LVAD: Image Acquisition Techniques and Pitfalls

Transcription

1 LVAD: Image Acquisition Techniques and Pitfalls Daniel Ocazionez, MD Assistant Professor Department of Diagnostic and Interventional Imaging The University of Texas Medical School at Houston

2 Nothing to Disclose

3 Objectives Brief overview of current left ventricular assist devices. Discuss imaging evaluation with CXR and CT Illustrate imaging pitfalls

4 Indications for mechanical circulatory support with LVAD As a bridge to cardiac transplantation As a lifelong support alternative for patients deemed ineligible for heart transplantation, so-called destination therapy As a bridge to myocardial recovery Miller, JACC 2013

5 LVAD Pulsatile vs non-pulsatile (continuous flow) Continuous flow devices, specifically Heart Mate II and HeartWare, are the focus of this presentation. The spinning turbine-like rotor blade propels blood continuously Patient may or may not have a blood pressure that is measurable by automatic blood pressure machines Pulsatility is determined by aortic valve opening

6 Heartmate II (2 nd generation) Approved indications: Bridge to cardiac transplantation Destination therapy Pump design: High speed, axial, rotatory Location: Preperitoneal Pump typical speed: rpm ratec_heartmateii.cfm HeartMate II CF-LVAD (Thoratec Corporation, Pleasanton, CA)

7 HM II Outflow cannula Inflow cannula Outflow cannula Inflow cannula The inflow cannula is inserted into the apex of the left ventricle and outflow cannula is anastomosed to the ascending aorta. The inflow and outflow cannula and associated flows are always defined relative to the device. [Estep JACC 2010] Drive line Inflow cannula Pump Drive line Pump The drive line extends to an electronic controller and battery pack that are worn on a belt and shoulder holster. The spinning of the rotor draws blood from the inflow cannula through cardiac diastole and systole into the ascending aorta. [Ammar KA Eur Heart J Cardiovasc Imaging 2012] Outflow cannula Pump

8 HeartWare HVAD (3 rd generation) Approved indications: Bridge to cardiac transplantation Pump design: Centrifugal Location: Intrapericardial Pump typical speed: rpm heartware%c2%ae-lvad

9 Drive line HW Inflow cannula Pump Outflow cannula Inflow cannula Outflow cannula Inflow cannula Pump Drive line The HeartWare (HW) is an implantable continuous-flow centrifugal blood pump, called the HVAD pump. In contrast to HM II, HW is small enough to implant into the pericardial space. Pump

10 Chest x-ray Abdomen vs

11 Plain Radiography Inflow Cannula Angle Outflow Cannula Angle Pocket Depth

12 Risk of pump thrombosis Comparison between HMII pump thrombosis vs no pump thrombus (control group) immediately postop and after 30 days. Angulation of the inflow cannula (48.2 +/- 6.8 versus /- 9.2 degrees, p<0.001). Youden index was maximized at an angle of 55.0 degrees and this cut-off point had the best trade-off for sensitivity and specificity. Angulation of the outflow cannula (No significant difference). Pump pocket depth (107 +/- 49 versus / cm, p<0.001). Taghavi, S et al. Ann Thorac Surg 2013;96:

13 Chest x-ray Abnormal Taghavi, S et al. Ann Thorac Surg 2013;96:

14 COMPUTED TOMOGRAPHY (CT) Imaging modality of choice High spatial resolution. 3D image dataset for evaluation of the device components and anatomic relationship Detailed resolution of the chest wall, mediastinum and lung parenchyma. Mohamed I, et al. RadioGraphics, 2015, 35:

15 CT Image Acquisition Protocol should be directed to answer the particular clinical question. Ideal protocol: FOV should include the aortic arch and upper abdomen. Restrospective ECG gated CCTA: Dynamic 4-D assessment of the inflow cannula and left ventricular chamber. Followed by a standard non ECG gated evaluation of the upper abdomen (dose reduction) to include the entire course of the driveline. Carr CM, et al. RadioGraphics 2010; 30(2): Mohamed I, et al. RadioGraphics, 2015, 35:

16 CT Image Acquisition Utility of unenhanced CT: a. Anatomic positioning of the cannulas. b. Detect non cardiac complications such as mediastinal or retroperitoneal hematomas. c. Differentiate between blood vs surgical material. Carr CM, et al. RadioGraphics 2010; 30(2): Mohamed I, et al. RadioGraphics, 2015, 35:

17 CT Criteria for optimal LVAD positioning A. The inflow cannula should be aligned posteriorly toward the mitral valve in the left ventricle B. The inflow cannula should not be pointed towards the septum or LV free wall C. The outflow cannula is attached to the ascending thoracic aorta and much less commonly to the descending thoracic aorta D. There should be absent to minimal aortic regurgitation Carr CM, et al. RadioGraphics 2010; 30(2): Mohamed I, et al. RadioGraphics, 2015, 35:

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19 PITFALLS

20 Is there a thrombus in the outflow cannula?

21 Normal outflow cannula * Axial contrast-enhanced CT image through the outflow cannula. Asterisk denotes contrast-filled outflow cannula. Arrows denote goretex graft used to cover the outflow cannula. Low attenuation between the outflow cannula and goretex graft is the space between the 2. Some amount of blood can seep through the pores of the outflow cannula into this space. The goretex graft helps prevent kinking of the outflow cannula and protects the outflow cannula when repeat sternotomy is needed (eg, for pump replacement or cardiac transplant).

22 Is there narrowing of the outflow cannula at the anastomosis?

23 Pseudo-narrowing of the outflow cannula at the anastomosis Coronal CT image demonstrating likely narrowing of the outflow cannula at the anastomosis with the ascending thoracic aorta. The hemodynamic LVAD pressures were normal and there were no low flow alarms. Patient was taken to catheter angiogram which demonstrated no luminal abnormality. The patient was discharged home.

24 Is there a thrombus in the inflow cannula/pump?

25 Is there a thrombus in the inflow cannula/pump?

26 Normal flow artifact through the inflow cannula simulating a thrombus Axial contrast-enhanced CT image through the inflow cannula. Arrow denotes flow artifact simulating an intraluminal hypodensity.

27 Is the outflow cannula fractured?

28 Normal goretex mimicking cannula fracture A. B. Coronal reformatted CT (A) and volume rendered image (B) show high attenuation goretex used to cover and protect the outflow cannula. Larger arrows denote overlapping goretex pieces. Smaller arrows denote gaps in the goretex.

29 Example # 2

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34 Is there infection?

35 Postoperative air mimicking infection A. B. Axial noncontrast CT (A) and sagittal reformation (B) from CT done 6 days after LVAD implantation show air (arrows) trapped between the outflow cannula and the outer protective goretex layer. Air can be a normal postoperative finding. There was no clinical evidence of infection or device malfunction.

36 Example # 2

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44 Is that blood or calcium in the pericardium?

45 Goretex patch A. B. C. Noncontrast axial CT images (A & B) and sagittal reformation (C) reveal high attenuation goretex patch material (arrows) anterior to the heart. The goretex patch is used to protect the heart from damage during re-entry for transplant surgery. The goretex patch should not be mistaken for pericardial calcification or hemorrhage.

46 Is there bleeding from the attachment site of the inflow cannula?

47 Is there bleeding from the attachment site of the inflow cannula?

48 A. B. Teflon felt E. * * * C. D. A-D. Sequential noncontrast CT images reveal high attenuation teflon felt (arrows) surrounding the inflow cannula. Teflon felt is used to prevent suture from tearing through the ventricle and also to seal suture holes/prevent bleeding. Teflon felt should not be mistaken for pericardial calcification, or, on contrast-enhanced exams, for active hemorrhage. E. Intraoperative photograph of teflon felt (asterisks).

49 END