Direct measurement of cardiac output by gated equilibrium blood pool scintigraphy: validation of scintigraphic volume measurements by a nongeometric technique

Effect at One Year of Adjuvant Trastuzumab for HER2+ Breast Cancer Combined with Radiation or an Anthracycline on Left Ventricular Ejection Fraction

To determine the impact of radiation therapy (XRT) in addition to trastuzumab (TZB) adjuvant chemotherapy for HER2+ breast cancer on left ventricular systolic function, we assessed demographics, oncologic treatment history including XRT exposure, and serial measurements of left ventricular ejection fraction (LVEF) in 135 consecutively identified women receiving TZB for treatment of adjuvant breast cancer. Longitudinal mixed effects models were fit to identify baseline to treatment changes in LVEF among those receiving TZB with or without concomitant anthracycline or XRT. Women averaged 53 ± 3 years in age, 77% were white, 62% patients had 1 or more cardiovascular risk factors at baseline, and mean duration of TZB was 11 ± 5 months. Seventy-seven women were treated with XRT and received between 4000 and 5500 cGy of radiation. The LVEF declined by an average of 3.4% after 1 year for those in the study. Relative to baseline upon completion of adjuvant TZB, LVEF remained reduced for those receiving anthracycline with or without XRT (p=0.002 for both), or XRT alone (p=0.002), but not in those without these therapies. Amongst patients treated only with XRT and TZB, LVEF declined 3.1% on average in those with left-sided disease and 6.9% on average in those with right-sided disease (p= 0.06, p= 0.008 respectively). Among women receiving TZB for adjuvant treatment of HER-2 positive breast cancer, the administration of XRT, anthracycline, or the combination of the 2 is associated with a persistent post-treatment as opposed to a temporary treatment related decline in LVEF.

End-systolic elastance and ventricular-arterial coupling reserve predict cardiac events in patients with negative stress echocardiography

Background. A maximal negative stress echo identifies a low-risk subset for coronary events. However, the potentially prognostically relevant information on cardiovascular hemodynamics for heart-failure-related events is unsettled. Aim of this study was to assess the prognostic value of stress-induced variation in cardiovascular hemodynamics in patients with negative stress echocardiography. Methods. We enrolled 891 patients (593 males mean age 63 ± 12, ejection fraction 48 ± 17%), with negative (exercise 172, dipyridamole 482, and dobutamine 237) stress echocardiography result. During stress we assessed left ventricular end-systolic elastance index (E_LVI), ventricular arterial coupling (VAC) indexed by the ratio of the E_LVI to arterial elastance index (E_aI), systemic vascular resistance (SVR), and pressure-volume area (PVA). Changes from rest to peak stress (reserve) were tested as predictors of main outcome measures: combined death and heart failure hospitalization. Results. During a median followup of 19 months (interquartile range 8–36), 50 deaths and 84 hospitalization occurred. Receiver-operating-characteristic curves identified as best predictors E_LVI reserve for exercise (AUC = 0.871) and dobutamine (AUC = 0.848) and VAC reserve (AUC = 0.696) for dipyridamole. Conclusions. Patients with negative stress echocardiography may experience an adverse outcome, which can be identified by assessment of E_LVI reserve and VAC reserve during stress echo.

Use of the Frank-Starling mechanism during exercise is linked to exercise-induced changes in arterial load

Effective arterial elastance(E(A)) is a measure of the net arterial load imposed on the heart that integrates the effects of heart rate(HR), peripheral vascular resistance(PVR), and total arterial compliance(TAC) and is a modulator of cardiac performance. To what extent the change in E(A) during exercise impacts on cardiac performance and aerobic capacity is unknown. We examined E(A) and its relationship with cardiovascular performance in 352 healthy subjects. Subjects underwent rest and exercise gated scans to measure cardiac volumes and to derive E(A)[end-systolic pressure/stroke volume index(SV)], PVR[MAP/(SV*HR)], and TAC(SV/pulse pressure). E(A) varied with exercise intensity: the ΔE(A) between rest and peak exercise along with its determinants, differed among individuals and ranged from -44% to +149%, and was independent of age and sex. Individuals were separated into 3 groups based on their ΔE(A)I. Individuals with the largest increase in ΔE(A)(group 3;ΔE(A)≥0.98 mmHg.m(2)/ml) had the smallest reduction in PVR, the greatest reduction in TAC and a similar increase in HR vs. group 1(ΔE(A)<0.22 mmHg.m(2)/ml). Furthermore, group 3 had a reduction in end-diastolic volume, and a blunted increase in SV(80%), and cardiac output(27%), during exercise vs. group 1. Despite limitations in the Frank-Starling mechanism and cardiac function, peak aerobic capacity did not differ by group because arterial-venous oxygen difference was greater in group 3 vs. 1. Thus the change in arterial load during exercise has important effects on the Frank-Starling mechanism and cardiac performance but not on exercise capacity. These findings provide interesting insights into the dynamic cardiovascular alterations during exercise.

Hemodynamic adaptations to stress with advancing age

With advancing adult aging an increase in vascular stiffness, an increase in systolic, pulse and mean arterial pressure, modest left ventricular hypertrophy, and a moderate decline in early diastolic filling rate have uniformly been observed. In some individuals these changes are not associated with enhanced systemic resistance if arterial pressure remains within the normotensive range. End-systolic volume, stroke volume, ejection fraction, velocity of ejection, and cardiac output are preserved in these elderly subjects. In other individuals both aortic impedance and peripheral vascular resistance are increased with age and modest declines in resting stroke volume and cardiac output have been observed. During maximal exercise a diminished heart rate and a diminished reduction of end-systolic volume occur in elderly subjects. In some, an enhanced end-diastolic volume prevents a reduction in or enhances stroke volume (Starling mechanism); this adaptation bears a striking resemblance to that observed during exercise when the beta-adrenergic system is pharmacologically inhibited. In other elderly subjects, stroke volume during exercise does not increase to the extent that it does in younger subjects. Even in these subjects in whom peak cardiac output during exercise declines, however, it is not entirely clear that the central circulation limits peak oxygen consumption (VO2). The nonuniformity of results of studies that have investigated the effect of aging on cardiac function and vascular resistance suggests that variables that impact on cardiovascular function other than aging per se, i.e. life style variables, e.g. nutrition, smoking, physical conditioning status, or the prevalence of occult coronary disease, differed among the various subjects studied.

Arterial-ventricular coupling: mechanistic insights into cardiovascular performance at rest and during exercise

Understanding the performance of the left ventricle (LV) requires not only examining the properties of the LV itself, but also investigating the modulating effects of the arterial system on left ventricular performance. The interaction of the LV with the arterial system, termed arterial-ventricular coupling (E(A)/E(LV)), is a central determinant of cardiovascular performance and cardiac energetics. E(A)/E(LV) can be indexed by the ratio of effective arterial elastance (E(A); a measure of the net arterial load exerted on the left ventricle) to left ventricular end-systolic elastance (E(LV); a load-independent measure of left ventricular chamber performance). At rest, in healthy individuals, E(A)/E(LV) is maintained within a narrow range, which allows the cardiovascular system to optimize energetic efficiency at the expense of mechanical efficacy. During exercise, an acute mismatch between the arterial and ventricular systems occurs, due to a disproportionate increase in E(LV) (from an average of 4.3 to 13.2, and 4.7 to 15.5 mmHg.ml(-1).m(-2) in men and women, respectively) vs. E(A) (from an average of 2.3 to 3.2, and 2.3 to 2.9 mmHg.ml(-1).m(-2) in men and women, respectively), to ensure that sufficient cardiac performance is achieved to meet the increased energetic requirements of the body. As a result E(A)/E(LV) decreases from an average of 0.58 to 0.34, and 0.52 to 0.27 in men and women, respectively. In this review, we provide an overview of the concept of E(A)/E(LV), and examine the effects of age, hypertension, and heart failure on E(A)/E(LV) and its components (E(A) and E(LV)) in men and women. We discuss these effects both at rest and during exercise and highlight the mechanistic insights that can be derived from studying E(A)/E(LV).

Left ventricular, peripheral vascular, and neurohumoral responses to mental stress in normal middle-aged men and women. Reference Group for the Psychophysiological Investigations of Myocardial Ischemia (PIMI) Study

BACKGROUND

The normal cardiovascular response to mental stress in middle-aged and older people has not been well characterized.

METHODS AND RESULTS

We studied 29 individuals 45 to 73 years old (15 women, 14 men) who had no coronary risk factors, no history of coronary artery disease, and a negative exercise test. Left ventricular (LV) volumes and global and regional function were assessed by radionuclide ventriculography at rest and during two 5-minute standardized mental stress tasks (simulated public speaking and the Stroop Color-Word Test), administered in random order. A substantial sympathetic response occurred with both mental stress tests, characterized by increases in blood pressure, heart rate, rate-pressure product, cardiac index, and stroke work index and rises in plasma levels of epinephrine and norepinephrine but not beta-endorphin or cortisol. Despite this sympathetic response, LV volume increased and ejection fraction (EF) decreased secondary to an increase in afterload. The change in EF during mental stress-varied among individuals but was associated positively with changes in LV contractility and negatively with baseline EF and changes in afterload. EF decreased > 5% during mental stress in 12 individuals and > 8% in 5; 3 developed regional wall motion abnormalities.

CONCLUSIONS

Mental stress in the laboratory results in a substantial sympathetic response in normal middle-aged and older men and women, but EF commonly falls because of a concomitant rise in afterload. These results provide essential age- and sex-matched reference data for studies of mental stress-induced ischemia in patients with coronary artery disease.

Ischemic, hemodynamic, and neurohormonal responses to mental and exercise stress. Experience from the Psychophysiological Investigations of Myocardial Ischemia Study (PIMI)

BACKGROUND

The pathophysiology of mental stress-induced myocardial ischemia, which occurs at lower heart rates than during physical stress, is not well understood.

METHODS AND RESULTS

The Psychophysiological Investigations of Myocardial Ischemia Study (PIMI) evaluated the physiological and neuroendocrine functioning in unmedicated patients with stable coronary artery disease and exercise-induced ischemia. Hemodynamic and neurohormonal responses to bicycle exercise, public speaking, and the Stroop test were measured by radionuclide ventriculography, ECG, and blood pressure and catecholamine monitoring. With mental stress, there were increases in heart rate, systolic blood pressure, cardiac output, and systemic vascular resistance that were correlated with increases in plasma epinephrine. During exercise, systemic vascular resistance fell, and there was no relationship between the hemodynamic changes and epinephrine levels. The fall in ejection fraction was greater with mental stress than exercise. During mental stress, the changes in ejection fraction were inversely correlated with the changes in systemic vascular resistance. Evidence for myocardial ischemia was present in 92% of patients during bicycle exercise and in 58% of patients during mental stress. Greater increases in plasma epinephrine and norepinephrine occurred with ischemia during exercise, and greater increases in systemic vascular resistance occurred with ischemia during mental stress.

CONCLUSIONS

Mental stress-induced myocardial ischemia is associated with a significant increase in systemic vascular resistance and a relatively minor increase in heart rate and rate-pressure product compared with ischemia induced by exercise. These hemodynamic responses to mental stress can be mediated by the adrenal secretion of epinephrine. The pathophysiological mechanism involved are important in the understanding of the etiology of myocardial ischemia and perhaps in the selection of appropriate anti-ischemic therapy.

The age-associated decline in glomerular filtration in healthy normotensive volunteers. Lack of relationship to cardiovascular performance

Whether the well-documented age-associated decline in the glomerular filtration rate, manifest as a decline in creatinine clearance, is secondary to an age-related change in cardiovascular performance is at present unknown. To answer this question, we measured arterial blood pressure, 24-hour creatinine clearance, and cardiac output determined from gated cardiac blood pool scans in the sitting position in healthy normotensive men (n = 75) and women (n = 42) (ages 25 to 82 years), from the Baltimore Longitudinal Study on Aging. These subjects were selected for the absence of cardiovascular disease, renal disease, and confounding medications. By linear regression analysis, creatinine clearance, expressed in mL/min/m2, declined cross-sectionally with age (creatinine clearance = 90 -0.33[age], r = .31, P less than .001), whereas systolic blood pressure in mm Hg increased with age (systolic blood pressure = 111 + 0.27[age], r = .30, P less than .001); cardiac output in L/min/m2 did not vary with age (r = .03, P = .74). In stepwise multiple regression analysis with age, cardiac index, and systolic blood pressure as independent variables and creatinine clearance as the dependent variable, only age was a significant predictor of creatinine clearance. (F = 11.31, DF + 116, r = .30, P less than .001). Thus, the age-associated decline in creatinine clearance is not modulated by changes in cardiac index or systolic blood pressure in healthy normotensive subjects.

Assessment of the sensitivity of hydrogen inhalation in the detection of left-to-right shunting

For the detection of left-to-right intracardiac shunting, the oximetric and standard indocyanine green techniques are relatively insensitive, in that neither can reliably detect a shunt with a ratio of pulmonary to systemic flow (Qp/Qs) less than 1.3 (percentage shunt, 23%). Although the hydrogen inhalation method is said to be much more sensitive in this regard, no previous study has measured its sensitivity. Accordingly, in 15 patients (4 men, 11 women, aged 38 to 67 years) without intracardiac shunting, hydrogen inhalation was performed 1) without and 2) with an artificially created femoral arteriovenous shunt of known size, and cardiac output was measured by thermodilution. For the 15 subjects with cardiac outputs of 3.64 to 8.10 liters/min, shunts of 22 to 248 ml/min were created, so that the shunts ranged from 0.5% to 3.3%. Hydrogen inhalation detected all shunts greater than or equal to 1.3% (Qp/Qs greater than or equal to 1.01). Of the 10 shunts less than 1.3%, it detected 5, with the smallest being 0.7%. Thus, the hydrogen inhalation technique is extremely sensitive in identifying the presence of left-to-right shunting, far more sensitive than the oximetric and standard indocyanine green methods.

The effect of oxygen on sodium excretion in hypoxemic patients with chronic obstructive lung disease

In advanced chronic obstructive lung disease (COLD), sodium retention is common, associated with reduction in renal plasma flow (RPF) and stimulation of the renin-aldosterone (PRA-PA) system, two abnormalities due to or influenced by hypercapnia: the independent role of hypoxemia in perturbing sodium homeostasis is unknown. In five stable patients with COLD (FEV1 = 0.9 +/- 0.21, mean +/- SE) with mild edema, during two weeks of a low sodium diet (one week on room air: pH = 7.39 +/- 0.02; PaO2 = 55 +/- 4 mm Hg; PaCO2 = 49 +/- 4 mm Hg; and one week on O2: pH = 7.38 +/- 0.01; PaO2 = 72 +/- 6 mm Hg; PaCO2 = 52 +/- 4 mm Hg) we monitored sodium balance, systemic and renal hemodynamics, plasma sodium and potassium, PRA, PA, and atrial natriuretic hormone (ANH). During air breathing, patients uniformly showed a depression of RPF despite normal cardiac output; plasma hormone levels did not differ from controls but there was elevation (greater than 2 SD above the normal mean) of PRA in four patients, PA in two patients, and ANH in two of five patients. During O2 breathing, urinary sodium increased significantly from 67 +/- 7 to 102 +/- 10 mEq/24 h. Surprisingly, the patients experienced a small but significant weight gain (0.6 +/- 0.1 kg). None of the other variables was affected by O2 therapy. The following conclusions were reached: in advanced COLD, correction of hypoxemia results in sodium diuresis, indicating that hypoxemia (in the presence of hypercapnia) contributes to sodium retention. The mechanism for this beneficial effect of O2 will require further investigation.

Atrial natriuretic peptide, renin and aldosterone in obstructive lung disease and heart failure

Elevations of atrial natriuretic peptide (ANP) in congestive heart failure (CHF) and chronic obstructive lung disease (COLD) are presumably due to atrial hypertension, while secondary hyperaldosteronism in these patients is thought to result from diminished renal perfusion. The responsiveness of the ANP and renin (PRA)-aldosterone (PA) systems to acute increases in right atrial pressure has not been studied in these patients, but in normals a reciprocal relationship between ANP with PRA and PA has been shown. The authors monitored venous pressure (VP, reflective of right atrial pressure), ANP, PRA and PA in 15 stable COLD patients, seven stable CHF patients and three normal controls at baseline and after elevation of VP by antishock trousers. Inflation of the trousers resulted in increased VP and ANP (p less than 0.05): control ANP, 84 +/- 17 to 108 +/- 23 pg/ml; COLD ANP, 176 +/- 5 to 200 +/- 7; and CHF ANP, 388 +/- 20 to 499 +/- 37. PRA and PA were not suppressed by increasing ANP levels and the delta ANP/delta VP ratio was similar among groups. No intergroup differences in resting PRA and PA were noted, but PRA was higher (p = 0.007) and PA tended to be higher (p = 0.08) in a sub-group of six edematous patients, as compared with non-edematous patients and controls. These findings: (1) confirm previously reported ANP differences between COLD and CHF; (2) indicate that the ANP system remains responsive to physiologic manipulations in COLD and CHF; and (3) demonstrate that ANP and the PRA-PA axis are not reciprocally related in either group.

Combined first pass and equilibrium radionuclide cardiographic determination of stroke volume for quantitation of valvular regurgitation

A new noninvasive procedure for quantitation of cardiac valve regurgitation was evaluated using a combination of first pass and gated equilibrium radionuclide cardiography in 38 subjects with and without cardiac valve disease. Left-sided cardiac catheterization was performed to determine the severity of mitral incompetence and aortic regurgitation semiquantitatively. In healthy subjects and in patients without valve disease, stroke volumes were nearly identical with the two methods and the correlation was high (r = 0.98 [p less than 0.001]). The mean regurgitation fraction was 13% in patients with mild mitral incompetence and 2+ aortic regurgitation, 37% in patients with moderate mitral incompetence and 3+ aortic regurgitation and 57% in patients with severe mitral incompetence and 4+ aortic regurgitation. These findings suggest that combined first pass and gated equilibrium radionuclide cardiography, being insensitive to intracardiac shunts and right-sided valve disorders, constitutes a valid noninvasive technique for quantitation of left-sided cardiac valve regurgitation.

Cardiac function at rest and during exercise in early and late alcohol intoxication

Seven healthy men, aged 21 to 30 years, were investigated by radionuclide cardiography at rest and during submaximal exercise at heavy (early) and during declining (late) alcohol intoxication. Control studies, in which alcohol was substituted by an isocaloric, isovolumic drink, were performed on a different day. The left ventricular ejection fraction at rest decreased from 59 to 56% during early intoxication (serum ethanol 35 +/- 6 mmol/l), whereas no change was observed in the ejection fraction during exercise. No significant change was recorded in stroke volume after alcohol consumption as opposed to a small increase after ingestion of the caloric drink. Plasma noradrenaline concentrations were elevated during exercise and early intoxication. During late intoxication (serum ethanol 21 +/- 5 mmol/l) the left ventricular ejection fraction at rest was increased by 7% compared with the baseline value. At rest the heart rate was increased from 68 +/- 7 to 84 +/- 15 beats/min, whereas cardiac output had reverted to the baseline value. Plasma noradrenaline at late intoxication was increased both at rest and during exercise compared with the baseline values. Apart from tachycardia and a reduction in left ventricular volumes during late intoxication no alcohol induced hemodynamic changes occurred during exercise.

Left-ventricular cavity dimensions in children with normal and dilated hearts

Studies were carried out to find how left-ventricular length and length/diameter ratio relate to body size and degree of dilation. By use of M-mode and two-dimensional echocardiography, diastolic cavity long axis (Led), diastolic cavity diameter (Ded), systolic cavity long axis (Les), systolic cavity diameter (Des), fractional L shortening (SFL), and fractional D shortening (SFD) were measured in children, adolescents, and young adults between two and 23 years of age, with body-surface area (BSA) between 0.5 and 2.1 m2 and with a variety of volume loads and SFD values. In normal subjects, Led/Ded was about 1.9. Regardless of age and pathology (in this age range), Led correlated consistently with BSA (Led = 3.9 + 3.2 BSA), indicating that the long axis changes rather little with pathological dilation. A plot of Led/Ded vs BSA/D2ed (in m2/cm2) formed a straight-line relation: Led/Ded = 0.77 + 16.4 BSA/D2ed. Similar relations were found for end-systolic dimensions. End-systolic L/D ratio exceeded end-diastolic L/D ratio to a degree that depended on both end-diastolic L/D ratio and SFD:Les/Des = Led/Ded + (0.22 + 2.67 Led/Ded)(SFD)2. Relations like these may be useful in the interpretation of echocardiographic images. The results suggest that left-ventricular L/D ratio may be influenced by myocardial anisotropy (dominance of hoop over meridional fiber orientation tending to promote prolate shape especially during systole) and external factors that antagonize extension of the long axis.

Noninvasive determination of the valvar area in aortic valve disease by Doppler echocardiography and radionuclide angiography

To assess the severity of outlfow obstruction in patients with aortic valve disease, the aortic valvar area was noninvasively determined in 22 patients with isolated aortic stenosis or combined stenosis and regurgitation. The ejection time (ET), maximal velocity (Vmax), and systolic velocity integral (SVI) of the aortic flow was obtained by continuous wave Doppler ultrasound. Left ventricular stroke volume (SV) was determined by radionuclide angiography, using a counts-based nongeometric technique with individual attenuation correction. Aortic valve area (AVA) was calculated using a modified Gorlin formula; AVA = SV/(71.2 X ET X Vmax), and also by dividing the stroke volume by the systolic velocity integral; AVA = SV/SVI. The two noninvasive determinations correlated closely with the valve areas obtained by invasive measurements; r = 0.95, SEE = +/- 0.13 cm2 by the modified Gorlin formula, and r = 0.94, SEE = +/- 0.14 cm2 by the integration method. The two noninvasive calculations showed almost uniform results; r = 0.98, SEE = +/- 0.09 cm2. In conclusion, aortic valve area can be determined with reasonable accuracy by combining Doppler echocardiography and radionuclide angiography. This noninvasive approach may reduce the need for invasive measurements in patients with suspected aortic valve disease. In addition, radionuclide angiography provides important information about left ventricular function.

Immediate effect of expiratory loading on left ventricular stroke volume

While the steady-state effects of positive pleural pressure on the circulation have been extensively studied, less is known about the immediate effects of positive intrathoracic pressure on cardiac dynamics. Therefore, we performed electrocardiographically gated radionuclide ventriculography with a respiratory gating technique in nine healthy subjects during quiet breathing and during expiration against a 24 cm H2O expiratory threshold load. During expiration, respiratory loading caused an increase in stroke counts by 29.4% (p less than .001) due to an increase in end-diastolic counts of 26.1% (p less than .001). End-systolic counts also rose 18.8% (p less than .05). The ejection fraction did not change significantly. These findings indicate that the increase in left ventricular stroke volume that occurs during the first 1 or 2 beats of a loaded expiration is due to an increase in left ventricular filling and not to augmentation of left ventricular ejection. This immediate increase in pulmonary venous return may reflect increased distensibility of the left ventricle due to decreased filling of the right ventricle.

Changes in left ventricular function during recovery from upright bicycle exercise in normal persons and patients with coronary artery disease

To characterize the hemodynamic changes during recovery after upright bicycle exercise, 56 normal subjects (group I) and 30 patients with documented myocardial ischemia (group II) were studied. Heart rate, blood pressure and radionuclide angiographically determined absolute left ventricular (LV) volumes were measured at baseline, peak exercise and 2 to 4.5 minutes and 4.5 to 7 minutes after upright bicycle exercise. Whereas ejection fraction and end-systolic volume responses at peak exercise differed between groups I and II, these parameters showed similar trends in both groups during recovery. Mean ejection fraction increased during 2 to 4.5 minutes in both groups, but remained elevated during 4.5 to 7 minutes only in normal subjects (group I). Elevation of cardiac output after exercise was accounted for predominantly by increased heart rate rather than increased stroke volume. Despite significantly decreased end-diastolic volume during recovery, stroke volume was maintained in both groups by a substantial decrease in end-systolic volume, suggesting the impact of decreased afterload or increased sympathetic tone during recovery. Thus, the Frank-Starling mechanism does not appear to be playing a major role during recovery after upright bicycle exercise, whereas enhanced contractility is evident in both normal subjects and patients with documented myocardial ischemia.

Postural changes in cardiac volumes in men in relation to adult age

Cardiac volumes by equilibrium gated cardiac blood pool scans and heart rate were measured in the supine and sitting positions in 64 male volunteer subjects (age 25-80 yrs) who had been rigorously screened to exclude cardiovascular disease. After the upright position was assumed, the average cardiac output of all subjects was unchanged but heart rate increased and stroke volume decreased due to a decrease in end diastolic volume. Neither the supine or sitting cardiac output nor the average postural change in cardiac output, cardiac volumes or heart rate was age-related. While the average cardiac output among the subjects was unaltered with a change in posture, in some individuals it increased slightly while in others it decreased. The postural change in cardiac output among the individuals correlated by linear regression analysis with a change in heart rate only in younger subjects and with a change in stroke volume in all age groups, but the slope of this relationship was greater in older than in younger subjects. The postural change in stroke volume was strongly correlated with a change in end diastolic volume and this relationship did not vary with age. Thus, although the average postural change in cardiac output among healthy subjects is not age-related, a given change in cardiac output with posture in an older individual depends more on a change in stroke volume and less on a heart rate change than in a younger one. This result, like the response to vigorous upright exercise previously demonstrated to occur with aging, indicates a greater reliance in the elderly on the Frank-Starling mechanism than on heart rate for a given change in cardiac output in response to perturbations from the basal supine state.

The reproducibility of nongeometric analysis of cardiac output and left ventricular volume by radionuclide angiography

This study examines the reproducibility of individual radionuclide attenuation factors used in the calculation of cardiac output and left ventricular volume by the nongeometric radionuclide method. Twenty male patients were studied at rest with thermodilution measurements of cardiac output on two separate days. Simultaneous equilibrium radionuclide angiograms were performed and left ventricular stroke volume and cardiac output were determined by the nongeometric method. Individual patient attenuation factors were calculated as the ratio of thermodilution and radionuclide cardiac output measurements at each study. There was a close linear relationship between radionuclide and thermodilution measurements of cardiac output in each study (r = 0.88 study 1, r = 0.97 study 2). A similar relationship was found for measurements of left ventricular stroke volume (r = 0.86, study 1, r = 0.97 study 2). Individual radionuclide attenuation factors ranged from 2.49 to 3.46 in study 1 and from 2.77 to 3.29 in study 2. The individual attenuation factors were reproducible to within 10% in 13 patients and to within 15% in 19 patients. When cardiac output was calculated from the radionuclide data of study 2, by means of individual attenuation factors previously determined in study 1, there was a good correlation with the simultaneous thermodilution measurements of cardiac output (r = 0.92, SEE = 0.38 L/min). Individual radionuclide attenuation factors show little variation in serial studies. Thus the nongeometric radionuclide technique can be used to make accurate serial measurements of cardiac output and left ventricular volume.

Accuracy of radionuclide ventriculography for estimation of left ventricular volume changes and end-systolic pressure-volume relations

Estimation of left ventricular end-systolic pressure-volume relations depends on the accurate measurement of small changes in ventricular volume. To study the accuracy of radionuclide ventriculography, paired radionuclide and contrast ventriculograms were obtained in seven dogs during a control period and when blood pressure was increased in increments of 30 mm Hg by phenylephrine infusion. The heart rate was held constant by atropine infusion. The correlation between radionuclide and contrast ventriculography was excellent. In the individual animals, the average r value for left ventricular volume was 0.96 +/- 0.03 (+/- SD) (p = 0.001, n = 7) and the mean r value for end-systolic volume changes was 0.90 +/- 0.08 (n = 7, range 0.76 to 0.99). For the entire series, there were 33 end-systolic volume changes, and there was an equally strong radionuclide-contrast correlation (r = 0.89, p less than 0.001, n = 33), even though the volume changes averaged only 11.9 +/- 8.2 ml (range 0.3 to 38.1). The systolic pressure-volume relations were linear for both radionuclide and contrast ventriculography (r = 0.98 and 0.97, respectively, n = 7). The mean slope for radionuclide ventriculography (2.9 +/- 1.4) was lower than the mean slope for contrast ventriculography (4.8 +/- 1.7) (p = 0.004); however, the slopes correlated well (r = 0.81, n = 7, p = 0.026). The radionuclide-contrast volume relation was compared using background subtraction, attenuation correction, neither of these or both. By each method, radionuclide ventriculography was valid for measuring small changes in left ventricular volume and for defining end-systolic pressure-volume relations.

Measurement of left ventricular volume using single-photon emission computed tomography

A count-based method for measuring left ventricular (LV) volume using technetium-99m-labeled red cells and ungated single-photon emission computed tomography is described. The tomographic slices were used to determine the counts per milliliter in the center of the left ventricle and total LV counts, which were used to derive mean LV volume. End-diastolic and end-systolic volumes were calculated from the mean volume using the LV time-activity curve from planar gated blood pool images. Phantom evaluation with simulated LV volumes (50 to 400 ml) in air, in a phantom filled with water, with 10% background, and with a simulated right ventricle, showed excellent accuracy. For clinical validation, 30 patients underwent electrocardiographically gated planar and nongated tomographic acquisition of the cardiac blood pool followed by single-plane cineangiography. For end-diastolic and end-systolic volumes combined, the correlation with cineangiography showed a standard error of the estimate (SEE) of 24 ml and 14 ml, respectively. Mean intra- and interobserver deviation was 12 ml and 14 ml (SEE 13 ml and 16 ml), respectively. It is concluded that this noninvasive count-based technique, requiring no assumptions regarding LV geometry, is an accurate and reproducible way to measure LV volume.

Measurement of left-ventricular volumes using an internal standard

When performing equilibrium radionuclide angiocardiography with two successive acquisition views, absolute left-ventricular volumes can be calculated using an 'internal standard' generated by a computer in the left-ventricular cavity. The method is based on the computed ratio of maximum to global activity in the 40 degree-left-anterior-oblique view after background correction and on the measured depth of the left ventricle in almost-orthogonal, 30 degree-left-posterior-oblique Fourier first-harmonic images. The method does not require blood sampling or correction for self attenuation. The intra- and interobserver reproducibility is excellent, even in patients with severe impairment of the ventricular-contractility pattern. When compared with a classical method requiring venous-blood counting and an attenuation correction factor, the accuracy of the internal-standard method was fairly good, with a regression coefficient of 0.90.

Value and limitations of exercise radionuclide angiography for detecting myocardial ischemia in healed myocardial infarction

Exercise radionuclide angiography was performed in 65 normal subjects (group I), in 31 patients with exercise-induced transient thallium defects after acute myocardial infarction (AMI) (group II), and in 16 patients without exercise-induced transient thallium defects, angina or electrocardiographic changes after AMI (group III). Absolute left ventricular (LV) volumes were measured using a correction for attenuation in each patient. Similar peak heart rate-blood pressure products were achieved in groups II and III. Although the mean LV ejection fraction (EF) response to exercise in group III (increase of 0.11 +/- 0.10 units) closely resembled that of normal persons (increase of 0.14 +/- 0.09 units) and was significantly different from that of group II (decrease of 0.04 +/- 0.12), there was considerable individual variation. An abnormal EF response to exercise, defined as failure of EF to increase by at least 0.05 units, was found in 6 subjects (9%) in group I, 26 patients (84%) in group II, and 2 patients (13%) in group III. End-systolic volume failed to decrease in 10 subjects (15%) in group I, 25 patients (81%) in group II and 7 patients (44%) in group III. New regional wall motion abnormalities were found in no subject in group I, in 16 patients (52%) in group II and in only 1 patient (6%) in group III. Thus, although group responses of EF or end-systolic volume appeared to correlate with the presence or absence of ischemia, some patients with exercise-induced transient thallium defects after AMI responded normally to exercise radionuclide angiography stress testing and some patients without other evidence of exercise-induced ischemia after AMI responded to exercise radionuclide angiography testing abnormally.(ABSTRACT TRUNCATED AT 250 WORDS)

Count-based scintigraphic method to calculate ventricular volumes in children: in vitro and clinical validation

A "phantom" was used to validate 1) estimates of different depths of a constant radioactivity source, and 2) the calculation of different volumes using a constant depth and different attenuation coefficients. Using data from this in vitro study, scintigraphic estimates of right ventricular volume and ejection fraction were compared with those obtained by cineangiography in 36 children with either a normal right ventricle or various right ventricular diseases. The static program accurately estimates the distance from the radiation source to the collimator surface (r = 0.99). Radionuclide count methods best predict "phantom" volumes using attenuation coefficients between 0.11(-1) and 0.13(-1) cm. A coefficient of 0.10(-1) underestimates, whereas 0.15(-1) cm grossly overestimates actual volumes. In vivo data were therefore analyzed using an attenuation coefficient of 0.11(-1) with right ventricular counts corrected using either right ventricular or left ventricular background. Closest agreement between scintigraphic and cineangiographic volumes was obtained using right ventricular background, although end-diastolic volumes larger than 100 ml were substantially underestimated. On the basis of this study, the use of two different attenuation coefficients is suggested: the smaller 0.11(-1) cm to calculate end-systolic and end-diastolic volumes and the larger 0.15(-1) cm for volumes greater than 100 ml.

Effect of hypoxemia on sodium and water excretion in chronic obstructive lung disease

To determine the role of hypoxemia in the pathogenesis of impaired sodium and water excretion in advanced chronic obstructive lung disease, 11 clinically stable, hypercapneic patients requiring long-term supplemental oxygen were studied. The renal, hormonal, and cardiovascular responses to sodium and water loading were determined during five-and-a-half-hour studies on a control day (arterial oxygen tension = 80 +/- 6 mm Hg) and on an experimental day under hypoxic conditions (arterial oxygen tension = 39 +/- 2 mm Hg). Hypoxemia produced a significant decrease in urinary sodium excretion but did not affect urinary water excretion. Hypoxemia also resulted in concomitant declines in mean blood pressure, glomerular filtration rate, and filtered sodium load. Renal plasma flow and filtration fraction were unchanged whereas cardiac index rose. On the control day, plasma renin activity and norepinephrine levels were elevated whereas aldosterone and arginine vasopressin levels were normal; none of these four hormones was affected by hypoxemia. Renal tubular function did not appear to be altered by hypoxemia as there was no significant change in fractional reabsorption of sodium. The concurrent decreases in glomerular filtration rate, filtered sodium load, and mean blood pressure at constant renal plasma flow suggest that the reduction in urinary sodium excretion was due to an effect of hypoxemia on glomerular function, possibly related to impaired renovascular autoregulation.

A new scintigraphic method for determining left ventricular volumes

A new scintigraphic count-based method for measuring absolute left ventricular volumes is presented. It is a fast and simple technique that allows geometrical assumptions to be avoided and is free of radiation attenuation corrections. This method requires the acquisition of an image of the left ventricle in the right anterior oblique projection and the collection of gated blood pool images in the left anterior oblique projection. To assess the accuracy of the method scintigraphic stroke volumes were compared with those derived from thermodilution measurements during cardiac catheterization in 20 subjects, and to assess its precision the technique was applied to phantom data of known radionuclide volumes. Excellent correlations were found between the scintigraphic and both the thermodilution (r = .98) and phantom data (r = .99). The reproducibility (r = .97) of results was investigated by repeating data acquisition and analysis for 15 subjects on two different days, and the interobserver variability (r = .97) of the method was studied by having two computer operators calculate volumes for the same patient data for 20 randomly selected studies.

Accuracy of absolute left ventricular volumes and cardiac output determined by radionuclide cardiography

We determined left ventricular (LV) volumes and derived variables by gated equilibrium radionuclide imaging at rest and during exercise in 12 patients without valve disease or intracardiac shunts. LV volume was determined as the product of the background-corrected LV count rate and an individual attenuation correction factor divided by the count rate in peripheral blood. Attenuation correction was based on measurement of LV depth within the chest from an initial first pass study in the left lateral view and a linear attenuation coefficient of 0.156 cm-1 determined in phantom studies. The average LV depth was 8.0 cm (range 6.9-9.1) in agreement with an average depth measured by echocardiography of 8.2 cm (6.3-9.4), P much greater than 0.05. The correlation between radionuclide (RC) and simultaneous thermodilution (TD) measurements was for cardiac output (CO): r = 0.95; CO (RC) = 1.00 X CO (TD) + 0.10 1/min with a standard error of the estimate (SEE) of 0.79 1/min; for stroke volume (SV): r = 0.90; SV(RC) = 0.93 X SV (TD) + 5 ml; SEE = 8 ml; for end-diastolic volume (EDV): r = 0.96; EDV(RC) = 1.06 X EDV(TD) -14 ml; SEE = 27 ml; and for end-systolic volume (ESV): r = 0.98; ESV(RC) = 1.05 X ESV (TD) -6 ml; SEE = 20 ml. The interobserver variation, expressed as the coefficient of variation, was for cardiac output 6%, for stroke volume 6%, for end-diastolic volume 4%, and for end-systolic volume 5%. This method permits non-invasive determination of LV volume and total LV output per beat based exclusively on data obtained during radionuclide imaging.

Mechanism of decreased left ventricular stroke volume during inspiration in man

Radionuclide ventriculography was performed in 15 healthy subjects during quiet breathing and during inspiration against a 24 cm H2O threshold load with a respiratory gating technique. Inspiratory threshold loading caused an inspiratory decrease in ejection fraction from 64% to 59% (p less than .001). Stroke counts proportional to stroke volume decreased by 9.6% (p less than .02) due to an increase in end-systolic counts of 15.9% (p less than .05). End-diastolic counts decreased in four subjects and increased in three subjects, but the mean counts did not change significantly. These findings suggest that negative pleural pressure causes an impediment to left ventricular ejection comparable to an increase in arterial pressure. Respiratory gating of radionuclide ventriculography during loaded breathing is suggested as a controlled stress on the ventricle for diagnostic purposes.

Left ventricular volumes by single-plane cineangiography: in vivo validation of the Kennedy regression equation

This study was performed to assess the accuracy and reliability of the regression equations of Kennedy et al and Wynne et al in the quantitation of single plane left ventricular (LV) volumes. In 15 patients with normal LV function and without intracardiac shunting or valvular insufficiency, gated equilibrium blood pool scintigraphy was performed simultaneously with the measurement of cardiac output (by thermodilution), after which left ventriculography was performed in the 30 degrees right anterior oblique (RAO) projection. From the scintigraphically determined LV ejection fraction (EF) and the thermodilution-measured stroke volume (SV), absolute LV volumes were calculated. The cineangiographic LV volumes obtained with the regression equation of Kennedy et al closely approximated those calculated by scintigraphy/thermodilution, whereas the volumes determined using the regression equation of Wynne et al were larger (p less than 0.05) than the calculated volumes. In 204 patients without intracardiac shunting or valvular insufficiency, SV was measured by the Fick or indicator dilution methods, after which single-plane left ventriculography was performed in the 30 degrees RAO projection. In the 83 patients without coronary artery disease with normal (n = 69) or depressed (n = 14) LVEF, cineangiographic SV (obtained using the regression equation of Kennedy et al) closely approximated forward SV. Similarly, this relation was excellent in the 142 patients whose LVEFs were greater than or equal to 0.50.(ABSTRACT TRUNCATED AT 250 WORDS)

Accurate estimates of absolute left ventricular volumes from equilibrium radionuclide angiographic count data using a simple geometric attenuation correction

To simplify and clarify the methods of obtaining attenuation-corrected equilibrium radionuclide angiographic estimates of absolute left ventricular volumes, 27 patients who also had biplane contrast cineangiography were evaluated. Background-corrected left ventricular end-diastolic and end-systolic counts were obtained by semiautomated variable and hand-drawn regions of interest and were normalized to cardiac cycles processed, frame rate and blood sample counts. Blood sample counts were acquired on (d degree) and at a distance (d') from the collimator. A simple geometric attenuation correction was performed to obtain absolute left ventricular volume estimates. Using blood sample counts obtained at d degree or d', the attentuation-corrected radionuclide left ventricular end-diastolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-diastolic volumes (r = 0.95 to 0.96). However, both mean radionuclide semiautomated variable left ventricular end-diastolic volumes (179 +/- 100 [+/- 1 standard deviation] and 185 +/- 102 ml, p less than 0.001) were smaller than the average cineangiographic end-diastolic volume (217 +/- 102 ml), and both mean hand-drawn left ventricular end-diastolic volumes (212 +/- 104 and 220 +/- 106 ml) did not differ from the average cineangiographic end-diastolic volume. Using the blood sample counts obtained at d degree or d', the attenuation-corrected radionuclide left ventricular end-systolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-systolic volumes (r = 0.96 to 0.98). Also, using blood sample counts at d degree, the mean radionuclide semiautomated variable left ventricular end-systolic volume (116 +/- 98 ml, p less than 0.05) was less than the average cineangiographic end-systolic volume (128 +/- 98 ml), and the other radionuclide end-systolic volumes did not differ from the average cineangiographic end-systolic volume. Therefore, it is concluded that: 1) a simple geometric attenuation-correction of radionuclide left ventricular end-diastolic and end-systolic count data provides accurate estimates of biplane cineangiographic end-diastolic and end-systolic volumes; and 2) the hand-drawn region of interest selection method, unlike the semiautomated variable method that underestimates end-diastolic and end-systolic volumes, provides more accurate estimates of biplane cineangiographic left ventricular volumes irrespective of the distance blood sample counts are acquired from the collimator.

Exercise cardiac output is maintained with advancing age in healthy human subjects: cardiac dilatation and increased stroke volume compensate for a diminished heart rate

To assess the effect of age on cardiac volumes and function in the absence of overt or occult coronary disease, we performed serial gated blood pool scans at rest and during progressive upright bicycle exercise to exhaustion in 61 participants in the Baltimore Longitudinal Study of Aging. The subjects ranged in age from 25 to 79 years and were free of cardiac disease according to their histories and results of physical, resting and stress electrocardiographic, and stress thallium scintigraphic examinations. Absolute left ventricular volumes were obtained at each workload. There were no age-related changes in cardiac output, end-diastolic or end-systolic volumes, or ejection fraction at rest. During vigorous exercise (125 W), cardiac output was not related to age (cardiac output [1/min] = 16.02 + 0.03 [age]; r = .12, p = .46). However, there was an age-related increase in end-diastolic volume (end-diastolic volume [ml] = 86.30 + 1.48 [age]; r = .47, p = .003) and stroke volume (stroke volume [ml] = 85.52 + 0.80 [age]; r = .37, p = .02), and an age-related decrease in heart rate (heart rate [beats/min] = 184.66 - 0.70 [age]; r = -.50, p = .002). The dependence of the age-related increase in stroke volume on diastolic filling was emphasized by the fact that at this high workload end-systolic volume was higher (end-systolic volume [ml] = 3.09 + 0.65 [age]; r = .45, p = .003) and ejection fraction lower (ejection fraction = 88.48 - 0.18 [age]; r = -.33, p = .04) with increasing age. These findings indicate that although aging does not limit cardiac output per se in healthy community-dwelling subjects, the hemodynamic profile accompanying exercise is altered by age and can be explained by an age-related diminution in the cardiovascular response to beta-adrenergic stimulation.

Acute and long-term hemodynamic effects of oral pirbuterol in patients with chronic severe congestive heart failure: randomized double-blind trial

In 20 patients with severe congestive heart failure (CHF), we studied the effects of the beta-adrenergic agonist pirbuterol compared to placebo in both an acute double-blind randomized trial and after long-term treatment. Acutely, pirbuterol patients (n = 10) demonstrated a significant rise in cardiac index (2.2 +/- 0.14 to 3.2 +/- 0.32 L/min/m2), stroke index (26 +/- 2.6 to 35 +/- 2.9 ml/beat/m2), stroke work index (22 +/- 2.4 to 30 +/- 2.7 gm X m/m2), and ejection fraction (22 +/- 4 to 30 +/- 5%). These hemodynamic variables did not significantly change in placebo patients (n = 10). After 3 weeks of pirbuterol therapy, 14 patients (70%) were symptomatically improved and were continued on the drug for another 3 weeks; 13 of 14 patients who were symptomatically improved underwent restudy. Compared to pretreatment baseline, there was continued improvement in cardiac index (2.5 +/- 0.16 to 3.2 +/- 0.24 L/min/m2), stroke index (30 +/- 2.5 to 38 +/- 2.9 ml/beat/m2), stroke work index (26 +/- 2.3 to 35 +/- 3.1 gm X m/m2), and ejection fraction (24 +/- 1 to 28 +/- 4%). Patients more frequently improved were those with nonischemic cardiomyopathy and those with higher initial ejection fractions. These results demonstrate the acute beneficial effects of oral pirbuterol versus placebo in a double-blind randomized trial. Improvement was maintained during long-term therapy in the majority of CHF patients.

Alterations in left ventricular volumes and ejection fraction during atrial pacing in patients with coronary artery disease: assessment with radionuclide ventriculography

The present study was performed to determine the utility of radionuclide ventriculography (RNV) in conjunction with atrial pacing in the identification of individuals with coronary artery disease. Accordingly, left ventricular end-diastolic volume index, end-systolic volume index, ejection fraction, and regional wall motion were measured with radionuclide ventriculography before and during atrial pacing in 37 patients: 27 with and 10 without (control subjects) coronary artery disease. In the control subjects, pacing caused a decrease in end-diastolic volume index (77 +/- 19 [mean +/- SD] ml/M2 at rest, 50 +/- 18 ml/M2 at peak pacing; p less than 0.001), a decrease in end-systolic volume index (34 +/- 14 ml/M2 at rest, 19 +/- 9 ml/M2 at peak pacing; p less than 0.001), an increase in ejection fraction (0.61 +/- 0.11 at rest, 0.66 +/- 0.11 at peak pacing; p = 0.006); and no deterioration in wall motion. In 16 patients with coronary artery disease who developed ECG and/or metabolic evidence of ischemia during pacing, end-diastolic volume index decreased (87 +/- 26 ml/M2 at rest, 69 +/- 24 ml/M2 at peak pacing; p less than 0.001), end-systolic volume index was unchanged (43 +/- 20 ml/M2 at rest, 44 +/- 21 ml/M2 at peak pacing; p = NS), ejection fraction decreased (0.55 +/- 0.12 at rest, 0.40 +/- 0.14 at peak pacing; p less than 0.001), and new wall motion abnormalities developed in 14. In 11 patients with coronary artery disease but no ECG or metabolic evidence of ischemia, pacing caused a decrease in end-diastolic volume index (80 +/- 26 ml/M2 to 61 +/- 31 ml/M2; p less than 0.001), a decrease in end-systolic volume index (36 +/- 17 ml/M2 to 28 +/- 20 ml/M2; p = 0.002), no change in ejection fraction (0.60 +/- 0.11 to 0.60 +/- 0.13; p = NS), and new wall motion abnormalities in four. Although the specificity of these scintigraphic measurements for the identification of patients with coronary artery disease was excellent (1.0), the combined sensitivity of all scintigraphic measurements was high only if ECG or metabolic evidence of ischemia was present: 0.94 in patients with evidence of ischemia but only 0.36 in those without ischemia. Thus radionuclide ventriculography during incremental atrial pacing is useful in the identification of patients with coronary artery disease only if ischemia is induced.

Prognostic value of resting and submaximal exercise radionuclide ventriculography after acute myocardial infarction in high-risk patients with single and multivessel disease

In patients who survive the acute phase of myocardial infarction, those with multivessel coronary artery disease generally have a worse prognosis than those with single-vessel disease. However, some patients with significant multivessel stenoses have a good prognosis, whereas some with a significant single-vessel stenosis have a poor prognosis. Thus, although definition of coronary anatomy may be helpful, it is a not a fail-safe prognosticator. In this retrospective analysis, the association of abnormalities at rest and during submaximal exercise testing with radionuclide ventriculography after acute myocardial infarction with major cardiac complications (death, recurrent infarction, severe angina or congestive heart failure) in the ensuing 6 months was assessed in patients with single and multivessel disease. Coronary angiography and submaximal exercise testing with radionuclide ventriculography were performed within 3 months of each other in 42 patients. Eleven of the 16 patients with single-vessel coronary stenosis had major cardiac complications. The subsequent course of these 16 patients was correctly predicted by left ventricular ejection fraction (LVEF) less than or equal to 0.40 in 8 patients, by LVEF less than 0.55 in 7 patients, by failure of LVEF to increase by 0.05 units in 13 patients, and by an increase in left ventricular end-systolic volume index (LVESVI) during exercise greater than 5% above baseline in 11 patients. Of the 26 patients with multivessel coronary artery disease, 24 had major cardiac complications. The subsequent course of these 26 patients was correctly predicted in 13 by LVEF less than or equal to 0.40, in 20 by LVEF less than 0.55, in 25 by a failure of LVEF to increase by 0.05 units during exercise, and in 20 by an increase in LVESVI by greater than 5% during exercise. Thus, submaximal exercise testing with radionuclide ventriculography may provide valuable prognostic information concerning the occurrence of major cardiac events after myocardial infarction not only in patients with multivessel disease, but also in those with single-vessel disease. Exercise-induced abnormalities of left ventricular function may have greater prognostic importance than the delineation of coronary arterial anatomy or the assessment of residual left ventricular function at rest.

Symptomatic, electrocardiographic, metabolic, and hemodynamic alterations during pacing-induced myocardial ischemia

Atrial pacing has been used to assess the physiologic impact of coronary artery disease (CAD). Several variables have served as markers of pacing-induced myocardial ischemia, but their specificities and sensitivities are unknown. Accordingly, in 28 patients, incremental atrial pacing was performed. Of the 28, 10 had no CAD. The left ventricular ejection fraction (LVEF) (by gated equilibrium blood pool scintigraphy) increased in this group (0.60 +/- 0.11 [mean +/- standard deviation] before pacing to 0.67 +/- 0.13 at peak-pacing, p = 0.002). In no patient did left ventricular end-diastolic pressure increase by greater than 5 mm Hg. No patient had lactate production, and 2 (20%) had electrocardiographic S-T segment depression greater than or equal to 0.1 mV. Four (40%) had chest pain with atrial pacing. In the remaining 18 patients with CAD, atrial pacing caused a decrease in LVEF greater than or equal to 0.05 (0.46 +/- 0.10 to 0.33 +/- 0.09, p less than 0.001) and new segmental wall motion abnormalities in all, indicating pacing-induced myocardial ischemia. Only 8 (44%) had an increase in left ventricular end-diastolic pressure of greater than 5 mm Hg, and only 9 (50%) had lactate production. Ten (56%) had ischemic electrocardiographic changes, and 12 (67%) had chest pain. Thus, the electrocardiographic, metabolic, and hemodynamic alterations that may accompany pacing-induced ischemia are specific but relatively insensitive markers of ischemia. In contrast, chest pain during atrial pacing is a nonspecific occurrence, appearing with similar frequency in normal subjects and patients with CAD and pacing-induced ischemia.

Efficacy of prazosin in the management of chronic congestive heart failure: a 6-month randomized, double-blind, placebo-controlled study

The beneficial effects of acute prazosin therapy in patients with congestive heart failure (CHF) have been well documented; however, its chronic efficacy over several months has not previously been evaluated in a placebo-controlled manner. Therefore, an assessment was made by radionuclide ventriculography of the effect of prazosin, 20 mg/day, on left ventricular ejection fraction and end-systolic and end-diastolic volumes at rest and on peak upright bicycle exercise, as well as its effect on right ventricular ejection fraction at rest, exercise time and work load, and standard clinical variables in 23 patients with stable class III symptoms of CHF. The study consisted of a 6-month randomized, double-blind, controlled evaluation of prazosin versus placebo in patients receiving a stable dose of digitalis and diuretics for at least 1 month. At entry, the prazosin and placebo groups did not differ in any respect. Prazosin caused no demonstrable effect on clinical variables such as status of symptoms, heart rate, mean arterial pressure, and cardiothoracic ratio when compared with placebo. Prazosin also caused no demonstrable effect compared with placebo on absolute or percent changes in radionuclide variables at rest or on peak exercise, or on exercise time or exercise work load. In addition, prazosin had no consistent effect compared with placebo on plasma renin activity or plasma catecholamine levels. However, there was a slight but significant increase in weight (p less than 0.0001) and in plasma renin activity in the upright position (p less than 0.002) with time, as well as a tendency for the diuretic dose to increase with time in both groups. Thus, long-term prazosin therapy generally produces no demonstrable subjective or objective improvement in patients with stable, chronic class III CHF receiving digitalis and diuretic therapy.

Radionuclide ventriculography to evaluate myocardial function

Developments over the past decade have allowed one to visualize the right and left ventricles using radionuclide techniques and to study the influence of a wide range of physiologic, pharmacologic and surgical interventions on global and regional ventricular function thereby providing important diagnostic insight and improved therapeutic capabilities. These tests are relatively non-invasive, they can be performed serially, they may be performed in patients that are seriously ill, and they have no recognized risk other than low level radiation exposure. With continued improvement in noninvasive imaging and processing and in the sophistication of associated computer systems, one may expect significant and wide ranging additional contributions in the assessment of myocardial function using radionuclide ventriculographic techniques.

Assessment of vasodilator therapy in patients with severe congestive heart failure: limitations of measurements of left ventricular ejection fraction and volumes

Although noninvasive techniques are often used to assess the effect of vasodilator therapy in patients with congestive heart failure, it is unknown whether changes in noninvasively determined left ventricular ejection fraction, volume, or dimension reliably reflect alterations in intracardiac pressure and flow. Accordingly, we compared the acute effect of sodium nitroprusside on left ventricular volume and ejection fraction (determined scintigraphically) with its effect on intracardiac pressure and forward cardiac index (determined by thermodilution) in 12 patients with severe, chronic congestive heart failure and a markedly dilated left ventricle. Nitroprusside (infused at 1.3 +/- 1.1 [mean +/- standard deviation] microgram/kg/min) caused a decrease in mean systemic arterial, mean pulmonary arterial, and mean pulmonary capillary wedge pressure as well as a concomitant increase in forward cardiac index. Simultaneously, left ventricular end-diastolic and end-systolic volume indexes decreased, but the scintigraphically determined cardiac index did not change significantly. Left ventricular ejection fraction averaged 0.19 +/- 0.05 before nitroprusside administration and increased by less than 0.05 units in response to nitroprusside in 11 of 12 patients. The only significant correlation between scintigraphically and invasively determined variables was that between the percent change in end-diastolic volume index and the percent change in pulmonary capillary wedge pressure (r = 0.68, p = 0.01). Although nitroprusside produced changes in scintigraphically determined left ventricular ejection fraction, end-systolic volume index, and cardiac index, these alterations bore no predictable relation to changes in intracardiac pressure, forward cardiac index, or vascular resistance. Furthermore, nitroprusside produced a considerably greater percent change in the invasively measured variables than in the scintigraphically determined ones.

Radionuclide ventriculography for assessment of absolute right and left ventricular volumes in children

We determined absolute right and left ventricular volumes and cardiac output from the equilibrium radionuclide angiogram in 26 children, ages 3 months to 18 years, with diverse types of heart disease. We validated these results by comparing them with left ventricular (20 patients) and right ventricular (16 patients) cineangiographic volumes and cardiac output. Radionuclide volumes and cardiac outputs were determined in two ways: by a geometric method (area-length for left ventricle, Simpson's rule for right ventricle) and by a count-based method (correcting ventricular regional counts for frame duration, acquisition time, venous blood counts and attenuation). Both methods for estimating left ventricular end-diastolic volume compared favorably with cineangiography (correlation coefficients greater than 0.90). The count-based method also correlated well for the right ventricle. End-systolic measurements were not possible. Count-based assessment of cardiac output also correlated well with cineangiographic values. We conclude that right and left ventricular volumes and cardiac output can be reliably measured in children with equilibrium radionuclide ventriculography.

Verapamil therapy for Prinzmetal's variant angina: comparison with placebo and nifedipine

This study was performed (1) to assess the efficacy and safety of verapamil in patients with variant angina, and (2) to compare verapamil and nifedipine in patients with this clinical syndrome. In 27 patients, placebo and verapamil were administered in a long-term randomized, and double-blind study of 9 months' duration. In comparison to placebo, verapamil reduced the frequency of angina, nitroglycerin usage, transient episodes of electrocardiographic S-T segment deviation (as assessed by 2-channel Holter monitoring), and hospitalizations required for clinical instability. Subsequently, 23 patients were treated with nifedipine in a nonblind fashion for 2 months, and this agent exerted a beneficial effect similar to that of verapamil. Finally, gated equilibrium blood pool scintigraphy, performed in 10 patients at rest and during exercise during treatment with placebo, verapamil, and nifedipine, demonstrated that neither calcium antagonist caused a deterioration of left ventricular performance. Thus, (1) long-term oral verapamil and nifedipine are each superior to placebo and are of similar efficacy in patients with variant angina, and (2) neither agent adversely influences left ventricular performance in patients with relatively normal left ventricular function.

Effect of exercise on erythrocyte count and blood activity concentration after technetium-99m in vivo red blood cell labeling

We studied the effect of exercise on blood radiotracer concentration after technetium-99m in vivo red blood cell labeling. After red blood cell labeling, 13 subjects underwent maximal supine bicycle exercise. Radioactivity, analyzed with a well counter, was measured in heparinized venous blood samples drawn at rest and during peak exercise. Changes in activity were compared with changes in erythrocyte count. Activity and erythrocyte counts increased during exercise in all 13 subjects. Percent increase in activity correlated with percent increase in erythrocyte count (r = -0.78), but did not correlate with either duration of exercise or maximal heart rate. Twenty minutes after termination of exercise, activity and erythrocyte count had decreased from peak exercise values but remained higher than preexercise values. In nine nonexercised control subjects, samples drawn 20 minutes apart showed no change in activity or in erythrocyte count. We conclude that exercise increases blood activity, primarily because of an increase in erythrocyte count. During radionuclide ventriculography, blood activity must be measured before and after any intervention, particularly exercise, before a change in left ventricular activity can be attributed to a change in left ventricular volume.

Effect of increasing heart rate in patients with aortic regurgitation. Effect of incremental atrial pacing on scintigraphic, hemodynamic and thermodilution measurements

This study was performed to assess the effect of pacing-induced tachycardia in patients with aortic regurgitation. In 12 patients (5 men and 7 women with a mean age of 53 years) with aortic regurgitation, left ventricular end-diastolic and end-systolic volume indexes were measured with multigated equilibrium blood pool imaging, and forward cardiac index was determined with thermodilution, both at rest (mean heart rate +/- standard deviation 72 +/- 8 beats/min) and during atrial pacing at 100 and 120 beats/min. Pacing caused a decremental reduction in left ventricular end-diastolic and end-systolic volume indexes and radionuclide-determined stroke volume index but no change in radionuclide-determined cardiac index or left ventricular ejection fraction. Forward cardiac index increased incrementally from the baseline value at rest to that at 120 beats/min despite a decremental reduction in stroke volume index. There was a stepwise decrease in regurgitant volume/stroke (46 +/- 20 ml/m2 at baseline, 27 +/- 15 at 120 beats/min; p less than 0.05) but no change in regurgitant volume/min (3.38 +/- 1.80 liters/min per m2 at baseline, 3.22 +/- 1.78 at 120 beats/min; difference not significant [NS]) or regurgitant fraction (0.54 +/- 0.13 at baseline, 0.49 +/- 0.13 at 120 beats/min; NS). Mean femoral arterial, pulmonary arterial and pulmonary capillary wedge pressures did not change with pacing.