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Precision Medicine
Precise measurements of the aortic morphologies are crucial for optimal endograft sizing
The morphology of the aorta changes continually during the various phases of the cardiac cycle. Diseases affecting the aorta – the largest artery in the human body – can cause a reduction in life span as well as disabilities. The ascending thoracic aorta (ATA) moves within the thoracic cavity in multiple directions; however, its movement is limited by its side branches and attachments. During the cardiac cycle, the internal shape of the ATA varies from round to oval to pear-shaped or other configurations as the ATA diameter changes in addition to longitudinal and circumferential pulsatile changes.
According to the Center for Disease Control and Prevention, there were 9,904 deaths in 2019 due to aortic pathologies such as dissections, coactions (narrowing) or aneurysms. Endovascular repair of aortic pathologies, which is less invasive than surgery, typically requires a landing zone in the ATA. An accurate preoperative measurement of aortic morphology is crucial for optimal endovascular stent-graft sizing for treating ATA conditions since incorrect sizing may lead to complications such as stent-graft migrations or endoleaks. Typically, the ATA diameter is measured for preoperative planning of thoracic endovascular aortic repair (TEVAR) using dynamic imaging modalities such as magnetic resonance imaging, computed tomography (CT) or electrocardiography (ECG)- gated CT.
Measuring the differences in the ATA diameter between the systole and diastole is critical for accurate stent-graft sizing. The impact of respiratory movements is also thought to be most conspicuous in the ATA. However, not enough studies have been performed to understand the significance of these measurements. To determine whether other parameters of the ascending aorta (such as the area or perimeter) are more significant for stent-graft sizing specifically in zone 0 of the aorta, Jean Bismuth, MD, associate professor of cardiovascular surgery at Houston Methodist, performed a retrospective study of 92 patients in which he measured the area, perimeter and diameter of the aorta in zone 0.
The study population included patients who were being evaluated for transcatheter aortic valve replacement and exclusion criteria were patients with aortic dissection, TEVAR, left ventricular ejection fraction of less than 40% and CTA scans without systolic or diastolic phases. The study population was primarily Caucasian (76%), male (53%) with a mean age of 77. This study cohort also had several comorbidities including diabetes, hypertension and chronic kidney disease. Analysis of the difference between the systole and diastole of the parameters of aorta area, perimeter and diameter revealed that the area in zone 0 was the most precise measurement.
Nowadays, ECG-gated scanning is becoming more available and much more widely used for TEVAR planning. However, it is still unknown which phase is the most accurate and results in the lowest complication rate, as the dimensions differ between the systolic and diastolic phases. Research findings in this paper need to be further investigated in a prospective study evaluating TEVAR patients to understand the clinical implications.”
Jean Bismuth, MD
Associate Professor of cardiovascular surgery at Houston Methodist
Using ECG-gated CT, measurements were made at three distinct locations of zone 0A (sinotubular junction), 0B (mid-ascending group) and 0C (proximal brachiocephalic artery) of the ATA during the systolic and diastolic phases that were defined by the lowest and highest left ventricular volumes, respectively. Out of the parameters of area, perimeter and diameter, the mean difference in the area was the smallest. This led Bismuth to conclude that the area is likely to be the best measurement for TEVAR planning.
According to Bismuth, “Nowadays, ECG-gated scanning is becoming more available and much more widely used for TEVAR planning. However, it is still unknown which phase is the most accurate and results in the lowest complication rate, as the dimensions differ between the systolic and diastolic phases. Research findings in this paper need to be further investigated in a prospective study evaluating TEVAR patients to understand the clinical implications.”
Since the movements of the aorta are dynamic, the most precise measurements need to be used for endograft selection to maximize clinical success. The research study led by Bismuth, which is published in the European Journal of Cardio-Thoracic Surgery, sheds light on which parameters provide the most precise measurement to minimize aortic mismatch during endograft sizing. Conversely, the study has a few limitations. Since the study cohort consisted of patients being evaluated for transcatheter aortic valve replacement, the results cannot be applied to patients undergoing endovascular aortic repair. Secondly, the literature suggests that as compared to men, women have greater distension and displacement. However, the majority of the study population was composed of men. Furthermore, most of the measurements were performed by a single physician.
A prospective study needs to be conducted to measure the parameters of area, perimeter and diameter of the aorta to better understand clinical outcomes. This will lead to more accurate stent-graft selection and sizing as well as post-operative evaluation of stent-graft performance.
Viony M Belvroy, M Mujeeb Zubair, Joost A van Herwaarden, Santi Trimarchi, Frans L Moll, Jean Bismuth. Important longitudinal and circumferential pulsatile changes in zone 0 of the aorta during the cardiac cycle. Eur J Cardiothorac Surg. 2020 Oct 1;ezaa306. doi: 10.1093/ejcts/ezaa306.
Abanti Chattopadhyay, PhD, March 2022
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