lower ejection fraction left ventricular normal limit lvef lln institutional ef ejection fraction ventricular left cardiac echocardiogram heart dimensional uncontrolled ejection left ventricular fraction cardiac rest function greater arrhythmias disease fraction liver shortening ejection portal capacity tlc approve pi supplementary fraction shortening ejection left ventricular fractional cardiac function cardiologist greater lvef left ejection fraction ventricular cardiac known improve symptomatic rest