Refining prediction of stroke in sinus node dysfunction patients without atrial fibrillation using a P-combined score: a multi-centre study

AIMS

Isolated sinus node dysfunction (ISND) is a sinus node dysfunction without atrial fibrillation. A high risk of ischaemic stroke (IS) has been reported in ISND populations. However, current guidelines do not recommend anticoagulation in ISND management. P-wave indicates ISND-related atrial remodelling. P-wave indices and the CHA2DS2-VASc score may contribute to risk stratification for ISND-related IS.

METHODS AND RESULTS

In this multi-centre longitudinal cohort, ISND patients were divided into development (n = 1185) and external validation (n = 988) cohorts. Ischaemic stroke prediction capacity of the P-combined score was assessed with regard to discrimination, calibration, and clinical effectiveness. The cut-off value of the score was confirmed by using a restricted cubic spline curve. One hundred and twenty-four (10.46%) ISND patients developed IS [1.63%/year; 95% confidence interval (CI): 1.49-1.78%/year] after a median 3.02-year follow-up in the development cohort. The P-wave terminal force in electrocardiogram-lead V1 (PTFV1) was the only significantly abnormal P-wave index (adjusted hazard ratio: 2.56; 95% CI: 1.72-3.80). Therefore, we incorporated the PTFV1 with the CHA2DS2-VASc score to generate a P-combined score. For a 5-year IS risk, the P-combined score improved Harrell's C-statistic (95% CI) from 0.678 (0.618-0.738) to 0.716 (0.657-0.774) and 0.747 (0.677-0.816) to 0.808 (0.747-0.868) in the development and validation cohorts, respectively, along with calibration and decision curve analyses. The cut-off value of the score was 3 in the development cohort and well-discriminated in the validation cohort.

CONCLUSION

Chinese ISND patients have a higher IS risk than the general population. Compared with the CHA2DS2-VASc score, the PTFV1-combined CHA2DS2-VASc score shows a better risk-stratification capacity for ISND-related IS.

Initial heart rate score predicts new-onset atrial tachyarrhythmias in pacemaker patients

AIMS

Heart rate score (HRSc), the per cent of atrial paced and sensed event in the largest 10 b.p.m. rate histogram bin of a pacemaker, predicts survival in patients with cardiac devices. No correlation between HRSc and development of atrial fibrillation (AF) has been reported. In this study, we evaluated the relationship between pacemaker post-implantation HRSc and the incidence of newly developed atrial tachyarrhythmias (ATAs).

METHODS AND RESULTS

Patients with dual-chamber pacemakers, implanted 2013-17, with the LATITUDE remote monitoring data with ≥600 000 beats of histogram data collected at baseline were included (N = 34 543). Heart rate score was determined from the initial 3-month post-implantation histogram data. Patients were excluded if they had ATAs, defined as atrial high-rate episodes >5 min or >1% of right atrial beats >170 b.p.m. during the initial 3 months post-implantation. New ATAs, after the baseline period, were defined by each of the following: >1, >10, or >25% of atrial beats >170 b.p.m. or atrial tachycardia response (ATR) events >24 h. Patients were followed a median of 2.8 (1.0-4.0) years. The incidence of ATAs increased in proportion to HRSc (log-rank P-value <0.001), and the initial HRSc ≥70% was associated with increased ATAs by all definitions. Patients with initial HRSc ≥70% were older, had a higher percentage of right atrium pacing (%RA pacing), had a lower percentage of right ventricular pacing (%RV pacing), and were more likely programmed with rate-response vs. subjects with HRSc <70%. Initial HRSc (hazard ratio: 1.07, 95% confidence interval: 1.05-1.09; P < 0.0001) independently predicted ATAs after adjusting for age, gender, %RV pacing, and rate-response programming. The %RA pacing and initial HRSc were correlated.

CONCLUSION

Heart rate score independently predicts any subsequent duration of ATAs in pacemaker patients.

Sinus node dysfunction and atrial fibrillation-Relationships, clinical phenotypes, new mechanisms, and treatment approaches

Although the anatomical basis of the pathogenesis of sinus node dysfunction (SND) and atrial fibrillation (AF) is located primarily in the left and right atria, increasing evidence suggests a strong correlation between SND and AF, in terms of both clinical presentation and formation mechanisms. However, the exact mechanisms underlying this association are unclear. The relationship between SND and AF may not be causal, but is likely to involve common factors and mechanisms, including ion channel remodeling, gap junction abnormalities, structural remodeling, genetic mutations, neuromodulation abnormalities, the effects of adenosine on cardiomyocytes, oxidative stress, and viral infections. Ion channel remodeling manifests primarily as alterations in the "funny" current (I_f) and Ca²⁺ clock associated with cardiomyocyte autoregulation, and gap junction abnormalities are manifested primarily as decreased expression of connexins (Cxs) mediating electrical impulse propagation in cardiomyocytes. Structural remodeling refers primarily to fibrosis and cardiac amyloidosis (CA). Some genetic mutations can also cause arrhythmias, such as SCN5A, HCN4, EMD, and PITX2. The intrinsic cardiac autonomic nervous system (ICANS), a regulator of the heart's physiological functions, triggers arrhythmias.In addition, we discuss arrhythmias caused by viral infections, notably Coronavirus Disease 2019 (COVID-19). Similarly to upstream treatments for atrial cardiomyopathy such as alleviating CA, ganglionated plexus (GP) ablation acts on the common mechanisms between SND and AF, thus achieving a dual therapeutic effect.

Predictors of permanent pacemaker implantation after sinus conversion of cavotricuspid isthmus-dependent atrial flutter

It is unclear which factors are associated with progressive sinus node dysfunction after cavotricuspid isthmus (CTI)-dependent atrial flutter (AFL) ablation. We sought to evaluate the incidence and predictors for permanent pacemaker (PPM) implantation after CTI-dependent AFL ablation. Between January 2011 and June 2021, 353 patients underwent CTI-dependent AFL ablation were studied. During a median follow-up of 31.6 months, 30 patients (8.5%) received PPM implantation, 24 for sick sinus syndrome and 6 for atrioventricular block. In multivariable model, prior atrial fibrillation (AF) (HR 3.570; 95% CI 1.034–12.325; P = 0.044), lowest previous sinus heart rate (HR 0.942; 95% CI 0.898–0.988; P = 0.015), and left atrial volume index (LAVI) (HR 1.067; 95% CI 1.024–1.112; P = 0.002) were independently associated with PPM implantation after CTI-dependent AFL ablation. The best cut-off points for predicting PPM implantation were 60.1 ml/m² for LAVI and 46 beats per minute for lowest previous sinus heart rate. Among the patients discharged without PPM implantation after ablation, sinus pause over three seconds at AFL termination during ablation was an independent predictor of PPM implantation (HR 17.841; 95% CI 4.626–68.807; P < 0.001). Physicians should be aware of the possibility of PPM implantation during follow-up after AFL ablation, especially in patients with the relevant risk factors.

Atrial High-Rate Event Incidence and Predictors in Patients With Permanent Pacemaker Implantation

Objective: The present study aims to investigate the incidence and predictors of atrial high-rate events (AHREs) in patients with permanent pacemaker implants. Methods: A total of 289 patients who were implanted with a dual-chamber pacemaker due to complete atrioventricular block or symptomatic sick sinus syndrome (SSS) and had no previous history of atrial fibrillation were included in the present study. AHREs are defined as events with an atrial frequency of ≥175 bpm and a duration of ≥5 min. The patients were divided into two groups according to whether or not AHREs were detected during the follow-up: group A (AHRE+, n = 91) and group N (AHRE-, n = 198). Results: During the 12-month follow-up period, AHREs were detected in 91 patients (31.5%). The multivariate Cox regression analysis revealed that patient age [odds ratio [OR] = 1.041; 95% confidence interval [CI], 1.018-1.064; and P < 0.001], pacemaker implantation due to symptomatic SSS (OR = 2.225; 95% CI, 1.227-4.036; and P = 0.008), and the percentage of atrial pacing after pacemaker implantation (OR = 1.010; 95% CI, 1.002-1.017; and P = 0.016) were independent AHRE predictors. Conclusion: The AHRE detection rate in patients with pacemaker implants was 31.5%. Patient age, pacemaker implantation due to symptomatic SSS, and the percentage of atrial pacing after pacemaker implantation were independent AHRE predictors.

Risk Prediction Model for Incident Atrial Fibrillation in a General Japanese Population - The Hisayama Study

BACKGROUND

The risk prediction of incident atrial fibrillation (AF) is useful to prevent AF and its complications. The aim of this study is to develop a new risk prediction model for incident AF using the prospective longitudinal data from a general Japanese population.

METHODS AND RESULTS

A total of 2,442 community-dwelling AF-free residents aged ≥40 years were followed up from 1988 to 2012 (46,422 person-years). The development of AF was confirmed by a standard 12-lead electrocardiogram at repeated health examinations and by medical records at clinics or hospitals. The risk prediction model for incident AF was developed using a Cox proportional hazards model. During the follow up, 230 AF events were confirmed. Age, sex, systolic blood pressure, waist circumference, estimated glomerular filtration rate, abnormal cardiac murmur, high R-wave amplitude, and arrhythmia other than AF were selected for inclusion in the model. This model showed good discrimination (Harrell's c statistics: 0.785) and calibration (Greenwood-Nam-D'Agostino test: P=0.87) for AF risk at 10 years.

CONCLUSIONS

The new risk prediction model showed good performance on the individual risk assessment of the future onset of AF in a general Japanese population. As this model included commonly used clinical parameters, it may be useful for determining the requirements for the careful evaluation of AF, such as frequent electrocardiogram examinations in clinical settings, and subsequent reductions in the risk of AF-related complications.

Impact of corrected sinus node recovery time in predicting recurrence in patients with paroxysmal atrial fibrillation

Objective

Atrial fibrillation (AF) and sinus node dysfunction (SND) have common underlying pathophysiological mechanisms. As an index of SND, corrected sinus node recovery time (CSNRT) may also reflect atrial function. The aim of the present study was to determine whether CSNRT predicts AF recurrence in patients undergoing AF ablation.

Methods

Consecutive patients with paroxysmal atrial fibrillation (PAF) who underwent radiofrequency catheter ablation between January 2017 and December 2018 were enrolled. Clinical data, CSNRT, and other electrophysiology indices were collected and analysed between patients with or without AF recurrence.

Results

A total of 159 patients with PAF who underwent the same radiofrequency catheter ablation procedure were enrolled, including 25 patients with SND. During the one-year follow-up period, 22 patients experienced AF recurrence. Patients with recurrence had a significantly longer CSNRT and a larger left atrial volume index (LAVI) than patients without AF recurrence. SND (CSNRT > 550 ms) and a larger LAVI were independently associated with AF recurrence after ablation. A statistically significant CSNRT cut-off value of 550 ms predicted AF recurrence with 73% sensitivity and 85% specificity.

Conclusion

CSNRT and LAVI are independent predictors of PAF recurrence following ablation.

Atrial fibrillation: Current and emerging surgical strategies

OBJECTIVE

(a) To provide a comprehensive review of current literature on the surgical management of atrial fibrillation (AF), highlighting surgical approaches and outcomes. (b) To summarize the latest guidelines pertinent to the surgical management of AF.

BACKGROUND

AF is associated with high rates of morbidity and mortality, primarily related to the associated risk of stroke. The mainstay of management is pharmacologic rate or rhythm control and catheter-based ablation. Surgical ablation (SA) is an alternative strategy that is effective in select patient populations. Recently, novel techniques and technologies have been introduced and this has expanded the surgical capacity to manage AF.

METHODS

A comprehensive review of the literature was conducted.

RESULTS

Surgery can be a highly effective alternative therapeutic option for the management of AF in the appropriate patient population. The need for permanent pacemaker implantation is controversial among patients undergoing surgical intervention for AF. Surgical outcomes are promising, with long-term control of AF and symptomatic relief achieved in select groups of patients.

CONCLUSIONS

This article provides a comprehensive review of the surgical management of AF. We have summarized the latest surgical outcomes and contextualized the most recent guidelines.

Age as a Critical Determinant of Atrial Fibrillation: A Two-sided Relationship

The incidence of atrial fibrillation (AF), the most common sustained arrhythmia and a major public health burden, increases exponentially with age. However, mechanisms underlying this long-recognized association remain incompletely understood. Experimental and human studies have demonstrated the involvement of aging in several arrhythmogenic processes, including atrial electrical and structural remodelling, disturbed calcium homeostasis, and enhanced atrial ectopic activity/increased vulnerability to re-entry induction. Given this wide range of putative mechanisms, the task of delineating the specific effects of aging responsible for AF promotion is not simple, as aging is itself associated with increasing prevalence of a host of AF-predisposing conditions, including heart failure, coronary artery disease, and hypertension. Although we usually think of old age promoting AF, there is also evidence that young age may actually have a protective effect against AF occurrence. For example, the low AF incidence among populations of young patients with significant structural congenital heart disease and substantial atrial enlargement/remodelling suggests that younger age might protect against fibrillation in the diseased atrium; efforts at understating how younger age may prevent AF might be helpful in elucidating missing mechanistic links between AF and age. The goal of this paper is to review the epidemiologic and pathophysiologic evidence regarding mechanisms underlying age-related AF. Although the therapeutic options for AF have recently improved, major gaps still remain and a better understanding of the special relationship between age and AF may be important for the identification of new targets for therapeutic innovation.

The Absence of Atrial Contraction as a Predictor of Permanent Pacemaker Implantation after Maze Procedure with Cryoablation

BACKGROUND

The absence of atrial contraction (AC) after the maze procedure has been reported to cause subsequent annular dilatation and to increase the risk of embolic stroke. We hypothesized that the lack of AC could increase the risk of permanent pacemaker (PPM) implantation in patients undergoing the maze procedure.

METHODS

In 376 consecutive patients who had undergone a cryo-maze procedure and combined valve operation, recovery of AC was assessed at baseline and at immediate (≤2 weeks), early (≤1 year, 4.6±3.8 months), and late (>1 year, 3.5±1.1 years) postoperative stages.

RESULTS

With a median follow-up of 53 months, 10 patients underwent PPM implantation. Seven PPM implants were for sinus node dysfunction (pauses of 9.6±2.4 seconds), one was for marked sinus bradycardia, and two were for advanced/complete atrioventricular block. The median (interquartile range) time to PPM implantation was 13.8 (0.5-68.2) months. Our time-varying covariate Cox models showed that the absence of AC was a risk factor for PPM implantation (hazard ratio, 11.92; 95% confidence interval, 2.52 to 56.45; p=0.002).

CONCLUSION

The absence of AC may be associated with a subsequent risk of PPM implantation.

Predictors and long-term clinical outcomes of newly developed atrial fibrillation in patients with cardiac implantable electronic devices

OBJECTIVE

To evaluate predictors and long-term prognosis of atrial fibrillation (AF) following cardiac implantable electronic device (CIED) implantation in patients without history of AF.

METHODS

From May 1994 to April 2014, 1825 patients with CIED were enrolled in a retrospective, single-center registry. A total of 880 patients from the registry without prior documented AF history were included in the final analysis and were placed into either non-detected AF (NDAF) group or CIED-detected AF group according to development of AF over a follow-up period of 7 years. AF development was defined as any paroxysmal atrial tachyarrhythmia (atrial rate ≥ 180 beats/min) lasting at least 5 minutes according to CIED records.

RESULTS

Overall, 122 (13.8%) of the 880 patients experienced new development of AF during follow-up period. According to multivariate analysis, the independent predictors for development of AF were prior heart failure (hazard ratio [HR], 2.40; 95% confidence interval [CI], 1.50-3.85; P < 0.001), prior sinus node dysfunction (HR, 2.33; 95% CI, 1.62-3.55; P < 0.001), and left atrium volume index of 38.5 mL/m or more (HR, 2.01; 95% CI, 1.23-3.30; P = 0.005). In CDAF group, the risk of heart failure readmission (adjusted HR, 3.79; 95% CI, 1.99-7.22; P < 0.001) and stroke readmission (adjusted HR, 5.33; 95% CI, 1.58-17.97; P = 0.007) was higher than in nondetected AF group.

CONCLUSION

In patients with CIED, prior history of heart failure, sinus node dysfunction, and LA volume index ≥38.5 mL/m were independent predictors of new AF cases. Newly developed AF was significantly associated with increased risk of HF and stroke readmission, according to long-term follow up.

Red blood cell distribution width and atrial fibrillation in patients with sick sinus syndrome

BACKGROUND

Sick sinus syndrome (SSS) is associated with atrial fibrillation (AF). Red blood cell distribution width (RDW) is a marker of anisocytosis of erythrocytes and is related to inflammatory stress. Recently, RDW has been associated with AF. The aim of the present study was to evaluate the potential association of RDW with AF history in patients with SSS.

METHODS

Consecutive patients with symptomatic SSS undergoing dual-chamber pacemaker implantation were screened. Baseline clinical, laboratory, echocardiographic, and electrocardiographic parameters were recorded. Conventional inflammatory indexes were also assessed. Multivariate logistic regression analysis and receiver operating characteristic (ROC) curve analysis for parameters associated with AF were performed.

RESULTS

The final study population consisted of 101 patients (47 men); median age: 77 [73-82] years. The demographic and clinical characteristics were comparable between tachy-brady (AF history) patients (n=32) and patients with other forms of SSS (n=69). Left atrial diameter was increased in tachy-brady patients [44 (39-48)mm vs. 39 (36-44)mm; p=0.05]. Also, the RDW was greater in these patients [14.7 (13.6-15.4)% vs. 13.7 (13.4-14.3)%; p=0.02]. Multivariate analysis showed that RDW is independently associated with AF (OR: 1.58; 95% CI: 1.06-2.85; p=0.04). The ROC curve analysis showed that the area under the curve was 0.69 (p=0.028). A RDW cut-off point of 14 was related to AF with a sensitivity of 70% and a specificity of 69%.

CONCLUSION

RDW is associated with AF history in patients with SSS. The prognostic value of RDW in terms of future AF development and arrhythmia perpetuation in these patients should be further examined.

Restoring Sinus Rhythm Improves Baroreflex Function in Patients With Persistent Atrial Fibrillation

BACKGROUND

Studies have suggested that patients with atrial fibrillation (AF) have impairment in the baroreflex. It is not clear whether these findings are the result of the associated comorbid conditions or the arrhythmia itself. We hypothesized that AF is associated with impairment in baroreflex function and that the arrhythmia itself is a contributing factor.

METHODS AND RESULTS

Twenty-four patients with persistent AF referred for cardioversion were enrolled. A second group of patients with no history of AF matched for age and left ventricular ejection fraction was identified and served as the control group. In the AF group, baroreflex gain (BRG) was measured on the day of cardioversion (Day 1) and again at 30 days post-cardioversion (Day 30) in patients who remained in sinus rhythm (SR). The clinical characteristics of patients with AF were not different than those of the control group. The mean BRG in the AF group on Day 1 was significantly lower than the mean BRG of the control group (5.2±3.6 versus 10.8±5.5 ms/mm Hg, P<0.05). Ten patients experienced AF recurrence before the 30-day follow-up and 14 patients remained in SR. In the group that remained in SR, BRG increased from 4.1±3.7 ms/mm Hg on Day 1 to 7.0±6.0 ms/mm Hg on Day 30 (P<0.01).

CONCLUSION

We have shown that AF is associated with impairment of the baroreflex and that restoration of SR improves BRG. Our data suggest that AF might be a contributing factor to the observed impairment in BRG and that restoring SR might help improve baroreflex function.

Protective effects of kaempferol against cardiac sinus node dysfunction via CaMKII deoxidization

Kaempferol exerts cardioprotective actions through incompletely understood mechanisms. This study investigated the molecular mechanisms underlying the cardioprotective effects of kaempferol in sinus node dysfunction (SND) heart. Here, we demonstrate that angiotensin II (Ang II) infusion causes SND through oxidized calmodulin kinase II (CaMKII). In contrast to this, kaempferol protects sinus node against Ang II-induced SND. Ang II evoked apoptosis with caspase-3 activation in sinus nodal cells. However, kaempferol lowered the CaMKII oxidization and the sinus nodal cell death. To block the CaMKII oxidization, gene of p47phox, a cytosolic subunit of NADPH oxidase, was deleted using Cas9 KO plasmid. In the absence of p47phox, sinus nodal cells were highly resistance to Ang II-induced apoptosis, suggesting that oxidized-CaMKII contributed to sinus nodal cell death. In Langendorff heart from Ang II infused mice, kaempferol preserved normal impulse formation at right atrium. These data suggested that kaempferol protects sinus node via inhibition of CaMKII oxidization and may be useful for preventing SND in high risk patients.

Pitx2-microRNA pathway that delimits sinoatrial node development and inhibits predisposition to atrial fibrillation

The molecular mechanisms underlying atrial fibrillation, the most common sustained cardiac arrhythmia, remain poorly understood. Genome-wide association studies uncovered a major atrial fibrillation susceptibility locus on human chromosome 4q25 in close proximity to the paired-like homeodomain transcription factor 2 (Pitx2) homeobox gene. Pitx2, a target of the left-sided Nodal signaling pathway that initiates early in development, represses the sinoatrial node program and pacemaker activity on the left side. To address the mechanisms underlying this repressive activity, we hypothesized that Pitx2 regulates microRNAs (miRs) to repress the sinoatrial node genetic program. MiRs are small noncoding RNAs that regulate gene expression posttranscriptionally. Using an integrated genomic approach, we discovered that Pitx2 positively regulates miR-17-92 and miR-106b-25. Intracardiac electrical stimulation revealed that both miR-17-92 and miR-106b-25 deficient mice exhibit pacing-induced atrial fibrillation. Furthermore electrocardiogram telemetry revealed that mice with miR-17-92 cardiac-specific inactivation develop prolonged PR intervals whereas mice with miR-17-92 cardiac-specific inactivation and miR-106b-25 heterozygosity develop sinoatrial node dysfunction. Both arrhythmias are risk factors for atrial fibrillation in humans. Importantly, miR-17-92 and miR-106b-25 directly repress genes, such as Shox2 and Tbx3, that are required for sinoatrial node development. Together, to our knowledge, these findings provide the first genetic evidence for an miR loss-of-function that increases atrial fibrillation susceptibility.

Pitx2, an atrial fibrillation predisposition gene, directly regulates ion transport and intercalated disc genes

BACKGROUND

Pitx2 is the homeobox gene located in proximity to the human 4q25 familial atrial fibrillation (AF) locus. When deleted in the mouse germline, Pitx2 haploinsufficiency predisposes to pacing-induced AF, indicating that reduced Pitx2 promotes an arrhythmogenic substrate. Previous work focused on Pitx2 developmental functions that predispose to AF. Although Pitx2 is expressed in postnatal left atrium, it is unknown whether Pitx2 has distinct postnatal and developmental functions.

METHODS AND RESULTS

To investigate Pitx2 postnatal function, we conditionally inactivated Pitx2 in the postnatal atrium while leaving its developmental function intact. Unstressed adult Pitx2 homozygous mutant mice display variable R-R interval with diminished P-wave amplitude characteristic of sinus node dysfunction, an AF risk factor in human patients. An integrated genomics approach in the adult heart revealed Pitx2 target genes encoding cell junction proteins, ion channels, and critical transcriptional regulators. Importantly, many Pitx2 target genes have been implicated in human AF by genome-wide association studies. Immunofluorescence and transmission electron microscopy studies in adult Pitx2 mutant mice revealed structural remodeling of the intercalated disc characteristic of human patients with AF.

CONCLUSIONS

Our findings, revealing that Pitx2 has genetically separable postnatal and developmental functions, unveil direct Pitx2 target genes that include channel and calcium handling genes, as well as genes that stabilize the intercalated disc in postnatal atrium.

Oxidized Ca(2+)/calmodulin-dependent protein kinase II triggers atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is a growing public health problem without adequate therapies. Angiotensin II and reactive oxygen species are validated risk factors for AF in patients, but the molecular pathways connecting reactive oxygen species and AF are unknown. The Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) has recently emerged as a reactive oxygen species-activated proarrhythmic signal, so we hypothesized that oxidized CaMKIIδ could contribute to AF.

METHODS AND RESULTS

We found that oxidized CaMKII was increased in atria from AF patients compared with patients in sinus rhythm and from mice infused with angiotensin II compared with mice infused with saline. Angiotensin II-treated mice had increased susceptibility to AF compared with saline-treated wild-type mice, establishing angiotensin II as a risk factor for AF in mice. Knock-in mice lacking critical oxidation sites in CaMKIIδ (MM-VV) and mice with myocardium-restricted transgenic overexpression of methionine sulfoxide reductase A, an enzyme that reduces oxidized CaMKII, were resistant to AF induction after angiotensin II infusion.

CONCLUSIONS

Our studies suggest that CaMKII is a molecular signal that couples increased reactive oxygen species with AF and that therapeutic strategies to decrease oxidized CaMKII may prevent or reduce AF.

Atrial fibrillation and sinus node dysfunction in human ankyrin-B syndrome: a computational analysis

Ankyrin-B is a multifunctional adapter protein responsible for localization and stabilization of select ion channels, transporters, and signaling molecules in excitable cells including cardiomyocytes. Ankyrin-B dysfunction has been linked with highly penetrant sinoatrial node (SAN) dysfunction and increased susceptibility to atrial fibrillation. While previous studies have identified a role for abnormal ion homeostasis in ventricular arrhythmias, the molecular mechanisms responsible for atrial arrhythmias and SAN dysfunction in human patients with ankyrin-B syndrome are unclear. Here, we develop a computational model of ankyrin-B dysfunction in atrial and SAN cells and tissue to determine the mechanism for increased susceptibility to atrial fibrillation and SAN dysfunction in human patients with ankyrin-B syndrome. Our simulations predict that defective membrane targeting of the voltage-gated L-type Ca(2+) channel Cav1.3 leads to action potential shortening that reduces the critical atrial tissue mass needed to sustain reentrant activation. In parallel, increased fibrosis results in conduction slowing that further increases the susceptibility to sustained reentry in the setting of ankyrin-B dysfunction. In SAN cells, loss of Cav1.3 slows spontaneous pacemaking activity, whereas defects in Na(+)/Ca(2+) exchanger and Na(+)/K(+) ATPase increase variability in SAN cell firing. Finally, simulations of the intact SAN reveal a shift in primary pacemaker site, SAN exit block, and even SAN failure in ankyrin-B-deficient tissue. These studies identify the mechanism for increased susceptibility to atrial fibrillation and SAN dysfunction in human disease. Importantly, ankyrin-B dysfunction involves changes at both the cell and tissue levels that favor the common manifestation of atrial arrhythmias and SAN dysfunction.