Patient Population and Clinical Measurements:
The Frankel Cardiovascular Center at the University of Michigan Health System (UMHS) is a regional center with expertise in managing a large variety of aortic diseases. Only adult patients (age between 18-99 years) will be included. Patients will be included regardless of race or ethnicity. The patient population consists of:
1. Patients with a descending thoracic aortic aneurysm (TAA). TAA is defined by a balloon-like dilatation of the thoracic aorta. Such a dilatation may grow and eventually rupture, associated with high mortality. In the United States, more than 10,000 patients die every year due to a ruptured aneurysm. Current United States guidelines state that when the diameter of a TAA in patients with no connective tissue disorder is larger than 55-60 mm, aortic repair is recommended. To date, TEVAR is the first choice of therapy unless the anatomy is unsuitable or the patient has a connective tissue disorder.
2. Patients with a penetrating aortic ulcer (PAU). PAU is a chronic aortic condition, defined by an ulcer-like disruption of the inner aortic wall. Up to 28% of patients with a PAU may have or may develop an aortic aneurysm. Treatment with TEVAR is recommended for these patients, especially when patients are complicated by aortic growth or rupture.
Study Design:
TEVAR Group. In this study, the investigators target both TAA and PAU treated with TEVAR. Patients are to be identified in the clinic setting. Patients who are planned for treatment TEVAR for TAA and PAU (based on their treating physician's decision) will be given information about this observational study. Results for the standard work-up examinations for TEVAR, which consist of computed tomography (CT), echocardiography, blood (BP) and heart (HR) measurements, and electrocardiogram (ECG) will be collected. Once patient consent is confirmed, and prior to the TEVAR procedure, this study will include a non-invasive MRI scan and a blood collection for the biomarker data, in addition to the standard of care. In this study, during the TEVAR procedure, intraluminal pressure measurements will be conducted using the catheters and guidewires that will be already in place for the deployment of the endograft. This study will neither delay or modify their endovascular procedure. One year (between a window of 275 - 455 days) following the TEVAR procedure, the subject will undergo and a second non-invasive MRI study in addition to the standard clinical imaging follow-up. During this follow-up imaging, the patients will also undergo BP and HR measurements, ECG and blood tests.
Control Group. Patients with a stable TAA or PAU who do not require surgery are monitored in the outpatient clinic as standard of care. In this study, these patients will be given information about our study and will be asked to be included in our investigation. Once consent of the patients is confirmed, participants will undergo BP and HR measurements, ECG, blood tests, and one non-invasive MRI scan, at baseline. One year (between a window of 275 - 455 days) after baseline, the participants will undergo additional observations; non-invasive MRI study, BP and HR measurements, ECG and blood tests.
Clinical Measurements:
BP, HR, ECG, and blood- tests will be collected by trained personnel on all at baseline, and at one year (between a window of 275 - 455 days) follow-up.
* BP and HR will be measured per standard protocol.
* ECG will consist of a standard 12 lead ECG.
* Standard blood tests include complete blood count with platelets (including white blood cells, hemoglobin, hematocrit, red blood cells), a basic metabolic panel (including sodium, potassium, glucose, and calcium. Cardiac biomarkers tests include natriuretic peptide (BNP), amino-terminal pro-BNP (NT-pro-BNP) and Troponin T.
Echocardiography - Preoperative echocardiography is standard of care in all patients requiring TEVAR. The obtained echocardiographic measurements in these patients will be collected and compared to the preoperative MRI data.
Intraluminal pressures - During TEVAR, an angiography will be performed as standard of care. In this study, intraluminal pressure measurements will be conducted in the TEVAR group, using the catheters and guidewires that will be already in place for the deployment of the endograft, as is commonly done at the UMHS.
MRI - This study will employ the following clinical and (FDA/IRB approved) research MRI sequences to assess multiple signs of cardiovascular remodeling:
Clinical sequences:
1. Phase-contrast MRI measurements will be acquired on different cross-sections of the aorta (through-plane velocity-encoding). Images will also be captured in an oblique sagittal view (in-plane velocity-encoding) to estimate the aortic vessel wall stiffness via pulse wave velocity measurements. Velocity-encoded phase-contrast MRI images will be acquired across the mitral valve to evaluate the left ventricular (LV) diastolic function through the measurement of early-to-atrial ratios. Myocardial perfusion images will be acquired after administration of gadolinium based contrast agent under pharmacological stress.
2. Cine measurements will include LV volume, LV wall volume and left atrial volume.
3. Tag-MRI will measure different components of myocardial strain in standard short-axis and four-chamber views.
Research sequences:
1. Strain encoding sequences will measure cardiac- and aortic strain. This sequence is IRB approved: IRBMED # 2004-0452.
2. Steady state free precession sequences will measure strain of the thoracic aorta through cine measurements in the ascending aorta just distal to the coronary branches and just proximal to the celiac trunk. The sequence is obtained in accordance within FDA safety guidelines and with FDA approved MRI machines. It is easily reproducible and quantifiable and confirms to all MRI safety parameters in the United States.
All these measurements are non-invasive and therefore do not impose additional risk or burden to the patient. Contrast will be administered, except for those patients with poor renal function (eGFR\<60). The total anticipated scan time is approximately 1 hour.
Computational Modeling - Using the imaging and clinical data, simulations of blood flow and pressure will be performed using computational fluid dynamics (CFD) techniques and the High-Performance Computer cluster "Flux" at the University of Michigan. Highly detailed descriptions of velocity, flow, pressure, wall shear stress and other hemodynamically significant quantities will be obtained. The results of these non-invasive simulations will be compared against the clinical measurements (BP, HR, echocardiography, MRI, and intraluminal pressures) to calibrate this tool. Once calibrated, computational analyses will be performed to virtually assess the impact of more compliant endografts on cardiac and aortic hemodynamics.
Statistical Analysis - Statistical analysis will include descriptive and comparative analysis of both clinical measurements and data acquired from computational modeling. In analysis, participants will be grouped by TEVAR or Control group. Sub-analysis will include grouping by endograft length, gender, and age. The patients identifying information and protected health data will be dealt with based on HIPAA guidelines.
Preliminary echocardiographic data of TAA patients treated with TEVAR at the University of Michigan Health System revealed an average LV mass increase of 39% (P = 0.047) at 1-year follow-up. Power analysis for a Mann-Whitney U test, based on these preliminary data, calculated that for a significant threshold of 5% (P \< 0.05, two-sided test) a total sample size of 20 patients (α = 0.05, power = 97%) would be needed to observe a significant effect of TEVAR on LV mass increase. To ensure a margin of error, the investigators aim to include 12 TEVAR patients and 12 control patients.
To sum up, the end-goal of this study is to assess the impact of TEVAR on adverse cardiovascular remodeling through imaging and computation. This impact remains unclear and may carry important implications for patient management and future endograft design. The additional measurements required for this study are almost risk-free for all included participants. Although there are no direct benefits for the enrolled subjects, future aortic patients might benefit from better patient management with improved aortic endograft designs and long-term outcomes.
