Single-Sided Magnet System for Quantitative MR Relaxometry and Preclinical In-Vivo Monitoring.

OBJECTIVE: We have developed a single-sided magnet system that allows Magnetic Resonance relaxation and diffusion parameters to be measured. METHODS: A single-sided magnet system has been developed, using an array of permanent magnets. The magnet positions are optimised to produce a B0 magnetic field with a spot that is relatively homogenous and can project into a sample. NMR relaxometry experiments are used to measure quantitative parameters such as T2, T1 and apparent diffusion coefficient (ADC) on samples on the benchtop. To explore preclinical application, we test whether it can detect changes during acute global cerebral hypoxia in an ovine model. RESULTS: The magnet produces a 0.2 T field projected into the sample. Measurements of benchtop samples show that it can measure T1, T2 and ADC, producing trends and values that are in line with literature measurements. In-vivo studies show a decrease in T2 during cerebral hypoxia that recovers following normoxia. CONCLUSION: The single-sided MR system has the potential to allow non-invasive measurements of the brain. We also demonstrate that it can operate in a pre-clinical environment, allowing T2 to be monitored during brain tissue hypoxia. SIGNIFICANCE: MRI is a powerful technique for non-invasive diagnosis in the brain, but its application has been limited by the requirements for magnetic field strength and homogeneity that imaging methods have. The technology described in this study provides a portable alternative to acquiring clinically significant MR parameters without the need for traditional imaging equipment.

Case Series of Early Structural Valve Deterioration of Trifecta Bioprosthesis - New Zealand Experience.

PURPOSE: Structural valve deterioration (SVD) remains a limitation on the use of bioprosthetic valves, with patient and valve-related factors contributing to early SVD. The Trifecta valve has been reported to have excellent hemodynamics but studies have highlighted early failure. We present a review and case series at a New Zealand tertiary hospital defining early SVD as failure within 3 years of implant. METHODS: A retrospective review from January 2015 to July 2019 included 525 patients undergoing surgical aortic valve replacement with 263 patients receiving an Abbott Trifecta or Trifecta Glide Technology (GT) valve. Our review found an acceptable safety profile for the valve with excellent hemodynamics, with a low mortality, stroke, and permanent pacemaker rate. RESULTS: Three patients out of 263 were identified from the study period as having early SVD requiring reintervention within 3 years of valve implantation leading to a 1.14% failure rate. One of the valves that had early SVD was a new generation Trifecta GT. An additional four patients were identified to have valves implanted prior to the study period and had valve failure at greater than 3 years post implantation. Five cases had cusp tears as their mechanism of failure, raising concerns about durability. CONCLUSION: The Trifecta valve has an acceptable safety profile and offers good hemodynamics due to the externally mounted leaflets. However, our experience of early SVD and failure is concerning for valve durability. Further comparison to other bioprosthetic valves and longer term follow-up are required to characterize the mechanism of failures.

Black Aorta from Alkaptonuria.

A-76-year old male with a past history of alkaptonuria with ochronosis (homogentisic acid deposition in tissues) had symptomatic aortic stenosis. Surgical replacement of the valve was undertaken, and he was noted to have a severely pigmented and porcelain aorta.

Total aortic repair: the new paradigm in the treatment of acute type A aortic dissection.

The surgical management of acute type A aortic dissection (ATAAD) is in a period of rapid evolution. Understanding the complex physiology and anatomy of both acute and chronic dissection has been enhanced by the ready availability of state of the art imaging techniques. Technical advances in the intraoperative monitoring of organ perfusion, together with adjuncts to limit organ injury and increasing sophistication in open and endovascular surgery have led to a major reduction in both perioperative morbidity and mortality. In many centers, there has been a transition in mindset and surgical approach away from a purely central aortic operation focusing on the ascending aorta and a 'live to fight another day' philosophy. The current more global perspective recognizes the importance of aortic valve function, malperfusion, false lumen (FL) patency and the potential for future complex aneurysm development. The time is now right to transition into the next phase of sophistication in the management of ATAAD with the aim of achieving not only a safe acute operation, but to either entirely prevent chronic complications or to greatly simplify their management by the creation of an anatomical situation that facilitates future endovascular intervention in place of complex re-do surgery. We present our view on the evolution of surgery for ATAAD leading to our current technique of Branch First Arch replacement and Total Aortic Repair, which not only provides a safe immediate operation, but also offers the hope of a simplified future management if not a total cure for the pathology.

Surgical management of acute type A aortic dissection: branch-first arch replacement with total aortic repair.

Acute type A dissection (ATAAD) remains a morbid condition with reported surgical mortality as high as 25%. We describe our surgical approach to ATAAD and discuss the indications for adjunct techniques such as the frozen elephant trunk or complete aortic repair with endovascular methods. Arch replacement using the "branch-first technique" allows for complete root, ascending aorta, and arch replacement. A long landing zone is created for proximal endografting with a covered stent. Balloon-assisted intimal disruption and bare metal stenting of all residual dissected aorta to the level of the aortic bifurcation is then performed to obliterate the false lumen (FL) and achieve single true lumen (TL) flow. Additional branch vessel stenting is performed as required.

Total Aortic Repair for Acute Type A Aortic Dissection Complicated by Malperfusion or Symptomatic Branch Vessel Malalignment.

Malperfusion or persistent perfusion of the false lumen with acute type A aortic dissections is a major cause of morbidity and mortality. We describe our experience with total aortic repair in patients with acute type A dissection with recurrent or ongoing branch ischemia, true lumen collapse, or rapid dilatation of a false lumen after initial surgical repair.

Aortic arch replacement without circulatory arrest or deep hypothermia: the "branch-first" technique.

OBJECTIVE: Although current developments in aortic arch replacement have demonstrated progressively improving mortality, cerebral morbidity remains significant. We describe a "branch-first" technique that avoids circulatory arrest and profound hypothermia, yielding excellent survival and low cerebral morbidity. METHODS: From September 2005 to February 2014, 64 patients underwent the "branch-first" technique for aortic arch replacement. Each arch branch is individually isolated for a brief period while it is anastomosed to a perfused trifurcation graft. The disconnection-reconnection sequence proceeds from the innominate artery to the left subclavian artery, with uninterrupted perfusion of the heart and viscera. After reconstruction of the debranched arch and ascending aorta, the common stem of the trifurcation graft is anastomosed to the arch graft. In this series, there were 39 male patients, and the mean age was 65 (range, 17-85) years. Twenty-five cases (39.1%) were of urgent/emergency status. Thirty-one patients (48.4%) underwent operation for aortic dissection, and the remaining patients underwent operation for aneurysms. Sixteen patients (25.0%) had previously undergone a cardiac surgical procedure. RESULTS: There were 2 (3.1%) early mortalities, and 1 patient (1.6%) had a permanent stroke. One patient (1.6%) required mechanical support, and 4 patients (6.3%) required hemofiltration for renal support. Ten patients (15.6%) did not require transfusion of red cells or any other blood product. CONCLUSIONS: The "branch-first" technique described brings us closer to the goal of arch surgery with cerebral, vital organ, and survival outcomes similar to those we expect from ascending aortic and root procedures.

Optimal management of acute type A aortic dissection with mesenteric malperfusion.

Acute type A aortic dissection (TAAD) remains a morbid condition; although overall outcomes have improved, patients presenting with preoperative malperfusion syndromes continue to have excessive mortality following conventional open surgical repair. Mesenteric malperfusion is generally associated with the worst prognosis and postoperative mortality in this group. With advances in the endovascular treatment of aortic pathology, options now exist to percutaneously manage mesenteric malperfusion prior to central aortic repair. This strategy may be associated with improved outcomes. To review this, a best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was 'In patients with acute type A aortic dissections with mesenteric malperfusion, does management of the malperfusion prior to central aortic repair reduce perioperative mortality'. Overall, more than 309 papers were found as a result of the reported search, of which 11 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that, in patients with acute TAAD complicated by mesenteric malperfusion, initial management with percutaneous interventional procedures to reverse the malperfusion followed by delayed central aortic repair is a reasonable strategy; this is because of the extremely poor prognosis associated with immediate central aortic repair in this group.

Desmopressin for reducing postoperative blood loss and transfusion requirements following cardiac surgery in adults.

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was, in adult patients undergoing cardiac surgery requiring extracorporeal cardiopulmonary bypass (CPB), does administration of desmopressin acetate (DDAVP) reduce postoperative blood loss and transfusion requirements? Altogether 38 papers were found using the reported search, of which 19 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Perioperative administration of DDAVP in adult patients undergoing cardiac surgery requiring CPB may result in a small but significant reduction in postoperative blood loss. However, this does not translate into a reproducible, clinically significant reduction in exposure to transfusion in unselected patients exposed to CPB. Several sub-groups of patients have been identified in whom DDAVP reduces postoperative blood loss and transfusion requirements. These sub-groups include patients who have received preoperative aspirin within 7 days of surgery, patients with CPB times in excess of 140 min and patients with demonstrable pre- or perioperative platelet dysfunction as determined by TEG analysis or platelet function assays. Platelet dysfunction at the time of surgery may be secondary to preoperative administration of antiplatelet medications, the result of pathological processes such as von Willebrands disease, uraemia or aortic stenosis with its associated sheer stress, as well as operative variables such as prolonged exposure to CPB. The evidence does not support the routine use of DDAVP in all cardiac surgery; indeed, it is clear that there is no significant reduction in postoperative blood loss or transfusion requirements with the administration of DDAVP in patients undergoing isolated coronary artery bypass grafting (CABG) in the absence of the features noted above. Given the absence of a clinically significant reduction in exposure to blood transfusion in unselected patients, we cannot recommend the routine use of DDAVP in patients exposed to CPB. However, DDAVP may reduce postoperative bleeding in patients who have received preoperative aspirin within 7 days of surgery, patients with CPB times in excess of 140 min and patients with demonstrable platelet dysfunction and should be used selectively in these subgroups.

Should the radial artery be used as a bypass graft following radial access coronary angiography.

The radial artery (RA) is often selected as the next conduit of choice following the internal thoracic artery for coronary artery bypass grafting operations (CABG). Radial access coronary angiography (RA-CA) has grown in popularity among cardiologists and has been advocated as the access route of choice for coronary angiography and intervention by many groups. However, sheath insertion and instrumentation may lead to structural and functional damage to the RA, which may preclude its use as a bypass conduit. The increasing use of RA-CA may therefore have an adverse effect on the ability to use the RA as a bypass conduit at subsequent CABG. To review this, a best evidence topic in cardiothoracic surgery was written according to a structured protocol. The question addressed was: 'should the radial artery be used as a bypass conduit following radial access coronary angiography'? Altogether, 167 papers were found using the reported search; 11 papers were identified that provided the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these studies were tabulated. Acute RA occlusion occurs in 2.3-30.5% of patients undergoing RA-CA. While a significant number of occluded RA's show recanalization on early follow-up, markers of endothelial function such as intima-media thickening (IMT) and flow-mediated dilatation remain impaired. RA-CA causes structural injury to the RA with evidence of histological injury (including intimal hyperplasia, periarterial tissue/fat necrosis and adventitial inflammation) along with intimal tears and medial dissections evident along the entire length of the vessel. Only one paper directly assesses patency rates of RA's used as bypass grafts following RA-CA finding a significant adverse effect on graft patency (77% patency in RA-CA, compared with 98% in the control group). We recommend avoiding the RA as a bypass conduit if it has previously been used for RA-CA. In situations where conduit options are limited, if possible, the RA should be avoided for at least 3 months following RA-CA and it may be beneficial to assess the RA's patency and flow characteristics with Doppler ultrasound preoperatively.

The history of arterial revascularization: from Kolesov to Tector and beyond.

Coronary artery bypass grafting (CABG) is the one of the most effective revascularization strategies for patients with obstructive coronary artery disease. Total arterial revascularization using one or both internal thoracic and radial arteries has been shown to improve early outcomes and reduce long-term cardiovascular morbidity. Although CABG has evolved from an experimental procedure in the early 1900's to become one of the most commonly performed surgical procedures, there is still significant variation in grafting strategies amongst surgeons. We review the history and development of CABG with a particular emphasis on the early pioneers and the evolution of arterial grafting.

Endovascular repair of iatrogenic aortic rupture.

Thoracic endovascular aortic repair (TEVAR) has been used for traumatic and acute spontaneous rupture of the descending thoracic aorta with good results. We present the case of a 40-year-old male whose thoracic spinal prosthesis eroded through the descending thoracic aorta; the aortic disruption was successfully managed with emergent deployment of an endovascular stent.