INTRACARDIAC ULTRASOUND MEASUREMENT OF VOLUMES AND EJECTION FRACTION IN NORMAL, INFARCTED, AND ANEURYSMAL LEFT-VENTRICLES USING A 10-MHZ ULTRASOUND CATHETER

Background Our objective was to examine the accuracy of intracardiac u ltrasound (ICUS) measurement of left ventricular (LV) volumes and ejec tion fraction (EF) using a 10-MHz ultrasound catheter. ICUS can image the LV in cross sections at all levels along the long axis with a tran sducer mounted on the tip of a catheter. Sequential serial LV cross-se ctional images can be obtained during cardiac catheterization and used to calculate LV volumes by Simpson's rule. This technique may be an a lternative to contrast LV angiography. Methods and Results A beating-h eart in vivo model was created to measure LV volume directly and conti nuously with an intracavity high-compliance latex balloon connected to a calibrated extracardiac reservoir in eight dogs in 35 experimental stages. A 10F ICUS catheter with a 10-MHz single-element transducer wa s introduced retrogradely via the aortic valve to the apex. Series of sequential LV cross-sectional images were recorded from the apex to th e base during a calibrated pullback of the catheter. At each 5-mm inte rval, the LV cross section was traced at end diastole and end systole. LV volume was calculated by Simpson's rule by integrating all segment al areas multiplied by segmental height. The effect on accuracy of sel ecting 5-, 10-, or 15-mm heights or a single section at the midventric ular level for measurement was assessed. The influence of distorted ve ntricular shape on the accuracy of ICUS measurements of LV volume was evaluated. This method was applied in 19 experimental stages in 10 int act dogs and pigs catheterized via the femoral artery. In the in vivo canine model, LV end-diastolic volume, end-systolic volume, and EF det ermined by ICUS using 5-, 10-, or 15-mm segments were not different fr om the actual measurements. But correlation and agreement between ICUS end-diastolic volume and direct measurements for 5- and 10-mm segment s were significantly better than for 15-mm segments or a single sectio n. Similar excellent correlations and agreement were observed for actu al and ICUS-derived end-systolic volumes using 5-, 10-, or 15-mm segme nts. The ICUS-derived EF correlated very well with actual EF with a sm all measurement error of 3.91+/-2.59% for 5-mm or 4.13+/-2.79% for 10- mm segments but a significantly greater measurement error for 15-mm se gments (5.35+/-3.76%) or single sections (14.8+/-12.2%). The presence of LV infarction or aneurysm did not significantly influence the accur acy of ICUS calculations for segmental heights less than or equal to 1 0 mm. Application in intact animals demonstrated a good correlation be tween stroke volume measured by ICUS and by thermodilution or flowmete r. ICUS-derived LV volumes correlated well with biplane angiographic v olumes, with a tendency toward underestimation. There was no significa nt difference between ICUS-determined LV EF and EF determined by angio graphy. Conclusions Intracardiac echocardiography accurately measures LV volumes and global systolic function in both regularly shaped and d istorted left ventricles. This technique directly and continuously vis ualizes circumferential LV endocardium and wall thickness without cont rast agents or geometric assumptions for calculation of LV volume. Thu s, it should be particularly useful in patients at high risk for contr ast-related complications or distorted LV shapes in which geometric as sumptions may not be valid.