Echocardiographic imaging options in ovine research subjects.

OBJECTIVES: To determine the feasibility of acquiring quality transesophageal (TEE), epicardial (EE), and intracardiac (ICE) echocardiographic images in ovine subjects and to discuss the merits of each technique with a focus on ICE image acquisition. ANIMALS: Eleven male castrated Dorset adult sheep. METHODS: Transesophageal echocardiography was performed under general anesthesia. Epicardial echocardiography was performed as part of an open chest (thoracotomy or sternotomy) experiment. Subjects were recovered with permanent jugular vein indwelling catheter and ICE from this approach was described. Feasibility of each technique was qualitatively assessed based on subjective image quality from three images for each image plane in each sheep. RESULTS: Transesophageal echocardiography was technically challenging and did not provide adequate image quality for consistent interpretation. Epicardial echocardiography and ICE had more favorable results with ICE demonstrating unique benefits for post-operative serial monitoring. CONCLUSIONS: Epicardial echocardiography and ICE were effective imaging techniques. Epicardial echocardiography required the least specialized training but was considered to have limited feasibility due to its requirement for an open chest procedure. Even with the necessity for permanent indwelling jugular cannulation, ICE was the least invasive of the three imaging techniques and potentially the most practical approach for chronic studies by minimizing post-operative stress. Transesophageal echocardiography was not a feasible technique in this study.

Effects of sampling interval on peak oxygen consumption in patients evaluated for heart transplantation.

BACKGROUND AND METHODS: Peak oxygen consumption is a commonly accepted criterion in patient selection for cardiac transplantation. To determine the effect of various gas exchange sampling intervals on the variability of peak oxygen consumption, 15 consecutive patients evaluated for cardiac transplantation performed maximal treadmill testing using a ramped protocol. Oxygen consumption was measured via breath-by-breath analysis of expired air. Peak oxygen consumption was determined for each test using the following sampling intervals: 60-, 30-, and 15-s averages, eight breath rolling average, and true breath by breath. Variability of the mean peak oxygen consumption for each sample average was compared using analysis of variance on repeated measures. RESULTS AND CONCLUSIONS: Measures of peak oxygen consumption differed significantly (p<0.001) between sampling averages. A maximum variability of 20% was noted between the largest and smallest averages (13.8+/-4.2 mL/kg/min for 60 s vs 17.3+/-4.2 mL/kg/min for breath by breath). No significant difference was found between the 30-s, 15-s, and eight breath rolling averages (14.2+/-3.7 vs 14.5+/-3.9 vs 14.7+/-4.3 mL/kg/min), respectively. Results of the study suggest (1) the sampling average can have a significant effect on peak oxygen consumption influencing patient selection for transplantation, and (2) sample averages larger than breath by breath but smaller than 60 s be used for determination of peak oxygen consumption.

Transesophageal echocardiographic assessment of systolic mitral leaflet displacement among patients with mitral valve prolapse.

Though qualitative transthoracic echocardiographic criteria for abnormal systolic leaflet motion are widely accepted as diagnostic characteristics of mitral valve prolapse, transesophageal echocardiographic criteria have not been evaluated against such a standard. Because transesophageal imaging planes are not identical to transthoracic imaging planes, validation of transesophageal echocardiographic criteria for mitral valve prolapse is needed. Eleven patients with mitral valve prolapse (based on physical findings and transthoracic echocardiographic criteria) and 11 healthy persons underwent prospective transesophageal echocardiography in two orthogonal imaging planes. Measurements of maximal leaflet displacement superior to the annular hinge points and mitral prolapse area subtended by the displaced mitral leaflets and the chord connecting the annular hinge points were performed in triplicate and averaged by a blinded observer. Though maximal systolic leaflet displacement was greater among patients with mitral valve prolapse than healthy subjects for both the transesophageal four-chamber (0.66+/-0.39 cm versus 0.05+/-0.11 cm, p < 0.001) and two chamber views (0.57+/-0.44 cm versus 0.20+/-0.25 cm, p < 0.04), no unique value differentiated patients with from those without mitral valve prolapse. Mitral prolapse area was greater for patients with mitral valve prolapse than for healthy subjects in both transesophageal four-chamber (1.23+/-1.18 cm2 versus 0.03+/-0.06 cm2, p < 0.02) and two-chamber views (1.73+/-1.65 cm2 versus 0.21+/-0.31 cm2, p < 0.02). Whereas a mitral prolapse area of 0.20 cm2 uniquely differentiated patients with from those without mitral valve prolapse in the four-chamber view, data overlap prevented determination of a similar diagnostic criterion for the two-chamber view. The difficulty in defining quantitative transesophageal echocardiographic criteria for mitral valve prolapse based on leaflet displacement alone suggested that the simple qualitative observation of leaflet displacement above the annular hinge points should not be used as a defining morphologic criterion for mitral valve prolapse.

Transesophageal echocardiographic assessment of the contribution of intrinsic tissue thickness to the appearance of a thick mitral valve in patients with mitral valve prolapse.

OBJECTIVES: This prospective, blinded transesophageal echocardiographic study was performed to determine the relative contributions of leaflet redundancy and overlap versus intrinsic tissue thickening as mechanisms for the apparent increase in diastolic thickness of the mitral valve. BACKGROUND: Increased diastolic thickness of the mitral valve has been identified as an echocardiographic feature that predicts subsequent adverse sequelae in patients with mitral valve prolapse (MVP). METHODS: Eleven patients with clinical and transthoracic echocardiographic evidence of MVP and 11 age-matched control subjects underwent protocol transesophageal echocardiography to image the mitral valve in two orthogonal planes and to measure its thickness in systole and diastole. RESULTS: Maximal diastolic width of the slack, unloaded anterior leaflet was significantly greater in patients with MVP than in control subjects (mean +/- SD: 0.64 +/- 0.20 cm vs. 0.30 +/- 0.04 cm, p < 0.001). Similarly, diastolic posterior leaflet width was greater in patients with MVP (0.67 +/- 0.39 cm vs. 0.31 +/- 0.06 cm, p < 0.01). In contrast, minimal systolic width of the distended pressure-loaded mitral valve was not significantly different between patients with MVP and control subjects for either the anterior (0.22 +/- 0.05 cm vs. 0.20 +/- 0.04 cm, p = NS) or the posterior (0.25 +/- 0.07 cm vs. 0.24 +/- 0.05 cm, p = NS) leaflets. The percent change in leaflet width from diastole to systole (% delta W), an index of the contribution of dynamic factors (e.g., leaflet redundancy and overlap) to the apparent increase in diastolic leaflet thickness, was significantly greater in patients with MVP than in control subjects for both the anterior (% delta W 62 +/- 13% vs. 34 +/- 16%, p < 0.001) and the posterior (% delta W 54 +/- 19% vs. 22 +/- 21%, p < 0.005) leaflets. CONCLUSIONS: The apparent increase in diastolic mitral leaflet thickness in patients with MVP versus control subjects is largely attributable to dynamic factors such as leaflet redundancy, overlap and deformation. During diastole, when the mitral leaflets are slack and unstressed, the leaflets appear markedly thickened in patients with MVP. In contrast, during systole, when developed intraventricular pressure distends the leaflets, causing them to stretch and balloon into the left atrium, the intrinsic tissue thickness is much less than that measured in diastole. These findings have important implications for the morphologic criteria used to diagnose MVP and the potential pathophysiologic mechanisms for adverse sequelae in this syndrome.

Transesophageal echocardiographic demonstration of distinct mechanisms for right to left shunting across a patent foramen ovale in the absence of pulmonary hypertension.

The optimal visualization of the atrial septum and fossa ovalis by transesophageal echocardiography was utilized to demonstrate saline contrast transit across the atrial septum and to relate it to the motion of the flap valve (septum primum) of the fossa ovalis. In three cases, three distinct mechanisms of right to left interatrial shunting in the absence of right ventricular systolic hypertension were identified: 1) transient spontaneous reversal of the left to right atrial pressure differential with each cardiac cycle; 2) sustained elevation of right atrial pressure above left atrial pressure induced by respiratory maneuvers; and 3) aberrant flow redirection across the foramen ovale due to a large right atrial mass. Any of these three mechanisms may be operative during paradoxic embolism in the absence of elevation of right ventricular pressures.