Transthoracic echocardiography supplements transesophageal echocardiography and provides useful additional information. Unfortunately, it is technically difficult to perform in critically ill patients who are frequently intubated, are in the supine position, and have injuries or surgical incisions, which limit the transducer access, or underlying pathological conditions, such as chronic obstructive pulmonary disease, that result in suboptimal images. Nevertheless, the apical four-chamber view can often be used (Fig 5), at least during the exhalation part of the respiratory cycle. This approach is useful for detecting right ventricular enlargement, and to estimate it by measuring the ratio of right to left ventricular area at end-diastole. This ratio is normally below 0.6. A ratio ranging from 0.6 to 1 indicates mild right ventricular dilatation, whereas a ratio greater than 1 denotes severe right ventricular dilatation. This view also provides a suitable angle for Doppler analysis of tricuspid backward flow. A small motion of the transducer also permits Doppler analysis of the left ventricular outflow tract. The parasternal short- or long-axis views enable visualization of a paradoxical motion of the interventricular septum, reflecting right ventricular systolic overload ( Fig.B). The subcostal long- and short-axis views are useful for examining patients with chronic obstructive pulmonary disease and emphysema. The subcostal long- and short-axis views are also the best way of accurately determining the diameter of the inferior vena cava ( F.igL.7) which closely correlates with central venous pressure in mechanically ventilated patients. Color Doppler and contrast echocardiography in the plane of the inferior vena cava and the hepatic vein can also be informative. The subcostal basal short-axis view allows Doppler analysis of the pulmonary arterial flow ( Fig 7), which can also be obtained by transesophageal echocardiography.
Fig. 5 Accurate measurements of right ventricular (RV) dimensions at end-diastole (ED) and end-systole (ES) and of right atrial (RA) dimensions at ES are best obtained from an apical transthoracic echocardiography four-chamber view (left). This approach can also be used to detect tricuspid regurgitation (TR) by color Doppler (dense cloud of echoes) (right upper panel) and to record backward flow velocity by continuous Doppler (right lower panel), permitting calculation of pulmonary artery systolic pressure.
Fiq. 6 Parasternal long-axis view of the interventricular septum (IVS). In this patient presenting with massive pulmonary embolism, M-mode recording visualizes paradoxical IVS motion, with its displacement towards the left ventricular (LV) cavity at the onset of diastole (first arrow), and then towards the right ventricular (RV) cavity at the onset of systole (second arrow). The result is a parallel motion of the iVs and the LV posterior wall instead of the normal pattern consisting of an alternating convergent (systole) and divergent (diastole) motion.
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