with 80% sensitivity and 71% specificity, which was associated with PIM ≥ 10.0%. Conclusion Intermediate monocytes were significantly positively correlated with SRM. PIM ≥ 10% was associated with a VR ≥ 13.3% on LGE-MRI, which predicted AF recurrence after catheter ablation.

BACKGROUND: A computer simulation model has demonstrated that an atrial fibrillation (AF) driver can be attached to heterogeneous fibrosis assessed by late gadolinium enhancement magnetic resonance imaging (LGE-MRI). However, it has not been well elucidated in patients with persistent AF. The aim of this study was to investigate whether radiofrequency (RF) applications in the fragmented LGE area (FLA) could terminate AF or convert it to atrial tachycardia (AT) and improve the rhythm outcome. METHODS: A total of 31 consecutive persistent AF patients with FLAs were enrolled (FLA ablation group, mean age: 69 ± 8 years, mean left atrial diameter: 42 ± 6 mm). A favorable response was defined as direct AF termination or AT conversion during RF applications at the FLA. The rhythm outcome was compared between the FLA ablation group and FLA burden-matched pulmonary vein isolation (PVI) group. RESULTS: Favorable responses were found in 15 (48%) of 31 patients in the FLA group (AF termination in 7, AT conversion in 8 patients), but not in the PVI group. AF recurrence at 12 months follow-up was significantly less in the FLA ablation group than in the PVI group (4 [13%] vs. 12 [39%] of 31 patients, log-rank p=0.023). In patients with a favorable response, AT recurred in 1 (7%) of 15 patients but AF did not. CONCLUSIONS: FLA ablation could terminate AF or convert it to AT in half of the patients. No AF recurrence was documented in patients with a favorable response. This article is protected by copyright. All rights reserved.

Background: Several algorithms have been proposed for differentiating the right and left outflow tracts (RVOT/LVOT) arrhythmia origins from 12-lead electrocardiograms (ECGs); however, the procedure is complicated. A deep learning (DL) model, a form of artificial intelligence, can directly use ECGs and depict the importance of the leads and waveforms. This study aimed to create a visualized DL model that could classify arrhythmia origins more accurately.Methods and Results: This study enrolled 80 patients who underwent catheter ablation. A convolutional neural network-based model that could classify arrhythmia origins with 12-lead ECGs and visualize the leads that contributed to the diagnosis using a gradient-weighted class activation mapping method was developed. The average prediction results of the origins by the DL model were 89.4% (88.2–90.6) for accuracy and 95.2% (94.3–96.2) for recall, which were significantly better than when a conventional algorithm is used. The ratio of the contribution to the prediction differed between RVOT and LVOT origins. Although leads V1 to V3 and the limb leads had a focused balance in the LVOT group, the contribution ratio of leads aVR, aVL, and aVF was higher in the RVOT group.Conclusions: This study diagnosed the arrhythmia origins more accurately than the conventional algorithm, and clarified which part of the 12-lead waveforms contributed to the diagnosis. The visualized DL model was convincing and may play a role in understanding the pathogenesis of arrhythmias.

Inflammation has been suggested to play a key role in the pathogenesis of atrial fibrillation (AF). Our hypothesis was that this inflammation, mediated by intermediate monocytes and toll-like receptor 4 (TLR4), causes the formation and expansion of low-voltage zones (LVZs). Prior to ablation, the monocyte subsets of 78 AF patients and TLR4 expression of 66 AF patients were analyzed via a flow cytometric analysis. Based on the CD14/CD16 expression, the monocytes were divided into three subsets: classical, intermediate, and non-classical. At the beginning of the ablation session, voltage mapping was performed. LVZs were defined as all bipolar electrogram amplitudes of

A 72-year-old woman was referred to our institution with decompensated congestive heart failure owing to subacute severe aortic regurgitation and mitral regurgitation. Her blood sample tested positive for myeloperoxidase anti-neutrophil cytoplasmic antibody (ANCA). Cardiac computed tomography revealed abnormal thickening and shortening of the aortic valvar leaflets as well as wall thickening of the sinuses of Valsalva. Based on the diagnosis of ANCA-associated vasculitis, predominantly involving the aortic root, prednisolone administration was initiated, which failed to improve the valvar dysfunction. The patient underwent aortic root replacement and mitral annuloplasty. Histopathology confirmed severe inflammation involving both the aortic valvar sinuses and leaflets.

Introduction: It has been reported that ventricular tachycardia (VT) non-inducibility at the end of ablation is associated with less likely VT recurrence. However, it is not clear whether we should use VT non-inducibility as routine end point in VT ablation. The aim of this study was to evaluate VT recurrence in patients in whom VT non-inducibility could not be achieved at the end of the RF ablation and the factors attributing to the VT recurrence. METHODS and RESULTS: We analyzed 84 consecutive patients that underwent RF ablation, and 64 patients in whom VT non-inducibility could not be achieved were studied. The primary endpoint was recurrence of any sustained VT during the follow-up. During a median follow-up period of 1.4 years (IQR:0.3-2.0), 22 (34%) of the cases had VT recurrences. In the multivariate analysis showed that an LVEF≥35% (HR:0.21; 95% CI:0.07- 0.54; P

Background: Some of atrial fibrillation (AF) drivers are found in normal/mild late-gadolinium enhancement (LGE) areas, as well as moderate ones. The atrial wall thickness (AWT) has been reported to be important as a possible AF substrate. However, the AWT and degree of LGEs as an AF substrate has not been fully validated in humans. Objective: The purpose of this study was to evaluate the impact of the AWT in normal/mild LGE areas on AF drivers. Methods: A total of 287 segments in 15 persistent AF patients were assessed. AF drivers were defined as non-passively activated areas (NPAs), where rotational activation was frequently observed, and were detected by the novel real-time phase mapping (ExTRa Mapping), mild LGE areas were defined as areas with a volume ratio of the enhancement voxel of 0% to

Background A successful Radiofrequency (RF) ablation of ventricular tachycardia (VT) can prevent VT recurrence. It has been reported that VT non-inducibility at the end of RF ablation is associated with less likely VT recurrence in ischemic cardiomyopathy (ICM) and non-ICM (NCIM). However, it is not clear whether we should use VT non-inducibility as routine end point in RF ablation of VT. Purpose The aim of this study was to evaluate VT recurrence in patients who couldn't be achieved VT non-inducibility at the end of RF ablation and the factors attributed to VT recurrence in ICM and NICM patients. Methods Between January 2009 and April 2020, 84 consecutive patients (ICM: 34, NICM: 50) underwent RF ablation for drug-resistant VT in our hospital. VT non-inducibility was defined as any ventricular tachy-arrhythmia, including clinical VT, non-clinical VT, and VF, was not induced by programed stimuli at the end of session. Non-inducibility was achieved in 37 patients but it was not achieved in 47 patients (ICM: 18, NICM: 29). To evaluate the validity of “non-inducibility” as an end point of VT ablation, 47 patients (male: 40, mean age: 66±15 years) in whom non-inducibility of any ventricular tachyarrhythmia was not achieved were studied. The primary endpoint was recurrence of any sustained VT and VF during follow up period (mean follow-up period was 1.4 (range, 0.0, 2.0) years.) Results Mean left ventricular ejection fraction (LVEF) was 36±13%. Epicardial ablation was required in 8 patients. 32 patients had electrical storm at the time of ablation. Among them, 21 patients had VT recurrence and 26 patients had non-VT recurrence during follow-up period. VT recurrence rate was significantly lower in patients with LVEF≥35% than those with LVEF Conclusions Even if non-inducibility of any ventricular tachyarrhythmia wasn't achieved at the end of ablation, the patients with LVEF≥35% or who had ablated of VT isthmus might prevent VT recurrence. The validity of non-inducibility of any ventricular tachyarrhythmia should be evaluated in each patient's background. Funding Acknowledgement Type of funding sources: Public hospital(s). Main funding source(s): Abbott, Medtronic

An 80-year-old woman with rheumatoid arthritis presented with chest pain. Clinical examination revealed new-onset paroxysmal atrial fibrillation with symptomatic sinus pauses and worsening mitral regurgitation, which were both resistant to conventional therapies. Based on her skin lesions, an increase in pleural and pericardial effusion, possible myocardial involvement, and a positive finding for immune complex testing, rheumatoid vasculitis was diagnosed. Subsequent glucocorticoid therapy suppressed systemic inflammation, resulting in structural, functional, and electrical reverse remodeling of the left atrium with complete remission of atrial arrhythmias and also an improvement of mitral regurgitation. This case highlights the importance of evaluating the underlying disease activity in a case of de novo paroxysmal atrial fibrillation associated with systemic autoimmune disease.

A 41‐year‐old man with persistent atrial fibrillation (AF) underwent radiofrequency (RF) catheter ablation using an online real‐time phase mapping system: ExTRa Mapping. Box isolation could not terminate AF. Subsequently, RF applications on nonpassively activated areas (NPAs), where rotational activations were frequently observed, at the posterior bottom of left atrium outside of box lesion could convert AF to common atrial flutter. Of interest, the NPA near the posterior bottom were located on the patchy fibrotic tissue area assessed by the late‐gadolinium enhancement magnetic resonance imaging. This indicated the possibility of the critical AF rotor meandering through the fibrotic tissue area.

A 79-year-old man with dilated cardiomyopathy and severe functional mitral regurgitation presented with general fatigue and dyspnea. Auscultation revealed a systolic regurgitant murmur with a minimized second heart sound due to a low output. On the other hand, the third heart sound was ultimately enhanced, being visible and palpable as a pulsatile knock of the precordium. Phonocardiography and echocardiography successfully confirmed early-diastolic rapid distension of the left ventricle along with rapid ventricular filling and abrupt deceleration of the atrioventricular blood flow to be the precise etiology of the ultimate third heart sound, indicating critically deteriorated hemodynamics due to massive mitral regurgitation combined with a low output.

Background: Some of atrial fibrillation (AF) drivers are found in lesser late-gadolinium enhancement (LGE) areas, as well as heterogenous ones. The atrial wall thickness (AWT) has been reported to be important as a possible AF substrate. However, the AWT and degree of LGEs as an AF substrate has not been fully validated in humans. Objective: The purpose of this study was to evaluate the impact of the AWT in lesser LGE areas on AF drivers. Methods: A total of 287 segments in 15 persistent AF patients were assessed. AF drivers were defined as non-passively activated areas (NPAs), where rotational activation was frequently observed, and were detected by the novel real-time phase mapping (ExTRa Mapping). Lesser LGE areas were defined as areas with a volume ratio of the enhancement voxel of

Background: A computational model demonstrated that atrial fibrillation (AF) rotors could be distributed in patchy fibrotic tissue and play an important role in AF drivers. However, this was not validated in humans. Objective: The purpose of this study was to evaluate the fibrotic tissue properties of AF rotors in patients with persistent AF. Methods: A total of 287 segments in 15 patients with persistent AF (longstanding persistent AF in 9 patients) that underwent AF ablation were assessed. Non-passively activated areas (NPAs), where rotational activation (AF rotor) was frequently observed, were detected by the novel real-time phase mapping (ExTRa Mapping). Atrial fibrosis was detected by late-gadolinium enhancement magnetic resonance imaging (LGE-MRI), and the fibrotic heterogeneity and density were assessed by the entropy (LGE-entropy) and volume ratio of the enhancement voxel (LGE-volume ratio), respectively. Results: NPAs were found in 61 (21%) of 287 segments and were mostly found around the pulmonary vein antrum. A receiver operating characteristic curve analysis yielded an optimal cutoff value of 5.7 and 10% for the LGE-entropy and LGE-volume ratio, respectively. The incidence of NPAs was significantly higher at segments with an LGE-entropy of >5.7 and LGE-volume ratio of >10% than at the other segments (38 [30%] of 126 vs. 23 [14%] of 161 segments, p = 0.001). No NPAs were found at segments with an LGE-volume ratio of >50% regardless of the LGE-entropy. Conclusion: AF rotors are mostly distributed in relatively weak and much more heterogenous fibrotic tissue.

Background: Computer simulation model demonstrated that atrial fibrillation (AF) driver attached to the patchy fibrosis assessed by late gadolinium enhancement magnetic resonance imaging (LGE-MRI). However, it has not been well elucidated in patients with persistent AF. The aim of this study is to investigate whether radiofrequency (RF) application on the patchy LGE site (PLS) could terminate AF or convert to atrial tachycardia (AT) and improve the rhythm outcome. Methods: A total of 31consecutive persistent AF patients with PLS were enrolled (PLS ablation group, mean age: 69 ± 8 years, mean left atrial diameter: 42 ± 6 mm). AF direct termination or AT conversion during RF application on the PLS were defined as favorable response. The rhythm outcome was compared between the PLS ablation group and the propensity matched conventional ablation group. Results: Favorable response was found in 15 (48%) of 31 patients (AF termination in 7, AT conversion in 8 patients). AF recurrence at 12 months follow-up was significantly less in the PLS group as compared to the control group (4 (13%) of 31 patients vs. 11 (35%) of 31 patients, log-rank p = 0.019). In patients with favorable response, AT recurred in 1 (7%) of 15 patients but AF. Conclusions: The PLS ablation could terminate AF or convert to AT in half of the patients and improve the rhythm outcome as compared to the conventional ablation. No AF recurrence was documented in patients with a favorable response.

Background Pulmonary vein isolation (PVI) lesions after cryoballoon ablation (CBA) are characterized as a wider and more continuous than that after conventional radiofrequency catheter ablation (RFCA) without the contact force (CF)-sensing technology. However, the impact on the lesion characteristics of ablation with a CF-sensing catheter has not been well discussed. We sought to assess the lesions using late-gadolinium enhancement magnetic resonance imaging (LGE-MRI) and to compare the differences between the two groups (CB group vs. RF group). Methods A total of 30 consecutive patients who underwent PVI were enrolled (CB group, 18; RF group, 12). The RF applications were delivered with a target lesion size index (LSI) of 5. The PVI lesions were assessed by LGE-MRI 3 months after the PVI. The region around the PV was divided into eight segments: roof, anterior-superior, anterior carina, anterior inferior, bottom, posterior inferior, posterior carina, and posterior superior segment. The lesion width and visual gap of each segment were compared between the two groups. The visual gaps were defined as no-enhancement site of >4 mm. Results The mean LSI was 4.7 ± 0.7. The lesion width was significantly wider but the visual gaps were more frequently documented at the bottom segment of right PV in the CBA group (lesion width: 8.1 ± 2.2 vs. 6.3 ± 2.2 mm; p = .032; visual gap at the bottom segment or right PV: 39% vs. 0%; p = .016). Conclusions The PVI lesion was wider after CBA, while the visual gaps were fewer after RFCA with a CF-sensing catheter.

Focal thinning of the basal muscular ventricular septum is a characteristic morphological finding in cases of cardiac sarcoidosis, usually detected on the parasternal long-axis image during echocardiography. Surprisingly, however, its circumferential extent has rarely been demonstrated and discussed. We present a case showing typical thinning of the basal ventricular septum. The extent of circumferential wall thinning was evaluated using both echocardiography and cardiac computed tomography. The present case highlights the importance of detailed multiplanar and three-dimensional evaluation of this characteristic abnormality, more so because its mechanism as well as the precise impact on conduction has not yet been elucidated.

Introduction The ablation index (AI) and lesion size index (LSI) are novel markers for predicting the ablation lesion quality, however, collateral damage is still a concern. This study aimed to compare the lesion characteristics and tissue temperature profiles between 20 W (20 Ws) and 40 W (40 Ws) ablation settings under the same AI and LSI. Methods An ex vivo model consisting of swine myocardium (5-6 mm thickness) in a circulating, warmed saline bath was used. Twenty-one tissue temperature electrodes were used. Radiofrequency applications with different power settings were performed with a 10 to 12 g contact force until the AI and LSI reached 350 and 4.5, respectively. Results A total of 120 radiofrequency (RF) applications and 2520 tissue temperature profiles were analyzed. The speed of the tissue temperature rise with 40 Ws was significantly faster than that with 20 Ws. However, the maximum tissue temperature did not significantly differ between 20 and 40 Ws with the same AI (44.6°C ± 3.9°C vs 45.1°C ± 6.4°C, P = .73), and was significantly lower for 40 Ws with the same LSI (42.8°C ± 3.4°C vs 40.0°C ± 3.4°C, P = .003). For both the AI and LSI, the number of electrodes exhibiting high temperatures (≥39°C) was significantly larger and the duration of high tissue temperatures was significantly longer with 20 Ws. The thermal latency with 40 Ws was greater. Conclusions Although the targeted AI and LSI were the same for both 20 and 40 Ws, the tissue temperature profiles differed greatly depending on the RF power setting. A high power setting based on the AI and LSI may reduce the collateral thermal damage.

INTRODUCTION Pulmonary vein isolation (PVI) lesions after cryoballoon ablation (CBA) are wide and continuous, however, the distribution can depend on the pulmonary vein (PV) size. We sought to assess the relationship between the lesion distribution and PV size after CBA and hotballoon ablation (HBA). METHODS AND RESULTS A total of 80 consecutive patients who underwent PVI were enrolled (40 with CBA). The lesions were visualized by late-gadolinium enhancement magnetic resonance imaging. The lesion width, lesion gaps, and distance from the PV ostium (PVos) to distal lesion edge (DLE) were assessed. If the DLE extended inside the PV, the value was expressed as a negative value. Although the lesion width was significantly wider in the CB group (7.8 ± 2.0 vs 4.9 ± 1.0 mm, P

Background Medium‐dose (25 gray) x‐ray radiation therapy has recently been performed on patients with refractory ventricular tachyarrhythmias. Unlike x‐ray, carbon ion and proton beam radiation can deliver most of their energy to the target tissues. This study investigated the electrophysiological and pathological changes caused by medium‐dose carbon ion and proton beam radiation in the left ventricle (LV). Methods and Results External beam radiation in the whole LV was performed in 32 rabbits. A total of 9 rabbits were not irradiated (control). At the 3‐month or 6‐month follow‐up, the animals underwent an open‐chest electrophysiological study and were euthanized for histological analyses. No acute death occurred. Significant LV dysfunction was not seen. The surface ECG revealed a significant reduction in the P and QRS wave voltages in the radiation groups. The electrophysiological study showed that the local conduction times in each LV site were significantly longer and that the local LV bipolar voltages were significantly lower in the radiation groups than in the control rabbits. Histologically, apoptosis, fibrotic changes, and a decrease in the expression of the connexin 43 protein were seen in the LV myocardium. These changes were obvious at 3 months, and the effects were sustained 6 months after radiation. No histological changes were seen in the coronary artery and esophagus, but partial radiation pneumonitis was observed. Conclusions Medium‐dose carbon ion and proton beam radiation in the whole LV resulted in a significant electrophysiological disturbance and pathological changes in the myocardium. Radiation of the arrhythmogenic substrate would modify the electrical status and potentially induce the antiarrhythmic effect.