Partial cut-off of the left ventricle: determinants and effects on volume parameters assessed by real-time 3-D echocardiography

Abstract

A total of 44 patients with coronary artery disease underwent real-time three-dimensional (3-D) echocardiography for end systolic (ES) and end diastolic (ED) left ventricular (LV) volumetric analysis to assess the effect of partial cut-off of the left ventricular (LV) apex on volumetric analysis by apical transthoracic echocardiography. Patients with LV cut-off were assigned to either group 1 (ejection fraction, (EF) < 49%) or group 2 (EF ≥ 49%). Patients were additionally classified as group A if they had anterior or apical wall motion abnormalities (WMA) or group B if they had only inferoposterior or lateral WMA. Partial LV cut-offs were found in 22 subjects (50%). The estimated end diastolic cut-off volumes were as follows: 8.6 ± 3.2 mL (group 1), 4.3 ± 2.4 mL (group 2), 9.1 ± 3.3 mL (group A) and 1.4 ± 0.8 mL (group B). In group 1, more patients with LV volume cut-off were found than in group 2: χ² = 4.52, p < 0.05; and in group A more than in group B: χ² = 8.08, p < 0.01. In all, partial LV cut-off led to underestimation of LV volumes: 5.9 ± 4.7 ml (ED) vs. 2.1 ± 1.3 ml (ES), p <0.02. In conclusion, LV cut-offs can potentially alter the accuracy of echocardiographic volumetric analysis, particularly in anterior or apical WMA. ([email protected])

Introduction

Conventional two-dimensional (2-D) echocardiographic left ventricular (LV) volume determination is based on geometric assumptions and requires high-quality image acquisition from standardized scanning planes King et al 1992, Schnittger et al 1982, Teichholz et al 1976, Wyatt et al 1980. Despite high quality images, 2-D echocardiography underestimates the true LV volumes Gopal et al 1994, Gopal et al 1993, Schiller et al 1979. This observation has been attributed to the fact that the LV apex might be cut off when asymmetric left ventricles are examined by 2-D echocardiography and to transducer displacement over the LV apex (Erbel et al. 1993, 1980). Erbel and colleagues compared simultaneous ventriculographic and echocardiographic results. Although these studies provided indirect evidence for the hypothesis that the apex might get partially cut off, it was never directly proven that an overlaying rib makes the echocardiographic image plane miss the ventricular apex. Impact of this artefact remained unknown, because no methods were sensitive enough to provide accurate quantitative data. Transthoracic three-dimensional 3-D echocardiography is not limited by geometric assumptions and has replaced 2-D echocardiographic methods for LV volume quantification Gopal et al 1995, Kupferwasser et al 1997, Müller et al 1996, Siu et al 1993. Other than 2-D echocardiography, 3-D echocardiography will either depict the apex or prove that it was cut off, if it is not included in the acquired data set. Scarce data exist on the frequency of LV volume underestimation due to apical cut-off in a general cardiologic patient population. A number of factors influencing the degree of volume underestimation, such as regional and global systolic LV function, have not been assessed.

This study was undertaken to evaluate if there is, in fact, such a phenomenon as LV volume cut-off in transthoracic apical echocardiography. The study was further designed to quantitate how much end systolic and end diastolic LV volumes are underestimated. Another objective was to examine if systolic LV function wall motion abnormalities in particular or any physical characteristics of the patient affect the occurrence and the degree of LV volume cut-offs.