Mobility Rates After Lower-Limb Amputation for Patients Treated with Physician-Led Collaborative Care Model.

BACKGROUND: Clinical outcomes after major lower-limb amputation have been historically poor. The current care provided to most amputees is often disorganized and without physician supervision. The primary purpose of this study is to examine rates of postamputation mobility achieved with a prosthesis by patients with chronic limb-threatening ischemia and/or diabetes who required major lower-limb amputation and were treated under an established physician-led collaborative care pathway. The secondary purpose is to describe the structure and utilization of the care pathway by multiple independent vascular surgery practices in the United States to enable future exploration of its impact on key clinical outcomes within this patient population. METHODS: Clinical records of 2,475 patients from 6 vascular practices that adopted this collaborative care pathway between 2017 and 2020 were retrospectively reviewed. Only records with sufficient documented histories of amputation surgeries, prosthetic services, and mobility status were included. RESULTS: Of 2,475 patient records reviewed, 1,787 patients (2,157 major amputations) were eligible for analysis. Sixty-two-point 2 percent (n = 1,111) of patients achieved mobility with the collaborative care pathway. Mobility rate varied by amputation level in the study. Prosthetic mobility was achieved in 73.5% of transtibial amputations, 40.4% of transfemoral amputations, and 35.7% of through-knee amputations, regardless of patient laterality, which is superior or equivalent to the best published rates of mobility. CONCLUSIONS: The study describes the structure and utilization of a physician-led collaborative care pathway for treating patients who require lower-limb amputation that meets 5 of the 7 recommendations from the 2019 Global Vascular Guidelines on the Management of Chronic Limb Threatening Ischemia. Internal data analysis results suggest that patients treated via this care pathway can potentially achieve improved mobility rates with a prosthesis following amputation. This collaborative care pathway should be further evaluated for its ability to directly improve mobility and other clinically relevant amputation outcomes.

Risk Factors for Acute Renal Failure After Endovascular Aneurysm Repair.

BACKGROUND: Acute kidney injury (AKI) after endovascular aortic aneurysm repair (EVAR) is uncommon though carries significant morbidity. Procedural risk factors are not well established for acute renal failure (ARF) that requires initiation of dialysis. The goal of this study was to examine the impact of ARF on patients undergoing EVAR and identify risk factors for ARF using a large, national dataset. METHODS: Patients undergoing EVAR were identified from the National Surgical Quality Improvement Program (NSQIP) database over 9 years, ending in 2019. Demographics, indication for repair, comorbidities, procedural details, complications, hospital and ICU LOS, and mortality were recorded. Patients were stratified by presence of ARF and compared. Patients were further stratified by indication for EVAR and presence of ARF. Multivariable logistic regression (MLR) analysis was performed to determine the independent predictors of ARF. RESULTS: 18 347 patients were identified. Of these 234 (1.3%) developed ARF requiring dialysis. Mortality (40 vs 1.8%, P < .0001), ICU LOS (5 vs 0 days, P < .0001), and hospital LOS (11 vs 2 days, P < .0001) were all significantly increased in patients with ARF. Multivariable logistic regression identified increasing diameter, creatinine, operative time, preoperative transfusions, ASA class, emergent repair, female gender, and juxtarenal/suprarenal proximal landing zone as predictors of ARF. CONCLUSIONS: ARF after EVAR causes significant morbidity, prolongs hospitalizations, and increases mortality rates. Those patients at risk of ARF after EVAR should be closely monitored to reduce both morbidity and mortality.

Prophylactic Left Atrial Appendage Exclusion in Cardiac Surgery Patients With Elevated CHA2DS2-VASc Score: Results of the Randomized ATLAS Trial.

OBJECTIVE: Patients with elevated CHA2DS2-VASc scores are at high risk for atrial fibrillation (AF) and thromboembolic events (TE) after cardiac surgery. Left atrial appendage exclusion (LAAE) is a permanent, continuous approach to stroke prevention in AF, overcoming limitations of oral anticoagulation (OAC). We report ATLAS trial results focused on LAAE technical success and perioperative safety and TE rates with and without LAAE in cardiac surgery patients who developed postoperative AF (POAF). METHODS: ATLAS (NCT02701062) was a prospective, multicenter, feasibility trial. Patients age ≥18 years, undergoing structural heart procedure, with no preoperative AF, CHA2DS2-VASc ≥2, and HAS-BLED ≥2 were randomized 2:1 to LAAE or no LAAE. Patients who developed POAF and/or received LAAE were followed for 1 year. LAAE was evaluated with intraoperative transesophageal echocardiography. RESULTS: A total of 562 patients were randomized to LAAE (n = 376) or no LAAE (n = 186). Mean CHA2DS2-VASc (3.4 vs 3.4) and HAS-BLED (2.8 vs 2.9) scores were similar for LAAE and no LAAE groups. LAAE success (no flow nor residual stump >10 mm) was 99%. One LAAE-related serious adverse event (0.27%) occurred and was resolved without sequelae. There were 44.3% of patients who developed POAF. Through 1 year, 3.4% of LAAE patients and 5.6% of no LAAE patients had TE. OAC was used by 32.5% of POAF patients. Bleeding was higher with OAC than without (16.1% vs 5.4%, P = 0.008). CONCLUSIONS: ATLAS demonstrated a high rate of successful LAAE with low LAAE-related serious adverse events in cardiac surgery patients. Study results should be considered in future trial design to further evaluate prophylactic LAAE for stroke prevention in cardiac surgery patients with elevated stroke risk.

Evaluating the optimal training paradigm for transcarotid artery revascularization based on worldwide experience.

BACKGROUND: Transcarotid artery revascularization (TCAR) is a new hybrid approach to carotid artery revascularization. Proctored training on live cases is an effort-, time-, and resource-intensive approach to learning new procedures. We analyzed the worldwide experience with TCAR to develop objective performance metrics for the procedure and compared the effectiveness of training physicians using cadavers or synthetic models to that of traditional in-person training on live cases. METHODS: Physicians underwent one of three mandatory training programs: (1) in-person proctoring on live TCAR procedures, (2) supervised training on human cadavers, and (3) supervised training on synthetic models. The training details and information from all subsequent independently performed TCAR procedures were recorded. The composite clinical adverse events (ie, transient ischemic attack, stroke, myocardial infarction, death) and composite technical adverse events (ie, aborted procedure, conversion to surgery, bleeding, dissection, cranial nerve injury, or device failure, occurring within 24 hours were recorded). Four procedural proficiency measures were recorded: procedure time, flow-reversal time, fluoroscopy time, and contrast volume. We compared the adverse event rates between the procedures performed by physicians after undergoing the three training modes and tested whether the proficiency measures achieved during TCAR after training on cadavers and synthetic models were noninferior to proctored training. RESULTS: From March 3, 2009 to May 7, 2020, 1160 physicians had undergone proctored (19.1%), cadaver-based (27.4%), and synthetic model-based (53.5%) TCAR training and had subsequently performed 17,283 TCAR procedures. The proctored physicians had treated younger patients and more patients with asymptomatic carotid stenosis and had had more prior experience with transfemoral carotid stenting. The overall 24-hour composite clinical and technical adverse event rates, adjusted for age, sex, and symptomatic status, were 1.0% (95% confidence interval, 0.8%-1.3%) and 6.0% (95% confidence interval, 5.4%-6.6%), respectively, and did not differ significantly by training mode. The proficiency measures of cadaver-trained and synthetic model-trained physicians were not inferior to those for the proctored physicians. CONCLUSIONS: We have presented key objective proficiency metrics for performing TCAR and an analytic framework to assess adequate training for the procedure. Training on cadavers or synthetic models achieved clinical outcomes, technical outcomes, and proficiency measures for subsequently performed TCAR procedures similar to those achieved with training using traditional proctoring on live cases.

Contemporary Outcomes After Partial Resection of Infected Aortic Grafts.

INTRODUCTION: Aortic graft infection remains a considerable clinical challenge, and it is unclear which variables are associated with adverse outcomes among patients undergoing partial resection. METHODS: A retrospective, multi-institutional study of patients who underwent partial resection of infected aortic grafts from 2002 to 2014 was performed using a standard database. Baseline demographics, comorbidities, operative, and postoperative variables were recorded. The primary outcome was mortality. Descriptive statistics, Kaplan-Meier (KM) survival analysis, and Cox regression analysis were performed. RESULTS: One hundred fourteen patients at 22 medical centers in 6 countries underwent partial resection of an infected aortic graft. Seventy percent were men with median age 70 years. Ninety-seven percent had a history of open aortic bypass graft: 88 (77%) patients had infected aortobifemoral bypass, 18 (16%) had infected aortobiiliac bypass, and 1 (0.8%) had an infected thoracic graft. Infection was diagnosed at a median 4.3 years post-implant. All patients underwent partial resection followed by either extra-anatomic (47%) or in situ (53%) vascular reconstruction. Median follow-up period was 17 months (IQR 1, 50 months). Thirty-day mortality was 17.5%. The KM-estimated median survival from time of partial resection was 3.6 years. There was no significant survival difference between those undergoing in situ reconstruction or extra-anatomic bypass (P = 0.6). During follow up, 72% of repairs remained patent and 11% of patients underwent major amputation. On univariate Cox regression analysis, Candida infection was associated with increased risk of mortality (HR 2.4; P = 0.01) as well as aortoenteric fistula (HR 1.9, P = 0.03). Resection of a single graft limb only to resection of abdominal (graft main body) infection was associated with decreased risk of mortality (HR 0.57, P = 0.04), as well as those with American Society of Anesthesiologists classification less than 3 (HR 0.35, P = 0.04). Multivariate analysis did not reveal any factors significantly associated with mortality. Persistent early infection was noted in 26% of patients within 30 days postoperatively, and 39% of patients were found to have any post-repair infection during the follow-up period. Two patients (1.8%) were found to have a late reinfection without early persistent postoperative infection. Patients with any post-repair infection were older (67 vs. 60 years, P = 0.01) and less likely to have patent repairs during follow up (59% vs. 32%, P = 0.01). Patients with aortoenteric fistula had a higher rate of any post-repair infection (63% vs. 29%, P < 0.01) CONCLUSION: This large multi-center study suggests that patients who have undergone partial resection of infected aortic grafts may be at high risk of death or post-repair infection, especially older patients with abdominal infection not isolated to a single graft limb, or with Candida infection or aortoenteric fistula. Late reinfection correlated strongly with early persistent postoperative infection, raising concern for occult retained infected graft material.

Evaluation of Staged TCAR and Cardiac Surgery or Structural Heart Intervention.

INTRODUCTION: The optimal treatment strategy for patients with concomitant carotid and cardiac disease remains controversial. Transcarotid artery revascularization stenting with reversed flow protection (TCAR) has achieved results equivalent to carotid endarterectomy (CEA) in high risk patients. METHODS: A retrospective review of all patients at a single center who received staged TCAR prior to cardiac intervention was performed. RESULTS: 37 patients underwent 42 TCAR procedures prior to cardiac intervention (25 requiring open cardiac surgery and 12 requiring percutaneous intervention). There were no myocardial or neurological complications following TCAR prior to cardiac intervention. Three patients (8%) developed a neck hematoma which required evacuation. CONCLUSION: A staged approach to combined carotid and cardiac pathology with TCAR prior to cardiac intervention appears to be a safe and effective strategy.

Intraoperative repair of mitral paravalvular leak with Amplatzer plug.

BACKGROUND AND AIM OF THE STUDY: Significant paravalvular leaks may complicate mitral valve replacement (MVR), especially in the setting of mitral annular calcification. Correction has been accomplished postoperatively by endovascular delivery of Amplatzer plugs (Abbott Medical) with good results. Intraoperative delivery of Amplatzer plugs at the index operation may reduce postoperative paravalvular leaks. METHODS: A retrospective review of eight patients who underwent placement of Amplatzer plugs for treatment of paravalvular leak during MVR at a single institution is reported. RESULTS: Seven patients had ≤1+ residual mitral valve insufficiency and one patient had 1-2+ residual mitral valve insufficiency intraoperatively by transesophageal echocardiogram. At 222 days average follow-up, echocardiogram revealed ≤ 1+ residual mitral valve insufficiency in all surviving patients. CONCLUSION: Intraoperative delivery of Amplatzer plugs for treatment of paravalvular leaks during MVR appears to be safe and effective at reducing postoperative mitral valve insufficiency.

In situ bypass and extra-anatomic bypass procedures result in similar survival in patients with secondary aortoenteric fistulas.

OBJECTIVE: The optimal revascularization modality in secondary aortoenteric fistula (SAEF) remains unclear in the literature. The purpose of this investigation was to determine the revascularization approach associated with the lowest morbidity and mortality using real-world data in patients with SAEF. METHODS: A retrospective, multi-institutional study of SAEF from 2002 to 2014 was performed using a standardized database. Baseline demographics, comorbidities, and operative and postoperative variables were recorded. The primary outcome was long-term mortality. Descriptive statistics, Kaplan-Meier survival analysis, and univariate and multivariate analyses were performed. RESULTS: During the study period, 182 patients at 34 institutions from 11 countries presented with SAEF (median age, 72 years; 79% male). The initial aortic procedures that resulted in SAEF were 138 surgical grafts (76%) and 42 endografts (23%), with 2 unknown; 102 of the SAEFs (56%) underwent complete excision of infected aortic graft material, followed by in situ (in-line) bypass (ISB), including antibiotic-soaked prosthetic graft (53), autogenous femoral vein (neoaortoiliac surgery; 17), cryopreserved allograft (28), and untreated prosthetic grafts (4). There were 80 patients (44%) who underwent extra-anatomic bypass (EAB) with infected graft excision. Overall median Kaplan-Meier estimated survival was 319 days (interquartile range, 20-2410 days). Stratified by EAB vs ISB, there was no significant difference in Kaplan-Meier estimated survival (P = .82). In comparing EAB vs ISB, EAB patients were older (74 vs 70 years; P = .01), had less operative hemorrhage (1200 mL vs 2000 mL; P = .04), were more likely to initiate dialysis within 30 days postoperatively (15% vs 5%; P = .02), and were less likely to experience aorta-related hemorrhage within 30 days postoperatively (3% aortic stump dehiscence vs 11% anastomotic rupture; P = .03). There were otherwise no significant differences in presentation, comorbidities, and intraoperative or postoperative variables. Multivariable Cox regression showed that the duration of antibiotic use (hazard ratio, 0.92; 95% confidence interval, 0.86-0.98; P = .01) and rifampin use at time of discharge (hazard ratio, 0.20; 95% confidence interval, 0.05-0.86; P = .03) independently decreased mortality. CONCLUSIONS: These data suggest that ISB does not offer a survival advantage compared with EAB and does not decrease the risk of postoperative aorta-related hemorrhage. After repair, <50% of SAEF patients survive 10 months. Each week of antibiotic use decreases mortality by 8%. Further study with risk modeling is imperative for this population.

Diagnosis and relining techniques for delayed type IIIB endoleaks with the second-generation AFX endograft.

Type IIIB endoleaks resulting from endograft fabric tear are an uncommon but serious late complication of endovascular aortic aneurysm repair. The Strata fabric used in the earlier generation AFX endograft (updated to Duraply in October 2014) has been associated with an increased frequency of these events. Herein we report on two patients exhibiting delayed type IIIB endoleaks after AFX device insertion to treat an abdominal aortic aneurysm and discuss optimal relining techniques.

Endosuture aneurysm repair in patients treated with Endurant II/IIs in conjunction with Heli-FX EndoAnchor implants for short-neck abdominal aortic aneurysm.

OBJECTIVE: Endovascular repair of abdominal aortic aneurysm (AAA) remains a challenging clinical scenario when there is a short or nonexistent segment of healthy infrarenal aorta. This study sought to determine the safety and effectiveness of endosuture aneurysm repair (ESAR) using the Endurant II/IIs endograft (Medtronic Vascular, Santa Rosa, Calif) in conjunction with Heli-FX EndoAnchors (Medtronic Vascular) in the treatment of short-neck AAA. METHODS: In this subgroup analysis, 70 patients were identified from the Aneurysm Treatment Using the Heli-FX EndoAnchor System Global Registry (ANCHOR) who had an infrarenal neck length <10 mm down to 4 mm based on core laboratory measurements. Primary outcomes included technical success of the index procedure, rate of type IA endoleak at 1 month and 12 months, and rate of secondary procedures at 12 months. RESULTS: In this short-neck cohort (n = 70), the average neck length and diameter were 6.9 ± 1.6 mm and 25.7 ± 4.0 mm, respectively. Investigators reported an overall procedural success rate of 97.1% and a technical success rate of 88.6%. The duration of the implant procedure, EndoAnchor implantation, and total fluoroscopy time was 148.0 ± 80.0 minutes, 17.1 ± 11.5 minutes, and 35.3 ± 22.0 minutes, respectively, and an average of 5.5 ± 2.1 EndoAnchors were implanted per patient. Through the 30-day follow-up, type IA endoleaks were reported in four patients, of which three resolved spontaneously by the 12-month follow-up. There was an additional type IA endoleak through the 12-month follow-up that has not resulted in AAA enlargement or required a secondary procedure. The Kaplan-Meier estimate for freedom from secondary endovascular procedures and all-cause mortality is 95.4% and 92.7% through 365 days, respectively. No patient in the short-neck cohort experienced main body stent migration, increase in maximum aneurysm diameter, or aneurysm rupture or required conversion to open surgical repair through 12 months. CONCLUSIONS: In this analysis of the short-neck cohort from ANCHOR, the Endurant II/IIs endograft in conjunction with Heli-FX EndoAnchor implants (ESAR) appears to be a safe and effective treatment option with a high technical success rate and low incidence of type IA endoleaks and secondary interventions. Despite the complex and hostile anatomies, the ESAR method required short procedure and fluoroscopy times. These short-term outcomes suggest that ESAR could be complementary to therapies currently available for treatment of hostile AAA anatomy and a viable off-the-shelf endovascular treatment option for patients with short-neck AAAs, although long-term follow-up is critically important.

Migrated embolization coil causes intestinal obstruction.

Visceral artery pseudoaneurysm is a rare, potentially fatal entity, but proper identification and management with coil embolization can lead to good outcomes. Embolization coils can migrate to various destinations, causing delayed complications in several case reports. A case of small bowel obstruction due to migrated embolization coils from a gastroduodenal pseudoaneurysm 6 years after initial treatment is presented.

Delayed Metallic Embolization of a Cor-Knot Fastener.

Background The Cor-Knot device is a titanium fastener which is widely used in cardiac valve procedures. Adverse events associated with use of the device have been rare. Case Description A patient underwent robotic mitral valve repair using the Cor-Knot fastener. Five years later, he suffered a cerebral vascular accident secondary to embolization of a metallic foreign body. He had had no other medical procedures which could account for a source of metallic embolization. Conclusion Long-term surveillance after use of the Cor-Knot fastener is limited. Metallic embolization may be possible with this device and warrants awareness within the medical community.

TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) US clinical trial: Performance of a rapid deployment aortic valve.

BACKGROUND: The TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) trial (NCT01700439) evaluated the performance of the INTUITY rapid deployment aortic valve replacement (RDAVR) system in patients with severe aortic stenosis. METHODS: TRANSFORM was a prospective, nonrandomized, multicenter (n = 29), single-arm trial. INTUITY is comprised of a cloth-covered balloon-expandable frame attached to a Carpentier-Edwards PERIMOUNT Magna Ease aortic valve. Primary and effectiveness endpoints were evaluated at 1 year. RESULTS: Between 2012 and 2015, 839 patients underwent RDAVR. Mean age was 73.5 ± 8.3 years. Full sternotomy (FS) was used in 59% and minimally invasive surgical incisions in 41%. Technical success rate was 95%. For isolated RDAVR, mean crossclamp and cardiopulmonary bypass times for FS were 49.3 ± 26.9 minutes and 69.2 ± 34.7 minutes, respectively, and for minimally invasive surgical 63.1 ± 25.4 minutes and 84.6 ± 33.5 minutes, respectively. These times were favorable compared with Society of Thoracic Surgeons database comparators for FS: 76.3 minutes and 104.2 minutes, respectively, and for minimally invasive surgical, 82.9 minutes and 111.4 minutes, respectively (P < .001). At 30 days, all-cause mortality was 0.8%; valve explant, 0.1%; thromboembolism, 3.5%; and major bleeding, 1.3%. In patients with isolated aortic valve replacement, the rate of permanent pacemaker implantation was 11.9%. At 1 year, mean effective orifice area was 1.7 cm2; mean gradient, 10.3 mm Hg; and moderate and severe paravalvular leak, 1.2% and 0.4%, respectively. CONCLUSIONS: INTUITY RDAVR performed effectively in this North American trial. It may lead to a relative reduction in aortic crossclamp time and cardiopulmonary bypass time and has excellent hemodynamic performance. Pacemaker implantation rate observed was somewhat greater than European trials and requires further investigation.

Options for treatment of spontaneous mesenteric artery dissection.

OBJECTIVE: Mesenteric artery dissection was once thought to be rare but has been identified more frequently with increasing use of computerized tomographic angiographic imaging. Multiple reports advocate a wide range of treatment including medical therapy, endovascular, and surgical intervention, with no clear guidelines for the application of each treatment. METHODS: A systematic review of the literature was analyzed and used to create a treatment algorithm that was applied to nine patients in our institution. RESULTS: Although medical therapy is adequate for most patients with mesenteric artery dissection, 14% failed medical therapy, sometimes with severe consequences. Asymptomatic status on presentation predicted successful medical therapy for superior mesenteric artery dissection (P = .0037). CONCLUSIONS: Intensive surveillance is indicated during medical therapy, and invasive intervention may be necessary.

Sternal closure with rigid plate fixation versus wire closure: a randomized controlled multicenter trial.

BACKGROUND: Rigid bone fixation is the standard of care for all bone reconstructions except that after sternotomy. Sternal reconstruction after median sternotomy using rigid fixation with plates may improve bone healing and reduce pain when compared with wire cerclage. METHODS: One-hundred forty patients at six centers who were determined preoperatively to be at high risk for sternal wound complications were randomly assigned to sternal closure with rigid plate fixation (n=70) or wire cerclage (n=70). Sternal healing was evaluated at 3 or 6 months by a core laboratory using computed tomography. Pain and function were evaluated at postoperative day 3 through discharge, 3 weeks, 6 weeks, 3 months, and 6 months. RESULTS: Sternal healing was superior in rigid plate fixation patients at both 3 and 6 months. Mean computed tomography scores in the rigid plate fixation and wire cerclage groups at 3 months were 1.7±1.1 and 0.9±0.8 (p=0.003). At 6 months, the scores were 3.2±1.6 and 2.2±1.1, respectively (p=0.01). At 6 months, 70% of rigid plate fixation patients had achieved sternal union, compared with 24% of conventional wire cerclage patients (p=0.003). Pain scores and narcotic usage were lower in rigid plate fixation patients. Significant differences in pain scores were observed at 3 weeks for total pain (p=0.020) and pain with coughing (p=0.0084) or sneezing (p=0.030). Complication rates were similar in both groups. CONCLUSIONS: Sternal reconstruction using rigid fixation with plates improved bone healing and reduced early postoperative pain compared with wire cerclage.

Aortoduodenal fistula after endograft repair of abdominal aortic aneurysm secondary to a retained guidewire.

Aortoduodenal fistula is a well-known complication of abdominal aortic aneurysm repair and has been described after endovascular repair. A unique complication of duodenal perforation by intentionally placed embolic material in the aneurysm sac is described. Intentional off-label use of material to promote aneurysm sac thrombosis should be avoided.

Carotid endarterectomy for treatment of in-stent restenosis.

In-stent restenosis (ISR) after carotid angioplasty and stenting is becoming evident as more patients undergo carotid stenting and duplex scan surveillance. While redo endovascular therapy has been immediately successful, recurrent stenosis remains a problem. The ideal management of ISR has not been determined. Three cases of symptomatic ISR that were successfully treated by standard carotid endarterectomy (CEA) with removal of the stent are reported herein. Current options for management of ISR are reviewed from the literature.

Staged total exclusion of the aorta for chronic type B aortic dissection.

Hybrid techniques using extra-anatomic bypass of critical aortic branches to enable endovascular treatment of complex aortic pathology have been previously described. A staged endograft repair of a complex, chronic Stanford type B aortic dissection with aneurysmal degeneration is reported in a 50-year-old man. The aneurysmal portion of the dissection extended from the distal arch to both common iliac arteries and was covered with an endograft from the ascending aorta to both external iliac arteries. Aortic arch branches, visceral, and renal arteries were bypassed using open technique. The patient had no neurologic complications. This case report illustrates the feasibility of the hybrid technique in selected high-risk patients when confronted with complex aortic pathology.