Peter Rask

Feature Extraction for Systolic Heart Murmur Classification

Heart murmurs are often the first signs of pathological changes of the heart valves, and they are usually found during auscultation in the primary health care. Distinguishing a pathological murmur from a physiological murmur is however difficult, why an “intelligent stethoscope” with decision support abilities would be of great value. Phonocardiographic signals were acquired from 36 patients with aortic valve stenosis, mitral insufficiency or physiological murmurs, and the data were analyzed with the aim to find a suitable feature subset for automatic classification of heart murmurs. Techniques such as Shannon energy, wavelets, fractal dimensions and recurrence quantification analysis were used to extract 207 features. 157 of these features have not previously been used in heart murmur classification. A multi-domain subset consisting of 14, both old and new, features was derived using Pudil’s sequential floating forward selection (SFFS) method. This subset was compared with several single domain feature sets. Using neural network classification, the selected multi-domain subset gave the best results; 86% correct classifications compared to 68% for the first runner-up. In conclusion, the derived feature set was superior to the comparative sets, and seems rather robust to noisy data.

Parasympathetic dysfunction in hypertrophic cardiomyopathy assessed by heart rate variability: comparison between short-term and 24-h measurements

In this study, we evaluate cardiac autonomic function in hypertrophic cardiomyopathy (HCM) by assessing heart rate variability (HRV), comparing a short‐term laboratory method with an ambulatory (24‐h) method, in patients with and without beta‐blockade. Reduced HRV is a risk factor for adverse events in some cardiac diseases, but is not a proven risk indicator in HCM. Analysis of HRV has been based on either short‐ or long‐term electrocardiographic recordings and previous studies in HCM have shown conflicting results. There is no consensus on which method to prefer, and we evaluate, for the first time, both short‐ and long‐term analyses in patients with HCM. Long‐ and short‐term HRV analyses were performed in 43 patients with HCM. They were divided in two groups, 22 patients on beta‐blockade and 21 non‐treated patients. As controls, 121 healthy subjects were used. Young patients without beta‐blockade showed a reduction in HRV parameters reflecting parasympathetic function, both in the short‐ and long‐term registrations, which was attenuated by beta‐blockade. Parasympathetic autonomic regulation was found to be impaired in young patients with HCM. This may be of clinical relevance as abnormal autonomic function might be a substrate for malignant dysrhythmias. The impairment was attenuated by beta‐blockade, which might indicate a clinically useful effect. We also show that short‐ and long‐term methods yield similar results, suggesting that a short‐term registration might be sufficient to assess HRV in patients with HCM.

Separating the left cardiac ventricle from the atrium in short axis MR images using the equation of the atrioventricular plane

Short axis (SA) images obtained from cardiac magnetic resonance imaging are used to advantage in the calculation of important clinical parameters such as the ejection fraction and stroke volume (SV). A prerequisite for these calculations is the separation of the left ventricle and the left atrium. When only using the information seen in the SA images this separation can be a source of error due to the through‐plane motion of the basal part of the left ventricle.

Left and right ventricular systolic long-axis function and diastolic function in patients with takotsubo cardiomyopathy

Aims:  Takotsubo cardiomyopathy is characterized by apical wall motion abnormalities without coronary stenosis. Limited information is available on the genesis of the underlying reversible contractile disorder. Our objective in this prospective study was to investigate biventricular changes in systolic long‐axis function and diastolic parameters in the acute phase and after recovery.

Atrial function after epicardial microwave ablation in patients with atrial fibrillation.

Objectives. To study epicardial microwave ablation of concomitant atrial fibrillation and its effects on heart rhythm and atrial function during follow-up. Design. The study included 20 open-heart surgery patients with concomitant atrial fibrillation. Transthoracic echocardiography with flow and tissue Doppler recordings was performed preoperatively and at 6 months postoperatively. Blood samples were obtained preoperatively and postoperatively for analysis of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and amino terminal precursor of brain natriuretic peptide (NT-proBNP). Results. Fourteen of 19 patients (74%) were in sinus rhythm with no antiarrhythmic drugs at 12 months. All patients in sinus rhythm had preserved left and right atrial-filling waves through atrioventricular valves during atrial contraction. Tissue velocity echocardiography on patients in sinus rhythm showed preserved atrial wall velocities, atrial strain, and atrial strain rate. Levels of natriuretic peptides tended to decrease in patients with stable sinus rhythm at one year compared to patients in atrial fibrillation. Conclusions. Epicardial microwave ablation results in sinus rhythm in a majority of patients and seems to preserve atrial mechanical function.

Serial assessment of variability in heart rate in children with the Fontan circulation.

Autonomic nervous control of the heart can be studied by analysing variability in heart rate. Although earlier studies have shown reduced variability in patients with the Fontan circulation, we are not aware of any previous study examining longitudinal changes in such children. We have examined 13 patients who had undergone total cavopulmonary connection, and 37 healthy controls matched for age and gender. The examinations included complete echocardiography, and 24-hour ambulatory electrocardiogram for analysis of the parameters for variability in heart rate. After the Fontan procedure, three follow-up examinations were performed at a mean of 4.4 years, 5.6 and 7.2 years. Reduced variability was found in those with the Fontan circulation. A significant difference was found between patients and their controls with respect to high-frequency power at the second, p equal to 0.05, and third, p equal to 0.03, examination. The ratio of low-to-high-frequency components progressively increased in those with the Fontan circulation, a phenomenon that led to a significant difference, p equal to 0.03, at the third examination. Our study shows that, in patients with the Fontan circulation, routine ambulatory electrocardiographic monitoring including analysis of variability in heart rate, detects over time a progressive sympatovagal imbalance.

Serum apolipoproteins, apoB/apoA-I ratio and objectively measured physical activity in elderly

Abstract Objectives. Several studies have suggested that subjectively reported physical activity is associated with favorable apolipoproteins and apoB/apoA-I ratio but this association has not been studied much in elderly, and seldom with objective methods. The specific aim of the current study was to increase our understanding of the association between objectively measured physical activity, and apolipoproteins and apoB/apoA-I ratio in elderly subjects. Design. In a long-term follow-up of coronary artery bypass graft surgery patients, a total of 89 subjects (55–88 years old) were recruited. Peak oxygen uptake was measured by ergospirometry and physical activity by accelerometry. Subjects were divided into two groups based on their activity levels (i.e. more or less than 30 minutes of moderate activity per day). Results. Only 26% (23/89) of participants achieved the recommended 30 min/day of moderate intensity activity. Objectively measured physical activity was associated with higher apolipoprotein A-I levels and smaller apoB/apoAI ratio and lower body mass index, whereas no significant association with apolipoprotein B was observed. Conclusion. The significant association of objectively measured physical activity with favorable apolipoprotein A-I levels and a apoB/apoA-I ratio stresses the importance of being physically active.

Flow and peak velocity measurements in patients with aortic valve stenosis using phase contrast MR accelerated with k-t BLAST

OBJECTIVE To investigate the accuracy of velocity measurements in patients with aortic valve stenosis using phase contrast (PC) imaging accelerated with SENSE (Sensitivity Encoding) and k-t BLAST (Broad-use Linear Acquisition Speed-up Technique). METHODS Accelerated quantitative breath hold PC measurements, using SENSE and k-t BLAST, were performed in twelve patients whose aortic valve stenosis had been initially diagnosed using echocardiography. Stroke volume (SV) and peak velocity measurements were performed on each subject in three adjacent slices using both accelerating methods. RESULTS The peak velocities measured with PC MRI using SENSE were -8.0±9.5% lower (p<0.01) compared to the peak velocities measured with k-t BLAST and the correlation was r=0.83. The stroke volumes when using SENSE were slightly higher 0.4±17.1 ml compared to the SV obtained using k-t BLAST but the difference was not significant (p>0.05). CONCLUSIONS In this study higher peak velocities were measured in patients with aortic stenosis when combining k-t BLAST with PC MRI compared to PC MRI using SENSE. A probable explanation of this difference is the higher temporal resolution achieved in the k-t BLAST measurement. There was, however, no significant difference between calculated SV based on PC MRI using SENSE and k-t BLAST, respectively.

Estimation of Ejection Fraction and Stroke Volume Using Single- and Biplane Magnetic Resonance Imaging of the Left Cardiac Ventricle

Background: In cardiac magnetic resonance imaging (MRI), left ventricular stroke volume (SV) and ejection fractions (EF) are occasionally calculated using single-plane and biplane ellipsoid models. In previous studies, the calculated SV and EF using single- and biplane ellipsoid models have been compared to reference values calculated from short-axis (SA) images. In these studies, however, it has been emphasized that through-plane motion of the basal SA images represents an important source of error, which may result in incorrect reference values. Purpose: To compare the calculated SV and EF using single-plane and biplane ellipsoid models with SV and EF calculated from SA images in which compensation was made for through-plane motion. Material and Methods: A group of 20 patients who underwent MRI examination were included in the study. SV and EF were calculated using the stack of SA images (which had been compensated for through-plane motion) and compared to the SV and EF calculated according to the single- and biplane ellipsoid models. Results: The mean difference between the single-plane model and the reference was -0.3±6.5 for EF and 7.2±17.1 ml for SV. Corresponding comparison between the biplane method and the reference resulted in a mean difference of 0.3±6.1 for EF and 11.8±14.9 ml for SV. Conclusion: The results from this study show that left ventricular EF can be adequately estimated using the single- and biplane ellipsoid models, while SV tends to be overestimated using both geometrical models.

Assessment of Suspected Aortic Stenosis by Auto Mutual Information Analysis of Murmurs

Mild sclerotic thickening of the aortic valve affects 25% of the population, and the condition causes aortic valve stenosis (AS) in 2% of adults above 65 years. Echocardiography is today the clinical standard for assessing AS. However, a cost effective and uncomplicated technique that can be used for decision support in the primary health care would be of great value. In this study, recorded phonocardiographic signals were analyzed using the first local minimum of the auto mutual information (AMI) function. The AMI method measures the complexity in the sound signal, which is related to the amount of turbulence in the blood flow and thus to the severity of the stenosis. Two previously developed phonocardiographic methods for assessing AS severity were used for comparison, the murmur energy ratio and the sound spectral averaging technique. Twenty-nine patients with suspected AS were examined with Doppler echocardiography. The aortic jet velocity was used as a reference of AS severity, and it was found to correlate with the AMI method, the murmur energy ratio and the sound spectral averaging technique with the correlation coefficient R = 0.82, R = 0.73 and R = 0.76, respectively.