Aims Patients with suspected non-ST-segment elevation acute coronary syndrome (NSTE-ACS) are routinely transferred to the emergency department (ED). A clinical risk score with point-of-care (POC) troponin measurement might enable ambulance paramedics to identify low-risk patients in whom ED evaluation is unnecessary. The aim was to assess safety and healthcare costs of a pre-hospital rule-out strategy using a POC troponin measurement in low-risk suspected NSTE-ACS patients. Methods and results This investigator-initiated, randomized clinical trial was conducted in five ambulance regions in the Netherlands. Suspected NSTE-ACS patients with HEAR (History, ECG, Age, Risk factors) score ≤3 were randomized to pre-hospital rule-out with POC troponin measurement or direct transfer to the ED. The sample size calculation was based on the primary outcome of 30-day healthcare costs. Secondary outcome was safety, defined as 30-day major adverse cardiac events (MACE), consisting of ACS, unplanned revascularization or all-cause death. : A total of 863 participants were randomized. Healthcare costs were significantly lower in the pre-hospital strategy (€1349 ± €2051 vs. €1960 ± €1808) with a mean difference of €611 [95% confidence interval (CI): 353–869; P < 0.001]. In the total population, MACE were comparable between groups [3.9% (17/434) in pre-hospital strategy vs. 3.7% (16/429) in ED strategy; P = 0.89]. In the ruled-out ACS population, MACE were very low [0.5% (2/419) vs. 1.0% (4/417)], with a risk difference of −0.5% (95% CI −1.6%–0.7%; P = 0.41) in favour of the pre-hospital strategy. Conclusion Pre-hospital rule-out of ACS with a POC troponin measurement in low-risk patients significantly reduces healthcare costs while incidence of MACE was low in both strategies. Trial registration Clinicaltrials.gov identifier NCT05466591 and International Clinical Trials Registry Platform id NTR 7346.

Background Coronary flow reserve (CFR) and microvascular resistance reserve (MRR) are physiological parameters to assess coronary microvascular dysfunction. CFR and MRR can be assessed using bolus or continuous thermodilution, and the correlation between these methods has not been clarified. Furthermore, their association with angina and quality of life is unknown. Methods and Results In total, 246 consecutive patients with angina and nonobstructive coronary arteries from the multicenter Netherlands Registry of Invasive Coronary Vasomotor Function Testing (NL‐CFT) were investigated. The 36‐item Short Form Health Survey Quality of Life and Seattle Angina questionnaires were completed by 153 patients before the invasive measurements. CFR and MRR were measured consecutively with bolus and continuous thermodilution. Mean continuous thermodilution‐derived coronary flow reserve (CFR abs ) was significantly lower than mean bolus thermodilution‐derived coronary flow reserve (CFR bolus ) (2.6±1.0 versus 3.5±1.8; P <0.001), with a modest correlation ( ρ =0.305; P <0.001). Mean continuous thermodilution‐derived microvascular resistance reserve (MRR abs ) was also significantly lower than mean bolus thermodilution‐derived MRR (MRR bolus ) (3.1±1.1 versus 4.2±2.5; P <0.001), with a weak correlation ( ρ =0.280; P <0.001). CFR bolus and MRR bolus showed no correlation with any of the angina and quality of life domains, whereas CFR abs and MRR abs showed a significant correlation with physical limitation ( P =0.005, P =0.009, respectively) and health ( P =0.026, P =0.012). In a subanalysis in patients in whom spasm was excluded, the correlation further improved (MRR abs versus physical limitation: ρ =0.363; P =0.041, MRR abs versus physical health: ρ =0.482; P =0.004). No association with angina frequency and stability was found. Conclusions Absolute flow measurements using continuous thermodilution to calculate CFR abs and MRR abs weakly correlate with, and are lower than, the surrogates CFR bolus and MRR bolus . Absolute flow parameters showed a relationship with physical complaints. No relationship with angina frequency and stability was found.

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