Thoracic aortic pulsatility decreases during hypovolemic shock: implications for stent-graft sizing

[Endovascular Treatment for Vascular Injuries of the Extremities]

Vascular injuries of the extremities are associated with a high mortality rate. Conventionally, open surgery is the treatment of choice for peripheral vascular injuries. However, rapid development of devices and techniques in recent years has significantly increased the utilization and clinical application of endovascular treatment. Endovascular options for peripheral vascular injuries include stent-graft placement and embolization. The surgical approach is difficult in cases of axillo-subclavian or iliac artery injuries, and stent-graft placement is a widely accepted alternative to open surgery. Embolization can be considered for arterial injuries associated with active bleeding, pseudoaneurysms, and arteriovenous fistula and in patients in whom embolization can be safely performed without a risk of ischemic complications in the extremities. Endovascular treatment is a minimally invasive procedure and is useful as a simultaneous diagnostic and therapeutic approach, which serve as advantages of this technique that is widely utilized for vascular injuries of the extremities.

Blunt Thoracic Aortic Injury and Acute Trauma: The Effect on Aortic Diameter and the Consequences for Stent-graft Sizing

BACKGROUND

Blunt thoracic aortic injury (BTAI) is associated with a high mortality and large trauma burden. Trauma and resuscitation after injury affect cardiovascular status, which may in turn affect aortic diameter. Measurement of aortic diameter is necessary to guide stent-graft sizing as part of BTAI management. Inaccurate measurement may lead to stent-graft complications. This pilot study aimed to assess the effect of acute major trauma on stent-graft sizing and stent-graft complications, in the context of BTAI and to assess whether any effect could be predicted.

METHODS

Patients who were admitted to a UK major trauma center between January 2007 and December 2017, and were diagnosed with BTAI, were identified. The thoracic aortic diameter was measured at six points on initial and surveillance computed tomography imaging. Data on patient demographics, admission heart rate, mean arterial pressure (MAP), and serum lactate were gathered.

RESULTS

Thirty-two patients were identified. Twenty met inclusion criteria. Of these, 12 were managed operatively and eight nonoperatively. The mean age was 40, the mean injury severity score was 43, and 85% were male. A mean increase in diameter between initial trauma scan and surveillance scan was noted throughout the thoracic aorta (P < 0.05). Stent-graft oversizing relative to aortic diameter changed significantly from initial trauma imaging to surveillance imaging (P < 0.05). Admission heart rate, MAP, and serum lactate were not predictive of the percentage change in aortic diameter. There were no complications at surveillance imaging (mean 45 days) or during medium term follow-up (mean 532 days).

CONCLUSIONS

Aortic diameter is affected by BTAI, acute major trauma, and resuscitation in a significant and variable manner. Measurements of the aorta in a patient with BTAI in the acute trauma setting should be viewed with uncertainty. A lack of complications in the short term is suggestive of a wide tolerance range regarding stent-graft sizing, but long-term results are unknown.

Important issues regarding planning and sizing for emergent TEVAR

In the past decades, treatment of acute thoracic aortic syndrome underwent drastic changes with a central role for thoracic endovascular aortic repair (TEVAR). One of the essential factors in the success of TEVAR is accurate sizing of the endograft, as both under- and oversizing can lead to suboptimal results and disastrous complications. The aim of this review was to give an overview of issues regarding endograft sizing in emergent TEVAR. Sizing of the endograft can be complicated by specific factors related to the underlying disease. For instance, different types of the acute thoracic aortic syndrome, i.e. blunt thoracic injury, thoracic aortic aneurysm or dissection with concomitant rupture are associated with hemorrhagic shock and the need for resuscitation, which leads to profound changes in diameter of the thoracic aorta. These diameter changes should be taken into account during endograft sizing. Measuring the thoracic aorta based on the admission CTA can lead to inaccurate sizing, even if proper centerline-based measurements are performed. The use of real-time imaging, in particular intravascular ultrasound (IVUS), has been shown to provide more accurate endograft sizing in acute thoracic aortic syndromes, especially if associated with hypovolemia. Future research should provide additional data on the exact role of different intra-operative imaging modalities (e.g. IVUS, transesophageal echocardiography [TEE], three dimensional CTA) on endograft sizing and long-term outcomes to ultimately improve patient outcome.

The Adenosine Hypothesis Revisited: Modulation of Coupling between Myocardial Perfusion and Arterial Compliance

For over four decades the thoracic aortic ring model has become one of the most widely used methods to study vascular reactivity and electromechanical coupling. A question that is rarely asked, however, is what function does a drug-mediated relaxation (or contraction) in this model serve in the intact system? The physiological significance of adenosine relaxation in rings isolated from large elastic conduit arteries from a wide range of species remains largely unknown. We propose that adenosine relaxation increases aortic compliance in acute stress states and facilitates ventricular-arterial (VA) coupling, and thereby links compliance and coronary artery perfusion to myocardial energy metabolism. In 1963 Berne argued that adenosine acts as a local negative feedback regulator between oxygen supply and demand in the heart during hypoxic/ischemic stress. The adenosine VA coupling hypothesis extends and enhances Berne's "adenosine hypothesis" from a local regulatory scheme in the heart to include conduit arterial function. In multicellular organisms, evolution may have selected adenosine, nitric oxide, and other vascular mediators, to modulate VA coupling for optimal transfer of oxygen (and nutrients) from the lung, heart, large conduit arteries, arterioles and capillaries to respiring mitochondria. Finally, a discussion of the potential clinical significance of adenosine modulation of VA coupling is extended to vascular aging and disease, including hypertension, diabetes, obesity, coronary artery disease and heart failure.

Impact of Thoracic Endovascular Repair on Pulsatile Aortic Strain in Acute Type B Aortic Dissection: Preliminary Results

BACKGROUND

The impact of thoracic endovascular aortic repair (TEVAR) on pulsatile aortic strain remains undetermined in patients with Type B aortic dissection (TBAD). Therefore, we quantified pulsatile aortic strain in TBAD patients and control subjects.

METHODS

We retrospectively analyzed two TBAD patients from our database with cardiac-gated computed tomography angiography imaging available before and after TEVAR and two control subjects (67- and 76-year-old males). Patient 1 (54-year-old female) presented with acute TBAD, and Patient 2 (55-year-old male) had Marfan syndrome and ruptured acute TBAD. Custom-developed software was used to compute aortic length, diameter, and area during the cardiac cycle. Pulsatile strain was calculated as systolic increments of length and circumference divided by corresponding diastolic values.

RESULTS

Before TEVAR, pulsatile longitudinal strain of the thoracic aorta was lower in TBAD patients (1.4-1.7%) than in control subjects (2.1-4.5%). After TEVAR, pulsatile longitudinal strain increased proximal to the stent-graft by 65% in the arch of Patient 1 and by 70% in the ascending aorta of Patient 2. Pulsatile circumferential strain was elevated in false lumen patency (4.4-6.2%) compared with thrombosed false lumen (1.4-2.1%) or control subjects (0.9-3.3%). Following TEVAR, circumferential measurements within stented segments were deemed unreliable due to artifacts.

CONCLUSIONS

TEVAR led to a considerable increase of pulsatile longitudinal strain proximal to the stent-grafts, and TBAD was associated with longitudinally stiffer aortas, which may be part of the pathophysiology of TEVAR-related complications such as retrograde dissection and aneurysmal dilatation. These preliminary data call for larger prospective studies.

Revealing Maximal Diameter of Upper Limb Superficial Vein with an Elevated Environmental Temperature

Ultrasonography is the primary tool for preoperative analysis of vein morphology for fistula creation in patients with end-stage renal disease. This study examines the effect of environmental temperature on the superficial vein size. Superficial veins of thirteen healthy volunteers were marked at three sites: cephalic vein in left lateral arm near cubital fossa, cephalic vein in left forearm at wrist, and basilic vein in left medial arm near cubital fossa. Mean diameters were recorded using ultrasound probe at 26°C and 43°C. Body temperature was increased using a Bair Hugger blanket. Mean values from the two temperatures were analyzed using paired sample t-test. All three superficial vein sites displayed statistically significant increase in diameter when the temperature was increased from 26°C to 43°C. Paired t-test showed p values of 0.001 for cephalic vein at wrist, 0.01 for cephalic vein near cubital fossa, and 0.01 for basilic vein near cubital fossa. This study proved that environmental temperature exerts a statistically significant effect on vein size measured by ultrasound during preoperative assessment for vascular access. Not to the extent of 43°C, the authors would recommend setting the room temperature higher during ultrasound vascular assessment to avoid underestimating the superficial vein size.

Activities at Thoracic Aortic Research Center, IRCCS Policlinico San Donato

The Thoracic Aortic Research Center (TARC) of the IRCCS Policlinico San Donato (PSD) aims to promote research on thoracic aortic diseases, to disclose the scientific knowledge and clinical experience and to develop new scientific paths within the Hospital and the aortic community, in collaboration with other national and international centres. Thoracic Aortic Research Center collaborates with many centres in both Europe (e.g. University of Utrecht, the Netherlands) and the USA (e.g. University of Michigan). This has led to multiple highly regarded publications in respected cardiovascular journals and has led to several PhD programmes resulting in doctorate degrees. Within Italy, in association with the Bioengineering School of the University of Pavia, TARC has founded the "BETA-lab" (Biomechanics for Endovascular Treatment of the Aorta laboratory), where MDs, Bioengineers, and PhD fellows conduct experimental studies using in vitro/ex vivo models of the physiologic aorta and aortic diseases. Furthermore, a database (iCardiocloud) where the medical imaging of cardiovascular patients from the PSD is structured, for in silico analysis utilizing computational fluid dynamics, and in vitro studies using also 3D printed aortic models. With the role of principal investigator or co-investigator, TARC at PSD has been participating in other several projects, including the International Registry of Acute Aortic Dissection, the International Aortic Arch Surgery Study Group, the European Registry of Endovascular Aortic Repair Complications, the ADSORB and ASSIST trials, and the GREAT registry. International collaborations have included also studies on predictors of aortic growth after dissection with the Yale University and University of Virginia, and on aortic biomarkers with the University of Tokyo.

Role of mechanotransduction in vascular biology: focus on thoracic aortic aneurysms and dissections

Thoracic aortic diseases that involve progressive enlargement, acute dissection, or rupture are influenced by the hemodynamic loads and mechanical properties of the wall. We have only limited understanding, however, of the mechanobiological processes that lead to these potentially lethal conditions. Homeostasis requires that intramural cells sense their local chemomechanical environment and establish, maintain, remodel, or repair the extracellular matrix to provide suitable compliance and yet sufficient strength. Proper sensing, in turn, necessitates both receptors that connect the extracellular matrix to intracellular actomyosin filaments and signaling molecules that transmit the related information to the nucleus. Thoracic aortic aneurysms and dissections are associated with poorly controlled hypertension and mutations in genes for extracellular matrix constituents, membrane receptors, contractile proteins, and associated signaling molecules. This grouping of factors suggests that these thoracic diseases result, in part, from dysfunctional mechanosensing and mechanoregulation of the extracellular matrix by the intramural cells, which leads to a compromised structural integrity of the wall. Thus, improved understanding of the mechanobiology of aortic cells could lead to new therapeutic strategies for thoracic aortic aneurysms and dissections.

Aortic emergencies-diagnosis and treatment: a pictorial review

Objectives

To demonstrate the various presentations of acute aortic pathology and to present diagnostic and therapeutic approaches.

Methods

Diagnostic imaging is the key to the reliable diagnosis of acute aortic pathology with multi-slice computed tomography angiography (CTA) as the fastest and most robust modality. Endovascular aortic repair (EVAR) with stent grafts and open surgical repair are therapeutic approaches for aortic pathology.

Results

CTA is reliable in diagnosing and grading aortic trauma, measuring aortic diameter in aortic aneurysms and detecting vascular wall pathology in acute aortic syndrome and aortic inflammation. CTA enables planning the optimal therapeutic approach. Stent graft implantation and/or an open surgical approach can address vascular wall pathology and exclude aortic aneurysms.

Conclusion

Aortic emergencies have to be detected quickly. CTA is the imaging method of choice and helps to decide whether elective, urgent or emergent treatment is necessary with EVAR and open surgical repair as the main treatment approaches.

Teaching Points

• To present aortic pathology caused by trauma

• To present acute aortic syndrome (aortic dissection, intramural haematoma and penetrating ulcers)

• To present symptomatic and ruptured aortic aneurysm

• To present infection (mycotic aneurysms/aorto-duodenal fistulae) or iatrogenic injury of the aorta

• To understand different presentations for treatment planning (EVAR and open surgery)

Intravascular ultrasound is a critical tool for accurate endograft sizing in the management of blunt thoracic aortic injury

BACKGROUND

Accurate measurement of true aortic luminal diameter (ALD) is critical for endograft sizing in endovascular treatment of blunt thoracic aortic injury (BTAI), but ALD is dynamic and changes with respect to patients' hemodynamic status. This study aimed to characterize how ALD at the time of diagnosis of BTAI compares with ALD at the time of endovascular repair and later at follow-up.

METHODS

This is an Institutional Review Board-approved, single-institution retrospective analysis of prospectively obtained data. Patients were included who presented between July 2007 and December 2012 with computed tomography angiography (CTA)-diagnosed BTAI; who underwent thoracic endovascular aortic repair (TEVAR); and who underwent preoperative CTA, intraoperative intravascular ultrasound (IVUS), and postimplantation CTA. Comparison measurements of the ALD were made among CTA and IVUS images at the level of the left subclavian artery (LSCA) and between initial CTA and postimplantation CTA at 10, 15, and 20 cm distal to the LSCA. Theoretical endograft sizes were determined and compared for each ALD at the LSCA.

RESULTS

Twenty-two patients were included in the analysis. Mean age was 38 ± 14 years (range, 17-61 years), with 82% men and mean Injury Severity Score of 43 ± 11 (range, 24-66). Mean time from emergency department admission to initial CTA was -1.2 ± 5 hours (range, -13 to 11.5 hours; negative time implies imaging at an outside facility before admission). Mean time from initial CTA to IVUS was 1.2 ± 1.4 days (range, 2.5 hours-5.7 days) and from IVUS to postimplantation CTA 33 ± 45 days (range, 17 hours-169 days). Overall, ALD measured by IVUS was significantly larger than that by initial CTA (Δ2.5 ± 3.1 mm; P < .05). ALD was also larger at 10, 15, and 20 cm distal to the LSCA in comparing the postimplantation CTA with the initial CTA (Δ2.4, 2.0, and 2.0 mm, respectively; all P < .05). More than half the devices would be sized differently with ALD measured by IVUS at the time of TEVAR vs initial CTA.

CONCLUSIONS

The ALD of patients with BTAI is significantly larger when it is measured by IVUS at the time of TEVAR compared with at the time of initial CTA. This difference in ALD may translate to undersizing of endografts used in TEVAR for BTAI. IVUS at the time of TEVAR provides a more accurate measurement of the actual ALD and should be used for endograft sizing for patients with BTAI.