Quantitative measurement of left ventricular volumes in man from radiopaque epicardial markers

Feasibility of creating estimates of left ventricular flow-volume dynamics using echocardiography

Background

This study explores the feasibility of non-invasive assessment of left ventricular volume and flow relationship throughout cardiac cycle employing echocardiographic methods.

Methods

Nine healthy individuals and 3 patients with severe left-sided valvular abnormalities were subject to resting echocardiography with automated endocardial border detection allowing real-time estimation of left ventricular volume throughout the cardiac cycle. Global and regional (6 different left ventricular segments) estimates of flow-volume loops were subsequently constructed by plotting acquired instantaneous left ventricular 2-D area data (left ventricular volume) vs. their first derivatives (flow).

Results

Flow-volume loop estimates were obtainable in 75% of all echocardiographic images and displayed in normal individuals some regional morphological variation with more pronounced isovolumic events in the paraseptal segments and significantly delayed maximal systolic flow paraapically. In patients with aortic stenosis, maximal systolic flow occurred at a lower estimated left ventricular systolic volume whereas in mitral stenosis, maximal diastolic flow was observed at a higher estimated left ventricular diastolic volume. Aortic regurgitation caused a complex alteration of the estimated flow-volume loop shape during diastole.

Conclusion

Non-invasive assessment of left ventricular flow-volume relationship with echocardiography is technically feasible and reveals the existence of regional variation in flow-volume loop morphology. Valvular abnormalities cause a clear and specific alteration of the estimates of the normal systolic or diastolic flow-volume pattern, likely reflecting the underlying pathophysiology.

The use of left ventricular epicardial surface velocity patterns as a marker of pacing site

Ectopic ventricular foci were simulated at selected endocardial sites in 15 closed-chest canines using ventricular pacing. During this pacing, a noninvasive x-ray backscatter imaging technique was used to measure epicardial LV displacements at 5-ms intervals during the cardiac cycle. These displacement measurements were used to calculate epicardial surface velocities in each study and were presented as a time sequence of color coded velocity maps. Characteristic patterns in the timing and spatial propagation of LV surface velocities were noted for each pacing site, particularly during the expansion of the LV during isovolumic contraction and the inward motion of the LV during ejection. Average surface velocity maps for the 15 canines were computed for each pacing site. These average maps were used as standards for comparison with individual pacing studies to determine the probable site of pacing. Comparisons were made using a computer algorithm, based upon auto- and cross-correlation techniques in the time domain. This algorithm correctly identified pacing sites with sensitivities of RA 74%, LV 76%, RV 79%, and RVOT 77% and specificities of RA 98%, LV 96%, RV 90%, and RVOT 93%. The results show that this noninvasive mapping procedure has potential for identifying the location of an ectopic ventricular focus.

Effects of intravenous verapamil on left ventricular systolic function and diastolic filling dynamics in patients with coronary artery disease: analysis of intramyocardial markers

Left ventricular (LV) intramyocardial markers (MM) were used to study the effects of intravenous verapamil on LV pump function and diastolic filling dynamics. Verapamil (0.1 mg/kg bolus followed by 0.005 mg/kg/min) was administered to 10 patients with severe coronary artery disease 4 years after coronary bypass grafting and implantation of 7 tantalum markers into the LV. MM were filmed at 100 frames/sec (biplane 30 degrees RAO/60 degrees LAO). The digitized biplane MM coordinates were transformed into 3-dimensional coordinates and maximal projection area was defined. LV volumes were calculated frame-by-frame and ejection fraction and peak filling rate derived. Pressure-volume relations were calculated in early-, mid-, and end-diastole. Verapamil caused a slight rise in end-diastolic pressure (12 to 14 mmHg, p less than 0.001) and end-diastolic volume (142 to 152 ml; p less than 0.005) and a fall in max dP/dt (1732 to 1570 mmHg/s; p less than 0.01) reflecting the drug's negative inotropic action. Verapamil reduced LV systolic pressure (136 to 126 mmHg; p less than 0.01), diastolic aortic pressure (74 to 68 mmHg; p less than 0.001) and peripheral resistance (1496 to 1348 dynes.s.cm-5; p less than 0.025); cardiac index was increased (2.7 to 2.9 l/min/m2; p less than 0.05), as were ejection fraction (47 to 49%; p less than 0.02) and stroke volume (67 to 75 ml; p less than 0.001). Great cardiac vein flow increased as well (88 to 102 ml/min; p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular wall motion: its dynamic transmural characteristics

Cardiac wall motion has been studied extensively. It is usually determined by indirect two-dimensional measurements for the true three-dimensional (3D) motion with its specific speed and direction. Errors are also introduced by using internally fixed reference systems and by the inability to identify precise points on the heart wall during the cardiac cycle. Because of these limitations, the endocardial and epicardial wall motion and their relationship are still unclear. This study was designed to assess endocardial and epicardial wall motion by measuring the direction and speed of implanted markers in an externally fixed 3D coordinate system. Fifty-seven pairs of endocardial and epicardial metallic markers were placed at anterior, lateral, posterior, basal, and apical regions of the left ventricles of 14 normal mongrel dogs. Biplane cineradiographs were performed at 50 frames/sec, and the 3D motions of the markers were analyzed using a specially designed computer system. It was found that the speeds, directions, displacements, and phases of the movements of corresponding endocardial and epicardial points were highly correlated. The correlation coefficients were 0.77 to 0.95 for the mean directions, 0.61 to 0.96 for the mean speeds, and 0.59 to 0.96 for the mean displacements at various regions of the heart, and the periodic movements of the endocardium and epicardium were always in phase. The mean epicardial speeds and displacements are fixed proportions (approximately 70%) of the mean endocardial speeds and displacements despite the differences in absolute values between regions in the same dog and the same regions in different dogs. The correlation coefficients for endocardial and epicardial instantaneous speeds, directions, and velocities ranged from 0.68 to 0.83, 0.81 to 0.88, and 0.77 to 0.86, respectively, for different regions of the heart. The correlation coefficients were significant for both the mean values and the instantaneous values. Thus, when only fixed epicardial points are accessible for wall motion measurements in clinical situations, it is possible to infer the endocardial motion from the epicardial motion.

Rapid assessment of ventricular function in acute volume overload using opaque myocardial markers

Radiopaque markers, implanted in the myocardium, have been used to analyze ventricular function. However, the inordinate time involved in measuring marker motion limited widespread use. This work describes the application of a marker recognition system, which provides automatic recording and storage of marker locations. Use of the system was demonstrated by repeated measurements of ventricular performance in a canine model of acute volume overload.

Regional left ventricular ejection fraction from real-time two-dimensional echocardiography

We studied regional left ventricular contraction patterns and ejection fraction from real-time two-dimensional echocardiograms in 8 normal subjects, 11 patients with coronary artery disease and 2 with congestive cardiomyopathy. The ventricle was divided into 12 regions and for each region, we calculated ejection fraction using a method which integrated the incremental volumes of a series of hemicylinders constructed within that region. The data obtained were displayed graphically to provide a detailed picture of regional ventricular function. Normal subjects had a uniform regional ventricular pattern (regional ejection fraction 54-74%). In patients with coronary disease, we found varying degrees of regional ventricular contraction abnormalities. In congestive cardiomyopathy global hypokinesis was present, and regional ejection fraction was reduced in all areas (11-39%). The study showed that two-dimensional echocardiography is a useful non-invasive bedside technique which may provide detailed quantitative information relating to regional left ventricular contraction abnormalities.

Nongeometric determination of left ventricular volumes from equilibrium blood pool scans

This study assesses the utility of a scintigraphic, nongeometric technique for the determination of left ventricular volumes. Accordingly, gated blood pool scintigraphy and cineangiography were performed within a 24 hour period in 22 patients. Scintigraphic volume measurements were calculated from individual frames of a modified 35 degrees left anterior oblique projection using an algorithm designed to consider (1) the background-corrected left ventricular activity normalized for activity per milliliter of peripheral venous blood; (2) total study time; (3) number of frames acquired per cardiac cycle; and (4) percent of the cardiac cycle acquired. Angiographic volumes were calculated by the area-length method and the Kennedy regression equation. There was an excellent correlation between scintigraphic and angiographic methods for all volume measurements grouped together (r = 0.985, standard error of the estimate [SEE] = 14.6 ml) as well as for segregated end-diastolic volumes (r = 0.985, SEE = 16.2 ml) and end-systolic volumes (r = 0.988, SEE = 14.7 ml). Prospective testing of the independent ability of scintigraphy to estimate ventricular volumes was provided for by studying an additional 13 patients, and good agreement was found between scintigraphic and angiographic determinations of left ventricular end-systolic and end-diastolic volumes. Thus, radionuclide techniques, which are independent of geometric assumptions, may be utilized for the quantitation of left ventricular volumes.

Cardiac dimensional analysis by use of biplane cineradiography: description and validation of method

Biplane cineradiography is a potentially powerful tool for precise measurement of intracardiac dimensions. The most systematic approach to these measurements is the creation of a three-dimensional coordinate system within the x-ray field. Using this system, interpoint distances, such as between radiopaque clips or coronary artery bifurcations, can be calculated by use of the Pythagoras theorem. Alternatively, calibration factors can be calculated in order to determine the absolute dimensions of a structure, such as a ventricle or coronary artery. However, cineradiography has two problems that have precluded widespread use of the system. These problems are pincushion distortion and variable image magnification. In this paper, methodology to quantitate and compensate for these variables is presented. The method uses radiopaque beads permanently mounted in the x-ray field. The position of the bead images on the x-ray film determine the compensation factors. Using this system, measurements are made with a standard deviation of approximately 1% of the true value.

The effect of supine rotation on left ventricular dimensions in man: a study using radio-opaque epicardial markers

It has been reported that patient rotation into the left lateral decubitus position (30 degrees rao) produces significant changes in the regression equations used for left ventricular volume determination and that normal values for echocardiographic left ventricular dimensions obtained from supine patients differ from those obtained after rotation. The purpose of this study was to establish whether patient rotation is associated with changes in left ventricular size and systolic function. The distances between left ventricular epicardial markers attached at the time of cardiac surgery were measured using biplane cineradiography in 14 patients in order to determine left ventricular dimensions before and after rotation. Supine epicardial left ventricular dimensions were not significantly different from those obtained with the patient rotated 30 degrees rao. These results suggest that reported changes in invasive and noninvasive measurements of left ventricular function associated with patient rotation are not primarily due to changes in left ventricular size.

Direct method for determining regional myocardial shortening after bypass surgery from radiopaque markers in man

A new method is described for determining localized epicardial shortening in regions newly perfused after saphenous vein bypass grafting. Four to six radiopaque markers are sutured to the ventricular epicardium in pairs, 2 cm apart and 0 to 3 cm distal to the coronary anastomosis. Shortening fraction and time to onset of shortening are reported in 56 patients examined noninvasively with use of cinefluorography 1 week to 6 months after operation. The right coronary bypass region showed the greatest improvement in shortening fraction in 6 months (from 10.1 to 16.7 percent); the left anterior descending region showed the least (but still significant) improvement (from 8.6 to 11.5 percent). Paradoxical systolic expansion occurred predominantly in the region of the left anterior descending coronary bypass (95 percent of all such occurrences). Measurement error, observer variability and beat to beat variability were less important than the physiologic changes in the postoperative period. This technique is a direct method providing heretofore unavailable follow-up information on localized shortening in newly perfused myocardium after coronary bypass grafting.

Differences in cardiac function with prolonged physical training for cardiac rehabilitation

Ten men aged 40 to 68 years with clinical manifestations of cardiovascular disease and who had participated for 2 to 59 months in a physical training program for cardiac rehabilitation were studied. All 10 underwent measurements of maximal oxygen uptake and invasive studies of cardiac output, using the direct Fick method, at rest and at graded levels of exercise in the upright posture. Of four men who left the training program, three continued activities individually. Physiologic measurements were repeated after a lapse of 13 to 38 months (average 23 months). The rate of change in maximal oxygen uptake relative to normal changes with aging was decelerated in four men over an average of 21.8 months and was accelerated in six men over an average of 23.2 months. At comparable oxygen requirements of exercise, stroke volume and cardiac output were unchanged in the former group but significantly decreased in the latter. Arterial oxygen content and arteriovenous oxygen difference increased in both groups. These results show that prolonged physical training results in physiologic adaptations of cardiac rehabilitation even though deterioration of cardiac function with advancing disease is probable in some patients.