Rate of change of left ventricular ejection fraction during exercise is superior to the peak ejection fraction for predicting functionally significant coronary artery disease

Impact of Positron Emission Tomographic Myocardial Perfusion Imaging on Patient Selection for Revascularization

BACKGROUND

Positron emission tomography (PET) myocardial perfusion imaging (MPI) quantifies left ventricular ejection fraction (LVEF) at peak stress. PET LVEF reserve (LVEF-R = stress LVEF - rest LVEF) offers diagnostic and prognostic value.

OBJECTIVES

The purpose of this study was to determine if PET LVEF-R identifies patients with survival benefit postrevascularization.

METHODS

We followed 14,649 unique consecutive patients undergoing 82Rb rest/stress PET MPI from January 2010 to January 2016 (excluding known cardiomyopathy). Adjusted Cox models were built to predict all-cause death, and the 3-way interaction of known coronary artery disease (CAD) (prior myocardial infarction/revascularization), LVEF-R, and 90-day revascularization was tested.

RESULTS

Known CAD was present in 4,982 (34.0%). Ischemia was detected in 5,396 (36.8%; ≥10% in 1,909 [13%]). Mean LVEF-R was 4.2% ± 5.7%, and was ≤0, 1 to 5, and >5 in 3,349 (22.9%), 5,266 (35.9%), and 6,034 (41.2%). Over median follow-up of 3.4 years (IQR: 1.9-5.2 years), 1,324 (8.1%) had 90-day revascularization, and there were 2,192 (15.0%) deaths. In multivariable modeling, there was a significant 3-way interaction among known CAD, LVEF-R, and 90-day revascularization (P = 0.025), such that LVEF-R ≤0 identified patients with survival benefit with 90-day revascularization in those without prior CAD (interaction P = 0.005), independently beyond percent ischemia and myocardial flow reserve. Among patients with known CAD, LVEF-R was not prognostic of death (HR: 0.99; 95% CI: 0.98-1.02; P = 0.98).

CONCLUSIONS

A lack of augmentation or drop in LVEF with vasodilator stress on PET MPI independently identifies patients who have better survival with revascularization within 90 days post-MPI compared with medical therapy, in absence of prior myocardial infarction or revascularization. Multiparametric assessment of ischemia with PET can optimize post-test management.

Continuous left ventricular ejection fraction monitoring by aortic pressure waveform analysis

We developed a technique to monitor left ventricular ejection fraction (EF) by model-based analysis of the aortic pressure waveform. First, the aortic pressure waveform is represented with a lumped parameter circulatory model. Then, the model is fitted to each beat of the waveform to estimate its lumped parameters to within a constant scale factor equal to the arterial compliance (C (a)). Finally, the proportional parameter estimates are utilized to compute beat-to-beat absolute EF by cancelation of the C (a) scale factor. In this way, in contrast to conventional imaging, EF may be continuously monitored without any ventricular geometry assumptions. Moreover, with the proportional parameter estimates, relative changes in beat-to-beat left ventricular end-diastolic volume (EDV), cardiac output (CO), and maximum left ventricular elastance (E (max)) may also be monitored. To evaluate the technique, we measured aortic pressure waveforms, reference EF and EDV via standard echocardiography, and other cardiovascular variables from six dogs during various pharmacological influences and total intravascular volume changes. Our results showed overall EF and calibrated EDV root-mean-squared-errors of 5.6% and 4.1 mL, and reliable estimation of relative E (max) and beat-to-beat CO changes. These results demonstrate, perhaps for the first time, the feasibility of estimating EF from only a blood pressure waveform.

Continuous ejection fraction estimation by model-based analysis of an aortic pressure waveform: comparison to echocardiography

Left ventricular ejection fraction (EF) is perhaps the most clinically significant index of global ventricular function. EF is measured in clinical practice using imaging methods such as non-invasive echocardiography. However, imaging methods generally require a skilled operator and expensive equipment. Thus, EF is not sufficiently monitored. To this end, we have recently developed a novel technique to continuously (i.e., automatically) estimate EF by model-based analysis of an aortic pressure waveform. Here, we review the technique and present its evaluation with respect to reference echocardiography measurements from three dogs during diverse interventions. We report an overall EF error of only 8.3%. With further successful testing, the technique may ultimately be utilized for continuous EF monitoring in research and clinical settings in which an aortic catheter is employed.

Monitoring of left ventricular ejection fraction with a miniature, nonimaging nuclear detector: accuracy and reliability over time with special reference to blood labeling

BACKGROUND

The purpose of this study was to determine the accuracy of determinations of left ventricular ejection fraction (LVEF) by a nonimaging miniature nuclear detector system (Cardioscint) and to evaluate the feasibility of long-term LVEF monitoring in patients admitted to the coronary care unit, with special reference to the blood-labeling technique.

METHODS AND RESULTS

Cardioscint LVEF values were compared with measurements of LVEF by conventional gamma camera radionuclide ventriculography in 33 patients with a wide range of LVEF values. In 21 of the 33 patients, long-term monitoring was carried out for 1 to 4 hours (mean 186 minutes), with three different kits: one for in vivo and two for in vitro red blood cell labeling. The stability of the labeling was assessed by determination of the activity of blood samples taken during the first 24 hours after blood labeling. The agreement between Cardioscint LVEF and gamma camera LVEF was good with automatic background correction (r = 0.82; regression equation y = 1.04x + 3.88) but poor with manual background correction (r = 0.50; y = 0.88x - 0.55). The agreement was highest in patients without wall motion abnormalities. The long-term monitoring showed no difference between morning and afternoon Cardioscint LVEF values. Short-lasting fluctuations in LVEFs greater than 10 EF units were observed in the majority of the patients. After 24 hours, the mean reduction in the physical decay-corrected count rate of the blood samples was most pronounced for the two in vitro blood-labeling kits (57% +/- 9% and 41% +/- 3%) and less for the in vivo blood-labeling kit (32% +/- 26%). This "biologic decay" had a marked influence on the Cardioscint monitoring results, demanding frequent background correction.

CONCLUSION

A fairly accurate estimate of LVEF can be obtained with the nonimaging Cardioscint system, and continuous bedside LVEF monitoring can proceed for hours with little inconvenience to the patients. Instability of the red blood cell labeling during long-term monitoring necessitates frequent background correction.