Emergency computed tomography for aortic valve vegetation mimicking disruption

A 47-year-old man presented with symptoms typical of infective endocarditis and history of streptococcal meningitis 8 months previously. Echocardiography showed a large aortic valve vegetation that was interpreted as disruption of the noncoronary cusp. This was ruled out by 64-slice cardiac computed tomography. Valve replacement was performed successfully.

Aortic root surgery in septuagenarians: impact of different surgical techniques

Background

To evaluate the impact and safety of different surgical techniques for aortic root replacement (ARR) on early and late morbidity and mortality in septuagenarians undergoing ARR.

Methods

Ninety-five patients (73.8 ± 3.2 years) were operated and divided into three groups according to the aortic root procedure; MECH-group (n = 51) patients with a mechanical composite graft, BIO-group (n = 22) patients with a customized biological composite graft, and REIMPL-group (n = 22) patients with a valve sparing aortic root reimplantation (David I). In 42.1% (40/95) of these patients the aortic arch was replaced. Follow-up was completed in 95.2% (79/83) of in-hospital survivors.

Results

Hospital mortality was 12.6% (12/95) in the entire population (MECH. 15.7% (8/51), BIO 19.7% (4/22), REIMPL 0% (0/22); p = 0.004). Two patients died intraoperatively. The most frequent postoperative complications were prolonged mechanical ventilation ((>48 h) in 16.8% (16/93) (MECH. 7% (7/51), BIO 36.4% (8/22), REIMPL 4.5% (1/22); p = 0.013) and rethoracotomy for postoperative bleeding in 12.6% (12/95) (MECH. 12% (6/51), BIO 22.7% (5/22), REIMPL 4.5% (1/22); p = 0.19). Nineteen late deaths (22.9%) (19/83) (MECH 34.8% (15/43), BIO 16.7% (3/18), REIMPL 4.5% (1/22); p = 0.012) occurred during a mean follow-up of 41 ± 42 months (MECH 48 ± 48 months, BIO 25 ± 37 months, REIMPL 40 ± 28 months, p = 0.028). Postoperative NYHA class decreased significantly (p = 0.017) and performance status (p = 0.027) increased for the entire group compared to preoperative values.

Conclusion

Our data indicate that valve sparing aortic root reimplantation is safe and effective in septuagenarians, and is associated with low early and late morbidity and mortality.

Prevention of sternal dehiscence and infection in high-risk patients: a prospective randomized multicenter trial

BACKGROUND

One factor for the development of sternal wound infection (SWI) is bony instability after sternotomy. This study compares two surgical techniques with respect to the occurrence of SWI in patients with an increased risk.

METHODS

In this multicenter study, 815 consecutive patients with an increased risk for SWI were prospectively randomly assigned to a conventional osteosynthesis (transsternal or peristernal wiring; n = 440) or to an osteosynthesis with additional lateral reinforcement (Robicsek; n = 375). Primary endpoints were the rate of sternal dehiscence as well as the occurrence of superficial sternal wound infections and deep sternal wound infections.

RESULTS

Both groups were comparable concerning preoperative and intraoperative variables. The rate of sternal dehiscence, superficial sternal wound infections, and deep sternal wound infections (conventional technique 2.5%, 3.4%, 2.5%; and Robicsek 3.7%, 5.6%, 3.7%) did not differ between the groups. Logistic regression analysis found independent risk factors for the development of sternal dehiscence: body mass indes greater than 30 kg/m(2) (odds ratio [OR]: 2.9; p = 0.05), New York Heart Association class more than III (OR: 2.4; p = 0.07), impaired renal function (OR: 3.9; p = 0.01), peripheral arterial disease (OR: 3.6; p = 0.001), immunosuppressant state (OR: 3.3; p = 0.001), sternal closure performed by an assistant doctor (OR: 2.5, p = 0.004), postoperative bleeding (OR: 4.2; p = 0.03), transfusion of more than 5 red blood units (OR: 3.7, p = 0.01), reexploration for bleeding (OR: 6.9, p = 0.001), and postoperative delirium (OR: 3.5, p = 0.01). There was an inverse relation between the numbers of wires and DSWI in patients with conventional sternal closure (p = 0.008).

CONCLUSIONS

In patients with an increased risk for sternal instability and wound infection after cardiac surgery, sternal reinforcement according to the technique described by Robicsek did not reduce this complication.

Large thoracic wall hematoma following sternal reconstruction with transversal plate fixation after deep sternal wound infection

We present the case of a 53-year-old male patient with a rare complication of a thoracic wall hematoma following thoracic wall reconstruction with transverse plate fixation and pectoralis advancement flaps. The patient could be subsequently discharged after surgical re-placement and an uneventful would healing. This case marks one of two complications occurring in a series of six patients treated for deep sternal wound infection with a combination of vacuum-assisted therapy and plate fixation.

Primary treatment of deep sternal wound infection after cardiac surgery: a survey of German heart surgery centers

There are various primary treatment modalities of managing deep sternal wound infection (DSWI) following cardiac surgery, namely surgical debridement with primary reclosure in conjunction with irrigation, Vacuum-assisted closure (V.A.C. therapy, and primary or delayed flap closure. The purpose of this study was to assess whether there is consensus of the primary management of DSWI using one method as a single line therapy or a combination of these procedures. Therefore, a questionnaire with regards to the primary treatment modalities of DSWI was distributed to all 79 German heart surgery centers. All replied to the questionnaire. V.A.C. is used in 28/79 (35%) heart centers as the 'first-line' treatment, 22/79 (28%) perform primary reclosure in conjunction with a double-tube irrigation/suction system, and in 29/79 (37%) clinics both treatment options were used according to intraoperative conditions. Mostly, as a primary management of DSWI two treatment modalities are mainly in use: primary reclosure coupled with a double-tube suction/irrigation system and V.A.C. therapy. The current understanding is based purely on retrospective studies, not evidence-based medicine. Since prospective randomized studies have not yet been performed, controlled clinical trials comparing these treatment modalities are pivotal to define evidence for patients presenting with DSWI.

Extra-Anatomic Management of Homograft Reinfection after Thoracic Aortic Rupture

Vascular graft infections involving the thoracic aorta have high morbidity and mortality rates. The management of homograft reinfection has not been discussed yet. A 23-year-old woman suffered a rupture of the descending thoracic aorta. Seven months after interposition of a Dacron graft she was readmitted for graft infection and a homograft was inserted. An esophageal lesion was oversewn. Follow-up CT showed several aneurysms around the homograft. She underwent implantation of an extra-anatomic ascending-descending aorta Dacron bypass with stump closure of the descending aorta. The patient is alive and free from reinfection seven years later.

Erste klinische Erfahrungen mit der 3FEnable-Aortenklappen-Bioprothese

BACKGROUND AND PURPOSE

Patients with aortic valve (AV) pathology and severe comorbidities should benefit from reduced myocardial ischemic and extracorporeal circulation (ECC) time. Sutureless implantation of AV prosthesis may reduce myocardial ischemic and ECC time significantly. The authors report on their preliminary results with the first implants of the 3F-Enable sutureless AV prosthesis.

MATERIAL AND METHODS

The 3F-Enable prosthesis was implanted in five patients. Prostheses sizes were 27 mm (n = 3), 23 mm (n = 1), and 21 mm (n = 1), respectively. Intraoperatively, at patient's discharge as well as 3 and 6 months postoperatively, the AV prosthesis was evaluated by echocardiography.

RESULTS

ECC time was 87 +/- 36 min (range 49-141 min), myocardial ischemic time 55 +/- 27 min (range 32-97 min), and AV implant time 184 +/- 195 s (range 10-420 s). The latest postoperative echo (5.2 +/- 1 months postoperatively) revealed a fully competent AV in three patients, in two patient paravalvular leakage was detected at the severity of an aortic regurgitation (AR) II degrees , and AR II degrees -III degrees , respectively. The mean pressure gradients were 5.8 +/- 1.3 mmHg (range 4.2-7.1 mmHg), valve orifice area was 3.2 +/- 0.4 cm2 (range 2.6-3.6 cm2).

CONCLUSION

The first clinical results of the 3F-Enable sutureless AV prosthesis are feasible; however, a paravalvular leakage was detected in two patients (40%). Thus, device and procedural enhancements are required to assure positioning and anchoring of the prosthesis.

Clinical Application of Tissue Engineered Human Heart Valves Using Autologous Progenitor Cells

Background— Tissue engineering (TE) of heart valves reseeded with autologous cells has been successfully performed in vitro. Here, we report our first clinical implantation of pulmonary heart valves (PV) engineered with autologous endothelial progenitor cells (EPCs) and the results of 3.5 years of follow-up.

Methods and Results— Human PV allografts were decellularized (Trypsin/EDTA) and resulting scaffolds reseeded with peripheral mononuclear cells isolated from human blood. Positive stain for von Willebrand factor, CD31, and Flk-1 was observed in monolayers of cells cultivated and differentiated on the luminal surface of the scaffolds in a dynamic bioreactor system for up to 21 days, indicating endothelial nature. PV reseeded with autologous cells were implanted into 2 pediatric patients (age 13 and 11) with congenital PV failure. Postoperatively, a mild pulmonary regurgitation was documented in both children. Based on regular echocardiographic investigations, hemodynamic parameters and cardiac morphology changed in 3.5 years as follows: increase of the PV annulus diameter (18 to 22.5 mm and 22 to 26 mm, respectively), decrease of valve regurgitation (trivial/mild and trivial, respectively), decrease (16 to 9 mm Hg) or a increase (8 to 9.5 mm Hg) of mean transvalvular gradient, remained 26 mm or decreased (32 to 28 mm) right-ventricular end-diastolic diameter. The body surface area increased (1.07 to 1.42 m 2 and 1.07 to 1.46 m 2 , respectively). No signs of valve degeneration were observed in both patients.

Conclusions— TE of human heart valves using autologous EPC is a feasible and safe method for pulmonary valve replacement. TE valves have the potential to remodel and grow accordingly to the somatic growth of the child.

Prognostic Significance of Multiple Previous Percutaneous Coronary Interventions in Patients Undergoing Elective Coronary Artery Bypass Surgery

Background— A possible relationship between increased perioperative risk during coronary artery bypass grafting (CABG) and previous percutaneous coronary intervention (PCI) is debatable. We sought to determine the impact of previous PCI on patient outcome after elective CABG.

Methods and Results— Between January 2000 and January 2005, 2626 consecutive patients undergoing first-time isolated elective CABG as the primary revascularization procedure (group 1) were evaluated for in-hospital mortality and major adverse cardiac events (MACEs) and were compared with 360 patients after single PCI (group 2) and with 289 patients after multiple PCI sessions (group 3) before elective CABG. Unadjusted univariate and risk-adjusted multivariate logistic-regression analysis revealed previous multiple PCIs to be strongly associated with in-hospital mortality (odds ratio [OR], 2.24; 95% confidence interval [CI], 1.52 to 3.21; P <0.001) and MACEs (OR, 2.28; 95% CI, 1.38 to 3.59; P <0.001). To control for selection bias, a computed propensity-score matching based on 13 patient characteristics and preoperative risk factors was performed separately comparing group 1 versus 2 and group 1 versus 3. After propensity matching, conditional logistic-regression analysis confirmed previous multiple PCIs to be strongly associated with in-hospital mortality (OR, 3.01; 95% CI, 1.51 to 5.98; P <0.0017) and MACEs (OR, 2.31; 95% CI, 1.45 to 3.67; P <0.0004).

Conclusions— In patients with a history of multiple PCI sessions, perioperative risk for in-hospital mortality and MACEs during subsequent elective CABG is increased.

Decade of aortic valve sparing reimplantation: are we pushing the limits too far?

BACKGROUND

This single center study assesses the outcome of aortic valve sparing reimplantation (AVS) in 284 consecutive patients who were operated on for various indications during the last 11 years.

METHODS AND RESULTS

From July, 1993, to July, 2004, 284 patients underwent AVS. Mean age was 53+/-16 (range 8 to 84) years. Of the 284 patients, 184 were male (64.8%) and 54 (19%) experienced Marfan's syndrome. Acute aortic dissection Stanford type A was present in 53 patients (19%) and a bicuspid aortic valve was present in 17 patients (6%). Concomitant arch replacement was necessary in 120 patients (42%). Additional procedures were performed in 66 patients (23.2%). Mean follow-up time was 41+/-32 (range 0 to 130) months. The 30-day mortality was 3.2% overall, 11.3% in emergency patients, and 1.3% in elective patients. Mean bypass time was 174+/-48 (range 90 to 440) minutes and aortic cross clamp time was 132+/-33 (range 64 to 283) minutes. In patients undergoing arch replacement, circulatory arrest was 25+/-17 (range 7 to 99) minutes. Rethoracotomy for bleeding was required in 4.6% of patients. During follow-up, there were 20 (7.3%) late deaths. Reoperation of the reconstructed valve was required in 15 patients (5.3%); underlying reasons were endocarditis (n=4) and aortic insufficiency (n=11) requiring aortic valve replacement. Average grade of aortic insufficiency increased significantly from 0.23+/-0.46 postoperatively to 0.34+/-0.59 at latest evaluation (P=0.026). Two patients experienced a transient ischemic attack early postoperatively; no further thromboembolic complications were noticed. The majority of patients (96%) presented with a favorable exercise tolerance at last contact.

CONCLUSIONS

The aortic valve reimplantation technique leads to excellent clinical outcome in patients with various pathologies. Lack of anticoagulation and favorable durability should encourage the extension of indications for this technique.

Endovascular stent-graft placement for complications of acute type B aortic dissection

PURPOSE OF REVIEW

To review the concepts and current clinical results of endovascular stent-graft placement for acute complicated type B aortic dissection.

RECENT FINDINGS

The optimal treatment for patients with dissections confined to the descending aorta (Stanford type B-AD) remains a matter of debate. Usually, antihypertensive medical therapy with strict blood pressure lowering below 135/80 mm Hg represents the first choice for patients with uncomplicated type B-AD. Patients with acute complicated type B-AD remain a major therapeutic challenge because surgery of the descending aorta is still associated with high morbidity and mortality. In 1999, endovascular stent-graft placement was introduced as a novel, less invasive treatment option for patients with type B aortic dissection. Current indications include acute (contained) aortic rupture, symptomatic ischemic branch vessel involvement, early aortic expansion, or unrelenting pain. So far, few studies on stent-graft placement in patients with acute complicated aortic dissection have been published reporting an early mortality between 0 and approximately 20%.

SUMMARY

To date, there is limited experience with endovascular stent-graft placement for acute complicated type B aortic dissection demonstrating its feasibility and life-saving potential. The endovascular approach can avoid the major trauma of open surgery and should help to get patients out of the acute life-threatening phase of the disease; however, long-term results are needed to assess the durability of this treatment.

[Functional aspects of endothelial phenotypes in the human heart. Immunohistochemical study for the evaluation of endothelial adhesion molecule expression]

BACKGROUND AND PURPOSE

The endothelial lining is a confluent monolayer of thin and rhomboid-shaped cells, that covers the inner surface of all blood vessels. However, the essential role of endothelial cells in all aspects of cardiovascular physiology, homeostasis and the pathogenesis of most cardiovascular diseases no longer remains controversial. Although much evidence has been achieved regarding the molecular functioning of transcription factors and regulatory proteins, many questions on endothelial heterogeneity with regard to function and morphology at various vascular sites remain unanswered. In this study, an immunohistochemical map of endothelial adhesion molecule expression at various vascular sites of the healthy human heart is created. Using this map, the authors examined whether expression patterns are distinctive by their molecular function at their site of origin. Furthermore, immunohistochemical findings were associated with the clinical situation.

MATERIAL AND METHODS

Tissue samples from eleven different vascular locations of healthy human hearts were analyzed using immunohistochemistry. Endothelial adhesion molecules of the selectin, immune globulin supergen, and integrin families, some complementary cellular adhesion molecules, and the von Willebrand factor were analyzed.

RESULTS

Endothelial adhesion molecule expressions were found to be characteristic of all vascular sites investigated. Thus, molecules involved in inflammatory reactions were predominantly expressed within the myocardial microvasculature, whereas molecules serving for endothelial anchorage toward extracellular matrix components could be observed especially on endocardial and valvular surfaces. Apart from that, a parallel expression of immunologically relevant as well as integrin molecules were found to be characteristic of coronary arteries.

CONCLUSION

To the authors' knowledge, this is the first report on site-specific expression characteristics for all vascular sites of the human heart. Thus, our data provide important novel information, which ultimately will help to bring some light into the field of cardiac physiology.

Could 37 degrees C storage temperature extend homovital valve allograft viability?

BACKGROUND AND AIM OF THE STUDY

Preservation of allograft valves is the most important determinant of their durability. Unprocessed, homovital valve allografts stored at 4 degrees C in nutrient medium have provided superior mid-term results over routinely used cryopreserved or antibiotic-sterilized allografts. As storage temperature may alter viability, it was hypothesized that allograft storage at 37 degrees C may maintain greater viability over time.

METHODS

Porcine aortic (n = 10) and pulmonary valve conduits (n = 10) were harvested under sterile conditions. Valve leaflets and sinus walls were separated, and each was divided into two specimens, which were stored in modified culture medium at 4 degrees C and 37 degrees C, respectively. Cell viability was tested by monitoring metabolic activity at 37 degrees C at days 1, 3, 7, 10, and 14. The proliferative ability of cells isolated from valve leaflets was assessed after 14 days by cell culture. Sterility testing of the storage medium was also carried out.

RESULTS

Valve leaflet cells and sinus wall cells had significantly higher metabolic activity when stored at 37 degrees C. The median number of isolated cells at 4 degrees C was 3,231.5 (range: 422-3,844), and at 37 degrees C was 8,317.50 (range: 4,329-8,650). The storage medium was sterile in all cases.

CONCLUSION

Storage at 37 degrees C significantly improved valve allograft cell metabolic activity and viability compared with storage at 4 degrees C for up to 14 days. The lower concentration of antibiotics did not affect the sterility of tissues stored at 37 degrees C.

Aortic root surgery in Marfan syndrome: comparison of aortic valve-sparing reimplantation versus composite grafting

OBJECTIVE

The objective of this study was to compare the results of aortic valve-sparing reimplantation and aortic root replacement with mechanical valve conduits in patients with Marfan syndrome undergoing operation for aortic root aneurysms. Patients and methods Between March 1979 and April 2002, 119 patients with clinical evidence of Marfan syndrome underwent composite graft replacement with mechanical valve conduits (n = 74) or aortic valve-sparing reimplantation according to David (n = 45). The underlying causes were aortic dissection type A (43 patients) and aneurysms (76 patients).

RESULTS

Patients undergoing aortic valve reimplantation were younger compared with patients undergoing composite grafting (28 vs 35 years, P =.002) and had longer intraoperative aortic crossclamp times (125 vs 78 minutes, P <.0001) and extracorporeal circulation times (162 vs 124 minutes, P <.0001). Early postoperative mortality was 6.8% (n = 5) in patients undergoing composite grafting and 0% in patients undergoing aortic valve reimplantation (P =.15). Mean follow-up was 30 months for patients undergoing aortic valve reimplantation and 114 months for patients undergoing composite grafting. Freedom from reoperation and death after 5 years postoperatively was 92% and 89% in patients undergoing composite grafting and 84% and 96% in patients undergoing aortic valve reimplantation (P =.31; P =.54), respectively. Thromboembolic complications or late postoperative bleeding occurred in 17 patients undergoing composite grafting, and an early postoperative event occurred in 1 patient undergoing aortic valve reimplantation.

CONCLUSIONS

The results of aortic valve reimplantation and composite grafting of the aortic valve and ascending aorta with mechanical valve conduits are similar with regard to early and mid-term postoperative mortality and to the incidence of late reoperations in patients with Marfan syndrome. The low risk of thromboembolic or bleeding complications favors aortic valve reimplantation in these patients.

Eine azellularisierte xenogene Matrix als Basis einer artifiziell hergestellten Herzklappe mittels ?Tissue engineering?

BACKGROUND

The ideal scaffold material for tissue engineered heart valves is discussed controversially. We evaluated acellularized xenogenic matrix constructs with and without seeding with autologous vascular cells in the pulmonary circulation in a sheep model.

METHODS

Porcine pulmonary valve conduits (n=16) were acellularized by trypsin/ EDTA incubation. Autologous myofibroblasts and endothelial cells were harvested from carotid arteries; xenogenic valve conduits (n=10) were repopulated with these autologous cells resulting in uniform cellular restitution of the pulmonary valve conduit surface. Using this method, we implanted autologous cell/xenogenic matrix constructs (XB) in ten animals. In six control animals acellularized/xenogenic matrix constructs (XA) were implanted. In each animal, cardiopulmonary bypass was used to resect the pulmonary valve and replace it with the xenogenic pulmonary valve conduits. The animals were killed after 6, 9 or 12 months. The explanted valves were examined histologically and biochemically.

RESULTS

After explantation XB showed severe cusp degeneration, which resulted in severe valvular regurgitation. In comparison, XA appeared macroscopically normal with preserved valvular function. The surface of XB were covered with an incomplete endothelial multilayer. The extracellular matrix (ECM) of XB showed pathological amounts of collagenous and elastic fibers as well as proteoglycan content combined with an increase cellularity. The XA were completely repopulated by an endothelial cell monolayer; the ECM was repopulated with a myofibroblast population comparable to native ovine heart valve tissue.

CONCLUSIONS

Approaches to heart valve engineering based on acellularized/xenogenic matrices provide promising results and will hopefully led to the "ideal" valve substitute in clinical heart valve replacement.

Hypothermic circulatory arrest during ascending and aortic arch surgery: the theoretical impact of different cerebral perfusion techniques and other methods of cerebral protection

Operations on the thoracic aorta using hypothermic circulatory arrest are still associated with significant morbidity and mortality due to neurological complications. During the last decades, different cerebral protection techniques have been introduced into clinical practice to reduce the incidence of such complications. Furthermore clinical as well as basic researches have been performed to improve the outcome after these operations. Currently different cerebral perfusion methods are in clinical use and the superiority of one or the other method is a matter of controversial discussion. This review has been undertaken to evaluate the theoretical impact of these different methods of cerebral protection. Based on the experience of the authors the pros and cons are discussed with clinical and experimental reports from the literature.

In vivo model for cross-species porcine endogenous retrovirus transmission using tissue engineered pulmonary arteries

OBJECTIVE

Acellularised porcine scaffolds have been successfully used for cardiovascular tissue engineering. However, there is concern about the possibility of porcine endogenous retrovirus (PERV) transmission. In this study we developed an in vivo model for cross-species PERV transmission.

METHODS

In vitro autologous repopulated porcine pulmonary arteries (n=6) were implanted in sheep in orthotopic position. Blood samples were collected regularly up to 6 months after implantation and tested for PERV by means of polymerase chain reaction and reverse transcriptase-polymerase chain reaction. Explanted tissue engineered pulmonary arteries were tested for PERV sequences.

RESULTS

PERV DNA was detectable in acellularised porcine scaffolds. No PERV sequences were detectable 6 months after implantation of in vitro repopulated acellularised porcine pulmonary arteries and in all tested peripheral blood samples.

CONCLUSIONS

Acellularised porcine matrix scaffolds can be used for cardiovascular tissue engineering of autologous grafts without risk of PERV transmission.

Role of inflammation in allogeneic and xenogeneic heart valve degeneration: immunohistochemical evaluation of inflammatory endothelial cell activation

BACKGROUND AND AIM OF THE STUDY

Biological heart valve prostheses undergo degenerative changes which lead ultimately to dysfunction or even complete destruction. The study aim was to evaluate immunological factors and their potential role in biological heart valve destruction.

METHODS

Allogeneic (n = 10) and xenogeneic (n = 3) aortic valve prostheses, as well as aortic valves retrieved from transplanted human hearts which had to be replaced due to chronic graft rejection (n = 4), were analyzed. Aortic valves from human donor hearts (n = 4) served as controls. Evaluated adhesion molecule expression included: selectin family ELAM-1, CD62; integrin family VLA-1, -2, -3, -4, -5 and -6; immuoglobulin supergene family PECAM-1, ICAM-1 and -2, and class I heavy chain proteins; complementary adhesion molecules CD34, CD44 and von Willebrand factor.

RESULTS

ELAM-1, ICAM-1 and -2, CD34, CD44 and class I heavy chain proteins, which play significant roles during inflammatory processes, showed stronger expression patterns in allogeneic and xenogeneic aortic heart valve prostheses compared to native or chronically rejected valves. Furthermore, allogeneic and xenogeneic valves showed a strong thrombogenicity which stained positive for von Willebrand factor outside endothelial cells on these valves. Integrin molecules as well as CD62 showed only mild differences.

CONCLUSION

Immunological reactions play a pivotal role in the degeneration of biological heart valve prostheses. As immunosuppressive therapy after heart valve replacement is not a viable option, novel approaches in 'tissue engineering' may help to avoid tissue degeneration while preserving the advantage of biological tissue origin.