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.

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.

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.

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.

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.

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.