Transthoracic 2D echo color Doppler assessment of internal mammary artery to left anterior descending coronary artery graft

Improved MR flow mapping in coronary artery bypass grafts during adenosine-induced stress

PURPOSE

To validate a recently developed fast high-temporal-resolution magnetic resonance (MR) flow sequence and use it to assess coronary artery bypass graft function during pharmacologic stress.

MATERIALS AND METHODS

Aortic and internal mammary artery flow was measured in 11 healthy volunteers by using conventional cine gradient-echo imaging as a reference standard method and turbo-field echo-planar imaging (TFEPI). By using TFEPI, breath-hold flow mapping with a spatial and temporal resolution of 0.8 mm(2) and 23 msec, respectively, can be performed. This sequence was applied in 20 angiographically normal grafts, and total blood flow at rest and during adenosine infusion (140 microgram/kg/min) was measured.

RESULTS

Good agreement in aortic and internal mammary artery flow values between conventional fast-field echo and TFEPI techniques was found. The mean bypass graft total flow (+/- SD), as assessed with TFEPI, increased from 30.8 mL/min +/- 13.5 to 76.7 mL/min +/- 36.5 (P <.05) to yield a flow reserve of 2.7. Furthermore, this sequence revealed a difference in total flow between single and sequential grafts at rest (25.4 mL/min vs 40.9 mL/min; P <.05) and during stress (65.2 mL/min vs 98.3 mL/min; P <.05).

CONCLUSION

Breath-hold TFEPI provides fast accurate flow measurements with high temporal resolution and allows motion-compensated flow quantification in multiple coronary artery bypass grafts during one 6-minute adenosine infusion.

Noninvasive assessment of left and right internal mammary artery graft patency with high-frequency transthoracic echocardiography

OBJECTIVES

The aim of this study was (1) to visualize internal mammary artery grafts (IMAG) on coronary artery by transthoracic echocardiography and (2) to assess the patency of the grafts.

METHODS

Twenty-three patients (21 men, 56 +/- 6 years) with previous coronary artery bypass grafting were studied at baseline and after they underwent low-dose dipyridamole infusion. The parameters obtained were systolic (SPV) and diastolic (DPV) peak velocities and their ratio (DPV/SPV); the dipyridamole infusion to baseline ratio of DPV was an index of IMAG blood flow reserve (FR). Two groups of patients were selected at baseline: group A, (n = 12) with a DPV/SPV >1, and group B (n = 11), with a DPV/SPV <1.

RESULTS

The IMAG was identified in all patients. Intraluminal flow signals obtained with pulsed wave Doppler showed a biphasic pattern (1 systolic and 1 diastolic wave). After dipyridamole infusion was administered, flow velocities increased in 11 of 12 patients in group A and in 5 of 11 patients in group B. In group A the DPV/SPV increased from 1.79 +/- 0.47 to 1.8 +/- 0.43 (P = not significant), and the FR was 1.8 +/- 0.4. In group B the DPV/SPV increased from 0. 46 +/- 0.05 to 0.5 +/- 0.09 (P = not significant), and the FR was 1. 3 +/- 0.41. Coronary angiography showed the graft patency in all patients in group A and in 5 patients in group B with increased flow velocity after dipyridamole infusion. In the identification of graft stenosis at baseline, DPV/SPV showed 100% sensibility and 58% specificity, and FR showed 92% sensibility and 84% specificity.

CONCLUSION

Doppler echocardiographic evaluation of the IMAG is a simple noninvasive method to assess the functional impairment of the vessel.

[The Doppler color detection of internal mammary artery anastomoses and a functional assessment of their patency]

BACKGROUND

Left internal mammary artery coronary graft patency is usually evaluated invasively by cardiac catheterization. The objective of this study was to assess the ability of a high-frequency transthoracic Doppler echocardiographic system in the evaluation of patency and flow velocities changes in left internal mammary artery.

METHODS

Twenty-two patients (63 +/- 9 years, 17 male) who had previously undergone left internal mammary artery to left anterior descending artery were evaluated by transthoracic echocardiography, with an Acuson Sequoia C256 equipment (Acuson, Mountain view, USA), placing the transducer (5 MHz) in the second-third left intercostal space. Left internal mammary artery flow was considered to be found in the presence of one systolic/diastolic biphasic blood flow. Dipiridamol 0.5 mg/kg was administered in absence of contraindications in order to evaluate the flow reserve.

RESULTS

In 16 patients (73%), a biphasic systolic-diastolic flow was visualized. Peak velocity of systolic and diastolic waves was 38 +/- 13 and 37 +/- 15 cm/s, respectively. Eleven patients received i.v. dipiridamol 0.5 mg/kg. After dipiridamol, systolic and diastolic velocities rose from 32 +/- 8 to 43 +/- 14 cm/s (p = 0.0429) and from 25 +/- 8 to 50 +/- 17 cm/s (p = 0.0002), respectively (an increasing of 33 +/- 22% and 103 +/- 46% over the baseline, respectively).

CONCLUSION

This descriptive study shows that a non-invasive functional evaluation of left internal mammary artery grafts by a transthoracic approach with a high-frequency echocardiographic equipment is possible.

Assessment of left internal mammary artery grafts using dipyridamole Doppler echocardiography

Color Doppler echocardiography of the left mammary artery was combined with dipyridamole testing in order to assess the presence of significant (>70%) graft stenosis in 87 patients with a mammary artery graft to the left anterior descending coronary artery presenting with chest pain. Occluded grafts are detected by absent diastolic flow velocities at baseline, whereas the response of the diastolic flow velocity to dipyridamole distinguishes patients with critical versus noncritical stenosis of a patent graft.