Mitral Annular Disjunction in Idiopathic Ventricular Fibrillation Patients: Just a Bystander or a Potential Cause?

AIMS

Previously, we demonstrated that inferolateral mitral annular disjunction (MAD) is more prevalent in patients with idiopathic ventricular fibrillation (IVF) than in healthy controls. In the present study, we advanced the insights into the prevalence and ventricular arrhythmogenicity by inferolateral MAD in an even larger IVF cohort.

METHODS AND RESULTS

This retrospective multicentre study included 185 IVF patients (median age 39 [27, 52] years, 40% female). Cardiac magnetic resonance images were analysed for mitral valve and annular abnormalities and late gadolinium enhancement. Clinical characteristics were compared between patients with and without MAD. MAD in any of the 4 locations was present in 112 (61%) IVF patients and inferolateral MAD was identified in 24 (13%) IVF patients. Mitral valve prolapse (MVP) was found in 13 (7%) IVF patients. MVP was more prevalent in patients with inferolateral MAD compared with patients without inferolateral MAD(42% vs. 2%, p < 0.001). Proarrhythmic characteristics in terms of a high burden of premature ventricular complexes (PVC) and non-sustained ventricular tachycardia (VT) were more prevalent in patients with inferolateral MAD compared to patients without inferolateral MAD (67% vs. 23%, p < 0.001 and 63% vs 41%, p = 0.046, respectively). Appropriate implantable cardioverter defibrillator therapy during follow-up was comparable for IVF patients with or without inferolateral MAD (13% vs. 18%, p = 0.579).

CONCLUSION

A high prevalence of inferolateral MAD and MVP is a consistent finding in this large IVF cohort. The presence of inferolateral MAD is associated with a higher PVC burden and non-sustained VTs. Further research is needed to explain this potential interplay.

Interpretable uncertainty estimation for automated triage of 12-lead electrocardiogram using deep convolutional neural networks

Background

Interpretation of electrocardiograms (ECGs) using artificial intelligence (AI) has shown very promising results recently, such as comprehensive triage of ECGs. Despite this progress, remarkably few of these AI algorithms have been implemented in clinical practice. Mayor challenges before safe widespread implementation is possible, are uncertainty estimation and interpretability. Without these, algorithms are forced to always provide a diagnosis or prediction. When the algorithm has never seen such an ECG before or when it is noisy or contains a difficult or ambiguous case, this could lead to unrecognized erroneous results.

Purpose

We propose a novel deep neural network (DNN) architecture that is able to overcome both the interpretability and uncertainty estimation challenges in automated diagnosis of ECGs.

Methods

A dataset with 320.000 raw 10s 12-lead ECGs was used to train and validate the DNN in separate 90:10 splits. All ECGs were interpreted by a physician and these free-text annotations were translated into 6 categories from normal to acute based on how quickly a cardiologist needs to be consulted.

Using a novel variational autoencoder DNN, the ECG is compressed into a latent space with 64 parameters. In the compressed space, each category has a separate distribution, instead of a single distribution for the whole dataset.

For clinical use, the ECG is represented in the compressed space and the category prior distribution that is the most likely to produce the input ECG representation is the predicted category. The smaller the probability of generating the data point under any of the known categories, the more uncertain the prediction. The compressed space is reduced using principal component analysis (PCA) to visualize where the input is represented in the compressed landscape.

Performance of the uncertainty estimation is assessed in the validation set by ranking the uncertainty in 10 bins from highest to lowest and comparing with the accuracy.

Results

We demonstrate that the accuracy of the algorithm decreases for ECGs where the model is more uncertain about its predictions (Figure 1). Prediction accuracies range from 90% for the ECGs where the algorithm is most certain, to 50% where it is most uncertain. The PCA of the latent space appears to be able to visually represent the categories in the latent space (Figure 2). Moreover, it indicates whether the new ECG belongs to a known category, the algorithm is doubting between categories or the ECG belongs to none of the categories.

Conclusion

The proposed novel method is promising in estimating uncertainty in an interpretable way, which could allow for safer implementation of AI-based ECG interpretation. Further research is needed to improve the baseline performance of the model, to compare to existing methods and to examine the detection of noisy or new ECGs. The interpretability can be further extended to highlight the uncertain regions on the ECGs.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): ZonMw Figure 1. Uncertainty versus accuracyFigure 2. Representation of ECG

Prevalence of mitral annulus disjunction and mitral valve prolapse in a multicenter cohort of idiopathic ventricular fibrillation patients

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

Background

Idiopathic ventricular fibrillation (IVF) is diagnosed in patients with sudden onset of ventricular fibrillation of which the origin is not identified after extensive evaluations. Recent studies suggest an association between mitral annulus disjunction (MAD), mitral valve prolapse (MVP) and ventricular arrhythmias[1,2]. The prevalence of MAD and MVP in IVF patients in this regard, is not well established.

Purpose

To explore prevalence of MAD and MVP in IVF patients.

Methods

In this retrospective multicenter cohort study, Cardiac Magnetic Resonance images from IVF patients (i.e., negative for ischemia, cardiomyopathy and channelopathies) and matched control subjects were analyzed for MAD (≥2mm) and MVP (&gt;2mm).

Results

In total, 71 IVF patients (mean age 39, 59% male) and 71 controls (mean age 41, 58% male) were included. MAD in the inferolateral wall was more prevalent in IVF patients versus healthy controls (6 [10%] vs. 1 [1%], p = 0.035). MVP was only seen in IVF patients and not in controls (4 [7%] vs. 0 [0%], p = 0.037). MVP was observed both in IVF patients with (n = 3) and without (n = 1) MAD. Patients with MAD did not show papillary muscle fibrosis. Four (67%) patients with MAD showed frequent ventricular ectopy from the basal myocardial region.

Conclusion

Inferolateral MAD and MVP were significantly more prevalent in IVF patients compared to healthy controls (figure). This is in line with previous studies suggesting a correlation between mitral valve disease and IVF. Our findings support further exploration of the pathophysiological mechanisms underlying a subset of IVF that associates with MAD and MVP.

Novel use of repolarization parameters in electrocardiographic imaging to uncover arrhythmogenic substrate

BACKGROUND

Measuring repolarization characteristics is challenging and has been reserved for experienced physicians. In electrocardiographic imaging (ECGI), activation-recovery interval (ARI) is used as a measure of local cardiac repolarization duration. We hypothesized that repolarization characteristics, such as local electrogram morphology and local and global dispersion of repolarization timing and duration could be of significance in ECGI.

OBJECTIVE

To further explore their potential in arrhythmic risk stratification we investigated the use of novel repolarization parameters in ECGI.

MATERIALS AND METHODS

We developed and compared methods for T-peak and T-end detection in reconstructed potentials. All methods were validated on annotated reconstructed electrograms (EGMs). Characteristics of the reconstructed EGMs and epicardial substrate maps in IVF patients were analyzed by using data recorded during sinus rhythm. The ECGI data were analyzed for EGM morphology, conduction, and repolarization.

RESULTS

We acquired ECGI data from 8 subjects for this study. In all patients we evaluated four repolarization parameters: Repolarization time, T-wave area, Tpeak-Tend interval, and T-wave alternans. Most prominent findings were steep repolarization time gradients in regions with flat EGMs. These regions were also characterized by low T-wave area and large differences in Tpeak-Tend interval.

CONCLUSIONS

Measuring novel repolarization parameters in reconstructed electrograms acquired with ECGI is feasible, can be done in a fully automated manner and may provide additional information on underlying arrhythmogenic substrate for risk stratification. Further studies are needed to investigate their potential use and clinical application.

Life-long tailoring of diagnosis and management of patients with idiopathic ventricular fibrillation-future perspectives in research

The diagnosis and management of idiopathic ventricular fibrillation is challenging, as it requires extensive diagnostic testing and offers few curative options due to unknown underlying disease. The resulting population is a heterogeneous group of patients with a largely unknown natural history. Structural patient characterisation, follow-up and innovations in diagnostic testing can improve our understanding of the disease mechanisms of idiopathic ventricular fibrillation, detect underlying disease during follow-up and aid in therapeutic management. Recently, initiatives have been launched in the Netherlands to investigate the role of high-resolution non-invasive electrocardiographic imaging and genetic and familial screening in idiopathic ventricular fibrillation.

Expression of a transgene encoding mutant p193/CUL7 preserves cardiac function and limits infarct expansion after myocardial infarction

BACKGROUND

Transgenic mice expressing the dominant interfering p193 protein in cardiomyocytes (MHC-1152stop mice) exhibit an induction of cell cycle activity and altered remodelling after experimental myocardial infarction (MI).

OBJECTIVE

To determine whether the altered remodelling results in improved cardiac function in the MHC-1152stop mice after MI, as compared with non-transgenic mice.

METHODS

MHC-1152stop mice and non-transgenic littermates were subjected to experimental MI via permanent occlusion of the coronary artery. Infarct size was determined at 24 h and at 4 weeks after MI, and left ventricular pressure-volume measurements were performed at 4 weeks after MI in infarcted and sham-operated animals.

RESULTS

Infarct size in MHC-1152stop mice and non-transgenic littermates was not statistically different at 24 h after MI, as measured by tetrazolium staining. Morphometric analysis showed that infarct scar expansion at 4 weeks after MI was reduced by 10% in the MHC-1152stop mice (p<0.05). No differences in cardiac function were detected between sham-operated MHC-1152stop mice and their non-transgenic littermates. However, at 4 weeks after MI, the ventricular isovolumic relaxation time constant (tau) was decreased by 19% (p<0.05), and the slope of the dP/dt(max)-EDV relationship was increased 99% (p<0.05), in infarcted MHC-1152stop mice as compared with infarcted non-transgenic littermates.

CONCLUSION

Expression of the dominant interfering p193 transgene results in a decrease in infarct scar expansion and preservation of myocardial function at 4 weeks after MI. Antagonism of p193 activity may represent an important strategy for the treatment of MI.

[High time for a total ban on smoking in the hotel, restaurant and catering industry: the arguments are mounting]

Active and passive smoking are well-known causes of disease, including respiratory and cardiovascular disease and cancer. In 2004 the Dutch government introduced new legislation to regulate smoking in the workplace. However, smoking is still allowed in hotels, bars and restaurants, despite the fact that two-thirds of the Dutch population support a total ban on smoking in public places. Several other European countries and American states have banned smoking in public places. Studies performed in these regions show that the new smoking regulations have had no negative economic effects. Moreover, various studies have shown that smoking bans have a positive impact on public health, even in the short-term, including a significant decrease in respiratory and cardiovascular disease. There is therefore no reason to continue to exclude hotels, bars and restaurants from the smoking ban in all public places in The Netherlands.

New and viable cells to replace lost and malfunctioning myocardial tissue

The use of stem cells for cardiac repair is a promising opportunity for developing new treatment strategies as the applications are theoretically unlimited and lead to actual cardiac tissue regeneration. Human embryonic stem cells were only recently cloned and their capacity to differentiate into true cardiomyocytes makes them in principle an unlimited source of transplantable cells for cardiac repair, although practical and ethical constraints exist. Also, the study of embryonic stem cells and their differentiation into cardiomyocytes will bring forth new insights into the molecular processes involved in cardiomyocyte-development and -proliferation, which could lead to the development of other strategies to augment in vivo cardiomyocyte numbers. On the other hand, somatic stem cells are alternative cell sources that can be used for cell transplantation purposes. They do not evoke ethical issues and bear less ethical constraints. However, they also appear to be much more restricted in their differentiation potential than the embryonic stem cells. Here we discuss the use of both cell types, embryonic and somatic stem cells, in relation with their importance for the clarification of cardiomyocyte-development and their possible usefulness for clinical therapy.

[Hypertrophic cardiomyopathy: from diagnosis to prevention]

In a 55-year-old man, his two sons aged 32 and 30 years and a 3-year-old grandchild, a gene mutation related to an increased chance of hypertrophic cardiomyopathy was found. The adults had complaints of cardiac arrhythmias varying from dizziness to cardiac arrest and received medication; a defibrillator was also implanted in the case of the sons. Familial hypertrophic cardiomyopathy can be diagnosed in an early stage with DNA screening methods. At that time 'patients' (carriers) often do not exhibit symptoms. This offers the possibility of taking therapeutic measures to prevent or slow down the disease process. However, the scientific basis for preventive therapy is inadequate, so that medical-ethical dilemmas arise which can affect the decision-making process with respect to genetic testing. Additional research must lead to satisfactory preventive therapies, so that in the future the genetic diagnosis 'hypertrophic cardiomyopathy' can be effectively translated into disease prevention.

The human adult cardiomyocyte phenotype

AIM

Determination of the phenotype of adult human atrial and ventricular myocytes based on gene expression and morphology.

METHODS

Atrial and ventricular cardiomyocytes were obtained from patients undergoing cardiac surgery using a modified isolation procedure. Myocytes were isolated and cultured with or without serum. The relative cell attachment promoting efficiency of several reagents was evaluated and compared. Morphological changes during long-term culture were assessed with phase contrast microscopy, morphometric analysis and immunocytochemistry or RT-PCR of sarcomeric markers including alpha-actinin, myosin light chain-2 (MLC-2) and the adhesion molecule, cadherin.

RESULTS

The isolation method produced viable rod-shaped atrial (16.6+/-6.0%, mean+/-S.E.; n=5) and ventricular cells (22.4+/-8.0%, mean+/-S.E.; n=5) in addition to significant numbers of apoptotic and necrotic cells. Cell dedifferentiation was characterized by the loss of sarcomeric structure, condensation and extrusion of sarcomeric proteins. Cells cultured with low serum recovered and assumed a flattened, spread form with two distinct morphologies apparent. Type I cells were large, had extensive sarcolemmal spreading, with stress fibers and nascent myofibrils, whilst type II cells appeared smaller, with more mature myofibril organisation and focal adhesions.

CONCLUSION

Characterization of the redifferentiation capabilities of cultured adult cardiac myocytes in culture, provides an important system for comparing cardiomyocytes differentiating from human stem cells and provides the basis for an in vitro transplantation model to study interaction and communication between primary adult and stem cell-derived cardiomyocytes.

Impaired autonomic function predicts dizziness at onset of paroxysmal atrial fibrillation

BACKGROUND

Paroxysmal atrial fibrillation is associated with various symptoms, including dizziness, which presumably reflects hemodynamic deterioration. Given the importance of the autonomic nervous system in mitigating the hemodynamic effect of atrial fibrillation, we hypothesized that autonomic function would be predictive of the severity of dizziness.

METHODS

The study group comprised 73 patients with paroxysmal atrial fibrillation (mean age 54.1 years, 51 males). Forty-three (59%) patients had lone atrial fibrillation. Mean ventricular rate during atrial fibrillation was 99+/-16 beats/min. On average, patients had a 3-year history of one paroxysm per week lasting 2 h. Autonomic function was assessed using autonomic function tests, including noninvasive measurement of baroreflex sensitivity. Head up tilting was used to test vasovagal reactivity. Severity of dizziness at onset of atrial fibrillation was quantified by the patients using a five-point scale (1=none; 2=light; 3=mild; 4=moderate; and 5=severe). Multivariate analysis was performed to identify the independent predictors of the severity of dizziness.

RESULTS

Mean severity of dizziness was 3.36+/-1.65. Multivariate predictors of moderate-to-severe dizziness as opposed to none-to-mild dizziness were a low 30-15 ratio after standing up and low baroreflex sensitivity. Though syncope was never reported nine patients showed a full vasovagal response during head up tilting.

CONCLUSIONS

It is concluded that dizziness in patients with "treated" atrial fibrillation in the setting of none to mild structural heart disease is predicted by impaired autonomic function. Vasovagal reactivity appears not to be involved in this connection.

Quality of life in patients with paroxysmal atrial fibrillation and its predictors: importance of the autonomic nervous system

AIMS

To determine the impact of paroxysmal atrial fibrillation on quality of life and to determine the predictors of quality of life, particularly the role of symptomatology and autonomic function.

METHODS AND RESULTS

The study group comprised 73 patients with paroxysmal atrial fibrillation (mean age 54.1 years, 51 males). On average, patients had a 3-year history of one paroxysm per week lasting 2 h. Quality of life was assessed using the SF-36 (Medical Outcomes Study Short-Form Health Survey) and compared with age-matched controls. Autonomic function was assessed using Holter monitoring with analysis of heart rate variability and autonomic function tests. Symptoms during paroxysms of atrial fibrillation were also scored. Multivariate analysis was performed to identify independent predictors of quality of life. Quality of life scores were markedly lower in patients than in controls in four of the eight subscales (P<0.001): physical role function, emotional role function, vitality and general health. Structural heart disease did not predict quality of life, whereas frequency of paroxysms was predictive only of physical role function. In contrast, autonomic variables (baroreflex-sensitivity, total power (heart rate variability), response to deep breathing, 30-15 ratio (standing up)) were predictive in all four respective subscales (P<0.05), depressed vagal function being predictive of low scores. Symptoms, particularly severe perspiration, were also predictive of low scores (P<0.05).

CONCLUSIONS

This study shows that paroxysmal atrial fibrillation causes significant impairment of quality of life. Further, symptomatology and autonomic function are important predictors of quality of life in this patient group.