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by troponin profiles after 90 min of ischaemic conditions in these cohorts [ 7 , 8 ]. The existing literature on DNC in adults with cross-clamp times over 90 min is currently limited to small patient cohorts or sub-analyses of larger studies and interchangeably defines aortic cross-clamp time and ischaemic time making direct comparisons challenging [ 4 , 9 – 16 ]. Ross et al recently reported our unit ’ s initial experience of DNC however only a small subset ( 40 patients ) had aortic cross-clamp times greater than 90 min in the DNC group [ 17 ], while Willekes et al . have reported a propensity matched study of patients with prolonged aortic cross-clamp times [ 18 ].
This study reports a review of the safety of DNC within our practice in patients with cross-clamp time exceeding 90 min . We compared those who received HKB with those who received DNC . The primary aim was to assess safety and efficacy based on post-operative Troponin T profile , with the secondary aim to compare post-operative major adverse cardiac events between the two groups .
Methods
This is a single centre , retrospective cohort study including patients who underwent cardiac or aortic surgery , without circulatory arrest , with a cross-clamp time longer than 90 min . Patients from both Flinders Medical Centre and Flinders Private Hospital were included . Patient data was prospectively collected from the Flinders Cardiac Surgery Registry and the Australian New Zealand Collaborative Perfusion Registry from June 2014 to December 2022 . During this interval 845 of 5094 patients had aortic cross-clamp times greater than 90 min , of which 188 were excluded from the study ( 10 no cardioplegia data , 178 as outside of the study period ) ( Figure 1 ). Ethics approval for this audit was granted by the Southern Adelaide Clinical Human Research Ethics Committee and the South Australia Local Health Network Office for Research ( Quality Registry ID : 2265 ).
Patients were analysed according to their cardioplegia regimen of either HKB or DNC . DNC was introduced in November 2018 . Clinical management , anaesthesia , composition and delivery methods of our DNC and HKB have been previously published [ 17 ]. Specifically for DNC , after placement of the aortic cross-clamp , cardioplegic arrest was induced with an antegrade induction dose of 1 L delivered at a flow rate of 200 – 300 mL / min at 6 ° C , targeting aortic root pressures > 100 mmHg and less than 150 mmHg . This dose was followed by subsequent 500 mL doses at 60-minute intervals delivered antegrade or retrograde as required . In cases of severe aortic regurgitation , a combination of retrograde and ostial cardioplegia was used . Hyperkalaemic blood cardioplegic arrest was induced with tepid ( 34 ° C ) hyperkalaemic blood / crystalloid cardioplegia ( induction , 30 mmol / L ) at induction and maintained with intermittent doses ( maintenance , 15 mmol / L ) every 20 – 30 min . Similar flows and pressures were targeted . In both groups , in addition to the timing of cardioplegia doses , the return of electrical or myocardial contractility was an indication for re-dosing .
Definitions of clinical demography and outcomes were standardised on those reported by the Australian and New Zealand Society of Cardiac and Thoracic Surgeons
( ANZSCTS ) National Database . Maximum ischemic time was defined as the maximum duration between completion of cardioplegia delivery and either the beginning of the next cardioplegia delivery or reperfusion with cross-clamp removal ; our data reflects expected redosing at > 90 min in DNC and > 30 min in HKB . Mortality was defined as death in a hospital or within 30 days from surgery . Perioperative myocardial infarction was defined as having at least two of the following criteria : DTroponin T > 20 ug / L , new regional wall motion abnormalities on echocardiography , Q wave changes on electrocardiogram ( ECG ). A positive troponin profile was defined as having a troponin value at 72 h following surgery which is the highest troponin measured within 72 h of the index procedure . Acute Kidney Injury ( AKI ) was defined as postoperative creatinine greater than 150 % baseline in accordance with the serum creatinine criteria of the renal Risk , Injury , Failure , Loss of renal function and End-stage renal disease ( RIFLE ) classification .
The registries meet the Australian Commission on Safety and Quality in Health Care National Operating Principles for Australian Clinical Quality Registries ( https :// www . safetyandquality . gov . au / publications-and-resources / resourcelibrary / framework-australianclinical-quality-registries ). Database managers and staff meet weekly to undertake quality assurance processes . The unit ’ s general anaesthetic , intraoperative monitoring , cardiopulmonary bypass ( CPB ), blood conservation and post-operative renal replacement protocols have been previously published [ 17 ]. Statistical analysis
Patients that received DNC were 1:1 propensity-matched without replacement with patients that received HKB , with cross-clamp-times greater than 90 min , providing 194 matched pairs ( Figure 1 ). Preoperative risk factor variables included in propensity matching were age , sex , diabetes , insulin-dependent diabetes , chronic obstructive pulmonary disease , pulmonary hypertension , New York Heart Association classification , left ventricular dysfunction , emergency procedure , cerebrovascular disease , redo procedure , smoking history , elevated preoperative troponin , procedure type , cardiopulmonary bypass time , aortic cross-clamp time , and procedure time . A sensitivity analysis was performed on patients with cross-clamp times greater than 120 min yielding 64 matched pairs .
Stata v 15.1 ( StataCorp LLC , Texas ) was used for all statistical analyses . Pre-operative , intra-operative and post-operative outcomes were compared between the cohorts . Continuous variables are reported as median with interquartile range and are compared using the Wilcoxon rank-sum test . Categorical variables are reported as a number of patients and group percentage and compared using Fisher ’ s exact test for variables with binary measures and Pearson ’ s v 2 test for categorical variables . A p-value of < 0.05 was considered statistically significant for all analyses without adjustment for multiple comparisons .
Equivalence in outcome for cardioplegia type was evaluated on the incidence of myocardial infarction , positive troponin profile , and continuous postoperative troponin values at 6 , 12 and 72 h , peak , and the 72 h area under the curve , calculated based