MR-Angiographie und Flussreservenbestimmung nach minimalinvasiver direkter Koronararterien-Bypass(MIDCAB)-Operation der linken Arteria mammaria interna im Vergleich zur Mehrzeilen-CT

Zusammenfassung

Ziel: Evaluation eines MR-Protokolls zur postoperativen Untersuchung des minimalinvasiv angelegten A.-mammaria-interna-Bypass (MIDCAB) mittels kontrastmittelgestützter 3D-MR-Angiographie und Bestimmung der Flussreserve. Material und Methoden: 19 symptomatische (Angina pectoris CCS I-III, intermittierende nicht anginatypische thorakale Schmerzen, Narbenschmerzen) Patienten (59,9 ± 7,9 Jahre) nach MIDCAB wurden 6,9 ± 1,5 Jahre postoperativ untersucht. Die Bypassdarstellung erfolgte mit einer nicht EKG-getriggerten MR-Angiographiesequenz (1,4 × 0,9 × 1,0 mm³, 22 s) in Atemstillstand nach Gabe von 25 ml Gd-DTPA. Phasenkontrastflussmessungen (1,1 × 1,1 × 5 mm³, 42 ms zeitliche Auflösung, retrospektives Gating, Venc 90 cm/s) im Bypass in Ruhe und nach medikamentöser Stressbelastung mit Dipyridamol (0,56 mg/kg KG) folgten. Als Referenz dienten die Multi-Detektor-CT-Angiographie (16-Zeilen-CT) und in 9 Fällen eine invasive Bypassangiographie. Ergebnisse: Von den MIDCAB waren 4/19 (koronarangiographisch bestätigt) verschlossen und 4/19 hochgradig (> 70 %) stenosiert. Die Beurteilung der distalen Anastomose des LIMA-Bypass gelang in 47 %. In den offenen Bypasses konnte ein signifikanter Flussanstieg von in Ruhe 75,4 ± 33,3 ml/min auf 202,7 ± 49,6 ml/min nach Stressinduktion (p < 0,002) gemessen werden. Mit der Kombination der MRA und Flussreservenbestimmung konnten alle stenotischen Bypasses detektiert werden. Schlussfolgerung: Die Kombination der MR-Angiographie mit Flussmessung erhöht die Aussagekraft und diagnostische Sicherheit der MRT in der postoperativen Verlaufskontrolle von Patienten nach MIDCAB.

Abstract

Purpose: To evaluate graft patency, flow and flow reserve in patients with minimal invasive direct coronary artery bypass (MIDCAB) of internal mammary artery (IMA) grafts using a combined MR protocol with phase-contrast technique and MR angiography. Material and Methods: At a 1.5T Magnetom Sonata (SIEMENS), 19 symptomatic (angina CCS I-III, intermittent thoracic discomfort, scar disorders) patients (59.9 ± 7.9 years old) with 19 left internal mammary artery (LIMA) grafts implanted in minimal invasive technique were examined 6.9 ± 1.5 years post surgery. Contrast enhanced MR angiography (TR 2.5 ms, TE 1 ms, flip angle 20^o, spatial resolution 1.4 × 0.9 × 1.0 mm³, breath hold technique, no ECG-triggering, 25 ml Gd-DTPA) was performed to assess bypass patency. Phase-contrast flow measurements with retrospective gating (TR 41 msec, TE 3.2 msec, flip angle 30°, spatial resolution 1.1 × 1.1 × 5 mm³, temporal resolution 42 msec, venc 90 cm/sec) were applied in the IMA grafts at rest and after stress induction with dipyridamole (0.56 mg/kg/BW). For comparison, graft patency was evaluated by multidetector-row computed tomography (16-row CT). In 9 patients a selective catheter angiography was performed. Results: MIDCAB grafts were occluded in 4/19 patients. In 4 patients the anastomosis to LAD was highly stenotic (> 70 %) at MDCT (2 experienced investigators in consensus reading). In MRA 9 grafts could be delineated completely including the distal anastomosis to LAD (47 %). In 9 patients the distal part could not be evaluated. In patients with patent grafts (MDCT), a significant improvement of graft flow (at rest 75.4 ± 33.3 ml/min; after stress 202.7 ± 49.6; P < 0.002) and flow reserve (patent grafts 3.0 ± 1.1; stenotic grafts 1.5 ± 0.2, P < 0.02; occluded grafts 0.9 ± 0.2, P < 0.01) after stress induction was detected. Diastolic-to-systolic peak velocity ratios (D/S-PVR) at baseline were not significant between patent and stenotic grafts. Mean flow at baseline and after stress induction and flow reserve show a high sensitivity (91/92 /83 %) and specificity (86 /100/83 %) for detection of graft stenosis. MR angiography combined with flow reserve measurements could distinguish between occluded/stenotic and patent grafts in all MIDCAB grafts. Conclusion: MR imaging allows combined assessment of bypass patency and flow with flow reserve in patients after MIDCAB. The protocol of this study is applicable for the evaluation of graft patency in patients after revascularization.

Key words

Magnetic resonance imaging - MR angiography - MIDCAB - MR flow quantification

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