Radionuclide angiocardiography in evaluation of patients after repair of transposition of the great arteries

The ability of first pass radionuclide angiocardiography to detect and quantitate residual intracardiac shunts and systemic venous obstruction after repair of transposition of the great arteries was evaluated in 29 children. Information from radionuclide scans was compared with data obtained during cardiac catheterization. Three children had a residual right to left shunt detected with both methods. There was good agreement between radionuclide and catheterization quantitation of left to right shunt in the nine patients with a residual defect, five of whom had significant shunting. Nineteen patients with signs suggesting superior vena caval obstruction were evaluated with both radionuclide and catheterization methods. In eight, complete obstruction was detected with both techniques; in one additional patient, partial obstruction was found on catheterization only. One of six patients evaluated for possible inferior vena caval obstruction was identified with both techniques. In the group as a whole, information obtained with radionuclide angiography correlated well with cardiac catheterization data in evaluation of residual shunts and obstruction to systemic venous return.     

Clinical application of radionuclide quantitation of left to right cardiac shunts in children

The results of 341 radionuclide studies, using the method of Maltz and Treves to quantify left to right shunts, were reviewed to evaluate Its clinical usefulness in routine practice. In 245 children in whom a shunt was suspected, 140 were shown to have shunts at cardiac catheterlzatlon, the pulmonary to systemic blood flow ratio ($\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$) being greater than 1.15 in 121. In 92 of 105 normal children, the ratio was less than 1.05. Nineteen children with a shunt had a ratio in the borderline range of 1.05 to 1.15 as did 13 normal children. Only one normal child had a $\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$ ratio greater than 1.10 whereas seven children with a shunt had a ratio of less than 1.10, including one with a ratio of less than 1.05. A highly significant correlation (r = 0.71) existed between the shunt sizes estimated with the radionuclide method and with oximetry. However, in 10 of these patients a small shunt shown with the radionuclide method was not detected with oximetry but observed on indocyanine green dye curves. In 41 children, therefore, shunt size measured with the radionuclide method, oximetry and indocyanine green dye curves was compared. The correlation of shunt size was comparable with the three techniques. The radionuclide estimation is therefore considered to be more sensitive than oximetry in the detection of small shunts. The procedure was also valuable in 96 children studied after cardiac surgery; a $\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$ value greater than 1.15 was present in 17 children, 12 of whom have to date been shown to have a residual shunt.     

Stress-induced ventricular arrhythmia after repair of tetralogy of fallot

The combination of ventricular arrhythmias found on routine electrocardiography at rest and elevated right ventricular pressures may be associated with sudden death in patients after repair of tetralogy of Fallot. In this study data were reviewed from 104 patients who underwent treadmill exercise testing with a modified Bruce protocol at a mean age of 13.8 years, an average of 7 years after repair of tetralogy of Fallot. The frequency and form of ventricular arrhythmias as manifested in an electrocardiogram at rest as well as before, during and after treadmill exercise tests were tabulated for each patient. Cardiac catheterizatlon was performed within 1 week of the treadmill test in 82 of the 104 patients and the right ventricular systolic pressure, right ventricular end-diastolic pressure, pulmonary arterial systolic pressure and pulmonary to systemic flow ($\text{Qp}\text{Qs}$) ratio were compared in patients with and without ventricular arrhythmias. In 15 (14 percent) of the 104 patients, ventricular arrhythmia was evident in the electrocardiogram at rest and in 31 (30 percent) it was induced by treadmill exercise; 5 of the 15 with arrhythmia at rest had no arrhythmia during exercise. Compared with the remaining 73 patients, the 31 patients who had ventricular arrhythmias during treadmill testing (1) were older (16.2 versus 12.8 years, p < 0.01, t test) and were tested at a longer interval after repair of tetralogy of Fallot, (2) had greater right ventricular systolic pressure (52.7 versus 41.3 mm Hg, p < 0.005), (3) had greater right ventricular end-diastolic pressure (8.0 versus 6.1 mm Hg, p < 0.001), and (4) had no difference in pulmonary arterial systolic pressure or $\text{Qp}\text{Qs}$ ratio. Uniform premature ventricular complexes were found in 28 patients, multiform premature ventricular complexes in two and ventricular tachycardia in one. Patients whose ventricular arrhythmia appeared with exercise had similar hemodynamic findings to-those whose arrhythmia disappeared with exercise. Two patients, each with elevated right ventricular systolic pressure and multiform premature ventricular complexes, had cardiac arrest at home.It is concluded that (1) treadmill exercise testing is a sensitive method for detecting ventricular arrhythmia in patients after repair of tetralogy of Fallot; (2) ventricular arrhythmia during treadmill exercise is related to abnormal hemodynamic status; (3) multiform premature ventricular complexes, couplets or ventricular tachycardia with exercise testing are highly associated with abnormal hemodynamic status and sudden death; (4) suppression of ventricular arrhythmia with exercise is neither the characteristic nor necessarily the benign response in these patients; and (5) ventricular arrhythmia may be a late developing phenomenon and may increase with longer postoperative intervals. Patients after repair of tetralogy of Fallot should be treated for ventricular arrhythmia detected in the electrocardiogram at rest or during treadmill exercise testing.     

Radioactive tracers in congenital heart disease

Radionuclide angiocardiography is a useful method in the evaluation of patients with congenital heart disease, safely and nontraumatically. Physiologic variables such as transit times, cardiac output, left ventricular ejection fraction, stroke volume, end-diastolic volume can be measured accurately with this technique. An important application of radionuclide angiocardiography in children with congenital heart disease is in the detection, localization and quantification (pulmonary to systemic flow ratio) of intracardiac shunts and shunts between the great vessels.This technique has been found useful in the evaluation of the newborn infant with cyanosis, the patient with a cardiac murmur and the patient who has had cardiovascular surgery. Newer mobile gamma camera-computer systems permit the performance of radionuclide angiocardiography in severely ill premature and newborn infants and patients during the early postoperative period. Specially designed magnifying collimators and the development of ultrashort-lived radionuclides should result in an overall improvement in the diagnostic capabilities of this technique and in a further reduction in the radiation dose.     

Radioisotopic diagnosis and quantitation of left to right shunts in childhood and adolescence.

In 187 patients (141 adults and 46 children) left to right shunts were assessed using quantitative radionuclide angiography. After injection of 99mTc into the femoral vein time activity curves were registered over both lungs and the heart (Ohio Nuclear Camera, ON SIGMA 400, 110, HP 5407 computer). Using a modified gamma function area ratio technique the shunt sizes were calculated. The radioisotopic method allows a precise quantitation of left to right shunts ranging from 15--80%. There was a good agreement between the shunt sizes calculated by the radioisotopic method and oximetry or dye-dilution at cardiac catheterization (adults r = 0,87, children r = 0,85). The shunts sizes assessed with this nontraumatic method appear sufficiently reliable to be a real alternative to conventional techniques in screening for shunts.     

Hemodynamics in endomyocardial fibrosis

Nine patients with endomyocardial fibrosis have been studied. The clinical diagnosis was confirmed by right ventricular angiography in all of them. They were submitted to right and left ventricular catheterization and had the cardiac pressures, the pulmonary arteriolar resistance, and the cardiac index measured. The ratio between the end-diastolic and systolic ventricular pressures has been taken as an index of the degree of impairment to ventricular filling, and, based on this, patients were classified into two groups: I, predominant or isolated right ventricular disease (seven patients); and II, predominant left ventricular disease (two patients).Group I patients were characterized by a right ventricular $\text{D}{}_2\text{S}$ ratio above 60 per cent, severe tricuspid regurgitation, a diastolic pulmonary artery pressure slightly lower than the right ventricular plateau and end-diastolic pressures, and a reversal of the gradient between the left ventricular end-diastolic pressure and the right atrial mean pressure; these two latter findings strongly suggesting a diastolic blood flow between the right atrium and the left ventricle.The two patients in Group II did not show evidences suggestive of tricuspid regurgitation or of an early opening of the pulmonic valve. Even presenting high values for the left ventricular $\text{D}{}_2\text{S}$ ratio, the pulmonary arteriolar resistance was normal in one patient and mildly elevated in the other patient.     

Management of adults with congenital bidirectional cardiac shunts,cyanosis, and pulmonary vascular obstruction: Successful operative repair in 3 patients

Patients with congenital cardiac shunts in whom marked functional disability, cyanosis and pulmonary arterial hypertension develop have been considered inoperable or at exceedingly high risk. Three adult patients, 2 with atrial septal defect (ASD) and 1 with patent ductus arteriosus (PDA), presented with New York Heart Association class IV symptoms, bidirectional shunting with cyanosis, polycythemia, severe pulmonary hypertension, and increased pulmonary vascular resistance. Pulmonary arterial pressure did not decrease in response to administration of 100% oxygen in any patient, and 2 had lung biopsy results showing advanced pulmonary vascular obstruction. While a right-to-left shunt caused cyanosis in all patients, the net shunt was left to right ($\text{Q}{}_{\mathrm{p}}\text{Q}{}_{\mathrm{s}}\text{> 1}$) and the resistance ratio $\text{(}\text{R}{}_{\mathrm{p}}\text{R}{}_{\mathrm{s}}\text{) <0.5}$. All 3 patients survived operation, became acyanotic with normal hematocrit, and are in functional class I or II a mean of 36 months post-operatively. At repeat cardiac catheterization, pulmonary arterial pressure and resistance had decreased substantially.This high-risk group of patients with bidirectional shunts, in whom cyanosis due to pulmonary vascular obstruction and polycythemia develop and who appear to be at very high operative risk, should still be considered for surgical correction if the usual criteria for operability exist: net left-to-right $\text{Q}{}_{\mathrm{p}}\text{Q}{}_{\mathrm{s}}$ and $\text{R}{}_{\mathrm{p}}\text{R}{}_{\mathrm{s}}\text{<0.50}$.     

Estimation of pulmonary/systemic resistance ratios from echocardiographic systolic time intervals in young patients with congenital or acquired heart disease

Previous work has shown the positive correlation of echocardiographic right ventricular preejection period/right ventricular ejection time ratio ($\text{RPEP}\text{RVET}$) with pulmonary vascular resistance and pulmonary arterial diastolic pressure obtained at cardiac catheterization. However, the correlation was insufficient to predict pulmonary arterial diastolic pressure or vascular resistance from a given $\text{RPEP}\text{RVET}$ ratio. In this study the $\text{RPEP}\text{RVET}$ ratio was compared with left ventricular preejection period/ejection time ratio ($\text{LVEP}\text{LVET}$) in 25 patients undergoing cardiac catheterization, and a strong correlation was found between the ratio $\text{(}\text{RPEP}\text{RVET}\text{)}\text{(}\text{LPEP}\text{LVET}\text{)}\text{=}\text{R}\text{L}$ and the ratio of pulmonary arteriolar resistance/systemic arteriolar resistance ($\text{PAR}\text{RS}$), especially when $\text{R}\text{L}$ was correlated with $\text{log}{}_{10}\text{PAR}\text{RS}$ (r = 0.902). A very high correlation (r = 0.960) was found between $\text{R}\text{L}$ and $\text{log}{}_{10}\text{PAR}\text{RS}$ when the group was restricted to patients with a ventricular septal defect or a complete endocardial cushion defect. Regression equations for prediction of $\text{PAR}\text{RS}$ have been derived for the various groups.     

Radionuclide angiocardiographic assessment of pulmonary vascular reactivity in patients with left to right shunt and pulmonary hypertension

Radionuclide angiocardiography was used to assess pulmonary vascular reactivity in eight patients (nine studies) with a large, relatively unrestrictive intracardiac defect and pulmonary arterial hypertension. Radionuclide angiocardiograms, using technetium-99m pertechnetate, were performed first with the patient breathing room air and then after 10 minutes of breathing a mixture containing 90 percent or more of oxygen. The pulmonary to systemic flow ratios obtained by gamma variate analysis of the radionuclide time-activity curves were compared with those calculated with the Fick principle at the time of cardiac catheterization. There was a good correlation between the two methods both in room air studies (r = 0.88) and in those obtained with 90 percent or more of oxygen (r = 0.94). All six studies (in five patients) with a reactive pulmonary vasculature (judged by a pulmonary vascular resistance at cardiac catheterization of less than 6 units/m2 with oxygen or after tolazoline) had a radionuclide pulmonary to systemic flow ratio of 3.0 or greater with oxygen. The three patients with a nonreactive pulmonary vasculature had a radionuclide pulmonary to systemic flow ratio of 2.3 or less with oxygen, a value that was unchanged from the room air value. These data suggest that radionuclide angiocardiography may be a useful, relatively noninvasive method of assessing pulmonary vascular reactivity in patients with a large, relatively unrestrictive intracardiac defect.     

Quantitation of shunting at the atrial level using rapid acquisition computed tomography with comparison with cardiac catheterization

Contrast-enhanced rapid acquisition computed tomography was employed to quantitate intracardiac shunts in two adult patients. Contrast medium was injected through a median antecubital vein and data were accumulated using the R wave-triggered flow mode. Time-density curves from a region of interest were generated by a gamma variate fit method and areas under the curves were calculated. Comparisons of calculated left to right shunts (Cases 1 and 2) with results of computed tomography and right to left shunt (Case 2) with cardiac catheterization data resulted in close agreement. This is the first report of quantitation of intracardiac shunts at the atrial level in humans by rapid acquisition computed tomography.     

Blood oxygen measurements in the assessment of intracardiac left to right shunts: A critical appraisal of methodology

The proper use of sequential diagnostic blood oxygen determinations for assessing left to right shunts requires a thorough understanding of the normal variability of blood oxygen measurements among the various right heart chambers and the influence of alterations in circulating hemoglobin levels and systemic blood flow. Oximetric measurements were obtained in 23 patients without a left to right shunt and compared with measurements obtained in 42 patients with a proved left to right shunt to examine the normal range of oxygen variability in blood samples from right heart chambers. The effect of fluctuations in hemoglobin levels was evaluated by comparing increases in percent oxygen saturation and oxygen content. Differences in percent saturation were found to be more useful than differences in oxygen content for detection of cardiac shunts. A mean difference of at least 7 percent oxygen saturation was found to be required for a firm diagnosis of a shunt at the atrial level, and 5 percent oxygen saturation for a shunt at the ventricular or great vessel level.The curvilinear relation between systemic blood flow and oxygen step-up in determining the pulmonary to systemic flow ($\text{Q}{}_{\mathrm{P}}\text{Q}{}_{\mathrm{S}}$) ratio was expressed in a series of equations and depicted by a three dimensional surface. Interventions such as exercise augment both systemic blood flow and oxygen step-up, resulting in a shift to a more steeply rising portion of the surface and a dramatic increase in shunt flow. The minimal left to right shunt detectable with oxlmetry is largely dependent on the level of systemic blood flow.     

Detection of mild aortic regurgitation by range-gated pulsed doppler echocardiography

In order to assess the sensitivity and specificity of the range-gated pulsed Doppler echocardiogram for the detection of aortic regurgitation, a study with use of this technique was carried out in 46 patients. They were classified into 3 groups: Group I was composed of 19 patients with a variety of heart diseases but with a competent aortic valve. Cardiac catheterization revealed no aortic regurgitation in any of the 19 patients, and the Doppler echocardiogram detected no turbulent diastolic flow in the left ventricular outflow tract. Group II was composed of 17 patients who clinically and by auscultation had aortic regurgitation, which was confirmed by cardiac catheterization in 6. In all 17 patients the Doppler echocardiogram detected several grades of turbulent diastolic flow compatible with aortic regurgitation in the left ventricular outflow tract. Group III was composed of 10 patients with aortic regurgitation but without the expected clinical or auscultatory evidence. The echocardiogram detected mitral valve flutter in only 1 patient. Cardiac catheterization revealed aortic regurgitation graded $\text{1}\text{4}$ and $\text{2}\text{4}$ in 9 patients, and the patient who did not undergo catheterization had a murmur of aortic insufficiency 6 months later. In all 10 patients the Doppler echocardiogram detected a regurgitating turbulent flow compatible with aortic regurgitation in the left ventricular outflow tract.It is concluded that the Doppler echocardiogram was more useful than auscultation and echocardiography for the detection of mild aortic regurgitation. In this study the range-gated pulsed Doppler echocardiogram proved 100% sensitive and specific. However, it will be necessary to study larger groups in order to assess its utility in more complicated conditions (obesity, emphysema, and heart failure) and the differential diagnosis with other diastolic murmurs.     

Unloading effects of prazosin in patients with chronic aortic regurgitation

Seventeen patients with chronic aortic regurgitation (AR) were examined by echocardiography and left and right heart catheterization. Cardiac output and regurgitation volume were measured by the dye dilution method. Administration of single and four repeated doses of prazosin (PZ) led to reductions of left ventricular (LV) end-diastolic, end-systolic, and left atrial end-systolic diameters, and decrease of left ventricular filling pressure. Regurgitation fraction, regurgitation flow, and volume indexes decreased significantly (p < 0.01). Total left ventricular output decreased (p < 0.001) as did derived parameters of left ventricular work and performance. Fractional shortening, ejection fraction, and mean circumferential fiber shortening velocity increased as did LV $\text{dP}\text{dt}$ and dP/dt/P. Changes in heart rate and cardiac and stroke indexes after PZ were not significant. Preload reduction (dilation of the venous bed and reduction of regurgitation) seems to be the most important effect of PZ in AR. We found PZ to be a suitable and effective drug for oral treatment of chronic AR.     

Accuracy of left ventricular ejection fraction determined by the nuclear stethoscope

We assessed left ventricular ejection fraction 47 times in 21 patients with sinus rhythm by a portable non-imaging nuclear probe. After ^99mTc blood pool labelling, left ventricular ejection fraction was determined by probe in two different ways: on a beat-to-beat basis, and by the so-called ventricular function mode, based on the gated equilibrium principle, and subsequently compared with left ventricular ejection fraction measured by gated equilibrium radionuclide angiocardiography using a gamma camera.Left ventricular ejection fraction by probe correlated well with left ventricular ejection fraction by gamma camera: beat-to-beat versus gamma camera: r = 0.90, y = 0.75x + 0.12; ventricular function versus gamma camera: r = 0.88, y = 0.87x + 0.08. Also, left ventricular ejection fraction values determined by the two probe methods correlated closely: r = 0.97, y = 0.83x + 0.07. Compared with the gamma camera, the probe overestimated slightly the small values of left ventricular ejection fraction and underestimated high values. Correct determination of left ventricular ejection fraction by a non-imaging probe depends on correct positioning over the left ventricle and selection of a proper background activity level.The main application of this instrument is probably non-invasive bedside determination and monitoring of changes of left ventricular function occurring spontaneously or caused by cardiac arrhythmias or treatment with cardiac drugs.     

Rapid method for determination of shunt ratio using a thermodilution technique

A new technique using thermodilution by which shunt ratio can be rapidly and conveniently determined in patients with left-to-right intracardiac shunts is described. A flow-directed balloon-tip thermistor catheter was positioned in the pulmonary artery to measure cardiac output in 20 patients with left-to-right intracardiac shunts. Shunt ratio measured by the Fick technique (Qp:Qs_F) varied between 1.3:1 and 3.6:1. Early recirculation was seen on the downslope of the thermodilution curves (TC). The first-pass curve before the point of early recirculation was extrapolated to the baseline and the area inscribed by this portion of the TC (A) was measured by planimetry. The area inscribed by the entire TC (A + B) was also measured by planimetry. Shunt size was determined by calculating the ratio (A + B):A. Shunt ratio determined by this technique (Qp:Qs_Th) correlated well with Qp:Qs_F (r = 0.89). The thermodilution technique provides a simple, rapid, and accurate method for determining the magnitude of left-to-right intracardiac shunts.     

Quantification of left to right cardiac shunts by multiple deconvolution analysis

A new method for quantification of left to right cardiac shunts was studied in 17 patients scheduled for cardiac catheterization who had also undergone radionuclide angiocardiography. The observed pulmonary transit curve was deconvoluted in two different ways: (1) by the superior vena caval (“bolus”) time-activity curve, to yield the deconvoluted pulmonary transit curve, which represented the theoretical pulmonary transit curve with a perfect bolus injection, and (2) by the right ventricular time-activity curve, to yield the pulmonary transfer function, which represented the theoretical pulmonary transit curve with a perfect bolus injection and with no intracardiac shunts. The pulmonary transfer function was superimposed on the deconvoluted pulmonary transit curve, and the area A under it obtained. The pulmonary transfer function was then subtracted from the deconvoluted pulmonary transit curve. The pulmonary transfer function was scaled to fit the resulting shunt recirculation peak in the difference curve, and the area B under this scaled pulmonary transfer function obtained. Shunt size was quantified as the pulmonary (QP) to systemic (QS) flow ratio QP/QS = A/(A − B). The method correlated closely with oximetry (r = 0.93). Use of this multiple deconvolution analysis technique provides accurate shunt quantification and reduces subjective operator decisions.     

Assessment of the intracardiac left to right shunts with a single scintillation probe

In order to assess the accuracy of pulmonary time-activity curves obtained at bedside with a single scintillation probe and Technetium-99m-labelled erythrocytes, pulmonary to systemic flow ratio (Qp:Qs) was calculated for radionuclide and hemodynamic investigations in 104 patients with suspected intracardiac left to right shunts. Cardiac catheterization confirmed the presence of shunts in 76 patients. Pulmonary time-activity curve was 100% sensitive, 88% specific, and 96% accurate in detecting the shunt. Correlation between the radionuclide and hemodynamic Qp:Qs was excellent (r = 0.93). Results were classified in four quantitative categories according to the Qp:Qs values. In 76 patients (73%) radionuclide and hemodynamic data fell in the same category. We conclude that radionuclide pulmonary time-activity curves generated with a scintillation probe is a reliable method in quantitative assessment of intracardiac left to right shunts.     

Gated radionuclide angiographic evaluation of valve regurgitation

Gated radionuclide angiography is a new noninvasive technique that can be used to calculate the ratio of left and right ventricular stroke volumes. This stroke volume ratio, which must be unity in normal subjects, increases in patients with aortic or mitral regurgitation in direct proportion to the degree of left ventricular volume overload, provided no shunts or regurgitant right heart lesions are present. In 22 patients with aortic or mitral regurgitation there was excellent correlation between the stroke volume ratio determined with gated radionuclide angiography and with standard quantitative catheterization methods (r = 0.79). Measurement of valve regurgitation with this radionuclide method also correlated well with data obtained from semiquantitative aortic root or left ventricular cineangiography (r = 0.72). Twenty-one of the 22 patients with valve regurgitation had an abnormally elevated stroke volume ratio, thereby suggesting that gated radionuclide angiography may be useful in detecting or excluding hemodynamically significant valve regurgitation.     

Echocardiographic assessment of discrete subaortic stenosis in childhood

The validity of Laplace's relation for assessing peak left ventricular pressure has previously been demonstrated in children with congenital aortic valve $\text{s}$tenosis by using the echocardiographically determined end-diastolic $\text{h}\text{r}$ ratio (that is, the ratio of mean left ventricular septal and posterior wall thicknesses to half the minor left ventricular cavity axis). This report examines the applicability of this ratio to the preoperatlve assessment of left ventricular pressure in 17 children with discrete subaortic stenosis. Because the regression equation derived from previously published data on patients with aortic valve stenosis and the present data on children with subaortic stenosis were similar, a pooled estimate of peak left ventricular pressure (LVP) in children $\text{w}$ith left ventricu$\text{l}$ar outflow tract obstruction is presented: $\text{LVP}\text{= 312.23 (}\text{h}\text{r}\text{) ± 28.01 (}\text{h}\text{r}\text{)}$.Additionally, the left ventricular outflow tract was measured as the anteroposterior dimension between the first recognizable closure point of the mitral valve and the interventricular septum and expressed as the left ventricular outflow tract/aortic root dimension ($\text{LVOT}\text{Ao}$) ratio. This ratio was tower in patients with subaortic stenosis than in control subjects and was helpful in differentiating patients with mild stenosis from those with more severe stenosis. The prevalence of echocardiographically observed features such as early systolic closure of the aortic valve and fluttering of the aortic valve leaflets could not be correl$\text{a}$ted with the severity of stenosis. It is concluded that the end-diastolic $\text{h}\text{r}$ ratio and the $\text{VOT}\text{Ao}$ ratio are quantitatively useful in the assessment of subaortic stenosis, whereas the commonly present motion abnormalities of the aortic valve are not indicative of the severity of the subaortic lesion.     

Gold-195m,a new generator-produced short-lived radionuclide for sequential assessment of ventricular performance by first pass radionuclide angiocardiography

The feasibility of performing rapid sequential first pass radionuclide angiocardiography using a new short-lived radiotracer, gold-195m (^195mAu) half-life 30.5 seconds) was evaluated. This radionuclide emits a 262 keV gamma ray and is the daughter of mercury-195 (^195mHg) (half-life 41.6 hours). The prototype tabletop ${}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Hg}{}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Au}$ generator produced 20 to 25 mCi of ^195mAu in 2 ml of eluate (yield of 40 percent). The breakthrough of ^195mHg in the eluate was 0.02 percent of the amount of ^195mHg in the generator. The eluate contained 20 μCi of ^195mHg per study, resulting in an estimated human radiation dose of 0.007 rad/study to the whole body and 0.34 rad/study to the kidney.Four dogs each had 15 to 20 sequential first pass studies performed with ^195mHg at 3 to 10 minute intervals using a computerized multicrystal gamma camera. During the left ventricular phase, 160,000 to 190,000 counts/s were acquired. The end-diastolic left ventricular region of interest contained 3,000 to 6,000 counts (background- and decay-corrected). Multiple reproducible values for left ventricular ejection fraction were obtained during stable conditions. The mean (± standard deviation) interstudy variability was 4 ±2 percent. During infusion of isoproterenol, rapid increase of left ventricular ejection fraction was demonstrated. Excellent agreement was observed between studies performed with technetium-99m diethylenetriaminepentaacetic acid (^99mTc-DTPA) and ^195mAu. The mean jnterstudy difference was 4 ±3 percent. Thus, sufficiently high yield and dose are obtained from the ${}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Hg}{}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Au}$ generator for reliable high count rate first pass determination of left ventricular ejection fraction. This new short-lived radiotracer makes possible rapid sequential assessments of ventricular function at greatly reduced patient exposure to radiation.