Temporal resolution requirements for left ventricular time-activity curves

Interassay reproducibility of myocardial perfusion gated SPECT in patients with atrial fibrillation

AIM

The aim of this study was to assess interassay reproducibility of myocardial perfusion gated-SPECT for calculation of end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction (LVEF) in patients with atrial fibrillation (AF).

METHODS

One hundred and fifteen consecutive patients with AF from three participating hospitals (mean age 68.9 years, 39 women) were included in the study. All patients underwent two image gated acquisitions at rest with a 30 minute interval between them. Quantitative data were obtained using the QGS and ECT software algorithms.

RESULTS

Heart rate was similar in both studies: 74.94 +/- 15.2 vs 73.03 +/- 15.57. QGS yielded an LVEF of 54.4%/53.8%, an EDV of 100 mL/101.5 mL, and an ESV of 51 mL/52.3 mL; and ECT showed an LVEF of 63.6%/62.9%, an EDV of 125.8 mL/127.4 mL and ESV of 54.1 mL/56.3 mL. Correlation between the two acquisitions was high (>0.948) for both methods for LVEF, EDV and ESV. Regression and Bland-Altman graphics showed a good agreement between all parameters. Interassay variation coefficients for each method (QGS/ECT) were 5.29% vs 4.83% for LVEF, 4.94% vs 5.17% for EDV, and 9.94% vs 12.78% for ESV.

CONCLUSIONS

Interassay reproducibility of LVEF and EDV with gated-SPECT in patients with AF is good, whereas for ESV it is suboptimal, particularly when ESV is small.

Measurement of left ventricular volumes by 3-dimensional echocardiography with tissue harmonic imaging: a comparison with magnetic resonance imaging

We hypothesized that tissue harmonic imaging (THI) in comparison with fundamental imaging (FI) would improve endocardial border detection, and therefore in combination with 3-dimensional echocardiography (3D echo), it would be a precise method for left ventricular (LV) volume measurement. Ten healthy subjects and 18 consecutive patients with dilated hearts underwent estimation of LV volumes by magnetic resonance imaging (MRI) and transthoracic 3D echo with THI and FI. In patients, the agreement between MRI and 3D echo was closer with THI in comparison with FI for assessment of LV volumes. Thus the mean +/- 2 SD of differences between MRI and 3D echo with THI versus FI, respectively, was -6.4 +/- 40.0 mL versus -17.4 +/- 57.6 mL (P <.01) for the end-diastolic volume (EDV), and 0.0 +/- 26.6 mL versus -8.1 +/- 35.6 mL (P <.01) for the end-systolic volume (ESV). In patients, THI in comparison with FI approximately halved observer variation on EDV and ESV. In healthy subjects, only ESV showed significantly reduced observer variation by THI. In conclusion, because THI demonstrated a clinically relevant reduction in observer variation and a closer agreement to the MRI technique in patients with dilated hearts, it should replace FI in LV volume measurements.

Effect of acquisition and analysis routines on gated blood pool measurements

Results obtained from gated equilibrium blood pool (GBP) studies are not only dependent on intrinsic variations, but also on the way in which images are acquired and analysed. The aim of this study was to investigate factors which could affect left ventricular time-activity curves. Temporal resolution was studied by comparing studies of 20 and 40 frames beat-1. Forty frames per beat resulted in a mean left ventricular ejection fraction of 0.48 compared to 0.46 for 20 frames beat-1. The mean difference of 0.02 was significant (P less than 0.01) as was the mean difference in maximum emptying rate (MER = 0.28, P less than 0.01) and in maximum filling rate (MFR = 0.38, P less than 0.01). No significant differences in ejection fraction (EF) values were found between acquisitions made in list and frame mode, but the mean differences for MER = 0.03 (P less than 0.05) and MFR = 0.01 (P less than 0.02) were significant. For patient repositioning and intra-observer variations no significant differences were found. In patients with normal EF values (greater than 0.5) no significant differences were found in the inter-observer study. In patients with anterior myocardial infarction (AMI), significant differences were found in EF, MER and MFR (EF = 0.02, P less than 0.001; MER = 0.2, P less than 0.01; MFR = 0.24, P less than 0.01). Significant differences were found in all values when comparing a semi-automatic method of evaluation with two automatic methods. In conclusion the results from this study suggest that acceptable reproducibility can be achieved in GBP studies, provided the method of analysis is not changed between studies.

Nuclear ejection fraction measurements with a small crystal detector: methodological investigations

A series of studies were performed with a single crystal detector system, nuclear stethoscope (N.S.) (Bios) used for measuring left ventricular function (ejection fraction [EF]). Counting capacity, validity, reproducibility, effect of repositioning of the instrument and of different operators were investigated. Counting capacity was found to be approximately linear up to a count rate of 40.000 cps. Validity was studied by comparing measurements in the same subject using the N.S. with those obtained by a gamma-camera computer system with software using a background subtraction similar to that in the N.S. The mean difference in EF (0.01) was not significant. Maximum emptying and filling velocity measurements with the two instruments were also compared r = 0.86 and r = 0.89, respectively, and a coefficient of variation of 18.1% and 17.9%. Reproducibility was determined from duplicate determinations under identical conditions. The standard error of a single determination was 5%. Repositioning by the same operator increased the variation to 9.1% without any systematic difference. Comparison between two operators did not increase the coefficient of variation (8.8%). There was a systematic difference between measurements using the two acquisition modes, ventricular function mode and position monitor mode. Beat-to-beat variation of EF values during 12 s in 25 patients with coronary heart disease studied under standardized resting conditions was 11.9%.

Nuclear techniques in ischemic heart disease

Until recently, it was necessary to measure parameters such as ventricular pressure to assess the effects of drugs on the force of myocardial contraction--the inotropic effect. Even simpler measurements such as cardiac output are not completely satisfactory, because they are determined not only by the contractile state but also by the diastolic volume of the ventricles, outflow impedance, and heart rate. Within the past few years, the use of radioactive tracer techniques has made it possible to measure the changes in ventricular volume that occur throughout the cardiac cycle. With these techniques, it is now possible to measure end-diastolic and end-systolic volumes, the rates of ventricular emptying and filling, stroke volume, and systolic and diastolic time intervals. In complicated diseases such as combined valvular and coronary artery disease the ventricular response to antiarrhythmic, vasodilator, and inotropic drugs can be assessed in individual patients.

Monitoring cardiac function with nuclear techniques

Noninvasive imaging with radioactive tracers has become widely used since its introduction in the early 1970s. Improvements continue to be made in the techniques and the clinical applications. Much of the information provided by these techniques is new. The first transit studies are used mainly in the evaluation of pulmonary transit time, detection of intracardiac shunting, evaluation of right ventricular function, measurement of ejection fraction and detection of wall motion abnormalities at rest and after exercise. The gated blood pool study is found to be most useful in assessment of global left ventricular function, regional wall motion, valve regurgitation and right ventricular function. The techniques of nuclear cardiac imaging are noninvasive, simple, successfully performed in almost 100 percent of cases. They are easy to interpret, able to be quantified and able to be almost totally automated. Their use is likely to become more widespread in the future.