Intraoperative evaluation of left ventricular volume and function: it is time to usher in the third dimension.

April 2014 • Volume 118 • Number 4 In the perioperative period, assessment of left ventricular (LV) volumes and ejection fraction (EF) is frequently needed for early detection of cardiac dysfunction and for guidance of therapeutic interventions. For the hemodynamically unstable patient, assessment of cardiac volume and function needs to be performed rapidly, easily, and accurately. In this issue, Meris et al.1 report the intraoperative measurement of LV volume and EF with 3-dimensional transesophageal echocardiography (3D TEE) in patients undergoing elective cardiac surgery. The authors found that LV volumes were consistently larger when measured with 3D than 2D TEE. Anesthesiologists and intensivists are increasingly relying on echocardiographic imaging for perioperative management of their patients. With TEE and increasingly, with transthoracic echocardiography (TTE), qualitative techniques such as “eye-balling,” the change of LV area in the midtransgastric short-axis and midesophageal views are used for estimation of left ventricular ejection fraction (LVEF) and LV volumes. Less frequently, the end-diastolic (ED) and end-systolic (ES) LV volumes are measured with the method of disks (MOD) by tracing the endocardial border in the midesophageal views, and the stroke volume and EF are subsequently calculated.2 Notwithstanding the constraints of the perioperative environment, which make the quantitative evaluation of LV function impractical, additional technical factors may introduce measurement errors. Qualitative evaluation is subjective, less accurate in the hands of an inexperienced echocardiographer, and has limited reproducibility even among experienced echocardiographers. If the true LV major axis, that is, the distance between the mitral plane and apex, is underappreciated, the LV cavity will appear smaller. Appreciation of the true LV major long-axis is important for the MOD technique to minimize error, as is the accurate tracing of the endocardial border for the correct calculation of LV volumes. Last but not least, the LV cavity is assumed to have the shape of a truncated ellipsoid, which is not the case for patients with dilated or aneurysmal ventricles. In such patients, volume measurements performed in only 2 orthogonal midesophageal views may be erroneous. It is therefore not surprising that LV volumes measured by 2D techniques underreport those derived by cardiac magnetic resonance imaging (CMRI), which is a widely accepted reference method for LV volume determination.3 In a meta-analysis by Dorosz et al.,4 which included 23 studies with 1638 echocardiograms, 3D echocardiography-derived LV volumes highly correlated with those derived from CMRI, the reference method. In a subanalysis of 9 studies comparing 2D TTE versus CMRI, the pooled biases were −48.2 ± 55.9 mL for left ventricular enddiastolic volume LVEDV), −27.7 ± 45.7 mL for left ventricular end-systolic volume (LVESV), and 0.1% ± 13.9% for LVEF.4 Others have pointed out that this underestimation of LV volumes with 2D echocardiography is more significant with reduced LV function (LVEF <50%), a group where accurate diagnosis and proper treatment is most important.5 Three-dimensional echocardiography has mitigated many of these limitations faced by the 2D technique for assessment of LV volume and function. The entire LV is sampled by means of 3 to 8 pyramidal datasets (“slices”). Each dataset is acquired over a single beat in real time, using the electrocardiograph signal as the trigger. These slices are then “stitched” together to generate a 3D image of the entire LV. Semiautomated analysis software available in current 3D echocardiographic platforms (under proprietary names but performing essentially similar functions) directs the echocardiographer to “point-and-click” 4 to 5 reference points or axes in the mitral annulus and cardiac apex in ED and ES frames. From these references, the software traces the endocardial border, producing a cast of the LV endocardial surface in LV ED and ES, thus measuring 3D volumes and EF. The operator has the ability to adjust the traced LV endocardial border to improve accuracy of measurements. However, this subjective technique may introduce errors. Despite its simplicity, the technique is dependent on impeccable echocardiographic imaging and is therefore liable to ultrasound artifacts (shadowing from the mitral annulus as may occur with TEE imaging) and irregular R-R intervals, such as nonsinus rhythms and other arrhythmias or respiration-induced artifacts, that may not allow for perfect Intraoperative Evaluation of Left Ventricular Volume and Function: It Is Time to Usher in the Third Dimension