key: cord-0907095-hb78kn8a
authors: McGuinness, Brandon; Troncone, Michael; James, Lyndon P.; Bisch, Steve; Iyer, Vikram
title: Reassessing the operative threshold for abdominal aortic aneurysm repair in the context of COVID-19
date: 2020-09-01
journal: J Vasc Surg
DOI: 10.1016/j.jvs.2020.08.115
sha: 14bb0c649be075e11b2b67aed02e37f0ee553b84
doc_id: 907095
cord_uid: hb78kn8a

OBJECTIVE: The worldwide pandemic involving the novel respiratory syndrome (COVID-19) has forced healthcare systems to delay elective operations, including abdominal aortic aneurysm (AAA) repair, to conserve resources. This study provides a structured analysis of the decision to delay AAA repair and quantify the potential for harm. METHODS: A decision tree was constructed modeling immediate repair of AAA relative to an initial non-operative (delayed repair) approach. Risk of COVID-19 contraction and mortality, aneurysm rupture, and operative mortality were considered. A deterministic sensitivity analysis for a range of patient ages (50 to >80), probability of COVID-19 infection (0.01%-30%), aneurysm size (5.5->7cm), and time horizons (3-9 months) was performed. Probabilistic sensitivity analyses (PSA) were conducted for three representative ages (60, 70, 80). Analyses were conducted for endovascular aortic aneurysm repair (EVAR) and open surgical repair (OSR). RESULTS: Patients with aneurysms 7cm or greater demonstrated a higher probability of survival when treated with immediate EVAR or OSR, compared to delayed repair, for patients under 80 years of age. When considering EVAR for aneurysms 5.5-6.9cm, immediate repair had a higher probability of survival except in settings with high probability of COVID-19 infection (10-30%) and advanced age (70-85+ years). A non-operative strategy maximized the probability of survival as patient age or operative risk increased. Probabilistic sensitivity analyses demonstrated that patients with large aneurysms (>7cm) faced a 5.4-7.7% absolute increase in the probability of mortality with a delay of repair of 3 months. Young patients (60-70 years) with 6-6.9cm aneurysms demonstrated an elevated risk of mortality (1.5-1.9%) with a delay of 3 months. Those with 5-5.9cm aneurysms demonstrated an increased survival with immediate repair in young patients (60), however this was small in magnitude (0.2-0.8%). The potential for harm increased as length of surgical delay increased. For elderly patients requiring OSR, in the context of endemic COVID-19, delay of repair improves probability of survival. CONCLUSION: The decision to delay operative repair of AAA should consider both patient age and local COVID-19 prevalence in addition to aneurysm size. EVAR should be considered when possible due to a reduced risk of harm and lower resource utilization.

with 6-6.9cm aneurysms demonstrated an elevated risk of mortality (1.5-1.9%) with a delay of 3 1 months. Those with 5-5.9cm aneurysms demonstrated an increased survival with immediate 2 repair in young patients (60), however this was small in magnitude (0.2-0.8%). The potential for 3 harm increased as length of surgical delay increased. For elderly patients requiring OSR, in the 4 context of endemic COVID-19, delay of repair improves probability of survival. novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) emerged 1 . It has now 12 progressed to a pandemic 2,3 . Health systems have been forced to re-assess the delivery of 13 elective care in the context of this new reality 4,5 . 14 15

The COVID-19 pandemic presents a challenge for medical conditions which are treated 16 electively but pose a substantial risk to life when definitive treatment is delayed. The American 17

College of Surgeons has released guidelines for the triage of surgical patients 6 . These guidelines To date no study has performed a structured analysis of the decision to postpone the management 1 of abdominal aortic aneurysms (AAA). The conservation of personal protective equipment 2 (PPE) and risk of exposing patients to COVID-19 in hospital must be balanced against the risk of 3 aneurysm rupture. The objective of this study was to perform a decision analysis, using the most 4 up to date metrics, for deciding when to delay AAA repair while mitigating patient risk. 5 6 Methods 7

A decision tree was constructed in order to model the choice between management strategies of 9 immediate operative versus initial non-operative (delayed operative) repair of AAA ( Figure 1 ). 10

Analysis was performed using Amua version 0.2.2 9 . Survival and death were the final outcomes 11 in the model, and the objective was to maximize the probability of patient survival. The model 12 assumes all individuals to be acceptable candidates for open or endovascular AAA repair. 13

Method of repair (EVAR versus OSR) is assumed to be based on patient characteristics and 14 aneurysm morphology, as they would have been prior to the COVID-19 pandemic. Patients are 15 assumed to be COVID negative at initial presentation and still at risk for contraction of the virus. 16

This model focuses only on the time interval in which care may be delayed due to the pandemic. In the non-operative arm patients were considered to be at risk for rupture. Those without rupture 4 were susceptible to community acquired COVID-19 with subsequent mortality. Those who 5 ruptured were first at risk of rupture related mortality (either out of hospital or operative 6 mortality). Those surviving were again at risk of hospital contraction of SARS-CoV2 and 7 subsequent mortality. 8 9

The model was developed with 3-month intervals (cycle length). Probabilities for contraction of 10 COVID-19 and rupture were scaled appropriately based the total duration of repair deferral. (i.e., 3-month cumulative incidence) of COVID-19 infection in a geographic area were 20 considered. These included a risk of contraction from 0.01% to 30% over the initial 3-month 21 interval (which is then scaled based on the time horizon). Contraction of COVID-19 is believed 22

to be greater in those admitted to hospital with a reported incidence two times greater than in the 23 J o u r n a l P r e -p r o o f community 13 . The probability of COVID-19 contraction for those admitted to hospital is 1 therefore increased by a factor of two. Following infection, individuals are considered to no 2 longer be at risk of virus contraction. repair with corresponding operative mortality 15 . Death secondary to rupture was based on 12 population level data and included pre-hospital and intra-operative mortality 16 . Case fatality 13 rates were only available in dichotomous format (less than or greater than 75 years old). The 14 lower threshold (<75yrs :61% mortality) was utilized for those under 65, the overall mortality 15 (74%) for those 65 to 79 years old, and the upper threshold (>75yrs:82% mortality) for those 16 eighty and over. 17

Initially a deterministic analysis was conducted to allow for a broad summary of unique patient 19 characteristics and the 3-month probability of infection with COVID-19. A probabilistic 20 sensitivity analysis (PSA) at three representative ages, 60, 70, and 80 years of age, was then 21 performed. A probabilistic sensitivity analysis samples values for the input parameters 22

(example: probability of mortality) from a distribution which reflects the uncertainty of the 23 reported data (Table II) This study demonstrates the optimal decision for deferral of operative repair of AAA varies with 8 patient age and aneurysm size when attempting to minimize mortality. In-line with current 9

guidelines, aneurysms over 7cm benefit from timely operative repair ( Figure gives the density plot for the probability of survival with either immediate EVAR or a delayed 1 strategy over a thousand iterations for each scenario. Perfect survival lies on the right end of the 2 x axis. The mean and 95% credibility interval for each curve is given at the bottom, along with 3 the mean difference in probability of survival. With large aneurysms (>7cm) there is minimal 4 overlap between the density plots for survival. Survival benefit with an immediate operative 5 strategy ranges from 5.8%-7.7% in 7cm AAA depending on probability of infection with 6 COVID-19, and patient age. As the probability of infection increases, the magnitude of 7 difference between strategies decreases, illustrated by an increased overlap of the two density 8 curves. In 60 and 70 year old patients there is still a 1.5-1.9% increased probability of survival if 9

repair is not delayed for 6-6.9cm aneurysms. While immediate repair still offers a benefit, this is 10 reduced in aneurysms between 5.5 and 5.9cm. 11 12 A similar PSA analysis was performed with a 6-month delay for EVAR (Table III) . There is an 13 increased risk of harm with increased time of delay for elective repair. Those with 6-6.9cm 14 aneurysms face a 2.4-4.5% increased risk of mortality with delay depending on local prevalence 15 of COVID-19 and patient age. While the risk is still lower for those with 5.5-5.9cm aneurysms, 16

there can be as high as a 1.9% increased risk of mortality in younger patients, when COVID-19 17 prevalence is low. 18

The results for open surgical repair in the PSA are consistent with the deterministic analysis. 20

There is an overall shift towards the non-operative (delay of OR) strategy, compared to the 21 results for EVAR. In those with small aneurysms and the elderly, there can be a significant risk 22 of harm if operative repair is not delayed. This was especially pronounced in those 80 years of This decision analysis demonstrates that the potential to cause harm by postponing AAA repair is 6 affected both by the age of the patient and local prevalence of COVID-19. This is in contrast to 7 current guidelines which focus primarily on aneurysm size only. This study acts as a framework 8 to aid physicians and hospital planning committees in policy regarding elective aneurysm 9

surgery. While no model will perfectly capture real world events, we believe this analysis 10 provides insight into how practitioners should approach this difficult dilemma. 11

The major trade-off in the analysis is the risk of aneurysm rupture relative to the risk of 13 contracting the virus in hospital. COVID-19 related mortality is known to be substantially 14 higher in the elderly. Infection fatality rates for patients less than 60 years of age are believed to 15 be <0.6%, while for those 80 years and older are estimated to be greater than 7% 8 . The baseline 16 COVID-19 mortality risk of a patient should be an important factor physicians consider when 17 deciding to delay elective surgery. Contraction of COVID-19 is greater in hospital than in the 18 community and elderly patients admitted for surgery therefore take on greater risk with elective 19 repair 13 . Peri-operative risk is also greater for elderly patients. As the incremental net survival 20 benefit of elective AAA surgery decreases, delaying surgery has a lower risk of harm. The 21 model does not include baseline medical comorbidities however these would impact outcomes in 22 a similar manner. Patients who are more comorbid will also face greater COVID-19 mortality 23 and peri-operative risk, therefore delaying surgery in this population is more likely to prevent 1 harm 1,15 . Practitioners can be guided by the VQI perioperative mortality risk score, per the SVS 2 guidelines, on the care of patient with abdominal aortic aneurysm, which should be used in 3 conjuncture with these findings 11 . 4

In contrast, the model demonstrates that delaying elective surgery in young patients, especially 6 with larger aneurysms, is likely to lead to increased risk of death. A 60 year old patient with even 7 a relatively small (5.5-5.9cm) aneurysm may suffer harm from delay of elective surgery (0.8% 8 increased risk of death at 3 months, 1.9% at 6 months). This is especially true if repair is 9 postponed for a prolonged period. Younger patients have a lower COVID-19 infection fatality 10 rate than elderly patients, and they have a low peri-operative risk. Elective repairs of small and 11 asymptomatic aneurysms have already been suspended frequently due to the pandemic and 12 therefore it is important to understand this risk 4 . As long as hospital infrastructure and hospital 13 resources are adequate consideration should be made to repair aneurysms in young individuals. 14 15 An important consideration is that the model focuses on patient specific outcomes. It is not 16 inclusive of hospital resources and use of personal protective equipment. A widely used decision 17 analytic approach is cost-effectiveness analysis, which typically compares cost per quality 18

adjusted life year (QALY) gained to a willingness to pay threshold. In the context of the 19 pandemic, however, conservation of PPE and ICU beds is the foremost concern. Given the 20 rapidity of the pandemic's onset, there has not yet been an effort to explicitly trade-off health 21 gains against resource use in the COVID-19 setting. Based on these results, however, this trade-22 off can be contextualized. 23 J o u r n a l P r e -p r o o f 1 As resources become more constrained, a greater risk to patient survival may be tolerated. For 2 example, at a 30% probability of COVID-19 infection in a three month interval, a 1.4% elevated 3 chance of patient mortality, caused by deferring OR by 3 months, may be tolerated (60-year-old 4 with a 6.5 cm AAA). At 10% probability of infection, when resources are less constrained this 5 patient may be operated on electively (increased probability of survival 1.8%). These decisions 6 will depend on the resource constraints of each hospital and health system. We therefore do not 7

propose concrete cut-offs as the choice will vary based on each unique situation. In the case of 8 elective EVAR, ICU utilization can be as low as 1%, and procedures can be performed with 9 minimal loss of mask and gowns 19 . We estimate 7 sets of PPE (mask, gown, gloves) would be 10 used for a case. In many instances we believe this "expenditure" would be justified to reduce a 11 patient's probability of mortality by 0.5% (which is close to the mortality faced by a person in 12 their 50s or 60s who has contracted COVID). 13 14 Exposure of healthcare providers to COVID-19 is not considered in the model, however, this 15 should be considered depending on regional circumstances. In scenarios where resource 16 constraints do not allow for adequate protection of healthcare providers, operative repair should 17 be delayed. Workers over 50 years in age who contract COVID face a 0.5% chance or greater of 18 mortality, which is greater than the net survival benefit in a 3-month time horizon for aneurysms 19 under 7 cm. Treatment of AAA requires the involvement and possible exposure of many 20 healthcare providers. asymptomatic aneurysm, delay of repair until the patient is clinically improved is advisable. In 18 the case of ruptured or symptomatic aneurysms, decisions will depend on a case by case basis. 19

The patient's age specific risk of mortality due to COVID-19, irrespective of surgical outcome, 20 should be considered prior to undertaking heroic surgical measures. The COVID-19 pandemic is constantly evolving and the length of time these recommendations 1 are applicable to practice is hard to predict. In the absence of an active outbreak health care 2 providers will have to evaluate their available resources including inpatient bed space relative to 3 the risk of an outbreak. This will depend both on that geographic region's history of COVID-19 4 infection, local public health precautions, and country or world-wide prevalence. These findings 5 should be utilized in conjuncture with the SVS guidelines on the management of AAA 11 . In the 6 absence of new COVID-19 cases and a low likelihood of COVID-19 outbreak, practitioners 7 should fully resume their normal practice. and open surgical repair with a 3-month time horizon (bottom). The mean absolute difference in probability of survival between the operative and delayed repair strategies is given with 95% credibility intervals. Boxes are shaded and italicized when delayed repair was the dominant strategy. assuming different community COVID-19 3-month probability of infection, patient age and 29 aneurysm size. The density distribution for probability of survival demonstrates the uncertainty 30 around this outcome, and is shown in each case for the operative (OR -red) and non-operative 31 (delayed repair) strategy (Non-OR-blue). The far-right of the x axis is 100% survival probability. 32

The mean of each distribution is given below each plot, with 95% credibility interval in 33

parentheses. The mean absolute differences in probability of survival for the two strategies 34

(Dif) are given, with 95% credibility intervals in parentheses. This difference is bolded when the 35 operative strategy is dominant, and italicized when the non-operative approach is dominant. 36 37

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