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

Ease of noninvasive measurement of cardiac output coupled with peak VO2 determination at rest and during exercise in patients with heart failure

Peak oxygen consumption (VO2) is a powerful prognostic predictor of survival in patients with heart failure (HF) because it provides an indirect assessment of a patient's ability to increase cardiac output (CO). However, many peripheral factors affect VO2. Inert gas rebreathing using low-concentration soluble and insoluble inert gases can derive CO by the Fick principle. The Innocor rebreathing system uses an oxygen-enriched mixture of an inert soluble gas (0.5% nitrous oxide) and an inert insoluble gas (0.1% sulfur hexafluoride) measured by photoacoustic analyzers over a 5-breath interval. The practicality of this device in measuring CO and VO2 during exercise was assessed in patients with HF. Ninety-two consecutive exercise tests were prospectively performed in 88 patients with HF using the Innocor system. Incremental bicycle exercise was performed with CO measurements at rest, at 50 W, and at peak exercise. The mean age of the 68 men and 20 women was 54 +/- 13 years; 33% had coronary artery disease, and 67% had dilated cardiomyopathy. The mean left ventricular ejection fraction was 24 +/- 9%. Patients were able to rapidly learn the rebreathing technique and easily integrate it into the exercise protocol. Eighty-six percent of the tests had successful measurement of metabolic and cardiac output data. Mean CO at rest was 3.5 +/- 1.1 L/min and increased to 7.2 +/- 2.7 L/min. Mean peak VO2 was 12.6 +/- 4.7 ml/kg/min. A significant linear correlation was observed between peak VO2 and peak CO (r = 0.64, p <0.0001). In conclusion, combined metabolic stress testing with inert gas rebreathing can be easily performed in patients with HF.

[Nuclear cardiology: technical bases and clinical applications]

Although the role of nuclear cardiology is currently well consolidated, the addition of new radiotracers and modern techniques makes it necessary to continuously update the requirements, equipment and clinical applications of these isotopic tests. The characteristics of the radioisotopic drugs and examinations presently used are explained in the first part of this text. In the second, the indications of them in diagnostic and prognostic evaluation of the different coronary diseases are presented.

Automated non-invasive measurement of cardiac output by the carbon dioxide rebreathing method: comparisons with dye dilution and thermodilution

The accuracy and reproducibility of indirect measurement of cardiac output at rest by the carbon dioxide rebreathing (indirect Fick) method with an automated respiratory analysis system (Gould 9000IV) were compared with simultaneous measurements made in duplicate by dye dilution and thermodilution in 25 patients having cardiac catheterisation studies. Measurements of cardiac output by the carbon dioxide rebreathing method were not significantly different from those obtained with dye dilution (mean difference -0.3 l/min, SD 0.76, 95% confidence interval -0.7 to 0.1). Thermodilution significantly over-estimated cardiac output by a mean of 2.2 l/min or 39% (SD 1.5, 95% confidence interval 1.6 to 2.8) compared with the carbon dioxide rebreathing method and significantly overestimated cardiac output by 1.9 l/min or 31% (SD 1.2, 95% confidence interval 1.2 to 2.5) compared with dye dilution. The reproducibility of measurements of cardiac output in individual patients was satisfactory with the dye dilution method but was poor with carbon dioxide rebreathing and thermodilution. Indirect measurement of resting cardiac output by the Gould 9000IV automated carbon dioxide rebreathing method is more accurate but the variability inherent with this method requires that multiple measurements be taken for each determination. Measurement of cardiac output by the thermodilution method by a commercially available cardiac output computer was not satisfactory because not only was there considerable variability between repeat measurements but the method also consistently overestimated cardiac output compared with the dye dilution method.

Patterns of left ventricular dilation during the six months after myocardial infarction

Changes in left ventricular volume after a first myocardial infarction were studied in 50 patients. Serial radionuclide angiograms were obtained 48 h, 10 days and 1 and 6 months after infarction and left ventricular volume measured by a nongeometric method. Left ventricular dilation (greater than or equal to 20% increase in end-diastolic volume) occurred within 10 days of infarction in 11 patients, who had a mean volume increase of 34 +/- 15% (p = 0.002 versus 48 h) at 10 days and 61 +/- 43% (p = 0.01 versus 10 days) at 6 months. Ten other patients manifested left ventricular dilation between 10 days and 6 months with a lesser volume increase of 42 +/- 18% by 6 months. Among the 21 patients with ventricular dilation, progressive dilation (serial volume increases greater than or equal to 20% on two or more occasions) occurred in 8 patients, who all had a large anterior infarct. Mean volume increases at 10 days and 1 and 6 months were 27 +/- 20%, 49 +/- 40% (p = 0.03 versus 10 days) and 79 +/- 37% (p = 0.006 versus 1 month), respectively, in this group. In patients with progressive dilation, left ventricular ejection fraction decreased from 35 +/- 6% at 48 h to 24 +/- 10% at 1 month (p less than 0.001) and 27 +/- 10% (p = 0.006) at 6 months. Between 1 month and 2 years after infarction six patients died, of whom four had progressive dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of noninvasive techniques for measuring cardiac output in hypertensive patients

The hemodynamic hallmark of hypertension is increased systemic vascular resistance, although this variable is usually not determined in hypertensive patients because it has generally required invasive procedures to measure cardiac output. Reliable, totally noninvasive methods are now available that measure cardiac output accurately enough under a variety of conditions, including rest, exercise, and pharmacologic interventions. These methods include echocardiography, Doppler echocardiography, CO2 rebreathing, and impedance cardiography. Their serial application to large numbers of patients offers the opportunity to significantly broaden our understanding of the spectrum and course of hemodynamic alterations associated with hypertension. A more complete knowledge of underlying hemodynamics could improve our diagnostic and prognostic accuracy in hypertensive patients and enhance our understanding of the pathophysiology of hypertension and the mechanism of action of antihypertensive interventions.

Quantitative radionuclide angiocardiography

Quantitation of cardiac pump function using radionuclide angiocardiography provides objective information for the management of patients with heart disease. Left and right ventricular ejection fraction, stroke volume ratio, ejection rate, diastolic function, ventricular volume, parametric imaging, amplitude and phase analysis, and shunt quantification can be measured from the radionuclide angiocardiogram at rest, during exercise, and during pharmacologic interventions. This review describes these methods and discusses their reliability and their role in the clinical assessment of patients with cardiac disease.

Infarct artery perfusion and changes in left ventricular volume in the month after acute myocardial infarction

The relation between perfusion of the infarct-related artery and changes in left ventricular volume and function during the month after a first myocardial infarction was examined in 40 patients who did not receive thrombolytic therapy. Infarct artery perfusion was documented at predischarge coronary angiography, and left ventricular volume was measured by nongeometric analysis of radionuclide angiograms performed within 48 hours of infarction and at 1 month. Left ventricular dilation (greater than or equal to 20% increase in volume) developed in 16 patients, whereas 5 patients had a decrease in left ventricular volume of greater than or equal to 20% by 1 month. Left ventricular dilation occurred in all 14 patients without perfusion of the infarct-related artery, compared with only 2 of 26 patients with perfusion of this artery due to subtotal occlusion or collateral vessels. All five patients whose left ventricular volume decreased by greater than or equal to 20% had a perfused infarct artery. Multiple linear regression analysis confirmed that the degree of perfusion of the infarct artery (partial r = 0.58, p = 0.001) was a more important predictor of volume change than was infarct size measured by peak creatine kinase (partial r = 0.30, p = 0.009) or QRS score (partial r = 0.20, p = 0.087). Left ventricular ejection fraction decreased from 0.38 +/- 0.10 to 0.30 +/- 0.16 (p = 0.05) in 11 patients with an anterior infarct and ventricular dilation; it increased from 0.45 +/- 0.10 to 0.62 +/- 0.07 (p = 0.02) in the 5 patients with a greater than or equal to 20% decrease in volume.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of age and gender on left ventricular response to supine exercise in asymptomatic normal subjects

The performance of normal subjects during radionuclide ventriculography has been related to age, but the combined effects of age and sex on exercise ventricular function are not well described. We studied 55 normal volunteers, 27 men (age = 30 +/- 10 years) and 28 women (age = 33 +/- 14 years), free of chest pain syndromes, during supine rest/exercise radionuclide ventriculography performed to fatigue. Resting left ventricular ejection fraction did not differ between male and female subjects (64 +/- 5.4 vs 64 +/- 6.1; p = NS). Both the peak left ventricular ejection fraction (78 +/- 4.4 vs 72 +/- 9.2; p less than 0.001) and the change in ejection fraction with exercise (14 +/- 4.0 vs 7.9 +/- 7.0; p less than 0.001) were significantly greater in men compared to respective values in women. Regression analysis showed that sex (r = 0.51; p less than 0.001) but not age (r = -0.18; p = 0.19) was a significant predictor of change in ejection fraction with exercise. Data on left ventricular volume response to exercise, available in 43 subjects, revealed that men had a greater percentage of decline in end-systolic volume with exercise than women (-47 +/- 15 vs -24 +/- 26; p less than 0.001). It is concluded that sex exerts a significant influence on normal left ventricular response to fatigue-limited supine exercise and that the gender difference is mediated, in part, by left ventricular end-systolic volume response to exercise.