Fibrosis, Connexin-43, and Conduction Abnormalities in the Brugada Syndrome.

BACKGROUND: The right ventricular outflow tract (RVOT) is acknowledged to be responsible for arrhythmogenesis in Brugada syndrome (BrS), but the pathophysiology remains controversial. OBJECTIVES: This study assessed the substrate underlying BrS at post-mortem and in vivo, and the role for open thoracotomy ablation. METHODS: Six whole hearts from male post-mortem cases of unexplained sudden death (mean age 23.2 years) with negative specialist cardiac autopsy and familial BrS were used and matched to 6 homograft control hearts by sex and age (within 3 years) by random risk set sampling. Cardiac autopsy sections from cases and control hearts were stained with picrosirius red for collagen. The RVOT was evaluated in detail, including immunofluorescent stain for connexin-43 (Cx43). Collagen and Cx43 were quantified digitally and compared. An in vivo study was undertaken on 6 consecutive BrS patients (mean age 39.8 years, all men) during epicardial RVOT ablation for arrhythmia via thoracotomy. Abnormal late and fractionated potentials indicative of slowed conduction were identified, and biopsies were taken before ablation. RESULTS: Collagen was increased in BrS autopsy cases compared with control hearts (odds ratio [OR]: 1.42; p = 0.026). Fibrosis was greatest in the RVOT (OR: 1.98; p = 0.003) and the epicardium (OR: 2.00; p = 0.001). The Cx43 signal was reduced in BrS RVOT (OR: 0.59; p = 0.001). Autopsy and in vivo RVOT samples identified epicardial and interstitial fibrosis. This was collocated with abnormal potentials in vivo that, when ablated, abolished the type 1 Brugada electrocardiogram without ventricular arrhythmia over 24.6 ± 9.7 months. CONCLUSIONS: BrS is associated with epicardial surface and interstitial fibrosis and reduced gap junction expression in the RVOT. This collocates to abnormal potentials, and their ablation abolishes the BrS phenotype and life-threatening arrhythmias. BrS is also associated with increased collagen throughout the heart. Abnormal myocardial structure and conduction are therefore responsible for BrS.

iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death.

Desmosomes are anchoring junctions that exist in cells that endure physical stress such as cardiac myocytes. The importance of desmosomes in maintaining the homeostasis of the myocardium is underscored by frequent mutations of desmosome components found in human patients and animal models. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a phenotype caused by mutations in desmosomal components in ∼ 50% of patients, however, the causes in the remaining 50% of patients still remain unknown. A deficiency of inhibitor of apoptosis-stimulating protein of p53 (iASPP), an evolutionarily conserved inhibitor of p53, caused by spontaneous mutation recently has been associated with a lethal autosomal recessive cardiomyopathy in Poll Hereford calves and Wa3 mice. However, the molecular mechanisms that mediate this putative function of iASPP are completely unknown. Here, we show that iASPP is expressed at intercalated discs in human and mouse postmitotic cardiomyocytes. iASPP interacts with desmoplakin and desmin in cardiomyocytes to maintain the integrity of desmosomes and intermediate filament networks in vitro and in vivo. iASPP deficiency specifically induces right ventricular dilatation in mouse embryos at embryonic day 16.5. iASPP-deficient mice with exon 8 deletion (Ppp1r13l(Δ8/Δ8)) die of sudden cardiac death, displaying features of ARVC. Intercalated discs in cardiomyocytes from four of six human ARVC cases show reduced or loss of iASPP. ARVC-derived desmoplakin mutants DSP-1-V30M and DSP-1-S299R exhibit weaker binding to iASPP. These data demonstrate that by interacting with desmoplakin and desmin, iASPP is an important regulator of desmosomal function both in vitro and in vivo. This newly identified property of iASPP may provide new molecular insight into the pathogenesis of ARVC.

Clinical characteristics and circumstances of death in the sudden arrhythmic death syndrome.

BACKGROUND: Sudden cardiac death (SCD) is a devastating event in the young. Referral to a specialist cardiac pathologist is recommended. Age, sex, and circumstances of death may reflect underlying diagnoses. We aim to describe the demographics of victims and circumstances surrounding sudden cardiac death with a normal heart (ie, sudden arrhythmic death syndrome). METHODS AND RESULTS: There were 2156 cases of sudden cardiac death from across the United Kingdom referred to a tertiary cardiac pathology service from 1994 to 2010. We analyzed 967 consecutive cases (61% male; median age 29 years) with a normal heart at postmortem. Information from referring coroners' reports was used to ascertain clinical information. Familial evaluation was performed in 5% of cases. Information from these cases was used to determine the likely accuracy of coronial reports. Deaths during sleep or at rest were more common than deaths during exercise or with emotional stress: 82% versus 16%. Death with exercise/stress was more common in males (relative risk, 2.33; 95% confidence interval, 1.56-3.47; P<0.001) and those under 18 years of age: males, relative risk, 2.41 (95% confidence interval, 1.69-3.13; P<0.001) and females, relative risk, 2.91 (95% confidence interval, 1.80-4.01; P<0.001)). Prior syncope (4.1%), documented arrhythmia (3.4%), and family history of sudden death (4.2%) were uncommon. Epilepsy had been diagnosed in 6.6%. CONCLUSIONS: Death caused by sudden arrhythmic death syndrome is more common at rest or during sleep. Death with exercise/stress is more common in males and those aged below 18 years. Up to 90% of SADS victims have no preceding symptoms or recognized risk factors for sudden death. Epilepsy may be considered a risk factor for SADS.

Calibration of myocardial T2 and T1 against iron concentration.

BACKGROUND: The assessment of myocardial iron using T2* cardiovascular magnetic resonance (CMR) has been validated and calibrated, and is in clinical use. However, there is very limited data assessing the relaxation parameters T1 and T2 for measurement of human myocardial iron. METHODS: Twelve hearts were examined from transfusion-dependent patients: 11 with end-stage heart failure, either following death (n=7) or cardiac transplantation (n=4), and 1 heart from a patient who died from a stroke with no cardiac iron loading. Ex-vivo R1 and R2 measurements (R1=1/T1 and R2=1/T2) at 1.5 Tesla were compared with myocardial iron concentration measured using inductively coupled plasma atomic emission spectroscopy. RESULTS: From a single myocardial slice in formalin which was repeatedly examined, a modest decrease in T2 was observed with time, from mean (± SD) 23.7 ± 0.93 ms at baseline (13 days after death and formalin fixation) to 18.5 ± 1.41 ms at day 566 (p<0.001). Raw T2 values were therefore adjusted to correct for this fall over time. Myocardial R2 was correlated with iron concentration [Fe] (R2 0.566, p<0.001), but the correlation was stronger between LnR2 and Ln[Fe] (R2 0.790, p<0.001). The relation was [Fe] = 5081•(T2)-2.22 between T2 (ms) and myocardial iron (mg/g dry weight). Analysis of T1 proved challenging with a dichotomous distribution of T1, with very short T1 (mean 72.3 ± 25.8 ms) that was independent of iron concentration in all hearts stored in formalin for greater than 12 months. In the remaining hearts stored for <10 weeks prior to scanning, LnR1 and iron concentration were correlated but with marked scatter (R2 0.517, p<0.001). A linear relationship was present between T1 and T2 in the hearts stored for a short period (R2 0.657, p<0.001). CONCLUSION: Myocardial T2 correlates well with myocardial iron concentration, which raises the possibility that T2 may provide additive information to T2* for patients with myocardial siderosis. However, ex-vivo T1 measurements are less reliable due to the severe chemical effects of formalin on T1 shortening, and therefore T1 calibration may only be practical from in-vivo human studies.

The importance of specialist cardiac histopathological examination in the investigation of young sudden cardiac deaths.

AIMS: Post-mortem examination of the heart in young sudden cardiac death (SCD) is vital as the underlying aetiology is often an inherited cardiac disease with implications for surviving relatives. Our aim is to demonstrate the improvement in diagnostic quality offered by a specialist cardiac pathology service established to investigate SCD with fast-track reporting on hearts sent by pathologists in cases of SCD. METHODS AND RESULTS: A tertiary centre prospective observational study was conducted. Detailed histopathological examination was performed in a tertiary centre specialized in the investigation of cardiac pathology in SCD. Hearts from 720 consecutive cases of SCD referred by coroners and pathologists from 2007 to 2009 were included. A comparison was drawn with diagnoses from referring pathologists. Most SCDs occurred in males (66%), with the median age being 32 years. The majority (57%) of deaths occurred at home. The main diagnoses were a morphologically normal heart (n = 321; 45%), cardiomyopathy (n = 207, 29%), and coronary artery pathology (n = 71; 10%). In 158 out of a sample of 200 consecutive cases, a cardiac examination was also performed by the referring pathologist with a disparity in diagnosis in 41% of the cases (κ = 0.48). Referring pathologists were more inclined to diagnose cardiomyopathy than normality with only 50 out of 80 (63%) normal hearts being described correctly. CONCLUSION: Expert cardiac pathology improves the accuracy of coronial post-mortem diagnoses in young SCD. This is important as the majority of cases may be due to inherited cardiac diseases and the autopsy guides the appropriate cardiological evaluation of blood relatives for their risk of sudden death.

Sudden cardiac death with autopsy findings of uncertain significance: potential for erroneous interpretation.

BACKGROUND: The sudden death of young individuals is commonly attributed to inherited cardiac disorders, and familial evaluation is advocated. The identification of pathognomonic histopathologic findings, or the absence of cardiac pathology (sudden arrhythmic death syndrome [SADS]) at postmortem, directs familial evaluation targeting structural disorders or primary arrhythmogenic syndromes, respectively. In a proportion of autopsies, structural abnormalities of uncertain significance are reported. We explored the hypothesis that such sudden cardiac deaths represent SADS. METHODS AND RESULTS: Families (n=340) of index cases of sudden cardiac deaths who underwent postmortem evaluation were evaluated in specialist cardiogenetics clinics. Families in whom the deceased exhibited structural abnormalities of uncertain significance (n=41), such as ventricular hypertrophy, myocardial fibrosis, and minor coronary artery disease, were included in the study. Results were compared with 163 families with normal postmortem (SADS). Relatives underwent comprehensive cardiac evaluation. Twenty-one families (51%) with autopsy findings of uncertain significance received a diagnosis based on the identification of an inherited cardiac condition phenotype in ≥1 relatives: 14 Brugada syndrome; 4 long-QT syndrome; 1 catecholaminergic polymorphic ventricular tachycardia; and 2 cardiomyopathy. A similar proportion of families (47.2%) received a diagnosis in the SADS cohort (P=0.727). An arrhythmogenic syndrome was the predominant diagnosis in both cohorts (46% versus 45%; P=0.863). CONCLUSIONS: Familial evaluation after sudden cardiac deaths with autopsy findings of uncertain significance identified a similar proportion of primary arrhythmogenic syndromes to a contemporary series of SADS. Our study highlights the need for accurate interpretation of autopsy findings to avoid erroneous diagnoses, with potentially devastating implications.

Myocardial infarction with normal coronaries: an autopsy perspective.

AIM: To analyse postmortem cases of myocardial infarction (MI) with normal coronary arteries in terms of patient characteristics, features of the MI and risk factors. METHODS: This retrospective non-case controlled study was carried out at a specialist cardiac pathology department at a tertiary cardiac referral centre. Cases of histologically confirmed MI and normal coronary arteries during the period 1996-2010 were identified and analysed for the presence of risk factors. RESULTS: Nineteen cases of histologically confirmed MI and normal coronary arteries were identified with a similar gender ratio 1:1.1 (male:female) and mean age of 33 ± 12 years (range 14-58). All patients died suddenly. The location of the infarct was variable, with left anterior descending artery territory being the single most prevalent (47%). Risk factors were identified in the majority of cases (n=14), with some cases experiencing more than one association, including alcohol and/or predominately class A drug use (n=7), including cocaine, inflammation (n=2), hypercoagulable state (n=3) and exertion (n=2). CONCLUSIONS: Current data regarding prognosis in MI with normal coronary arteries suggests a favourable outcome in the context of major cardiovascular events. No large series of fatal cases have been reported. This study highlights that this entity can be fatal and its prognosis may be less favourable than currently considered. This autopsy series also demonstrates that the causation of MI with normal coronary arteries is complex and multifactorial, including a history of alcohol and/or drug use. It also highlights the importance of accurate epidemiological data from referring pathologists.

Sudden cardiac death caused by coronary vasculitis.

Coronary vasculitis is a rare and diagnostically challenging cause of sudden cardiac death (SCD). There are currently no large-scale series on this rare entity. A retrospective non-case-control observational study of SCD with coronary vasculitis referred to a tertiary cardiac pathology referral centre at the National Heart and Lung Institute at the Royal Brompton Hospital between 1996 and 2010 was completed. Ten cases of SCD with coronary artery vasculitis were retrieved from a database of 1,980 SCD cases (0.5%) with a 1:1 male/female ratio; median age was 39 years and range 15-71 years. Six deaths occurred in hospital following symptoms or cardiac arrest in the community; the remaining died at rest at home (n = 4). Appearances ranged from aneurysms of the coronary artery to occlusive lesions mimicking atheroma or masses imitating tumour. Types of vasculitis detected were: eosinophilic (n = 5), two associated with Churg-Strauss syndrome; lymphoplasmacytic vasculitis (n = 4); and idiopathic giant cell arteritis (n = 1). This study shows coronary vasculitis as a rare cause of SCD with a variable macroscopic and microscopic presentation that pathologists need to be aware of.

On T2* magnetic resonance and cardiac iron.

BACKGROUND: Measurement of myocardial iron is key to the clinical management of patients at risk of siderotic cardiomyopathy. The cardiovascular magnetic resonance relaxation parameter R2* (assessed clinically via its reciprocal, T2*) measured in the ventricular septum is used to assess cardiac iron, but iron calibration and distribution data in humans are limited. METHODS AND RESULTS: Twelve human hearts were studied from transfusion-dependent patients after either death (heart failure, n=7; stroke, n=1) or transplantation for end-stage heart failure (n=4). After cardiovascular magnetic resonance R2* measurement, tissue iron concentration was measured in multiple samples of each heart with inductively coupled plasma atomic emission spectroscopy. Iron distribution throughout the heart showed no systematic variation between segments, but epicardial iron concentration was higher than in the endocardium. The mean ± SD global myocardial iron causing severe heart failure in 10 patients was 5.98 ± 2.42 mg/g dry weight (range, 3.19 to 9.50 mg/g), but in 1 outlier case of heart failure was 25.9 mg/g dry weight. Myocardial ln[R2*] was strongly linearly correlated with ln[Fe] (R²=0.910, P<0.001), leading to [Fe]=45.0×(T2*)⁻¹·²² for the clinical calibration equation with [Fe] in milligrams per gram dry weight and T2* in milliseconds. Midventricular septal iron concentration and R2* were both highly representative of mean global myocardial iron. CONCLUSIONS: These data detail the iron distribution throughout the heart in iron overload and provide calibration in humans for cardiovascular magnetic resonance R2* against myocardial iron concentration. The iron values are of considerable interest in terms of the level of cardiac iron associated with iron-related death and indicate that the heart is more sensitive to iron loading than the liver. The results also validate the current clinical practice of monitoring cardiac iron in vivo by cardiovascular magnetic resonance of the midseptum.

Impaired dendritic-cell homing in vivo in the absence of Wiskott-Aldrich syndrome protein.

Regulated migration and spatial localization of dendritic cells (DCs) are critical events during the initiation of physiologic immune responses and maintenance of tolerance. Here we have used cells deficient in the Wiskott-Aldrich syndrome protein (WASp) to demonstrate the importance of dynamic remodeling of the actin cytoskeleton for these trafficking processes to occur in vitro and in vivo. On fibronectin-coated surfaces, WASp-null immature murine DCs exhibited defects both of attachment and detachment, resulting in impaired net translocation compared with normal cells. The chemokinetic response to CCL21, which is critical for normal lymphatic trafficking, was also abrogated in the absence of WASp. In vivo in both fluorescein isothiocyanate (FITC) and oxazolone contact hypersensitivity models, WASp-null Langerhans cell (LC) migration was compromised, as judged by exit from the skin as well as by homing to the draining lymph node (LN). Furthermore, following systemic challenge with lipopolysaccharide (LPS) or toxoplasma-derived antigen, WASp-null DCs showed incomplete redistribution to T-cell areas in the spleen. Instead, they were retained ectopically in the marginal zone. DC trafficking in vivo is therefore dependent on a normally regulated actin cytoskeleton, which performs an essential function during maintenance of physiologic immunity and when disturbed may contribute significantly to the immunopathology of Wiskott-Aldrich Syndrome.