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2.
Eur J Hum Genet ; 2024 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-38605126

RESUMO

Primary ciliary dyskinesia (PCD), a disorder of the motile cilia, is now recognised as an underdiagnosed cause of bronchiectasis. Accurate PCD diagnosis comprises clinical assessment, analysis of cilia and the identification of biallelic variants in one of 50 known PCD-related genes, including HYDIN. HYDIN-related PCD is underdiagnosed due to the presence of a pseudogene, HYDIN2, with 98% sequence homology to HYDIN. This presents a significant challenge for Short-Read Next Generation Sequencing (SR-NGS) and analysis, and many diagnostic PCD gene panels do not include HYDIN. We have used a combined approach of SR-NGS with bioinformatic masking of HYDIN2, and state-of-the-art long-read Nanopore sequencing (LR_NGS), together with analysis of respiratory cilia including transmission electron microscopy and immunofluorescence to address the underdiagnosis of HYDIN as a cause of PCD. Bioinformatic masking of HYDIN2 after SR-NGS facilitated the detection of biallelic HYDIN variants in 15 of 437 families, but compromised the detection of copy number variants. Supplementing testing with LR-NGS detected HYDIN deletions in 2 families, where SR-NGS had detected a single heterozygous HYDIN variant. LR-NGS was also able to confirm true homozygosity in 2 families when parental testing was not possible. Utilising a combined genomic diagnostic approach, biallelic HYDIN variants were detected in 17 families from 242 genetically confirmed PCD cases, comprising 7% of our PCD cohort. This represents the largest reported HYDIN cohort to date and highlights previous underdiagnosis of HYDIN-associated PCD. Moreover this provides further evidence for the utility of LR-NGS in diagnostic testing, particularly for regions of high genomic complexity.

3.
Artigo em Inglês | MEDLINE | ID: mdl-38650520

RESUMO

BACKGROUND: Early guidance recommended a bolus of intravenous heparin at the beginning of leadless pacemaker (LP) implantation procedures. However, due to concern about bleeding complications, more recent practice has tended toward omitting the bolus and only running a continuous heparin infusion through the introducer sheath. The impact of omitting the heparin bolus on procedural outcomes is not clear. METHODS: We reviewed all Medtronic Micra LP implants at our institution from 9/2014 to 9/2022. The decision to bolus with heparin was at operator discretion. RESULTS: Among 621 LP implants, 326 received an intravenous heparin bolus, 243 did not, and 52 patients were excluded because heparin bolus status could not be confirmed. There was a trend toward more frequent omission of the heparin bolus with more recent implants. Median follow-up after LP implant was 14.3 (interquartile range [IQR]: 8.4-27.9) months. There was no difference between heparin bolus and no bolus groups in the number of device deployments/recaptures (1.42 ± 0.81 vs. 1.31 ± 0.66, p = .15). Implant-related adverse events were also similar between heparin bolus and no bolus groups: access-site hematoma requiring intervention (7 vs. 5, p = .99), pseudoaneurysm (1 vs. 1, p = .99), cardiac perforation (1 vs. 1, p = .99), intraprocedural device thrombus formation (2 vs. 4, p = .41), 30-day rehospitalization (21 vs. 15, p = .98), and 30-day all-cause mortality (16 vs. 14, p = .70). There was one additional nonfatal cardiac perforation in a patient who was excluded due to unknown heparin bolus status. Regarding device electrical parameters between heparin bolus and no bolus groups, there were no significant differences at the time of implant: pacing capture threshold 0.5 ± 0.4 vs. 0.5 ± 0.3, p = .10; pacing impedance 739.9 ± 226.4 vs. 719.1 ± 215.4, p = .52; R wave sensing 11.7 ± 5.7 vs. 12.0 ± 5.4, p = .34). Long-term device performance was also similar between groups. CONCLUSION: Omission of the systemic heparin bolus at the time of LP implantation appears safe in appropriately selected patients. Heparin bolus may still be considered in long cases requiring multiple device deployments or in patients at high risk for thrombotic complications.

4.
Heart Rhythm ; 2024 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-38437891

RESUMO

BACKGROUND: Human in vivo data on the chemical stability of different transvenous lead materials, particularly OptimTM leads, are lacking. OBJECTIVES: The purpose of this study was to determine the chemical reactivity of insulation materials by analyzing the molar mass of extracted pacing and defibrillator leads METHODS: We collected extracted leads at Emory University Hospitals and sent the leads with thermoplastic outer insulation material for molar mass analysis, a material characteristic that informs biostability. Leads were separated based on the chemical identity of the outer insulation material, and the molar mass was measured by an independent party. The extent of chemical reaction was compared across leads having different materials: poly(ether)urethane 55D, poly(ether)urethane 80A, and Optim. RESULTS: A total of 70 leads were extracted. The subset of extracted leads having outer insulation materials composed of PEU or Optim were analyzed for molar mass, where implant times ranged from 0.12 to 16.26 years. The rate of chemical degradation was compared by plotting the extent of reaction [Mn(t = 0)/Mn(t)] as a function of implant time. The Optim molar mass decreased to 40% of its initial value at 10 years of implant. No change in the molar mass of the PEU insulations could be resolved over the same 10-year implant time. CONCLUSION: Because the molar mass of a polymer is directly related to its mechanical integrity, the observed decrease in molar mass of Optim likely translates into premature insulation defects and is consistent with the observed increased rate of electrical malfunction/noise in this subset of cardiac leads.

6.
J Cardiovasc Electrophysiol ; 35(5): 929-938, 2024 May.
Artigo em Inglês | MEDLINE | ID: mdl-38450808

RESUMO

INTRODUCTION: Transvenous leads have been implicated in tricuspid valve (TV) dysfunction, but limited data are available regarding the effect of extracting leads across the TV on valve regurgitation. The aim of this study is to quantify tricuspid regurgitation (TR) before and after lead extraction and identify predictors of worsening TR. METHODS: We studied 321 patients who had echocardiographic data before and after lead extraction. TR was graded on a scale (0 = none/trivial, 1 = mild, 2 = moderate, 3 = severe). A change of >1 grade following extraction was considered significant. RESULTS: A total of 321 patients underwent extraction of a total of 338 leads across the TV (1.05 ± 0.31 leads across the TV per patient). There was no significant difference on average TR grade pre- and postextraction (1.18 ± 0.91 vs. 1.15 ± 0.87; p = 0.79). TR severity increased after extraction in 84 patients, but was classified as significantly worse (i.e., >1 grade change in severity) in only 8 patients (2.5%). Use of laser lead extraction was associated with a higher rate of worsening TR postextraction (44.0% vs. 31.6%, p = 0.04). CONCLUSION: In our single-center analysis, extraction of leads across the TV did not significantly affect the extent of TR in most patients. Laser lead extraction was associated with a higher rate of worsening TR after extraction.


Assuntos
Remoção de Dispositivo , Insuficiência da Valva Tricúspide , Humanos , Insuficiência da Valva Tricúspide/fisiopatologia , Insuficiência da Valva Tricúspide/cirurgia , Insuficiência da Valva Tricúspide/diagnóstico por imagem , Insuficiência da Valva Tricúspide/etiologia , Insuficiência da Valva Tricúspide/diagnóstico , Masculino , Feminino , Remoção de Dispositivo/efeitos adversos , Idoso , Resultado do Tratamento , Pessoa de Meia-Idade , Estudos Retrospectivos , Fatores de Risco , Índice de Gravidade de Doença , Valva Tricúspide/fisiopatologia , Valva Tricúspide/cirurgia , Valva Tricúspide/diagnóstico por imagem , Desfibriladores Implantáveis , Fatores de Tempo , Marca-Passo Artificial , Idoso de 80 Anos ou mais , Dispositivos de Terapia de Ressincronização Cardíaca
7.
Artigo em Inglês | MEDLINE | ID: mdl-38413483

RESUMO

BACKGROUND: Following catheter ablation, vascular access management involves potential complications and prolonged recovery. Recently, suture-mediated closure (SMC) devices were approved for venous access procedures. The objective of this study is to evaluate the safety of a commercially available SMC for multiple access site venous closure by duplex ultrasound (DUS) in asymptomatic subjects with non-visible complications. METHODS: Thirty-six subjects (63 ± 10.7 years old, 12 female) were enrolled. Following catheter ablation for atrial fibrillation, all subjects had SMC of every venous access site. Subjects underwent DUS of femoral veins and arteries. DUS was performed at discharge, and again at 30 days. Subjects were evaluated for clinically apparent vascular complications. RESULTS: Mean procedure duration was 138.6 min, and the time to hemostasis was 3.1 min/access site and 9.5 min/subject. Median time to ambulation was 193.5 min, and median time to discharge was 5.95 h, with discharge as early as 2.4 h. A median of 2 sheaths/vein and a median of 2 SMC devices/vein were used. There were no major complications and a 16.7% (6/36) minor complication rate at discharge. All complications resolved at 30 days. The complication rate was not higher in patients with 2 SMC per access site as compared to the patients who just received 1 SMC per access site. CONCLUSIONS: This study demonstrates the safety of multi-access closure using SMC, following catheter ablation procedures, for closure of sites that use sheath sizes from ≤ 8F to ≥ 15F and for those that use 2 or more SMCs per access site.

8.
Clin Med (Lond) ; 24(1): 100019, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-38281665

RESUMO

This collaborative article presents a review of chronic pulmonary aspergillosis (CPA) from the perspective of a multidisciplinary team comprising of respiratory physicians, radiologists, mycologists, dietitians, pharmacists, physiotherapists and palliative care specialists. The review synthesises current knowledge on CPA, emphasising the intricate interplay between clinical, radiological, and microbiological aspects. We highlight the importance of assessing each patient as multidisciplinary team to ensure personalised treatment strategies and a holistic approach to patient care.


Assuntos
Clínicos Gerais , Aspergilose Pulmonar , Humanos , Aspergilose Pulmonar/diagnóstico , Aspergilose Pulmonar/terapia , Cuidados Paliativos , Radiologistas
9.
Int Orthop ; 48(3): 657-666, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38195946

RESUMO

PURPOSE: The aim of this review is to appraise the current evidence on the epidemiology, pathophysiology, diagnosis and management of os acetabuli. METHODS: A scoping review was conducted according to the Joanna Briggs Institute guidelines. A systematic search was performed on Medline (PubMed), Embase and Cochrane Library. Inclusion criteria comprised observational and interventional studies and review articles published in the English language that focused on patients with os acetabuli according to the PRISMA extension of scoping reviews checklist using the terms 'Os Acetabuli' or 'os acetabula' or 'acetabular ossicles'. A narrative synthesis of results was undertaken, and the included articles were divided into (i) definition, (ii) aetiology, (iii) diagnosis and imaging and (iv) management of os acetabuli. RESULTS: 107 articles were screened, with 22 meeting the eligibility criteria. A total of 8836 patients were considered, of which 604 had os acetabuli. The mean age was 32.8 years. The prevalence of os acetabuli ranged from 3.4 to 7.7%, with a higher prevalence in males compared to females. True os acetabuli was defined as an unfused secondary ossification centre along the acetabular rim. The aetiology of os acetabuli is thought to be secondary to acetabular dysplasia and/or femoroacetabular impingement. Standard of care for management of symptomatic os acetabuli is considered to be arthroscopic excision unless the excision results in acetabular undercoverage and/or instability, in which case, fixation is recommended. CONCLUSIONS: Successful management of os acetabuli depends on understanding the pathology and treating the underlying cause rather than treating the os acetabuli in isolation. Future work needs to focus on establishing clear diagnostic criteria, consensus on definition and an evidence-based treatment algorithm.


Assuntos
Impacto Femoroacetabular , Luxação Congênita de Quadril , Luxação do Quadril , Masculino , Feminino , Humanos , Adulto , Articulação do Quadril/cirurgia , Acetábulo/diagnóstico por imagem , Acetábulo/cirurgia , Impacto Femoroacetabular/cirurgia , Luxação do Quadril/cirurgia , Luxação Congênita de Quadril/complicações , Artroscopia/métodos
10.
Cancer ; 2024 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-38183671

RESUMO

BACKGROUND: Population-based cancer survival is a key indicator for assessing the effectiveness of cancer control by a health care system in a specific geographic area. Breast cancer is the most common cancer among women in India, accounting for over one quarter of all female cancers. The objective of this study was to estimate the 5-year survival of female patients who were diagnosed with breast cancer between 2012 and 2015 from the existing Population-Based Cancer Registries (PBCRs) in India. METHODS: In total, 17,331 patients who had breast cancer diagnosed between 2012 and 2015 from 11 PBCRs were followed until June 30, 2021. Active methods were used to track the vital status of registered breast cancer cases. The study conducted survival analysis by calculating the difference between the date of first diagnosis and the date of death or censoring to estimate observed survival and relative survival using the actuarial survival approach and the Ederer-II approach, respectively. RESULTS: The 5-year age-standardized relative survival (95% confidence interval [CI]) of patients with breast cancer was 66.4% (95% CI, 65.5%-67.3%). Mizoram (74.9%; 95% CI, 68.1%-80.8%), Ahmedabad urban (72.7%; 95% CI, 70.3%-74.9%), Kollam (71.5%; 95% CI, 69.2%-73.6%), and Thiruvananthapuram (69.1%; 95% CI, 67.0%-71.2%) had higher survival rates than the national average. Conversely, Pasighat had the lowest survival rate (41.9%; 95% CI, 14.7%-68.6%). The 5-year observed survival rates for localized, regional, and distant metastasis in the pooled PBCRs were 81.0%, 65.5%, and 18.3%, respectively. CONCLUSIONS: The overall disparity in survival rates was observed across 11 PBCRs, with lower survival rates reported in Manipur, Tripura, and Pasighat. Therefore, it is imperative to implement comprehensive cancer control strategies widely throughout the country.

11.
Clin Gastroenterol Hepatol ; 22(2): 324-338, 2024 02.
Artigo em Inglês | MEDLINE | ID: mdl-37460005

RESUMO

BACKGROUND & AIMS: The coronavirus disease-2019 pandemic profoundly disrupted preventative health care services including cancer screening. As the largest provider of cirrhosis care in the United States, the Department of Veterans Affairs (VA) National Gastroenterology and Hepatology Program aimed to assess factors associated with hepatocellular carcinoma (HCC) stage at diagnosis, treatment, and survival. METHODS: Veterans with a new diagnosis of HCC in 2021 were identified from electronic health records (N = 2306). Structured medical record extraction was performed by expert reviewers in a 10% random subsample of Veterans with new HCC diagnoses. Factors associated with stage at diagnosis, receipt of treatment, and survival were assessed using multivariable models. RESULTS: Among 199 patients with confirmed HCC, the average age was 71 years and most (72%) had underlying cirrhosis. More than half (54%) were at an early stage (T1 or T2) at diagnosis. Less-advanced liver disease, number of imaging tests adequate for HCC screening, HCC diagnosis in the VA, and receipt of VA primary care were associated significantly with early stage diagnosis. HCC-directed treatments were administered to 145 (73%) patients after a median of 37 days (interquartile range, 19-54 d) from diagnosis, including 70 (35%) patients who received potentially curative treatments. Factors associated with potentially curative (vs no) treatments included HCC screening, early stage at diagnosis, and better performance status. Having fewer comorbidities and better performance status were associated significantly with noncurative (vs no) treatment. Early stage diagnosis, diagnosis in the VA system, and receipt of curative treatment were associated significantly with survival. CONCLUSIONS: These results highlight the importance of HCC screening and engagement in care for HCC diagnosis, treatment, and survival while demonstrating the feasibility of developing a national quality improvement agenda for HCC screening, diagnosis, and treatment.


Assuntos
Carcinoma Hepatocelular , Neoplasias Hepáticas , Veteranos , Humanos , Estados Unidos , Idoso , Carcinoma Hepatocelular/diagnóstico , Carcinoma Hepatocelular/terapia , Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/terapia , Melhoria de Qualidade , Cirrose Hepática/diagnóstico , Cirrose Hepática/terapia , Cirrose Hepática/complicações , Estudos Retrospectivos
14.
J Oncol Pharm Pract ; : 10781552231217686, 2023 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-38043938

RESUMO

INTRODUCTION: For patients with metastatic head and neck squamous cell cancer (HNSCC), the outcomes of pembrolizumab in combination with a platinum agent and taxane as first-line therapy remain unknown. The purpose of this study is to characterize the impact of substituting the 5-fluorouracil (5-FU) backbone for a taxane in this chemoimmunotherapy regimen on safety/tolerability and survival outcomes. METHODS: This was an IRB-approved, single-center, retrospective, active comparator, new-user design study in adult patients with HNSCC treated between January 2018 and September 2021. The primary objective was to assess safety and tolerability of pembrolizumab in combination with a platinum agent and taxane against an active comparator arm of pembrolizumab in combination with a platinum agent and 5-FU. Safety and tolerability were evaluated by assessing differences in overall toxicities, with further secondary analysis evaluating differences in hematologic toxicities and pre-defined non-hematologic toxicities. RESULTS: There was no statistical difference demonstrated with the primary endpoint between the cohorts. Reduced toxicity rates were found in the taxane arm for mucositis and creatinine levels. No grade 4 non-hematologic toxicities were reported. Patients receiving 5-FU were more likely to have dose reductions upfront, discontinue treatment due to intolerances and had significantly higher mucositis. CONCLUSIONS: This study helps to characterize the safety profile and activity of pembrolizumab in combination with a platinum agent and taxane derivative in HNSCC patients. Within our study, substitution of 5-FU with a taxane did not show an increased risk of toxicities, worsened survival, or decreased odds of achieving a response. Mucositis and elevated creatinine rates were significantly reduced within the taxane arm.

15.
Hum Vaccin Immunother ; 19(3): 2289242, 2023 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-38078840

RESUMO

Long-term follow-up of a cohort of unmarried girls who received one, two, or three doses of quadrivalent HPV vaccine, between 10 and 18 years of age, in an Indian multi-centric study allowed us to compare antibody responses between the younger and older age cohorts at 10-years post-vaccination, and study the impact of initiation of sexual activity and cervical HPV infections on antibody levels. Among the younger (10-14 years) recipients of a single dose, 97.7% and 98.2% had detectable binding antibody titers against HPV 16 and HPV 18 respectively at ten years post-vaccination. The proportions among those receiving a single dose at age 15-18 years were 92.3% and 94.2% against HPV 16 and HPV 18 respectively. Mean HPV 16 binding antibody titers were 2.1 folds (95%CI 1.4 to 3.3) higher in those vaccinated at ages 10-14 years, and 1.9 folds (95%CI 1.2 to 3.0) higher in those vaccinated at 15-18 years compared to mean titers seen in the unvaccinated women. Compared to previous timepoints of 36 or 48 months, binding antibodies against HPV 16 and neutralizing antibodies against both HPV 16 and HPV 18 were significantly higher at 10 years. This rise was more pronounced in participants vaccinated at 15-18 years. No association of marital status or cervical HPV infections was observed with the rise in titer. Durability of antibody response in single dose recipients correlated well with the high efficacy of a single dose against persistent HPV 16/18 infections irrespective of age at vaccination, as we reported earlier.


Assuntos
Infecções por Papillomavirus , Vacinas contra Papillomavirus , Adolescente , Criança , Feminino , Humanos , Anticorpos Neutralizantes , Anticorpos Antivirais , Papillomavirus Humano 16 , Papillomavirus Humano 18 , Vacina Quadrivalente Recombinante contra HPV tipos 6, 11, 16, 18 , Infecções por Papillomavirus/prevenção & controle , Vacinação , Vacinas Combinadas
17.
Europace ; 25(12)2023 12 06.
Artigo em Inglês | MEDLINE | ID: mdl-38000900

RESUMO

AIMS: Single-connector (DF4) defibrillator leads have become the predominantly implanted transvenous implantable cardioverter-defibrillator lead. However, data on their long-term performance are derived predominantly from manufacturer product performance reports. METHODS AND RESULTS: We reviewed medical records in 5289 patients with DF4 leads between 2011 and 2023 to determine the frequency of lead-related abnormalities. We defined malfunction as any single or combination of electrical abnormalities requiring revision including a sudden increase (≥2×) in stimulation threshold, a discrete jump in high-voltage impedance, or sensing of non-physiologic intervals or noise. We documented time to failure, predictors of failure, and management strategies. Mean follow-up after implant was 4.15 ± 3.6 years (median = 3.63), with 37% of leads followed for >5 years. A total of 80 (1.5%) leads demonstrated electrical abnormalities requiring revision with an average time to failure of 4 ± 2.8 years (median = 3.5). Of the leads that malfunctioned, 62/80 (78%) were extracted and replaced with a new lead and in the other 18 cases, malfunctioned DF4 leads were abandoned, and a new lead implanted. In multivariable models, younger age at implant (OR 1.03 per year; P < 0.001) and the presence of Abbott/St. Jude leads increased the risk of malfunction. CONCLUSION: DF4 defibrillator leads demonstrate excellent longevity with >98.3% of leads followed for at least 5 years still functioning normally. Younger age at implant and lead manufacturer are associated with an increased risk of DF4 lead malfunction. The differences in lead survival between manufacturers require further investigation.


Assuntos
Desfibriladores Implantáveis , Humanos , Desfibriladores Implantáveis/efeitos adversos , Falha de Equipamento , Estudos Retrospectivos
19.
Europace ; 25(12)2023 12 06.
Artigo em Inglês | MEDLINE | ID: mdl-38006390

RESUMO

AIMS: The mechanisms of transition from regular rhythms to ventricular fibrillation (VF) are poorly understood. The concordant to discordant repolarization alternans pathway is extensively studied; however, despite its theoretical centrality, cannot guide ablation. We hypothesize that complex repolarization dynamics, i.e. oscillations in the repolarization phase of action potentials with periods over two of classic alternans, is a marker of electrically unstable substrate, and ablation of these areas has a stabilizing effect and may reduce the risk of VF. To prove the existence of higher-order periodicities in human hearts. METHODS AND RESULTS: We performed optical mapping of explanted human hearts obtained from recipients of heart transplantation at the time of surgery. Signals recorded from the right ventricle endocardial surface were processed to detect global and local repolarization dynamics during rapid pacing. A statistically significant global 1:4 peak was seen in three of six hearts. Local (pixel-wise) analysis revealed the spatially heterogeneous distribution of Periods 4, 6, and 8, with the regional presence of periods greater than two in all the hearts. There was no significant correlation between the underlying restitution properties and the period of each pixel. CONCLUSION: We present evidence of complex higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex vivo human hearts. We infer that the oscillation of the calcium cycling machinery is the primary mechanism of higher-order dynamics. These higher-order regions may act as niduses of instability and may provide targets for substrate-based ablation of VF.


Assuntos
Ventrículos do Coração , Coração , Humanos , Arritmias Cardíacas , Fibrilação Ventricular/cirurgia , Potenciais de Ação/fisiologia
20.
medRxiv ; 2023 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-37662394

RESUMO

Background: Repolarization alternans, defined as period-2 oscillation in the repolarization phase of the action potentials, provides a mechanistic link between cellular dynamics and ventricular fibrillation (VF). Theoretically, higher-order periodicities (e.g., periods 4, 6, 8,...) are expected but have minimal experimental evidence. Methods: We studied explanted human hearts obtained from recipients of heart transplantation at the time of surgery. Optical mapping of the transmembrane potential was performed after staining the hearts with voltage-sensitive fluorescent dyes. Hearts were stimulated at an increasing rate until VF was induced. Signals recorded from the right ventricle endocardial surface prior to induction of VF and in the presence of 1:1 conduction were processed using the Principal Component Analysis and a combinatorial algorithm to detect and quantify higher-order dynamics. Results were correlated to the underlying electrophysiological characteristics as quantified by restitution curves and conduction velocity. Results: A prominent and statistically significant global 1:4 peak (corresponding to period-4 dynamics) was seen in three of the six studied hearts. Local (pixel-wise) analysis revealed the spatially heterogeneous distribution of periods 4, 6, and 8, with the regional presence of periods greater than two in all the hearts. There was no significant correlation between the underlying restitution properties and the period of each pixel. Discussion: We present evidence of higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex-vivo human hearts. We infer from the independence of the period to the underlying restitution properties that the oscillation of the excitation-contraction coupling and calcium cycling mechanisms is the primary mechanism of higher-order dynamics. These higher-order regions may act as niduses of instability that can degenerate into chaotic fibrillation and may provide targets for substrate-based ablation of VF.

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