Ultrasonic backscatter system for automated on-line endocardial boundary detection: evaluation by ultrafast computed tomography.

OBJECTIVES: The purpose of this study was to evaluate the accuracy of the recently developed echocardiographic on-line endocardial border detection system using ultrafast computed tomography, an independent and proved tomographic imaging modality. BACKGROUND: The automated system for on-line endocardial border detection identifies the blood-tissue interface by acoustic quantification of the ultrasonic backscatter signal. METHODS: Eighteen subjects were screened by conventional echocardiography and acoustic quantification. Ten of these, with high quality echocardiographic images, were also examined by ultrafast computed tomography. Comparable image planes at the midpapillary level were analyzed. Measurements of left ventricular cavity area were compared at end-diastole and end-systole and time course analyses of cavity area during the cardiac cycle were performed. RESULTS: There was good correlation between values for left ventricular end-diastolic area (r = 0.99), end-systolic area (r = 0.93) and fractional area change (r = 0.91) using the two methods. The on-line backscatter system underestimated end-diastolic area (p < 0.001), but the negative bias was small (-1.6 cm2) and the 95% confidence intervals were narrow (-3.6 cm2 to +0.4 cm2). In contrast, the backscatter system overestimated end-systolic area (p < 0.02); the positive bias for this variable was also small (+2.6 cm2) but the confidence intervals were relatively wide (+7.9 to -2.8 cm2). The negative bias of backscatter values for cavity area was fairly constant during diastole and early systole (range -5% to -10%), but during the second half of systole, backscatter values increased progressively relative to computed tomographic values. Real time values for fractional area change measured by the backscatter system were 13% smaller than those determined by ultrafast computed tomography (p < 0.001), with wide confidence intervals (+3% to -30%). Absolute peak rates of area change during systole and diastole were lower by 39% (p < 0.001) and 41% (p < 0.01), respectively, using the on-line ultrasonic backscatter system. Time course analyses revealed the errors to be consistent with cardiac cycle-dependent alterations in gain sensitivity of the ultrasonic backscatter system. CONCLUSIONS: The ultrasonic backscatter system is associated with cyclic cavity area measurement errors that need to be addressed if its early promise for on-line assessment of ventricular function is to be fulfilled. Incorporation of an electrocardiographically triggered time-varying gain control may improve accuracy for on-line analysis of ventricular performance.

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes.

OBJECTIVES: The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction. BACKGROUND: Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent. METHODS: Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min). RESULTS: Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups. CONCLUSIONS: Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Effects of left ventricular pressure on sonicated albumin microbubbles: evaluation using an isolated rabbit heart model.

OBJECTIVES: We used an isolated, crystalloid-perfused rabbit heart model to test the hypothesis that the phasic changes in left ventricular contrast are due to bubble compression and decompression during systole and diastole, respectively. BACKGROUND: Contrast enhancement of the left ventricular cavity has been shown to decrease during ventricular systole. This phenomenon has been attributed to pressure-induced microbubble destruction. Such destruction, if confirmed, would severely confound the quantitative interpretation of contrast echocardiographic data. METHODS: A fixed volume of contrast solution (5% human albumin and Albunex, approximately 400:1 ratio) was introduced into a latex balloon placed within the left ventricular cavity of an isolated paced rabbit heart preparation (n = 12). Instantaneous left ventricular pressure was measured using a high fidelity microtip catheter and digitized on-line. The beating heart was placed in a water tank, and ultrasound images were obtained using a 7.5-MHz transducer and were recorded and digitized off-line at 12 frames/s. Simultaneously, the pacing signal was used for gated on-line acquisition of end-diastolic frames. A simple theoretic model based on surface tension physical principles was used to predict changes in bubble size and, consequently, the reflection intensity in response to the measured changes in left ventricular pressure. RESULTS: We found that under peak left ventricular systolic pressures ranging from 89 to 155 mm Hg, 1) end-diastolic videointensity decreased by 8 +/- 6% (mean +/- SD) over 25 consecutive heart beats; and 2) intracyclic variations in measured videointensity were in close agreement with the theoretic calculations: 80.1 +/- 2.9% versus 80.2 +/- 4.6% of diastolic videointensity at systole. CONCLUSIONS: The major cause of systolic decrease in contrast enhancement is periodic bubble compression (as opposed to bubble destruction) induced by high systolic pressures. The minor progressive decrease in end-diastolic videointensity reflects the degree of instability of Albunex microbubbles under left ventricular pressures. However, the clinical impact of these destructive effects is likely to be only minor because of the rapid transit of microbubbles through the left heart chambers and myocardial microcirculation.

Echocardiography for hemodynamic assessment of patients with advanced heart failure and potential heart transplant recipients.

OBJECTIVES: This study sought to assess the accuracy of Doppler echocardiographic techniques for the determination of right heart catheterization hemodynamic variables in patients with advanced heart failure and in potential heart transplant recipients. BACKGROUND: Doppler echocardiographic techniques permit the noninvasive acquisition of hemodynamic variables traditionally used for the assessment of patients with advanced heart failure and potential heart transplant candidates. However, the accuracy of these techniques has not been sufficiently well documented for clinical application in individual patients. METHODS: Echocardiographic data required for estimation of mean right atrial, pulmonary artery and mean left atrial pressures and cardiac output were obtained. Right heart catheterization was performed immediately after Doppler echocardiographic data were acquired, before any intervention that might have altered the subject's hemodynamic status. RESULTS: A complete Doppler echocardiographic hemodynamic data set was acquired in 21 (84%) of 25 subjects. For all variables, invasive and noninvasive hemodynamic values were highly correlated (p < 0.001), with minimal bias and narrow 95% confidence limits. An algorithm constructed from the noninvasive hemodynamic variable values identified all patients with adverse pulmonary vascular hemodynamic variables (i.e., transpulmonary gradient > or = 12 mm Hg, pulmonary vascular resistance > or = 3 Wood units or pulmonary vascular resistance index > or = 6 Wood units x m2). This algorithm identified 12 (71%) of 19 patients for whom right heart catheterization was unnecessary. CONCLUSIONS: Doppler echocardiographic estimates of hemodynamic variables in patients with advanced heart failure are accurate and reproducible. This noninvasive methodology may assist with monitoring and optimization of medical therapy in patients with advanced heart failure and may obviate the need for routine right heart catheterization in potential heart transplant candidates.

Comparison of estimates of right atrial pressure by physical examination and echocardiography in patients with congestive heart failure and reasons for discrepancies.

Clinical estimates of right atrial pressure from the jugular venous pulse were accurate when right atrial pressure was normal, but systematically underestimated elevated right atrial pressures. Because the increased distance from the mid-right atrium to the sternal angle is not accounted for, apparently normal right atrial pressure estimates by this technique do not reliably exclude elevated right atrial pressure in patients with congestive heart failure.

Comparison of intravenous amrinone and dobutamine in congestive heart failure due to idiopathic dilated cardiomyopathy.

A prospective randomized study was performed in 46 consecutive patients with refractory congestive heart failure (CHF) due to idiopathic dilated cardiomyopathy to compare the hemodynamic responses to 48-hour infusions of amrinone and dobutamine. Both drugs substantially reduced pulmonary arterial wedge pressure, right atrial pressure and systemic vascular resistance and increased cardiac index. Amrinone caused a greater decrease in right atrial pressure than dobutamine (p less than 0.02) and had a positive chronotropic effect not observed with dobutamine (p less than 0.01). The increase in heart rate produced by amrinone correlated inversely with the changes in right atrial and pulmonary arterial wedge pressures, suggesting a baroreceptor response to reduced preload. Dobutamine produced a larger increase in stroke volume index than amrinone (p less than 0.01). Ninety-one percent of patients receiving amrinone and only 65% receiving dobutamine had reduction of greater than or equal to 30% in pulmonary arterial wedge pressure (p less than 0.05). Cardiac index increased greater than or equal to 30% in similar numbers of patients given amrinone (74%) and dobutamine (65%). Negative fluid balance was recorded in all patients receiving amrinone and in 78% of patients receiving dobutamine (p less than 0.05). Target hemodynamic criteria were achieved in 83% of patients receiving 10 micrograms/kg/min of amrinone. The effective maintenance dose of dobutamine was extremely variable. No clinically important adverse effects were observed with either drug regimen. Both amrinone and dobutamine are effective and safe agents for short-term parenteral therapy of patients with dilated cardiomyopathy in severe CHF that is unresponsive to oral medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effect of atrial pacing in severe acute aortic regurgitation and role of M-mode echocardiography in determining the optimal pacing interval.

The effect of atrial pacing on cardiac performance was assessed in 11 men (aged 20 to 64 years) with recent-onset severe aortic regurgitation (AR), all of whom had diastolic closure of the mitral valve on the echocardiogram. Thermodilution cardiac outputs were determined, and aortic, left ventricular and pulmonary arterial wedge pressures recorded. Once baseline recordings were completed, the pacing rate was increased by increments of 10 beats/min (70, 80, 90...) to a maximal rate of 140 beats/min. The optimal pacing interval, obtained from hemodynamic data, was defined as that at which the lowest filling pressure was associated with the highest cardiac index. This was then compared with a pacing interval derived from the R wave of the electrocardiogram to the diastolic mitral closing point on the M-mode echocardiogram. Such an interval would shorten diastole without affecting forward mitral flow. Atrial pacing improved the overall hemodynamic state in all patients; the most favorable hemodynamics were achieved at heart rates between 110 and 130 beats/min (mean: 120 +/- 8). At the optimal rate, left ventricular end-diastolic pressure decreased from 46 +/- 7 to 23 +/- 12 mm Hg (p less than 0.001), and the pulmonary arterial wedge pressure from 28 +/- 8 to 16 +/- 7 mm Hg (p less than 0.001), while the cardiac index increased from 2.34 +/- 0.46 to 2.63 +/- 0.49 liters/min/m2 (p less than 0.01). The mean difference between the optimal pacing interval determined from the hemodynamic data and the interval derived from the echocardiogram was 18 +/- 21 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional anatomy of severe mitral regurgitation in active rheumatic carditis.

The mechanism of severe mitral regurgitation (MR) due to active rheumatic carditis is ill defined. This study involved 73 patients, aged 7 to 27 years (mean 13), with severe MR and active rheumatic carditis who were subjected to surgery. Sixty-one were studied retrospectively (group 1) and 12 prospectively (group 2). Active rheumatic carditis was diagnosed according to the modified Jones' criteria, morphologic appearances of the heart at operation and histology of the valve. All patients had preoperative 2-dimensional echocardiographic and intraoperative assessment of the mitral valve apparatus. The presence of mitral valve prolapse--defined as failure of leaflet edge coaptation resulting in systolic displacement of the free edge of the involved leaflet toward the left atrium--was determined in all patients. Mitral anular diameter and maximal systolic chordal length were measured at 2-dimensional echocardiography in group 2 patients and compared to values obtained from matched control subjects. Anular and chordal dimensions in 6 of the group 2 patients were correlated with precise measurements obtained at surgery. Mitral valve prolapse involving the anterior leaflet was detected on echocardiography and confirmed at surgery in 69 patients (94%). Mitral anular dilatation was observed at operation in 70 patients (96%). Maximal anular diameter was significantly greater (p less than 0.0001) than in matched control subjects (37 +/- 4 vs 23 +/- 2 mm). The mean anular dimension measured at surgery (36 +/- 3 mm) was similar to that obtained by echocardiography and individual values using the 2 methods correlated well (r = 0.93). Chordal elongation was observed in 66 patients at operation (90%).(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal and fetal sequelae of anticoagulation during pregnancy in patients with mechanical heart valve prostheses.

Previous reports indicate an increased risk of thrombotic and embolic events in patients with mechanical heart valve prostheses during pregnancy. We prospectively followed 50 pregnancies in 49 patients with 62 cardiac prostheses from presentation at the antenatal clinic through the remainder of the pregnancy. Of the 60 mechanical prostheses, 39 were Medtronic-Hall, 7 St. Jude Medical, 7 Starr-Edwards and 7 Björk-Shiley. Forty-three patients were in New York Heart Association functional class I or II and 6 were in functional class III or IV. Forty-five patients were in sinus rhythm and 4 had chronic atrial fibrillation. All patients received warfarin during the first and second trimesters. Forty-one pregnancies proceeded beyond 28 weeks. In 23 of these (group I) warfarin was replaced with heparin at 36 weeks gestation. In the remaining 18 (group II) warfarin was not substituted owing to premature onset of labor. The target prothrombin ratio (international normalized ratio) in patients receiving warfarin was 2.0 to 2.5. The partial thromboplastin time was maintained at 1.5 to 2.5 times the control value in patients receiving heparin. Eleven patients received dipyridamole plus warfarin for the duration of pregnancy. There were no maternal thromboembolic complications or deaths associated with pregnancy. Antepartum hemorrhage occurred in 1 patient at 35 weeks gestation. One patient (group I) experienced peripartum hemorrhage. All patients were hemodynamically stable before delivery, but 2 developed pulmonary edema during labor. The mean fetal birth weight was low (2.54 +/- 0.98 kg). There were 9 abortions (18%), 7 stillbirths (14%), 2 neonatal deaths (4%) and 2 instances of warfarin embryopathy (4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Paradoxic improvement in regional wall motion during high-dose dobutamine stress echocardiography. A marker for hibernating myocardium?

Dobutamine stress echocardiography detects myocardial ischemia by inducing regional left ventricular systolic dysfunction. Augmentation of wall motion in hypokinetic segments has also been noted with low-dose dobutamine, suggesting myocardial viability. We report a case of regional ventricular improvement during high-dose dobutamine therapy, which may represent relief from myocardial hibernation or changes in regional loading conditions.

Venous air embolism. Diagnosis by spontaneous right-sided contrast echocardiography.

This report describes the definitive diagnosis of venous air-embolism by documentation of spontaneous echo contrast in the right cardiac chambers following removal of a jugular venous catheter in a patient with hepatic failure. This complication was potentiated by the presence of concurrent hepatic coagulopathy which prejudiced effective hemostasis at the central venous puncture site.

A time-course study of the effects of pentobarbital, fentanyl, and morphine chloralose on myocardial mechanics.

Cardiovascular physiological studies in anesthetized animals may be confounded by the hemodynamic actions of the anesthetic agents themselves. To identify an anesthetic regimen that does not significantly influence cardiovascular physiology, the hemodynamic responses of 28 dogs were studied. Animals were equally divided among groups with 1) no anesthesia (i.e., trained conscious preparation), 2) pentobarbital sodium, 3) fentanyl citrate, and 4) a combination of morphine sulfate and alpha-chloralose. Anesthesia was maintained for 3 h. Data were acquired with the use of ultrasound imaging of the heart in conjunction with invasive pressure measurements. Left ventricular ejection phase indexes and end-systolic force-velocity relations were used to evaluate the effects of each anesthetic agent on overall systolic performance and myocardial contractility. Compared with the conscious animals, pentobarbital profoundly depressed systolic performance (P less than 0.05 vs. control) because of a reduction in myocardial contractility (P less than 0.01) and an increase in left ventricular afterload (end-systolic wall stress, P less than 0.05). Fentanyl increased myocardial contractility (P less than 0.05) but also tended to increase afterload with the net result that overall systolic performance remained unchanged. Morphine-chloralose did not affect overall ventricular systolic performance or its individual determinants. Pentobarbital and fentanyl also caused progressive time-dependent deteriorations in all parameters of systolic function during prolonged anesthesia. In contrast, cardiac function was stable for greater than or equal to 3 h after induction of morphine-chloralose anesthesia. The hemodynamic profile of dogs anesthetized with morphine-chloralose most closely resembled that of the conscious animals. Morphine-chloralose is recommended when prolonged anesthesia is required for studies of cardiovascular physiology.

Double-chambered left ventricle: submitral accessory valvular tissue causing inlet and outlet obstruction.

We report a patient with a large submitral ridge of muscular and fibrous tissue that divides the left ventricle into two distinct chambers causing inlet and outlet obstruction. Doppler echocardiography revealed obstruction to both filling and ejection. Echocardiography demonstrated that the obstruction was in series with the mitral apparatus. Surgery was done with resection of much of this ring of tissue. Subsequent studies revealed morphologic and hemodynamic improvement.

Valve orifice area alone is an insufficient index of aortic stenosis severity: effects of the proximal and distal geometry on transaortic energy loss.

BACKGROUND AND AIMS OF THE STUDY: Standard measures of hemodynamic severity of aortic valve stenosis vary widely among patients with and without clinical symptoms. Our hypothesis is that valve orifice area alone is not the sole determinant of adverse clinical outcome. Stenotic orifice area ratio is ratio of the cross-sectional stenotic orifice area to the down-stream, ascending aorta cross-sectional area. Determination of workload together with aortic valve orifice area ratio might improve risk stratification among asymptomatic patients with critical aortic stenosis. Accordingly, application of both parameters together might be useful in guiding management decisions in this condition. METHODS: In this study the dependency of transaortic fluid mechanical energy transfer (one component of left ventricular workload) on aortic valve orifice area is shown using modeling and experimental techniques. RESULTS: For a stroke volume of 62 ml at a heart rate of 60 beats/min, the piston work (analogous to left ventricular work) increased by 17% as the stenotic orifice area ratio decreased from 0.60 to 0.25, by 35% as the ratio fell from 0.25 to 0.20, and by 73% as the ratio fell from 0.20 to 0.10. CONCLUSIONS: As predicted by the fundamental fluid mechanical theory, simulated left ventricular work and energy loss in aortic stenosis are influenced not only by the effective stenotic valve orifice area, but also by the geometry of the inflow and outflow conduits, proximal and distal to the valve. These findings might explain clinically observed discrepancies between valve orifice area and the onset of the classical symptoms of severe aortic stenosis that reflect the left ventricular workload. Consideration of the left ventricular work in addition to the effective valve orifice area should enhance clinical evaluation, prognostication and risk stratification among patients with severe aortic stenosis.

Left ventricular outflow tract obstruction as a cause for hypotension and symptoms during dobutamine stress echocardiography.

BACKGROUND: Hypotension has been found to occur in more than one-third of patients during DBSE. Unlike traditional treadmill exercise stress testing, hypotension does not appear to be associated with significant coronary artery disease or left ventricular (LV) dysfunction. Several ischemic and nonischemic mechanisms such as dynamic LV intracavitary obstruction have been implicated in the pathogenesis of hypotension and the induction of symptoms during DBSE. HYPOTHESIS: The purpose of this study was the prospective evaluation of patients referred for dobutamine stress echocardiography (DBSE) to determine (1) the frequency of hypotension during DBSE, (2) the underlying mechanisms responsible for the induction of hypotension, and (3) to describe the cardiac chamber sizes and mass of patients in whom hypotension occurs. METHODS: Seventy-eight consecutive patients were studied during DBSE. Pulsed and continuous-wave Doppler echocardiography were performed at baseline and at each dobutamine infusion stage. Maximum velocities were recorded. Cardiac output was determined noninvasively at each stage in patients who developed an outflow tract gradient. Echocardiography was used to characterize LV dimensions and mass. RESULTS: During dobutamine infusion, 14 of 78 (18%) patients developed a left ventricular outflow tract (LVOT) velocity > or = 2.5 m/s. Pulsed Doppler echocardiography verified that the maximal velocity originated in the LVOT. Of the patients who developed an LVOT gradient, 57% had a concomitant hypotensive response to dobutamine compared with 33% of patients without a gradient (not significant). Four of nine patients had a simultaneous fall in cardiac output. Patients who developed an LVOT gradient had smaller LV dimensions and increased wall thicknesses compared with those who did not develop a gradient. CONCLUSIONS: Dobutamine stress echocardiography precipitates LVOT obstruction in certain patients. The development of a gradient corresponded with a fall in blood pressure and a decline in cardiac output in nearly half of the patients. These findings suggest that stress-induced LVOT obstruction may be responsible in part for the hemodynamic changes and symptoms experienced by these patients during exercise.

Improved risk stratification in unstable angina: identification of patients at low risk for in-hospital cardiac events by admission echocardiography.

BACKGROUND: Current protocols for risk stratification of patients with acute chest pain syndromes rely on clinical parameters and are oriented toward identification of patients at high risk for adverse cardiac events; however, this paradigm for risk stratification does not adequately address the observation that adverse cardiac events are relatively uncommon in this population. In an era of cost containment, consideration also should be given to identification of patients at low risk for adverse cardiac events, who may be safely discharged without expensive inpatient hospitalization. HYPOTHESIS: The purpose of this study was to develop echocardiographic predictors that identify unstable angina patients at low risk for adverse cardiac events and that discriminate between low- and high-risk patients. METHODS: The predictive accuracy of retrospectively determined echocardiographic predictors were compared in a population-based sample of 66 consecutive unstable angina patients undergoing echocardiography within 24 h of admission. RESULTS: Echocardiographic predictors of adverse events included wall motion score index > or = 0.2, ejection fraction < or = 40%, and mitral regurgitation severity > 2. One or more echocardiographic predictors of adverse events were present in 32 patients (48%). A composite echocardiographic predictor of adverse events was specific, had a high positive predictive value for the identification of high-risk patients, and discriminated between unstable angina patients at high and low risk for adverse cardiac events. CONCLUSION: Echocardiographic predictors of adverse events are specific and discriminate between unstable angina patients at high and low risk for adverse cardiac events.