Steve M. Teague

Detection of paradoxical cerebral echo contrast embolization by transcranial Doppler ultrasound.

Contrast echocardiography has been shown to be a sensitive method for detecting patent foramen ovale in embolic stroke, implying paradoxical embolization. However, not all two-dimensional echocardiographic studies are of diagnostic quality, and direct evidence for paradoxical cerebral embolization remains lacking. We addressed these problems by simultaneously using transcranial Doppler ultrasound and contrast echocardiography to compare relative sensitivity and concordance in the detection of right-to-left vascular shunting. Forty-six patients with stroke, transient neurologic defect, or question of atrial septal defect underwent study at rest and during Valsalva strain. Two-dimensional echocardiography detected shunting in 26% at rest and 15% during Valsalva strain, whereas transcranial Doppler study returned rates of 41% and 41%, respectively. Concordance was 82% and 75%, respectively. Discordant studies almost always had evidence of paradoxical contrast embolization by transcranial Doppler and intermediate findings by two-dimensional echocardiography. Transcranial Doppler is a sensitive, unambiguous technique for the detection of anatomic substrates and target organ involvement in patients suspected to have paradoxical cerebral embolization.

Clinically Silent Atrial Septal Defects with Evidence for Cerebral Embolization

The cause of stroke in young patients frequently cannot be established. Eleven consecutive patients, age 50 and younger, had clinical evidence of cerebral embolization. Results of physical, radiographic, electrocardiographic, and two-dimensional echocardiographic examinations were normal in all patients. During normal respiration, eight of the patients had right-to-left shunts at the atrial level shown by microcavitation contrast two-dimensional echocardiography. Six of the eight patients with positive contrast studies had cardiac catheterization. Five of six patients had an atrial septal defect, normal right and left heart pressures, and small right-to-left shunts during a Valsalva strain. Four patients had surgical closure of the defect, which ranged in size from 5 to 10 mm. The remaining patients received anticoagulants. Interatrial communications appear to be common in young patients with stroke, suggesting paradoxical embolization as a possible mechanism. Contrast two-dimensional echocardiography should be done in such patients because it is the only noninvasive technique that reliably finds these defects.

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 transthoracic 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 improved by this hybridized approach.

Doppler echocardiographic profiles in obstructive right and left atrial myxomas

Previous reports have suggested that atrioventricular (AV) flow disturbances accompanying atrial myxomas mimic mitral stenosis. Two patients complaining of orthostatic syncope and positional intolerance had a large right and left atrial myxoma, respectively. Doppler flow records showed abrupt early diastolic flow cessation and normal velocity half-times, unlike AV valve stenosis. Large, obstructing atrial myxomas may behave as ball valves.

Beat-by-beat monitoring of systemic vascular resistance during head-up tilt for assessment of orthostatic stress response

A method is described for noninvasive cardiovascular evaluation of vasovagal syncope. Continuous electrocardiogram, impedance cardiogram, and finger-cuff blood pressure recordings are acquired and analyzed on a beat-by-beat basis for calculation of heart rate, cardiac contractility, cardiac output, mean arterial pressure, and systemic vascular resistance. In a patient with near-syncopal head-upright tilt response, a 200% increase in cardiac contractility 20% decrease in mean arterial pressure, and 66% reduction in systemic vascular resistance was demonstrated. Comprehensive cardiovascular assessment of orthostatic stress response may improve diagnosis and understanding of vasovagal syncope.<<ETX>>

Doppler left ventricular ejection dynamics: Correlation with nuclear ejection indices during exercise

Exercise testing is commonly used in both the diagnosis of coronary artery disease and in assessment of its physiological significance. Stress electrocardiography has a diagnostic sensitivity and specificity of 64% and 93% [1], respectively, using 1.0 mm depression as an ischemic threshold. The sensitivity of exercise testing can be significantly increased by adding radionuclide angiography [2], but exercise nuclear ventriculography is expensive and technically difficult to perform. Two dimensional echocardiography has been used to detect ischemic wall motion abnormalities occurring with exercise, but the success rate of obtaining an optimal study has been disappointing. The use of Doppler echocardiography to interrogate flow in the ascending aorta offers the advantage of a high success rate (81–100%) [3, 4], except in obese subjects and those with hypertrophied neck muscles. In addition, Doppler echocardiography entails little equipment, and can be performed at relatively low cost. Both pulsed and continuous wave systems can be used to analyze maximal acceleration, peak velocity, and systolic velocity integral.

Effects of beta blockade, beta stimulation, and afterload upon Doppler ejection dynamics

Studies of the early phase of ventricular ejection and aortic blood flow primarily have involved pressure and flow measurements in the left ventricle and the ascending aorta [1–3]. Early studies in dogs used electromagnetic flowmetry and fluid-filled catheter systems with adequate frequency responses (> 50 Hz) to demonstrate that peak acceleration occurred at the time of the peak transvalvular pressure gradient [1]. Peak velocity of flow was thought to coincide with the time of transvalvular pressure crossover. Murgo et al. [2] studied pressure and flow relationships in humans using high fidelity pressure and velocity catheter tip transducers. Their data confirmed that peak acceleration and the peak transvalvular pressure gradient were temporally related at rest, but that peak velocity occurs prior to the time of left ventricular-aortic pressure crossover.

Theoretical analysis of the left ventricular ejection pulse

The preceding chapters have discussed analysis of the Doppler ejection pulse based upon descriptive time domain measurements. Maximal acceleration, peak velocity, stroke integral, and the systolic time intervals all key upon features of the flow profile easily measured in hard copy records. Clinical evaluations have been restricted to correlative studies evaluating pulse timing, rate of rise, and peak deflection with commonly accepted invasive and noninvasive reference standards of ventricular performance; dP/dt, ejection fraction, Vcf, and power of left ventricular ejection. Ischemic mass, extent of coronary disease, exercise tolerance, and thallium perfusion defects have also been referenced. No prior study has addressed the genesis of the flow pulse in the ascending aorta.

Functional and anatomic correlates of asymptomatic and symptomatic stress responses in patients free from prior infarction

To identify the noninvasive indices most likely to detect asymptomatic myocardial ischemia or its consequences we evaluated exercise induced changes in electrocardiographic (ECG) ST segments radionuclide left ventricular ejection dynamics and doppler assessments of ascending aortic flow in patients free from prior myocardial infarction referred for coronary angiography