Ventricular Outflow Tract Flow Research Articles

In vitro hemodynamic investigation of the embryonic aortic arch at late gestation

This study focuses on the dynamic flow through the fetal aortic arch driven by the concurrent action of right and left ventricles. We created a parametric pulsatile computational fluid dynamics (CFD) model of the fetal aortic junction with physiologic vessel geometries. To gain a better biophysical understanding, an in vitro experimental fetal flow loop for flow visualization was constructed for identical CFD conditions. CFD and in vitro experimental results were comparable. Swirling flow during the acceleration phase of the cardiac cycle and unidirectional flow following mid-deceleration phase were observed in pulmonary arteries (PA), head-neck vessels, and descending aorta. Right-to-left (oxygenated) blood flowed through the ductus arteriosus (DA) posterior relative to the antegrade left ventricular outflow tract (LVOT) stream and resembled jet flow. LVOT and right ventricular outflow tract flow mixing had not completed until ∼3.5 descending aorta diameters downstream of the DA insertion into the aortic arch. Normal arch model flow patterns were then compared to flow patterns of four common congenital heart malformations that include aortic arch anomalies. Weak oscillatory reversing flow through the DA junction was observed only for the Tetralogy of Fallot configuration. PA and hypoplastic left heart syndrome configurations demonstrated complex, abnormal flow patterns in the PAs and head-neck vessels. Aortic coarctation resulted in large-scale recirculating flow in the aortic arch proximal to the DA. Intravascular flow patterns spatially correlated with abnormal vascular structures consistent with the paradigm that abnormal intravascular flow patterns associated with congenital heart disease influence vascular growth and function.

Doppler echocardiogram, oxygen saturation and submaximum capacity of exercise in patients with cystic fibrosis

Study objectives To determine the relationship between pulmonary arterial systolic pressure (PASP) and submaximum capacity of exercise, using the six-minute walk test (6MWT) in patients with cystic fibrosis (CF), and to investigate the relation between echocardiographic findings and results of 6MWT, clinical scores, chest radiograph scores and lung function tests. Design This was a prospective cross-sectional study in patients with CF (16 years and older) with clinical stability, attending the Adult CF Program at the Hospital de Clínicas de Porto Alegre. The patients had Doppler echocardiography and performed a 6MWT. As well as pulmonary function tests and chest roentgenograms, and a clinical score was obtained for all patients. Results The study included 39 patients with a mean age of 23.7 ± 6.3 years. There were no significant correlation between the distance walked and PASP, diameter of the right ventricle (DRV) and pulmonary acceleration time ( p > 0.05). We observed a significant correlation among PASP and the SpO 2 at rest ( r = − 0.73; p < 0.001), SpO 2 at the end of the 6MWT ( r = −0.45; p = 0.006), clinical score ( r = − 0.55; p = 0.001), chest radiograph score ( r = − 0.33; p = 0.049), FEV1 ( r = − 0.63; p < 0.001), and FVC ( r = − 0.55; p = 0.001). Right ventricular outflow tract flow acceleration time (Ac T) was significantly correlated only with the FEV1 ( r = 0.32; p = 0.047). RVD was significantly correlated with SpO 2 at rest ( r = − 0.44; p = 0.005) and clinical score ( r = − 0.38; p = 0.017). The SpO 2 at rest was the single best predictor of PASP and this effect was independent of the relationship between other independent variables ( p = 0.001). The declining pulmonary function was significantly associated with PASP ( p < 0.001), SpO 2 at rest ( p = 0.001), SpO 2 at the end of the 6MWT ( p = 0.007) and difference between peripheral oxygen saturation at resting and at the end of the 6MWT ( p = 0.025). Conclusion The PASP was not significantly correlated with the distance walked during the 6MWT in patients with CF. The PASP was strongly correlated with oxygen status at rest. The SpO 2 at rest was the best predictor of PASP. Also, PASP was strongly correlated with Shwachman–Kulczycki score, FEV 1, and FVC in this population.

Echocardiographic indices in normal German shepherd dogs

Sixty clinically normal German shepherd dogs, 31 males and 29 females, ranging in age from 1 and 5 years and with a body weight ranging from 22 to 37.2 kg, were examined by the two-dimensional mode, M-mode, and Doppler echocardiography. In Doppler mode, the mitral valve flows were obtained, where the aim was to determine the velocity peaks and ratios of the E and A waves and the mitral E wave deceleration time. The velocity peaks were obtained for the tricuspid, pulmonary and aortic valves. On the left ventricular outflow tract flow, the time velocity integral and aortic cross-sectional area was used to calculate the cardiac output. A statistically significant correlation with the body weight was found for the systolic left atrial and diastolic aortic diameter on two-dimensional mode. On M-mode, there was a significant correlation between the body weight and the systolic left atrium and diastolic aortic dimension, systolic and diastolic left ventricular, septal and posterior wall dimensions. Doppler echocardiography showed that there was no significant correlation between the body weight and the mitral, tricuspid, pulmonary and aortic valves flows. These results demonstrate that it is important to know the normal echocardiographic values for German shepherd dogs because there are some characteristics peculiar to this particular breed. The data obtained is expected to be helpful for studies on small animal cardiology.

Chronic renal failure in an English bull terrier with polycystic kidney disease

An entire female English bull terrier, aged five years and one month, was diagnosed with polycystic kidney disease by renal ultrasonography. It had thickening and abnormal motion of the mitral valve on 2D and M mode echocardiography, and left ventricular outflow tract obstruction, characterised by turbulence in the left ventricular outflow tract and elevated aortic blood flow velocity, detected by colour flow and spectral Doppler echocardiography, respectively. Two years later, haematology, serum biochemistry and urinalysis data suggested the presence of compensated renal failure. The dog was euthanased at 10 years and eight months of age, with haematology, serum biochemistry and urinalysis data Indicating decompensated chronic renal failure. Postmortem examination confirmed polycystic kidney disease, chronic renal disease, mitral and aortic valvular myxomatous degeneration, and mixed mammary neoplasia. This case demonstrates that bull terriers with polycystic kidney disease may develop associated chronic renal failure.

Prosthetic mitral regurgitation can be mimicked by Doppler color flow mapping: Avoiding misdiagnosis

Objectives We sought to characterize a region of apparent systolic flow resembling mitral regurgitation (MR) in patients with mechanical disk mitral prostheses as artifact. Background Diagnosing MR in the presence of mechanical prostheses is challenging. Occasionally, important MR is suggested by a substantial region of systolic Doppler color flow in an acoustically shadowed region of the left atrium when, in fact, only trace MR exists. We hypothesized this pseudo-MR is caused by acoustic mirroring of the left ventricular outflow tract (LVOT) flow by sound reflected off the prosthesis, projecting flow into the left atrium because of longer transit time. Methods We reviewed 19 patients with mechanical mitral valves and trace MR by transesophageal echocardiography who had transthoracic echocardiography studies within 1 week (group A), and prospectively studied 22 consecutive patients by transthoracic echocardiography with subtle transducer angulation variation to detect pseudo-MR and characterize it by pulsed Doppler (group B). Results In group A, 12 of 19 patients had evidence of pseudo-MR on review of their transthoracic echocardiograms, absent by transesophageal echocardiography. In group B, this pseudo-MR signal was present in 13 of 22 patients, with velocity and timing by pulsed Doppler comparable with LVOT flow (onset at 125 ± 27 milliseconds vs 135 ± 11 milliseconds from QRS, P = not significant). The angle between the mitral plane and the LVOT, which determines whether this mirroring can occur, was smaller for patients with pseudo-MR. Conclusion Artifactual pseudo-MR is often seen with mechanical mitral prostheses. Its behavior and sensitivity to geometric relationships are consistent with mirroring of LVOT flow. Practically, potential misdiagnosis can be readily avoided by pulsed Doppler sampling, sparing the patient further procedures.

Dobutamine-inducible left ventricular obstruction: head-up tilt and autonomic balance

Background: Dobutamine-inducible left ventricular obstruction lacks a sound clinical meaning. This phenomenon may be related to an abnormal response of the heart to the sympathetic stimulation, and head-up tilt would elicit intraventricular obstruction in patients known to develop it during dobutamine administration, through the synergistic effects of reduced preload, hypercontractility, and reflex increase in the cardiac sympathetic tone. Methods: Twenty-one patients with normal coronaries and available dobutamine stress-echocardiography underwent 60°-head-up tilt on echocardiographic and electrocardiographic monitoring in drug-free and nitroglycerin infusion (0.3 mcg/kg/min) protocols. Twelve patients had (group 1: 7 males, aged 61±7 years), and nine had not (group 2: 3 males, aged 60±9 years) developed left ventricular obstruction during dobutamine stress-echocardiography. Doppler echocardiographic measurements of left ventricular diameters, function and outflow tract flow velocity were performed; power heart rate variability was analysed on short electrocardiographic recordings (low/high frequency ratio); plasma catecholamines were determined at baseline and during the tilt manoeuvres. Results: Intraventricular obstruction did not develop in group 1. There were baseline differences in ventricular dimensions and mitral early-to-late velocity ratio between group 1 and 2, but hemodynamic behaviour during either tilt manoeuvre was similar. Low/high frequency ratio, that was similar at baseline and similarly increased on head-up tilt, increased significantly less on nitroglycerin-tilt in group 1. No difference in plasma catecholamines was found. Conclusions: Reflex cardiovascular adaptive responses as those elicited by passive tilt are not involved in dynamic intraventricular obstruction in dobutamine-inducible obstruction patients, data indicating that left ventricular geometry and hypercontractility are not sufficient pathophysiological determinants.

Doppler mirror image artifacts mimicking mitral regurgitation in patients with mechanical bileaflet mitral valve prostheses.

To characterize the origin and mechanisms of generation of Doppler mirror images in the left atrium observed in patients with mechanical bileaflet mitral valve prosthesis. We hypothesized that these systolic colour Doppler images are artifactual and generated by reflection of the left ventricular outflow tract flow at the leaflet of the mitral valve prosthesis. Fifty patients with mechanical bileaflet mitral valves were prospectively examined by means of transthoracic Doppler-echocardiography. From different apical views, the left atrium was carefully interrogated for systolic colour flow signals, which were further analysed by pulsed wave Doppler. In all patients, a systolic colour Doppler signal was detected in the left atrium. Pulsed wave Doppler analysis revealed a low velocity signal (= mirror image) corresponding to the shape and duration of the left ventricular outflow tract signal. The peak velocities of these mirror images, however, were consistently lower than the velocities obtained from the left ventricular outflow tract. In addition, if paravalvular mitral valve leakage was present, a high velocity signal identical to the duration of mitral regurgitation time was detected outside the ring of the prosthesis. Mirror image artifacts mimicking mitral regurgitation occur in patients with mechanical mitral valves prosthesis. As mirror image artifacts can be specifically identified by analysis of shape. velocity, and duration of pulsed wave Doppler spectra, their identification will help to avoid misinterpretation of both spectral and colour Doppler signals in patients with prosthetic mitral valves.

Validation of the accuracy of both right and left ventricular outflow volume determinations and semiautomated calculation of shunt volumes through atrial septal defects by digital color Doppler flow mapping in a chronic animal model

OBJECTIVESThe aim of the present study was to quantitate shunt flow volumes through atrial septal defects (ASDs) in a chronic animal model with surgically created ASDs using a new semiautomated color Doppler flow calculation method (ACM).BACKGROUNDBecause pulsed Doppler is cumbersome and often inappropriate for color flow computation, new methods such as ACM are of interest.METHODSIn this study, 13 to 25 weeks after ASDs were surgically created in eight sheep, a total of 24 hemodynamic states were studied at a separate open chest experimental session. Electromagnetic (EM) flow probes and meters were used to provide reference flow volumes as the pulmonary and aortic flow volumes (Qpand Qs) and shunt flow volumes (Qpminus Qs). Epicardial echocardiographic studies were performed to image the left and right ventricular outflow tract (LVOT and RVOT) forward flow signals. The ACM method digitally integrated spatial and temporal color flow velocity data to provide stroke volumes.RESULTSLeft ventricular outflow tract and RVOT flow volumes obtained by the ACM method agreed well with those obtained by the EM method (r = 0.96, mean difference = 0.78 ± 1.7 ml for LVOT and r = 0.97, mean difference = −0.35 ± 3.6 ml for RVOT). As a result, shunt flow volumes and Qp/Qsby the ACM method agreed well with those obtained by the EM method (r = 0.96, mean difference = −1.1 ± 3.6 ml/beat for shunt volumes and r = 0.95, mean difference = −0.11 ± 0.22 for Qp/Qs).CONCLUSIONSThis animal study, using strictly quantified shunt flow volumes, demonstrated that the ACM method can provide Qp/Qsand shunt measurements semiautomatically and noninvasively.

Correction of anterior mitral prolapse: Results of chordal transposition

From 1986 to 1992 102 mitral valve repairs were done for mitral regurgitation due to a degenerative disease. Forty-eight patients had an anterior prolapse or prolapse of both leaflets at initial presentation and underwent chordal transposition from the mural leaflet to the anterior leaflet. The corrective procedure was completed by polytetrafluoroethylene or pericardial posterior annuloplasty. Operative mortality was 2.9%, and follow-up (average 22 months) was 100% complete. There were three postreconstruction valve replacements (one earlier and two later) for a probability of freedom from reoperation of 91.5% +/- 5.2% at 3 years. Freedom from all morbidity was 85.5% +/- 5.5% at 3 years. Postoperative echocardiographic studies demonstrated a good mitral valve function: (1) Eighty-seven percent of patients presented no or mild residual regurgitation; (2) transmitral flow indexes were within the norm; (3) left ventricular outflow tract flow was normal in all patients. This study shows that chordal transposition is a safe and effective technique for prolapse of anterior or both leaflets and improves the chances of repair in patients with mitral degenerative disease.

Dynamic changes in left ventricular outflow tract flow velocities after amyl nitrite inhalation in hypertrophic cardiomyopathy

Doppler echocardiography was performed in 21 patients with hypertrophic cardiomyopathy (HC), in nine patients with no evidence of left ventricular (LV) hypertrophy by two-dimensional echocardiography, and in five patients with systemic hypertension and concentric LV hypertrophy. The LV outflow tract (LVOT) peak velocity was recorded by continuous wave Doppler technique at rest and after amyl nitrite inhalation. The LVOT pressure gradient was calculated by the modified Bernoulli equation. A significant increase in heart rate and a drop in systolic blood pressure were observed in all patients after amyl nitrite inhalation; no adverse effects were encountered. The peak LVOT velocity and pressure gradient increased significantly after provocation in all patients, but the increase was much more pronounced in patients with HC (peak LVOT velocity increased from 2.2 ± 0.8 to 4.3 ± 1.0 m/sec and peak gradient increased from 22 ± 17 to 78 ± 36 mm Hg). The Doppler spectral signal in patients with HC demonstrated a characteristic contour, with peak velocity occurring in late systole. However, the observed increase in LVOT peak velocity was not statistically different between treated (with β-blockers and calcium blockers) and untreated patients with HC. We conclude that LVOT peak velocity and pressure gradients in patients with HC can be readily assessed by Doppler echocardiography both at rest and after amyl nitrite inhalation. The dynamic changes in LVOT velocity induced by this provocation have certain characteristic features in obstructive HC but appear to be independent of the medical regimen used, at least in the dosages tested in our study.

Usefulness of color-flow Doppler in diagnosing and in differentiating supracristal ventricular septal defect from right ventricular outflow tract obstruction

Color-flow Doppler is used for special localization of cardiac flows. The transeptal jet in supracristal ventricular septal defect (VSD) is directed toward the pulmonary valve and is often difficult to distinguish from the right ventricular (RV) outflow tract flow. Pulsed- and continuous-wave Doppler can misread the VSD jet as a stenotic lesion in the RV outflow tract. This study describes the color-flow Doppler characteristics of supracristal VSD and determines if color-flow Doppler can differentiate supracristal VSD jets from RV outflow tract flow. The study group comprised 28 patients ranging in age from 3 days to 23 years (mean 6.4), with catheter-diagnosed supracristal VSD in 14, isolated pulmonary valve stenosis in 10 and RV infundibular obstruction in 4. The echocardiographic Doppler and color-flow Doppler data of all patients were reviewed without knowledge of catheterization diagnosis. In all patients with supracristal VSD, colorflow Doppler revealed an abnormal transeptal jet directed toward the pulmonary valve that occurred 5 to 10 ms before RV outflow tract flow was identified. VSD and RV outflow tract jet could be differentiated by pulsed- and continuous-wave Doppler alone in 10 of 14 patients (71%). In 4 patients, differentiation was possible only with color-flow Doppler and electrocardiographic gating. Associated aortic regurgitation, or a fistula, or both, were detected in 6 patients. Pulsed- and continuous-wave Doppler with or without color-flow Doppler correctly identified the level of obstruction in all patients with RV outflow tract lesions (14 of 14). Supracristal VSD jet occurs in early systole and is directed toward the pulmonary valve. Color-flow Doppler is essential for the localization, assessment and accurate echocardiographic differentiation of transeptal jet from RV outflow tract flow in neonates and infants with supracristal VSD.

Doppler Characteristics of Late-diastolic Flow in the Left Ventricular Outflow Tract

This study characterizes the relationship between late-diastolic Doppler detected forward flow in the left ventricular outflow tract and diastolic transmitral flow. Pulsed-wave Doppler interrogation of the left ventricular outflow tract, in a prospective consecutive series (n = 137), revealed the presence of end-diastolic forward flow in 83% of the patients studied. Further quantification of both flow signals was performed in 67 patients. Pulsed-wave mapping demonstrated that peak velocity of the end-diastolic left ventricular outflow tract signal (J wave) was maximal, 2.6 +/- 0.7 cm from the aortic valve anulus, and occurred 48 +/- 34 milliseconds after the peak transmitral atrial velocity flow signal. Peak J velocity ranged from 25 to 118 cm per second and correlated with peak A velocity (r = 0.69, p less than 0.001). Peak J velocity was inversely related to left ventricular end-diastolic dimension (r = -0.53, p less than 0.0001) and left ventricular end-diastolic volume (r = -0.43, p less than 0.004). There was no relationship between J wave velocity and early diastolic filling. We concluded that a late-diastolic forward flow signal is commonly observed in the left ventricular outflow tract. It is a manifestation of transmitral atrial systolic flow in the left ventricular outflow tract and is determined predominantly by peak transmitral atrial velocity and left ventricular size.

Doppler color flow mapping studies of jet formation and spatial orientation in obstructive hypertrophic cardiomyopathy

To help clarify the mechanism of outflow tract obstruction and systolic anterior motion of the anterior leaflet of the mitral valve and their relation to the geometry of the left ventricle, we studies left ventricular outflow tract flow in 20 patients with hypertrophic cardiomyopathy (HCM) using two-dimensional Doppler flow mapping. We compared our results with outflow tract flow in 10 patients with isolated valvular aortic stenosis, (AS) and with those in 10 healthy volunteers. In HCM, a 94- to 145-degree angle (mean 111.4 ± 11.9 degrees) developed between the direction of left ventricular outflow tract flow acceleration and aortic valve outflow, resulting in posterolaterally directed left ventricular outflow jets. The angle of the outflow jet and the peak velocity of the jet measured with continuous wave Doppler (as an indicator of the severity of obstruction) correlated well ( r = −0.81, SEE = 7.8 degrees). Jet narrowing during ejection measured just proximal to the point of systolic anterior motion was 42 ± 11% in HCM and was outflow occurred proximal to systolic anterior motion of the mitral valve, and color M-mode demonstrated temporal and spatial flow acceleration proximal to systolic anterior motion, providing evidence for obstruction at that site. In AS, left ventricular outflow tract jets were more parallel to the axis of aortic outflow (129 to 153 degree, 138.4 ± 8.1 degrees). Jet narrowing was only 8 ± 5% compared to HCM (both p < 0.05), and flow acceleration occurred proximal to the stenotic valve. In normal subjects, turbulent jets were not observed and the angle between left ventricular outflow tract flow and aortic flow was 149.6 ± 2.5 degrees. Our results are consistent with a venturi effect proximal to the mitral valve contributing to the development of systolic anterior motion and outflow tract obstruction, and highlight the importance of ventricular geometry as a determinant of obstruction in HCM.

Noninvasive evaluation of aortic stenosis severity utilizing Doppler ultrasound and electrical bioimpedance

Aortic valve area was calculated noninvasively in 30 patients with aortic stenosis undergoing cardiac catheterization. Continuous wave Doppler ultrasound was employed to estimate the mean transvalvular pressure gradient. The mean left ventricular outflow tract flow velocity and cross-sectional area were determined from pulsed Doppler and two-dimensional ultrasound recordings. Electrical Irans-thoracic bioimpedance cardiography performed simultaneously with the ultrasonic study and repeated at the time of catheterization measured heart rate, systolic ejection period and cardiac output. These noninvasive data permitted calculation of aortic valve area using the Gorlin equation (range 0.21 to 1.75 cm2) and the continuity equation (range 0.25 to 1.9 cm2). Subsequent cardiac catheterization showed valve area to range from 0.21 to 1.75 cm2.The mean Doppler pressure gradient estimate was highly predictive of the gradient measured at catheterization (r = +0.92, SEE = 10). Bioimpedance cardiac output measurements agreed with the average of Fick and indicator dye estimates (r = +0.90, SEE = 0.52). Valve area estimates utilizing continuous wave Doppler ultrasound and electrical bioimpedance were superior (r = +0.91, SEE = 0.12) to estimates obtained utilizing the continuity equation (r = +0.76, SEE = 0.29) and were more reliable in the detection of patients with severe aortic stenosis (9 of 11 versus 6 of 11).These data show that 1) electrical bioimpedance methods accurately estimate cardiac output in the presence of aortic stenosis; 2) the hybridized bioimpedance-Doppler ultrasound method yields accurate estimates of aortic stenosis area; and 3) the speed, accuracy and cost-effectiveness of aortic stenosis evaluation may be unproved by this hybridized approach.