Multiphysics computational models for cardiac flow and virtual cardiography

A multiphysics simulation approach is developed for predicting cardiac flows as well as for conducting virtual echocardiography (ECHO) and phonocardiography (PC) of those flows. Intraventricular blood flow in pathological heart conditions is simulated by solving the three-dimensional incompressible Navier-Stokes equations with an immersed boundary method, and using this computational hemodynamic data, echocardiographic and phonocardiographic signals are synthesized by separate simulations that model the physics of ultrasound wave scattering and flow-induced sound, respectively. For virtual ECHO, a Doppler ultrasound image is reproduced through Lagrangian particle tracking of blood cell particles and application of sound wave scattering theory. For virtual PC, the generation and propagation of blood flow-induced sounds ('hemoacoustics') is directly simulated by a computational acoustics model. The virtual ECHO is applied to reproduce a color M-mode Doppler image for the left ventricle as well as continuous Doppler image for the outflow tract of the left ventricle, which can be verified directly against clinically acquired data. The potential of the virtual PC approach for providing new insights between disease and heart sounds is demonstrated by applying it to modeling systolic murmurs caused by hypertrophic cardiomyopathy.

Assessment of the right ventricle with cardiovascular magnetic resonance at 7 Tesla

BACKGROUND

Functional and morphologic assessment of the right ventricle (RV) is of clinical importance. Cardiovascular magnetic resonance (CMR) at 1.5T has become gold standard for RV chamber quantification and assessment of even small wall motion abnormalities, but tissue analysis is still hampered by limited spatial resolution. CMR at 7T promises increased resolution, but is technically challenging. We examined the feasibility of cine imaging at 7T to assess the RV.

METHODS

Nine healthy volunteers underwent CMR at 7T using a 16-element TX/RX coil and acoustic cardiac gating. 1.5T served as gold standard. At 1.5T, steady-state free-precession (SSFP) cine imaging with voxel size (1.2 x 1.2 x 6) mm3 was used; at 7T, fast gradient echo (FGRE) with voxel size (1.2 x 1.2 x 6) mm3 and (1.3 x 1.3 x 4) mm3 were applied. RV dimensions (RVEDV, RVESV), RV mass (RVM) and RV function (RVEF) were quantified in transverse slices. Overall image quality, image contrast and image homogeneity were assessed in transverse and sagittal views.

RESULTS

All scans provided diagnostic image quality. Overall image quality and image contrast of transverse RV views were rated equally for SSFP at 1.5T and FGRE at 7T with voxel size (1.3 x 1.3 x 4)mm3. FGRE at 7T provided significantly lower image homogeneity compared to SSFP at 1.5T. RVEDV, RVESV, RVEF and RVM did not differ significantly and agreed close between SSFP at 1.5T and FGRE at 7T (p=0.5850; p=0.5462; p=0.2789; p=0.0743). FGRE at 7T with voxel size (1.3 x 1.3 x 4) mm3 tended to overestimate RV volumes compared to SSFP at 1.5T (mean difference of RVEDV 8.2 ± 9.3 ml) and to FGRE at 7T with voxel size (1.2 x 1.2 x 6) mm3 (mean difference of RVEDV 9.3 ± 8.6 ml).

CONCLUSIONS

FGRE cine imaging of the RV at 7T was feasible and provided good image quality. RV dimensions and function were comparable to SSFP at 1.5T as gold standard.

Towards a time-feature independent phonocardiogram segmentation

Delimitation and classification of each heart sound is a rather difficult task. Elevated heart rates, as found in pediatrics and in some adults as well, influence some of the most reliable features used by existing methods. Furthermore, in real life scenarios, cardiologists will not have the time to acquire the signal's length required by some of the existing algorithms, which make us think that different approaches ought to be pursued. This paper presents the work on heart sound segmentation using structural and energy based features. It is an attempt to not rely on features considered crucial to most existing approaches. Yet, it achieves a high sensitivity and specificity comparable to some literature.

[Spectral analysis and LDB based classification of heart sounds with mechanical prosthetic heart valves]

Auscultation, the act of listening for heart sounds to aid in the diagnosis of various heart diseases, is a widely used efficient technique by cardiologists. Since the mechanical prosthetic heart valves are widely used today, it is important to develop a simple and efficient method to detect abnormal mechanical valves. The study on five different mechanical valves showed that only the case of perivalvular leakage could be detected by spectral estimation. Though it is possible to classify different mechanical valves by using time-frequency components of the signal directly, the recognition rate is merely 84%. However, with the improved local discriminant bases (LDB) algorithm to extract features from heart sounds, the recognition rate is 97.3%. Experimental results demonstrated that the improved LDB algorithm could improve classification rate and reduce computational complexity in comparison with original LDB algorithm.

The cardiac malpositions

Dextrocardia was known in the 17th century and was 1 of the first congenital malformations of the heart to be recognized. Fifty years elapsed before Matthew Baillie published his account of complete transposition in a human of the thoracic and abdominal viscera to the opposite side from what is natural. In 1858, Thomas Peacock stated that "the heart may be congenitally misplaced in various ways, occupying either an unusual position within the thorax, or being situated external to that cavity." In 1915, Maude Abbott described ectopia cordis, and Richard Paltauf's remarkable illustrations distinguished the various types of dextrocardia. In 1928, the first useful classification of the cardiac malpositions was proposed, and in 1966, Elliott et al's radiologic classification set the stage for clinical recognition. The first section of this review deals with the 3 basic cardiac malpositions in the presence of bilateral asymmetry. The second section deals with cardiac malpositions in the presence of bilateral left-sidedness or right-sidedness. Previous publications on cardiac malpositions are replete with an arcane vocabulary that confounds rather than clarifies. Even if the terms themselves are understood, inherent complexity weighs against clarity. This review was designed as a guided tour of an unfamiliar subject.

Determination of cardiac reserve in preterm infants

We aimed in this study to determine the cardiac reserve in preterm infants with phonocardiogram. One hundred and fifty-four preterm infants participated in this study. The ratio of the first heart sound to the second heart sound (S1/S2), the ratio of diastolic to systolic duration (D/S) and the cardiac contractility change trend after stimulation (CCCTS) were measured in all infants. The preterm neonatal S1/S2 decreased with increasing gestational age, but the differences between each gestational stage were not significant (p > 0.05), while the D/S significantly increased with increasing gestational age (p < 0.05). After crying induced by vaccination, the D/S was significantly lower than that in quiet state at each gestational stage (p < 0.05). The CCCTS increased with increasing gestational weeks, but the differences between each gestational stage were not significant (p > 0.05).

Cardiac performance in relation to age of onset of menopause

It is well known that post menopausal women are more prone to cardiovascular diseases, osteoporosis and cancer. This study was done to detect the effect of early onset of menopause on the cardiac performance in postmenopausal women. The cardiac functions were evaluated by the noninvasive technique of measuring systolic time intervals (STI) in the form of total electromechanical systolic time (OS2), left ventricular ejection time (LVET), pre-ejection period (PEP) and PEP/LVET ratio. The study included 50 postmenopausal women with age at the onset of menopause ranging from 29 years to 55 years, divided into three groups I, II and III with mean age at onset of menopause being 36.80 +/- 2.97, 43.97 +/- 2.97 and 52.05 +/- 1.61 years, respectively. In group I, there was a highly significant increase in QS2, PEP and PEP/LVET ratio and in group II, there is a significant decrease in LVET with a highly significant increase in PEP and PEP/LVET ratio. This signifies asymptomatic and subclinical cardiac systolic dysfunction in groups I and II as compared to group III. Early onset of menopause could thus be considered as a risk factor for increased cardiovascular morbidity; hence efforts should be made to timely detect and prevent these diseases in the postmenopausal stage.

Analysis of the vascular sounds of the arteriovenous fistula's anastomosis

In this paper, the vascular sounds of the arteriovenous fistula at the anastomosis and five centimeters downstream the anastomosis were analyzed. The analysis of the sounds was based on features extracted from the power spectral density (PSD) and wavelet decomposition. The database consists of 15 recordings at the anastomosis and 15 reference recordings obtained from 15 patients. The results showed that the vascular sounds at the anastomosis can be characterized as an extra energy in the higher frequencies (200-1000 Hz) i.e. higher mean frequency of the PSD than the reference recordings. Moreover, the wavelet decomposition of the anastomosis recordings showed a similar energy pattern, in the finer scales, to that found in studies of arterial and venous stenosis.

Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla

BACKGROUND

To demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms.

RESULTS

ECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34).

CONCLUSIONS

The applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.

Non-invasive estimation of pulmonary capillary wedge pressure at rest and during exercise by electrocardiography, phonocardiography and Doppler echocardiography

Non-invasive estimation of the mean pulmonary capillary wedge pressure was accomplished by simultaneous electrocardiographic, phonocardiographic and continuous wave Doppler echocardiographic recordings. The interval from the onset of the QRS complex to the Doppler determined mitral valve closure (Q-MC) and the interval from the phonocardiographic aortic component of the second heart sound to the Doppler determined mitral valve opening (A2-MO) were measured. The non-invasive registrations were carried out simultaneously with direct measurements of the wedge pressure. In an initial group of 22 patients, a significant correlation was observed between the intervals alone and the wedge pressure, r = 0.60, SEE = +/- 6.9 mmHg, p less than 0.01, for the Q-MC interval and r = -0.70, SEE = 6.2 mmHg, p less than 0.001 for the A2-MO interval. A closer correlation was observed between the ratio Q-MC/A2-MO and the measured wedge pressure, r = 0.93, SEE = +/- 3.1 mmHg, p less than 0.001. The linear regression equation, PCW = 19.5 (Q-MC/A2-MO) + 3.0 (mmHg), was applied prospectively to a second group of 23 patients. Again the relationship between estimated and measured wedge pressure was highly significant, r = 0.90, SEE = +/- 3.1 mmHg, p less than 0.001. Twenty-two patients were also studied during an exercise test, and acceptable non-invasive recordings were obtained in 19 of them. The change in estimated wedge pressure during activity related closely to the change in actual wedge pressure, r = 0.80, SEE = +/- 5.7 mmHg, p less than 0.001. A simplified equation suitable for routine clinical practice, PCW = 24 (Q-MC/A2-MO) (mmHg), yielded almost equally accurate estimates of the wedge pressure over a wide range of pressures. The simplicity and reasonable accuracy of Doppler-assisted estimation of the wedge pressure makes it useful in the evaluation and follow-up of patients with suspected cardiac disorders. The method may assist in evaluating the effects of diagnostic or therapeutic procedures, since it is sufficiently sensitive to detect acute directional changes in wedge pressure.

Severity of aortic stenosis assessed by carotid pulse recordings and phonocardiography

The external carotid pulse, the PCG, and the ECG were studied in 26 adult patients with valvular aortic stenosis whose systolic peak pressure gradients ranged from 18 to 165 mmHg. A significant correlation was found between the rapidity of the pulse upstroke, as measured by the T-time, and the location of the peak of the systolic murmur during ventricular ejection, on the one hand, and the gradient, on the other. The left ventricular ejection time (LVET) related directly and the pre-ejection period (PEP) indirectly with the gradient. There was a signficant inverse relationship between the PEP/LVET quotient and the pressure gradient but this quotient did not classify the patients according to the severity of the stenosis as well as the T-time and the location of the peak of murmur. When a combination of the T-time, the PEP/LVET, and the location of the peak of the murmur was used in each patient, a good discrimination between the patients was achieved. When the pressure gradient was above 50 mmHg, at lease one of the measurements was abnormal and when it exceeded 100 mmHg, at least two measurements were abnormal. The study further showed that it is possible to separate patients with valvular aortic stenosis from those with hypertrophic obstructive cardiomyopathy lidiopathic hypertrophic subaortic stenosis) or mitral insufficiency on the basis of carotid pulse tracings and PCGs.

The diagnosis of atrial myxomas. Difficulties and pitfalls

Altogether seven patients with the preoperative diagnosis of atrial myxoma were admitted to our hospital in 1968-78 and referred for surgery. In two patients no tumour was found at operation. In one of them the reason for the misinterpretation was severely malformed mitral leaflets. In the other the contrast medium was injected into a pulmonary vein, which caused a contrast defect due to inadequate mixing.

Systolic time intervals in acute myocardial infarction

Systolic time intervals (STI) have been measured in 50 individuals without heart disease. Electromechanical systole (QS2), left ventricular ejection time (LVET) and preejection period (PEP), but not PEP/LVET, were correlated to heart rate (HR). Regression equations were made and used when correcting STI for HR in two groups of patients: a) 51 patients with acute myocardial infarction (AMI) b) 22 patients with chest pains, but no AMI. STI was measured on the first 4 days, on the 7th day, on the day of discharge and at a control about 60 days later. In the AMI group there was a reduction in left ventricular performance from the 1st to the 4th day, and the difference in shortening of LVET was significant (p less than 0.001), while PEP and PEP/LVET increased from the 1st to the 3rd day (p less than 0.001). Between the AMI and the control groups there were significant differences (p less than 0.001) in LVET and PEP/LVET on the 3rd, 4th and 7th day, and in PEP on the 3rd and 4th day. STI was not found to separate clinical groups with heart failure of different severity. The survivors had a lower (p less than 0.05) PEP/LVET on the 1st day than those who died. The various localization of the infarction made no difference in STI. LVET was found to be strongly correlated (p less than 0.001) to the hydroxybutyric dehydrogenase values.

Prevalence of mitral valve prolapse in younger patients with cerebral ischaemic attacks. A blinded controlled study

The association between cerebral ischaemic attacks (CIA) and mitral valve prolapse (MVP) was investigated in a blinded study of 30 consecutive patients with cerebrovascular disease and 30 control patients matched by age, sex, and immediately apparent neurological signs. All patients were below the age of 40 years. Phonocardiography, motion-mode and two-dimensional echocardiography were performed at rest and during various manoeuvres. MVP demonstrated by all three diagnostic modalities was classified as definite and prolapse in at least one but not in all three tests were designated as ambiguous. Regarding the frequency of definite MVP, no statistically significant difference was demonstrated between patients with CIA (3%) and controls (0%). Ambiguous MVP was rather common in patients with cerebrovascular disease (13%) but equally frequent in control patients (20%). It is concluded that MVP does not appear particularly common in Northern Europe in younger patients with cerebral ischaemic events.

Systolic time intervals in cardiac tamponade

Systolic time intervals (STI) have been measured in three patients with cardiac tamponade. The left ventricular ejection time (LVET), the preejection period (PEP) and the ratio PEP/LVET deviated significantly from the normal values. All three parameters improved immediately after pericardiocentesis and aspiration. The total electromechanical systole changed to only a minor degree. Measurement of STI may be a valuable tool in the diagnosis and treatment of cardiac tamponade.

Left atrial myxoma moving from right atrium to left ventricle. Non-invasive and invasive techniques and surgical findings

A case of left atrial myxoma, prolapsing through a large atrial septal defect during systole and through the mitral valve orifice during diastole, is presented. To our knowledge this is the third such case and only the second one in which the diagnosis was made before operation. Echocardiography and phonocardiography were of great value in establishing the diagnosis of left atrial myoxoma; the features before and after operation are presented. In this patient the "swinging" of the tumor in the left atrium and in the left ventricle was echocardiographically visible. Correlations of tumor movement and heart sounds could be made. The diagnosis of a 36% left-to-right shunt on atrial level could not be made with the help of non-invasive techniques alone; cardiac catheterization revealed the shunt. The role of non-invasive techniques and of cardiac catheterization is discussed, together with a review of the relevant literature.

Assessment of left ventricular filling pressure in myocardial infarction using the first derivative of the apexcardiogram

We recorded the apexcardiogram (ACG) and its first derivative (dA/dt) in 24 patients with acute or recent myocardial infarction. From dA/dt, an index I = X 10 dRFW/dS was defined (dRFW and dS = peaks of dA/dt corresponding to the rapid filling wave and to the systolic upstroke of the ACG). A significant correlation was found between I and pulmonary capillary wedge pressure (PCW, mmHg). PCW = 2.3 X I + 6.5 (r = 0.80, p less than 0.001). Normal PCW was found in 15 patients who all had an I less than 2.8. Elevated PCW was found in 9 patients who all had an I greater than 2.8. Thus the ability of I to predict elevated PCW was 100% (95% confidence limit greater than 66.4%). The ability to predict normal PCW was 100% (95% confidence limit greater than 76.2%). No significant correlation was found between I and cardiac index (r = 0.29, p greater than 0.1).

Hemodynamic correlates of the third heart sound and systolic time intervals

Bedside diagnostic tools remain important in the care of patients with heart failure. Over the past two centuries, cardiac auscultation and phonocardiography have been essential in understanding cardiac pathophysiology and caring for patients with heart disease. Diastolic heart sounds (S3 and S4) and systolic time intervals have been particularly useful in this regard. Unfortunately, auscultation skills have declined considerably, and systolic time intervals have traditionally required carotid pulse tracings. Newer technology allows the automated detection of heart sounds and measurement of systolic time intervals in a simple, inexpensive, noninvasive system. Using the newer system, the authors present data on the hemodynamic correlates of the S3 and abnormal systolic time intervals. These data serve as the foundation for using the system to better understand the test characteristics and pathophysiology of the S3 and systolic time intervals, and help to define their use in improving the bedside diagnosis and management of patients with heart failure.

The utility of heart sounds and systolic intervals across the care continuum

Acoustic cardiography is an exciting, new, easy-to-use, modernized technology that incorporates already proven techniques of phonocardiography. Application of acoustic cardiography to clinical practice can improve diagnosis and management of heart failure patients. Its clinical use should help address some of the need for robust, inexpensive, and widely accessible technology for proactive heart failure diagnosis and management. Acoustic cardiographically recorded measurements have been correlated with both cardiac catheterization and echocardiographically determined hemodynamic parameters. Heart sounds captured by acoustic cardiograms have proven to assist clinicians in assessing dyspneic patients in the emergency department by utilizing the strong specificity of an S3 for detecting acute decompensated heart failure. Acoustic cardiography offers a cost-efficient, easy-to-use method to optimize the devices used in cardiac resyncronization therapy. The rapidly and easily obtainable information gathered by acoustic cardiography should foster its more widespread use in diagnosis and treatment of heart failure, including cardiac resyncronization therapy device optimization.