Heart failure (HF) remains a deadly, progressive disease with substantive and increasing morbidity, mortality, cost, and prevalence.1 Lifetime risk for developing HF is high (20–45%) and is driven in part by risk factors including obesity, hypertension, and nonfatal myocardial infarction.2 Modern therapies for HF include lifestyle modification, optimal use of survival prolonging medications, and use of cardiac resynchronization or defibrillators when appropriate to optimize both quantity and quality of life.3 Even with these options, 50,000–100,000 patients progress to late-stage HF annually, developing refractory symptoms for which advanced therapies may be considered.4 Cardiac transplantation has long been considered the gold standard option for these individuals, but limited availability of donor organs limits this to approximately 2,000 patients annually in the United States.5
Use of left ventricular assist devices (LVADs) as treatment for refractory HF has been steadily rising during the past decade. The initial use was to bridge patients to transplantation (BTT), focusing on patients who were unlikely to survive until a donor organ became available. Later, based on these successes, LVADs were approved for use as “destination therapy” (DT) for individuals who were not eligible for a donor organ. In January of 2010 a durable, continuous flow LVAD was approved as an alternative to cardiac transplantation, launching a period of rapid growth in the implantation of these devices.6 Recent scientific statements recommend the elective use of LVADs in patients with advanced HF and other markers of risk,7 with this recommendation driven by the remarkable improvements in survival seen in trials of this therapy.8,9 Growth in the use of LVADs for late-stage HF is therefore likely to continue at a rapid pace.
Although LVADs have proven to be reliable overall, potential complications remain for patients on long-term support. The primary areas of challenge are thrombosis (either manifesting as embolic events or hemolysis), infections (involving the driveline, pump pocket, or endovascular), and bleeding. This reality has led to the development of recommendations for the monitoring for and management of potential complications of these devices,10 which can include the need to image the native heart, the implanted components of the LVAD, and the spatial relationship between them. Echocardiography and plain radiography are commonly utilized for imaging LVADs, but have their limitations including and not limited to, complete visualization of the inflow and outflow cannulas and anastomotic sites,11 which can be seen with the use of cardiac computed tomography angiography (CCTA). Although echocardiography and plain radiography may be more easily accessible and more customarily used as the first line for imaging LVADs, the use and benefits of CCTA continues to grow and will likely not only become more accessible and overall cost effective. Radiation exposure may also be a concern for the use of CCTA, although radiation from CCTA is not much more elevated from background radiation (~3 mSv/year), and often less than a coronary interventional procedure. Recent recommendations for management of patients with LVADs include a recommendation for use of CCTA when other imaging modalities have not been revealing.10 More focused recommendations on the evaluation and management of pump thrombosis have suggested CCTA as a useful modality as well.12 Below, we hope to provide some insight into the roles and utility of CCTA imaging in the assessment and management of patients with LVADs based on our experiences at one high volume LVAD center.
Materials and Methods
We retrospectively reviewed all CCTAs performed on LVAD patients at our center during a period of 36 months. Seventy-four LVAD patients who met an indication for CCTA based on current guidelines and recommendations or perceived clinical need were referred for scanning at our center for a total of 94 studies. All recipients had received a Heart Mate II (Thoratec, Pleasanton, CA) LVAD at a previous time. All patients underwent gated CCTA on a 320 row multidetector scanner (Aquilion ONE, Toshiba America Medical Systems, Irvine, California, USA). The protocol utilized wide volume scanning with the parameters in Table 1. The scans covered 16 cm in one rotation, which in most instances encompassed a range from just above the aortic arch to below the cardiac apex. This enabled the entire LVAD and driveline to be captured including the entire outflow graft to the aorta. Image reconstruction utilized a program designed to image at the time of least cardiac motion. Images were then reconstructed on a Vitrea workstation (Vital Images, Minnetonka, Minnesota, USA) and analysis was performed using multiple oblique views that best demonstrated the position of the inflow and outflow cannulas, the left ventricle, aortic root, left atrial appendage, and the motor. In addition, the driveline connection and the track of the driveline were analyzed for possible complications.
All patients were included in the survival analysis, if patients had more than one CCTA performed, the initial CCTA was used. Survival in the abnormal and normal CCTA groups was compared using one-sided independent t test. Results were considered significant at p < 0.05.
Evaluation for thrombus was the most frequent indication for CCTA scanning (53/94 cases), followed by evaluation of cannula position (30/94), evaluation of infection (8/94), aortic dissection (2/94), and left ventricular pseudoaneurysm (1/94). For the purpose of the remainder of the article, the three studies performed for aortic dissection and left ventricular pseudoaneurysm were excluded leaving 91 studies, which were focused on LVAD-specific complications. All 74 patients had technically good images (Figures 1 and 2). Scans were analyzed for the position of the inflow cannula in the apex, the presence of thrombus in the left ventricle, inflow cannula, or outflow graft of the device, left atrial appendage, or aortic root. A total of 37 surgical interventions were performed on the 74 patients with 26 patients receiving pump replacement therapy and 11 patients eventually receiving heart transplant therapy. Roughly 50% of the patients who had a surgical intervention had positive findings on CT scanning (15/31 patients). Table 2 shows the indications and clinical scenario of each case and the CCTA findings. The 53 individuals who were referred for hemolysis and concern for probable pump thrombosis were managed medically during the process of assessment. This was accomplished with intensified anticoagulation via use of intravenous heparin or bivalirudin, eptifibatide, and rarely thrombolytics. Of these individuals, 9/53 that presented with hemolysis went on to have pump replacements successfully. Thrombus or foreign material within the explanted devices was confirmed in all of these individuals. Six of the 53 patients evaluated for thrombus had visible thrombus on their CCTA that were confirmed directly during the pump replacement procedure as well, and the information was of value in the operative planning (Figure 3A–D show aortic root thrombus and outflow graft thrombus). Of the six patients identified with thrombus on CCTA, five patients underwent pump replacement and one patient remains alive after CVA (LA appendage thrombus as source). Two patients were identified as having an active infection, one died and one went on to transplant. In the group of 30 patients referred for assessment of cannula position and outflow graft kinking, there were nine pump replacements, three deaths, and one explant due to a significant reduction in LV size after LVAD therapy. Three patients with positive findings on CCTA underwent additional pump replacement. An example of suboptimal cannula position after implant is demonstrated in Figure 4A, B. The survival duration of all 74 patients is demonstrated in Table 3.
Of the 74 LVAD patients 12 had multiple CCTAs performed. In our survival analysis, if multiple CCTAs were performed, the initial CCTA was included in the analysis. Forty patients were found to have negative or normal findings. Of those, 40 (93%) patients were alive at 6 months, 34 (79%) patients were alive at 12 months, and 33 (77%) were alive at 18 months. There were 31 LVAD patients with positive or abnormal findings. Of those patients, 22 (71%) patients were alive at 6 months, 19 (61%) were alive at 12 months, and 19 (61%) patients were alive at 18 months, with overall survival between the two groups being significantly different (p = 0.003; Figure 5).
To date, this study represents the largest number of CCTAs done in an LVAD population. Our study demonstrates that 320 row multidetector computed tomography is a noninvasive imaging modality that can be used to aid clinical decision making, risk stratification, and may have provide prognostic indicators for short- and long-term outcomes. The ability of this type of high-end CT scanner to perform whole heart imaging in one rotation offers the advantage of high spatial and temporal resolution compared with scanners with less coverage and slower acquisition times.
With LVAD therapy becoming increasingly available and the use of LVADs as DT increasing,6 there has been a steady rise in complications related to these devices that require evaluation with the aid of imaging. The importance of effectively and efficiently troubleshooting these devices cannot be understated as pump replacement carries with it significant morbidity and cost.
Our study reinforces previous findings that CCTA is a useful tool in the diagnosis of LVAD thrombosis,13–15 cannula positioning,14,16,17 and anatomical abnormalities.18 Although, echocardiography has been used for diagnosis of thrombosis in LVAD patients with high sensitivity and specificity,19,20 it is very limited because of its dependence on acoustic windows, operator technique, and artifact, along with patient body habitus. Although echocardiography can aid in diagnosis of complications such as thrombosis, certain parameters used in the diagnosis of thrombosis, such as Doppler flow velocities,19 remain dependent on sonographer technique, and accuracy of the data relies on the ability to obtain optimal acoustic windows and image angulation for accurate measurements of these parameters.
Cardiac computed tomography angiography carries the advantage of not only direct visualization of thrombus but can also be used for the evaluation of cannula positioning,14,17,21,22 and complications because of cardiac anatomy.17,18,22 Three-dimensional reconstruction with CCTA provides multiple views to adequately assess cannula position, which echocardiography may not facilitate. Four of the patients showing severe cannula malposition by CCTA had echocardiography performed which did not reveal these findings. Sacks et al.23 reported the importance of identification of inflow cannula malalignment as these may be related to future adverse events.
The use of CCTA in LVAD patients may provide prognostic indicators in this population. Similar to our findings, Acharya et al.22 found that six of 14 patients, whose CCTAs did not demonstrate any abnormalities in the LVAD or associated structures, were without subsequent adverse outcomes. To the best of our knowledge, our study is the only study of this size to demonstrate that LVAD patients with negative or normal CCTA findings have favorable 6, 12, and 18 months survival when compared with those with abnormal findings. Our Kaplan–Meier curve also suggests that after about 2 months the survival curves become parallel, suggesting that if a patient survives more than 2 months after an abnormal CCTA finding, their survival appear to be similar to the normal group. The use of CCTA in LVAD patients may be a compelling clinical tool used in conjunction with clinical parameters for risk stratification.
Submillimeter-gated CCTA imaging (minimum 64 slice) is remarkably able to provide unique information because of its excellent temporal and spatial resolution, especially with ongoing improvements in technology. As we have shown, the level of detail provided in terms of the interface of the cannula with the left ventricle and the aorta as well as the path of the driveline with fewer artifacts is often valuable in the evaluation of these devices. The most recent guidelines from the International Society for Heart and Lung Transplantation suggest incorporating CT in their algorithm for pump evaluation10—“Class 1 Recommendations for use of CT angiography: CT angiography allows visualization of the native heart and MCSD components and may be valuable when other imaging modalities have not been revealing, Level of evidence: B.”10
One additional question that remains is the optimal protocol for imaging LVADs with CCTA. Newer scanners and programs have improved the ability to visualize these pumps. The ability to obtain the entire heart with one cycle of the scanner, built-in programs to improve opacification, reduce imaging artifacts (“blooming” and motion related artifacts), and limit radiation exposure to the patient are vitally important qualities of an advanced CT system. However, the CT evaluation of LVAD patients is still in its infancy. Further collaboration between advanced HF centers with advanced cardiac imaging programs is needed to further advance the field.
Cardiac computed tomography angiography is an imaging modality, which can be employed in LVAD patients to provide additional critical clinical data to assist in the management of these patients and complications from LVADs. Cardiac computed tomography angiography can provide visualization of LVAD components that may not readily be seen with echocardiography or plain film radiography. Most importantly, CCTA can be used as an aid for risk stratification and potential indicator of short- and long-term prognosis in LVAD patients. This noninvasive method of imaging is beneficial in the clinical management of this patient population. Cardiac computed tomography angiography allows for more uniform imaging of LVADs, independent of factors such as operator technique and body habitus, with high degree of reproducibility.
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