Clinical application of power Doppler imaging to visualize coronary arteries in human beings

Delineation of intracardiac shunts using contrast echocardiography

Contrast echocardiography is useful to visualize the endocardial borders of the left ventricle and improve the signal intensity of spectral Doppler signals. It can also help to define intracardiac flow dynamics in complex situations. We report 2 cases where contrast echocardiography improved the delineation of complex shunts and also provided new information not available by conventional echocardiography.

Intraoperative assessment of coronary grafts by novel digital epivascular imaging

OBJECTIVE

We sought to validate and evaluate 2 novel intraoperative ultrasound probes for epicoronary and epiaortic imaging.

BACKGROUND

The noninvasive intraoperative assessment of successful coronary artery bypass grafting remains a challenge.

METHODS

A total of 19 consecutive patients (4 female, 15 male; mean age 60.5 +/- 13.8 years SD, range 34-84) underwent coronary artery bypass grafting. The epivascular probes (GE Ultrasound) were validated in vitro and intraoperatively. Coronary arteries, grafts, and ascending aorta were imaged and quantified.

RESULTS

Mean adjusted flow measured by flowmeter was 3.25 L, SE 0.47 (range: 1-5.5 L) and was 3.15 L, SE 0.46 (range: 1-5.0 L) by ultrasound, with r = 0.97, P <.0001. Intraoperatively, 56 native coronary vessels were bypassed using 15 left internal mammary artery grafts, 25 vein grafts, and 16 venous jump grafts. A total of 15 left internal mammary artery grafts (100%), 12 left internal mammary artery anastomoses (80%), 20 vein grafts (15 left anterior descending coronary arteries, left circumflex artery grafts, 5 right coronary artery grafts) (80%), 4 jump grafts (25%), and 15 ascending aortas (78%) were successfully imaged by inexperienced surgeons. Doppler flow measurements were possible in 50 vessels (89%). Mean lumen diameter for graft arteries (veins) was 2 mm (2.87 mm), maximal velocity was 72 cm/s (46 cm/s), and mean velocity was 29 cm/s (21 cm/s) with a mean flow rate of 70 mL/m (55 mL/m).

CONCLUSIONS

We conclude that: (1) the novel intraoperative probes measure validated flow; (2) intraoperative hemodynamic assessment of graft patency is feasible without a learning curve; and (3) these findings should encourage the routine use of these intraoperative epivascular digital ultrasound probes.

Fourier phase and amplitude analysis for automated objective evaluation of myocardial contrast echocardiograms

AIMS

Objective methods for evaluating myocardial contrast echocardiography (MCE) are not yet widely available. We applied a Fourier analysis to myocardial contrast echocardiograms to identify myocardial perfusion defects.

METHODS

Harmonic power-Doppler contrast echocardiograms were performed in 21 patients undergoing Tl-201-SPECT imaging and in 13 controls. Images were transformed using Fourier analysis to obtain phase of the first harmonic sinusoidal curve displayed as color coded sequence of myocardial intensity changes. Means and standard deviations of regional phase angles were measured. The method was validated in an in vitro model. A contrast filled latex balloon was imaged at different gain settings mimicking defined time-intensity curves. An intraoperative porcine infarction model served to prove feasibility of Fourier transformation to analyze real-time pulse inversion contrast echocardiography.

RESULTS

In patients, phase imaging and intensity analysis showed focal areas with marked phase shifts (106 +/- 90 degrees) and heterogeneous distribution of phase angles (SD 66 +/- 17 degrees), correctly identifying 13/14 perfusion defects. The in vitro validation yielded increasing phase angles with increasing beta-values. This method was successfully applied to real-time MCE, identifying all infarction areas during occlusion of the left anterior descending artery.

CONCLUSION

Phase analysis can be used to display dynamics of myocardial opacification.

Cyclic variation of myocardial signal intensity in real-time myocardial perfusion imaging

BACKGROUND

The presence of cyclic intensity variation during real-time myocardial perfusion imaging (RTPI) has been controversially discussed. We investigated whether cyclic intensity variation is systematically found during RTPI and whether such variations are related to regional functional parameters.

METHODS

Intraoperative RTPI were obtained in 12 pigs before, during, and after left descending coronary artery occlusion with 60 mL/h SonoVue infusion. Furthermore, RTPI was performed in 14 patients after slow bolus injection of 0.7 mL of Optison. Instantaneous regional systolic to diastolic (S/D) myocardial intensity ratios were calculated after high mechanical index bubble destruction. S/D ratios were correlated with A- and beta-values, and fractional area shortening.

RESULTS

Systematic cyclic S/D changes were present in both experimental settings showing significantly higher systolic values (animals, S/D 1.28 +/- 0.44; patients, S/D 1.25 +/- 0.7). Cyclic S/D variation was not related to fractional area shortening, or A- or beta-values (all r < 0.3, not significant).

CONCLUSION

Consistent cyclic changes in myocardial contrast intensity can be measured both in intraoperative animals and in patients, showing higher systolic values. S/D ratios are not related to regional functional parameters.

Intraoperative color Doppler ultrasound assessment of LIMA-to-LAD anastomoses in off-pump coronary artery bypass grafting

BACKGROUND

Although techniques for off-pump coronary artery bypass grafting (CABG) are continually being refined, angiographic follow-up studies have indicated a higher rate of anastomoses-related stenoses than expected after traditional on-pump CABG. This study was performed to evaluate the use of intraoperative epicardial color Doppler ultrasound to quality-assess left internal mammary artery (LIMA) to left anterior descending coronary artery (LAD) anastomoses performed on the beating heart.

METHODS

Twenty-four LIMA-to-LAD anastomoses were evaluated with real-time epicardial ultrasound imaging using an ultrasound transducer positioned between the paddles of the stabilizer during off-pump procedures. The length of the anastomosis (D(A)), diameters of LIMA (D(M)), LAD at the toe of the anastomosis (D1), and 5 mm distally to the anastomosis (D2) were measured, and the ratios between these variables were calculated. The flow velocity through the anastomoses was visualized by color Doppler coding, and flow was assessed with transit-time flowmetry.

RESULTS

The epicardial color Doppler ultrasound allowed accurate assessment of the anastomoses. Twenty-three (96%) of the primary anastomoses were confirmed as patent. Mean ratios of D1/D2, D(A)/D2, and D(M)/D2 were 0.89 +/- 0.13, 3.01 +/- 1.04 and 1.32 +/- 0.32, respectively. One anastomosis had a stenosis more than 50% detected by color Doppler ultrasound. After surgical revision, transit-time flow increased from 22 to 40 ml/min.

CONCLUSIONS

Intraoperative color Doppler ultrasound allowed adequate imaging for quality assessment of LIMA-to-LAD anastomoses performed on the beating heart. One anastomosis was revised due to a technical error detected by epicardial color Doppler imaging. Epicardial ultrasound scanning is a valuable tool for intraoperative assessment of LIMA-to-LAD anastomoses during off-pump coronary surgery.

Epicardial colour-Doppler scanning of coronary artery stenoses and graft anastomoses

OBJECTIVE

Epicardial ultrasound scanning was applied during coronary surgery to assess coronary artery stenoses and quality of distal graft anastomoses, with special emphasis to the left anterior descending artery (LAD).

DESIGN

Twenty-three patients with coronary artery disease (M:F 19:4, mean age 65.0 +/- 9.5 years) had coronary artery bypass grafting (CABG) on cardiopulmonary bypass. Intraoperative scanning of coronary artery stenoses and graft anastomoses was performed with a new 10 MHz linear array Vingmed transducer connected to a GE Vingmed System FiVe echocardiography unit. Coronary stenoses detected by ultrasound were compared with preoperative angiograms. Intraoperatively, coronary graft flow was assessed with a Medi-Stim transit-time flowmeter.

RESULTS

Twenty LADs were investigated. In 17 LADs (85%) stenoses were clearly identified. In three LADs (15%) stenoses were not identified because LADs were deeply intramyocardial or the stenosis was very proximal. There was a significant correlation between LAD stenoses detected by ultrasound and angiogram (R = 0.7; p < 0.01). Mean number of grafts was 3.8 +/- 0.9. Of 26 LAD anastomoses assessed, good images were obtained in 22 cases (84.4%); the mean LAD diameter measured 1 cm below the anastomosis was 1.6 +/- 0.2 mm. In two LADs images were rated fair and in two LADs images were poor because of intramyocardial LAD. No technical error of the anastomoses was detected. All grafts had good flows as ascertained by flow measurements.

CONCLUSION

Epicardial ultrasound scanning with the new 10 MHz transducer allowed satisfactory imaging of coronary stenoses and graft anastomoses. Factors limiting the quality of imaging are proximal lesions, intramyocardial vessel, vessel tortuosity, and extensive calcifications. Epicardial ultrasound scanning with updated technology should become a further advancement to graft assessment during off-pump coronary surgery.

Power Doppler imaging for detection of harvest injury of internal mammary artery

Harvest injury of the internal mammary artery can lead to early thrombosis, which may be difficult to differentiate from atherosclerosis or harvest spasm in some cases. We describe the efficacy of intraoperative evaluation of the internal mammary artery by power Doppler imaging during off-pump or minimally invasive direct coronary artery bypass grafting.

Intraoperative echocardiographic imaging of coronary arteries and graft anastomoses during coronary artery bypass grafting without cardiopulmonary bypass

BACKGROUND

No accepted approach exists for the intraoperative evaluation of the quality of coronary arteries and the technical adequacy of graft anastomoses during coronary artery bypass grafting without cardiopulmonary bypass.

METHODS AND RESULTS

We assessed the accuracy of high-frequency epicardial echocardiography and power Doppler imaging in evaluating coronary arteries during coronary artery bypass grafting without cardiopulmonary bypass. To validate measurements of coronary arteries and graft anastomoses by high-frequency epicardial echocardiography and power Doppler imaging, we compared luminal diameters determined by these methods with diameters determined histologically in a study of off-pump coronary artery bypass grafting in 20 dogs. Technical errors were deliberately created in 10 grafts (stenosis group). The results of these animal validation studies showed that the maximum luminal diameters of coronary arteries and graft anastomoses measured by high-frequency epicardial echocardiography (HEE) and power Doppler imaging (PDI) correlated well with the histologic measurements: HEE = 1.027 x Histologic measurements + 0.005 (P <.0001); PDI = 0.886 x Histologic measurements + 0.0453 (P =.0001). Similar results were found in the evaluation of the stenosis group: PDI = 0.991 x Histologic measurements + 0.074 (P <.0001). Subsequently, we demonstrated the clinical applicability of this approach in 12 patients who underwent minimally invasive or off-pump coronary artery bypass grafting. Twenty graft anastomoses were examined intraoperatively by high-frequency epicardial echocardiography and power Doppler imaging, and luminal diameters determined by power Doppler imaging were compared with those determined by postoperative coronary angiography. The results demonstrated that graft anastomosis by power Doppler imaging correlated well with the angiographic measurements: PDI = 1.018 x Angiographic measurements - 0.106 (P <.0001).

CONCLUSION

High-frequency epicardial echocardiography can provide meaningful information on the target coronary artery, and power Doppler imaging can accurately measure graft anastomoses and can detect technical errors and inadequacies during coronary artery bypass grafting without cardiopulmonary bypass.

Recent advances in echocardiographic evaluation of left ventricular anatomy, perfusion, and function

This article provides a brief overview of several recently developed, emerging technologies and discusses their potential uses on clinical grounds. These new technologies include three-dimensional imaging, objective automated evaluation of ventricular function with acoustic quantification, assessment of regional ventricular performance using color kinesis and tissue Doppler imaging, harmonic imaging, and power Doppler imaging. Our hope is that readers will gain a better understanding of the principles underlying these technological advances, which will help them to integrate these new techniques efficiently into their clinical practices.

Identification of cardiac masses and abnormal blood flow patterns with harmonic power Doppler contrast echocardiography

Power Doppler is an ultrasound technique that color-encodes the change in amplitude of the ultrasound signal, which reflects changes in the position of scatterers between ultrasound pulses. Power Doppler can be used with echocardiographic contrast agents in a harmonic imaging mode to opacify a cardiac chamber. The opacification of a cardiac chamber can aid in visualizing the silhouette of intracardiac masses and displaying blood flow patterns. Four cases are presented that demonstrate the use of harmonic power Doppler to aid in the identification of a left ventricular apical thrombus, a left atrial thrombus, and a left ventricular pseudoaneurysm.

Acoustically stimulated transient power scattering explains enhanced detection of the very low velocities in myocardial capillaries by power Doppler imaging: an in vitro study

BACKGROUND

Although enhanced detection of myocardial perfusion signals by power Doppler imaging during contrast echocardiography has been noted, flow velocities in the coronary microvasculature should generally be below the threshold for Doppler motion detection. It has been suggested that in this situation nonlinear scattering related to acoustically stimulated microsphere oscillation or destruction may be responsible for the detected Doppler shift.

METHODS AND RESULTS

This study examined the behavior of MRX 115 (ImaRx Pharmaceuticals) microbubbles during harmonic and nonharmonic power Doppler imaging at varying power outputs (mechanical indexes 0. 3, 0.5, 0.7, and 0.9) in a perfusion tube model under zero-flow conditions. Boluses of MRX 115 0.5-mL suspension were introduced into the model, and flow was halted during each imaging period. Once power Doppler imaging was implemented, a signal was detected as unique sparkling color pixels corresponding to individual bubble destruction events, even in the absence of contrast movement. This phenomenon continued until all contrast bubbles disappeared from the region subjected to power Doppler imaging, usually within 35 to 40 seconds. Off-line videointensity measurements showed that initial power Doppler signal intensity and maximum signal decay rates increased parallel to increasing power output and were substantially greater for nonharmonic than for harmonic imaging modes.

CONCLUSION

This relationship between signal intensity and decay rate and acoustic power output suggests that transient scattering related to bubble destruction is responsible for generation of the power Doppler signal in the absence of flow. This would explain the enhanced detection of the very low velocity flows in the myocardial capillaries by power Doppler contrast imaging.

Intraoperative application of power Doppler imaging: visualization of myocardial perfusion after anastomosis of left internal thoracic artery to left anterior descending coronary artery

The purpose of this study was to determine the role of power Doppler imaging in assessing patency of coronary artery bypass graft (CABG) anastomosis. Twelve consecutive patients referred for CABG with the use of anastomosis of the internal thoracic artery to the left anterior descending coronary artery (LAD) were studied. A linear 6.5-MHz wide-band transducer was used during cardioplegic administration and reperfusion. Baseline power Doppler signals were obtained in the LAD in 11 patients, and post-CABG signals were obtained in 11 patients. In one patient the LAD was poorly visualized because of extensive calcification. In another patient the flow after bypass worsened and the graft was revised. Visualization of the LAD and internal thoracic artery grafts by epicardial intraoperative power Doppler imaging is feasible in almost all patients and allows rapid and simple intraoperative assessment of graft patency. In addition, myocardial perfusion is limited by heavily calcified coronaries.