Influence of transducer frequency and imaging modality on the intraoperative assessment of myocardial perfusion with transesophageal echocardiography

Objective: To determine factors that improve intraoperative myocardial perfusion assessment with conventional ultrasound imaging and intravenous ultrasound agents. Design: Prospective cohort study with repeated interventions on each patient. Setting: Single university hospital. Participants: Fourteen patients scheduled for elective coronary artery bypass graft surgery. Interventions: Myocardial perfusion was evaluated with contrast transesophageal echocardiography during conventional imaging after central venous injections of the contrast agent Optison (0.3 ML) before cardiopulmonary bypass. Eight patients received the injection during continuous sampling at each of 4 transducer frequency settings (3.5, 5.0, 6.0, 7.0 MHz). In another 6 patients, injections were administered during continuous and intermittent sampling (electrocardiogram-gated) at 3.5 and 5.0 MHz. Generalized estimating equations were used to compare mean responses, with p less than or equal to 0.05 considered significant. Measurements and Main Results: All recorded images were analyzed with off-line videodensitometry. Background-corrected peak pixel intensity (PPIcorr) and rate of change in pixel intensity (PPIcorr/T-PPI) were determined for each injection. PPIcorr was greater at 3.5 MHz than at 5.0, 6.0, and 7.0 MHz (p < 0.001). PPIcorr/T-PPI was greater at 3.5 MHz than at 5.0 (p < 0.001), 6.0 (p = 0.003), and 7.0 MHz (p < 0.001). PPIcorr was greater for gated than for nongated sampling conditions at 3.5 (p < 0.05) and 5.0 MHz (p < 0.05). Conclusion: To optimize myocardial contrast opacification, intraoperative transesophageal echocardiography should be performed with intermittent sampling at a transducer frequency close to the intrinsic frequency of the contrast agent. Copyright (C) 2001 by W.B. Saunders Company.