|Brett W. Sperry, MD
Left ventricular assist devices (LVADs) are surgically placed in patients with end-stage heart failure and have shown improvements in survival and quality of life versus standard of care.(1)
The main device that is currently being implanted in adults is the HeartMate 3, which is a continuous-flow centrifugal pump with a magnetically levitated rotor. The body of the LVAD pump is connected to the left ventricular apex through a titanium inflow cannula and to the ascending aorta through a Dacron polyester outflow graft that is sometimes covered in polytetrafluoroethylene (PTFE). The LVAD pump power is delivered from external batteries that are connected to the pump by a driveline covered in polyester velour. The driveline is tunneled from the pump body, out of the thoracic cavity into the subcutaneous skin tissue and exits out a site in the abdominal skin (Figure 1). After the driveline exits the skin, it is covered with a dressing and is anchored to the skin with an anchoring patch before it connects to the external power source and controller (Figure 2).
|Figure 1 depicting LVAD pump body, outflow graft, driveline, controller, and batteries. (2)|
|Figure 2 showing the normal appearance of the driveline exit site dressing and anchor.|
LVAD driveline infection is one of the most common post-operative complications and can occur at any time during the disease course. The driveline is a portal of entry for bacteria into the subcutaneous tissue and eventually into the bloodstream, and the prosthetic driveline material is a nidus for the formation of bacterial biofilm, making infection difficult to eradicate. Repetitive movement of the driveline at the point of skin exit can lead to inflammation around the exit site, which predisposes to infection. Infection is identified by discolored drainage from the driveline exit site and is sometimes associated with discomfort. (3)
F18-FDG PET is suggested for confirming and localizing an infectious site and may be valuable for predicting clinical outcomes and guiding therapy. (4,5)
Imaging protocols for 18F-FDG PET imaging of cardiovascular devices and prosthetic valves are similar to those employed in cardiac inflammation and infective endocarditis. Patient preparation to suppress myocardial glucose utilization is important to avoid spillover of myocardial counts to the region of interest around the LVAD. In addition, whole-body imaging can be useful to identify remote sites of infection.
As in any F18-FDG cardiovascular indication, interpretation begins with review of patient preparation, image quality, and co-registration. The clinical scenario and type of LVAD system is important to review. The CT scan used for attenuation correction is reviewed to identify the location of the pump and its inflow and outflow cannulas, and the driveline course. Abnormalities like pump malposition or abscess formation should be examined.
There is limited utility to looking at the standard cardiac display when evaluating for LVAD infection, as the entire pump hardware must be inspected. Instead, co-registered fused CT/F18-FDG images are reviewed to identify abnormal FDG uptake along any part of the device. Infection usually starts from the driveline exit site out of the skin and migrates inward along the driveline and to the pump body (Figure 3). As the condition worsens, the pump body (Figure 4) and outflow graft (Figure 5) can be involved.
It is important to review the uncorrected images, as attenuation-corrected images can suffer from an increase in F18-FDG intensity and SUV measurements due to metal artifact. (5) Metal artifact reduction software can also be used to improve diagnostic accuracy around metal artifacts. (6) Review of the fused CT/F18-FDG images with a focus on non-cardiac structures also is important to identify intrathoracic FDG-avid lymphadenopathy or other loci of infection. There is difficulty in interpreting LVAD, CIED, and valve infections in the setting of recent surgical implantation, as there is a varying degree of inflammation post-operatively that can be identified with F18-FDG imaging that does not signify active infection.
As of yet, metrics to quantify FDG uptake have not been published, but target-to-background ratio may be helpful to quantify in cases of serial studies. As SUVs are generated from the attenuation-corrected images, absolute measurements may not be accurate due to the aforementioned artifacts around metal objects.
Figure 3: Example of an infected driveline showing FDG uptake starting at the driveline exit site (A) and progressing inward (B and C).
Figure 4: Example of LVAD driveline infection that has migrated centrally and is now circumferentially involving the pump body.
Figure 5: Example of a patient with an LVAD who developed fungemia and evidence of FDG uptake along the outflow graft consistent with infection.
1. Rose EA., Gelijns AC., Moskowitz AJ., et al. Long-Term Use of a Left Ventricular Assist Device for End-Stage Heart Failure. N Engl J Med 2001;345(20):1435–43. Doi: 10.1056/NEJMoa012175.
2. Felix SEA., de Jonge N., Caliskan K., et al. The role of long-term mechanical circulatory support in patients with advanced heart failure. Neth Heart J 2020;28(Suppl 1):115–21. Doi: 10.1007/s12471-020-01449-3.
3. Leuck A-M. Left ventricular assist device driveline infections: recent advances and future goals. J Thorac Dis 2015;7(12):2151–7. Doi: 10.3978/j.issn.2072-1439.2015.11.06.
4. Kim J., Feller ED., Chen W., Liang Y., Dilsizian V. FDG PET/CT for Early Detection and Localization of Left Ventricular Assist Device Infection: Impact on Patient Management and Outcome. JACC Cardiovasc Imaging 2019;12(4):722–9. Doi: 10.1016/j.jcmg.2018.01.024.
5. Chen W., Dilsizian V. Diagnosis and Image-guided Therapy of Cardiac Left Ventricular Assist Device Infections. Semin Nucl Med 2020. Doi: 10.1053/j.semnuclmed.2020.11.002.
6. van der Vos CS., Arens AIJ., Hamill JJ., et al. Metal Artifact Reduction of CT scans to Improve PET/CT. J Nucl Med 2017;58(11):1867–72. Doi: 10.2967/jnumed.117.191171.
BLOGGER BIO: Brett W. Sperry, MD (@BrettSperryMD), is an associate professor of medicine at the University of Missouri-Kansas City and an advanced heart failure, transplant, and nuclear cardiologist at Saint Luke's Mid America Heart Institute. He is the associate program director of the Advanced Heart Failure Fellowship and the director of the Cardiac Amyloidosis Program.
Disclosures: Brett Sperry has received consulting / speaking fees from Pfizer, Alnylam, and Novartis.