Myocardial External Efficiency in Asymptomatic Severe Primary Mitral Regurgitation Using 11C-Acetate PET.

Subjects with asymptomatic moderate-to-severe or severe primary mitral regurgitation are closely observed for signs of progression or symptoms requiring surgical intervention. The role of myocardial metabolic function in progression of mitral regurgitation is poorly understood. We used 11C-acetate PET to noninvasively measure myocardial mechanical external efficiency (MEE), which is the energetic ratio of external cardiac work and left ventricular (LV) oxygen consumption. Methods: Forty-seven patients in surveillance with mitral regurgitation and no or minimal symptoms prospectively underwent PET, echocardiography, and cardiac MRI on the same day. PET was used to simultaneously measure cardiac output, LV mass, and oxygen consumption to establish MEE. PET findings were compared between patients and healthy volunteers (n = 9). MEE and standard imaging indicators of regurgitation severity, LV volumes, and function were studied as predictors of time to surgical intervention. Patients were followed a median of 3.0 y (interquartile range, 2.0-3.8 y), and the endpoint was reached in 22 subjects (47%). Results: MEE in patients reaching the endpoint (23.8% ± 5.0%) was lower than in censored patients (28.5% ± 4.5%, P = 0.002) or healthy volunteers (30.1% ± 4.9%, P = 0.001). MEE with a cutoff lower than 25.7% was significantly associated with the outcome (hazard ratio, 7.5; 95% CI, 2.7-20.6; P < 0.0001) and retained independent significance when compared with standard imaging parameters. Conclusion: MEE independently predicted time to progression requiring valve surgery in patients with asymptomatic moderate-to-severe or severe primary mitral regurgitation. The study suggests that inefficient myocardial oxidative metabolism precedes clinically observed progression in mitral regurgitation.

Test-retest reliability of new and conventional echocardiographic parameters of left ventricular systolic function.

BACKGROUND: Reliability of left ventricular function measurements depends on actual biological conditions, repeated registrations and their analyses. OBJECTIVE: To investigate test-retest reliability of speckle-tracking-derived strain measurements and its determinants compared to the conventional parameters, such as ejection fraction (EF), LV volumes and mitral annular plane systolic excursion (MAPSE). METHODS: In 30 patients with a wide range of left ventricular function (mean EF 46.4 ± 16.4%, range 14-73%), standard echo views were acquired independently in a blinded fashion by two different echocardiographers in immediate sequence and analyzed off-line by two independent readers, creating 4 data sets per patient. Test-retest reliability of studied parameters was calculated using the smallest detectable change (SDC) and a total, inter-acquisition and inter-reader intra-class correlation coefficient (ICC). RESULTS: The smallest detectable change normalized to the mean absolute value of the measured parameter (SDCrel) was lowest for MAPSE (10.7%). SDCrel for EF was similar to GLS (14.2 and 14.7%, respectively), while SDCrel for CS was much higher (35.6%). The intra-class correlation coefficient was excellent (> 0.9) for all measures of the left ventricular function. Intra-patient inter-acquisition reliability (ICCacq) was significantly better than inter-reader reliability (ICCread) (0.984 vs. 0.950, p = 0.03) only for EF, while no significant difference was observed for any other LV function parameter. Mean intra-subject standard deviations were significantly correlated to the mean values for CS and LV volumes, but not for the other studied parameters. CONCLUSIONS: In a test-retest setting, both with normal and impaired left ventricular function, the smallest relative detectable change of EF, GLS and MAPSE was similar (11-15%), but was much higher for CS (35%). Surprisingly, reliability of GLS was not superior to that of EF. Acquisition and reader to a similar extent influenced the reliability of measurements of all left ventricular function measures except for ejection fraction, where the reliability was more dependent on the reader than on the acquisition.

Changes in global longitudinal strain and left ventricular ejection fraction during the first year after myocardial infarction: results from a large consecutive cohort.

Aims: To determine changes of global longitudinal strain (GLS) and their predictors in relation to classical echocardiographic parameters of left ventricular (LV) function, over 1 year, in consecutive patients with myocardial infarction (MI) and initially normal or impaired LV ejection fraction (EF). Methods and results: A total of 285 patients with MI prospectively included in the REBUS (RElevance of Biomarkers for future risk of thromb-oembolic events in UnSelected post-myocardial infarction patients) study underwent echocardiography within 72 h from admission and after 1 year. At baseline, 213 (74.7%) of MI patients had a normal EF (≥52% in men or ≥54% in women), but in 70.4% of them, an impaired GLS ( ≥ -18.0%) was observed. During 1-year follow-up, in patients with normal EF at baseline, GLS improved from -15.8% to - 17.4% (10.1% relative change); EF decreased from 62.5% to 59.9% (4.0% relative change); indexed end-diastolic volume, indexed end-systolic volume, and indexed stroke volume increased with 15.6%, 24.8%, and 10.0% of relative change, respectively (P < 0.001 for all the comparisons). In the whole cohort, initial impairment of LV function [by EF, wall motion score index (WMSI), or GLS], male gender, non-smoking, and treatment with beta-blockers were the independent predictors of GLS improvement. In the group with initially impaired EF, over 1 year GLS improved from -11.9% to - 14.8% (24.4% relative change) and EF from 44.6% to 52.6% (18.2% relative change) (P < 0.001 for both). Improvement in GLS significantly correlated with EF increase in the group with impaired EF (r = -0.41, P = 0.001) but not in the patients with normal EF (r = -0.14, P = ns). Conclusions: Despite diveregent evolution of GLS compared with EF and ventricular volumes, one year after MI GLS significantly improved in patients with initially both normal and impaired EF. Initial impairment of LV function (by EF, WMSI, or GLS), male gender, non-smoking, and treatment with beta-blockers were independent predictors of GLS improvement. LV remodelling was present even in patients with normal EF at baseline and during follow-up, confirming limited functional assessment by EF alone.

Case Studies in Physiology: Ventilation and perfusion in a giraffe-does size matter?

The trachea in the giraffe is long but narrow, and dead space ventilation is considered to be of approximately the same size as in other mammals. Less is known about the matching between ventilation and lung blood flow. The lungs in the giraffe are large, up to 1 m high and 0.7 m wide, and this may cause considerable ventilation/perfusion (VA/Q) mismatch due to the influence of gravitational forces, which could lead to hypoxemia. We studied a young giraffe under anesthesia using the multiple inert gas elimination technique to analyze the VA/Q distribution and arterial oxygenation and compared the results with those obtained in other species of different sizes, including humans. VA/Q distribution was broad but unimodal, and the shunt of blood flow through nonventilated lung regions was essentially absent, suggesting no lung collapse. The VA/Q match was as good as in the similarly sized horse and was even comparable to that in smaller sized animals, including rabbit and rat. The match was also similar to that in anesthetized humans. Arterial oxygenation was essentially similar in all studied species. The findings suggest that the efficiency of VA/Q matching is independent of lung size in the studied mammals that vary in weight from less than 1 to more than 400 kg.

Usefulness of traditional echocardiographic parameters in assessment of left ventricular function in patients with normal ejection fraction early after acute myocardial infarction: results from a large consecutive cohort.

AIMS: The aim of this study was to assess the frequency of left ventricular (LV) systolic function impairment using classical echocardiographic parameters and their relation to myocardial damage in patients hospitalized for acute myocardial infarction (MI) with normal LV ejection fraction (LVEF ≥52% in males or ≥54% in females). METHODS AND RESULTS: All 421 consecutive patients with MI included in the REBUS (RElevance of Biomarkers for future risk of thromboembolic events in UnSelected post-myocardial infarction patients) study underwent two-dimensional and Doppler echocardiography within 72 h after admission. A normal LVEF was present in 262 (73.8%) of the 355 patients ultimately enrolled in the study. Patients with normal LVEF more often presented with non-ST-elevation myocardial infarction and had less comorbidities when compared with those with impaired LVEF. No differences in demographic factors or relevant medications were observed. Higher value of mean annular plane systolic excursion (MAPSE), lower wall motion score index (WMSI), lower LV as well as left atrial volumes characterized patients with normal LVEF. Impaired MAPSE was present in 64.4%, WMSI >1 in 72.1%, and dilated left atrium in 33.6% of those patients. Maximal cardiac troponin concentration reflecting infarct size showed the strongest association with WMSI (ß = 0.35), followed by LVEF (ß = -0.29), MAPSE (ß = -0.25), and indexed LV end-systolic volume (ß = 0.19; P < 0.001 for all the models). CONCLUSION: In two-third of patients with MI and normal LVEF, at least one of the other markers of systolic function was outside of the normal range. WMSI reflected the size of MI better than global LV function parameters as LVEF or MAPSE.