Our study has illustrated current practice of ECPR in a referring center in northern Taiwan. The protocol of LV decompression/modified LVAD has been established at the end of 2017, and hence the study began in 2018. First of all, coronary artery disease contributed to 63.3% of our registry of cardiac arrest. Secondly, peak serum lactate and LVEF predicted mortality in our cohort. Most intriguing, modified LVAD, mandated by poorer LVEF, seemed to benefit those who were expected to come with worse outcome.
OHCA vs. IHCA
Our cohort enrolled patients of both OHCA and IHCA of any causes. The composition of diagnosis was compatible with known literature, with the consensus that nearly two-thirds of cardiac arrest events were attributed to coronary artery disease [10–12]. Previously, the survival of OHCA patients was expected to be inferior to IHCA ones, as IHCA patients might merit more efficient CPR efforts. The overall survival to discharge of ECPR-treated IHCA patients was 37.9%, while that of ECPR-treated OHCA patients was heterogeneously between 6.9%and 56.0%, averagely around 20% [13, 14]. OHCA patients were inevitably afflicted with longer low-flow time, which was believed to be detrimental in prognosis. In our series, OHCA patients got longer low-flow time by 35.2 mins, in comparison with their IHCA counterparts. (80.7 ± 44.5 vs 45.6 ± 31.3 min, p < 0.001, 95% conf Int. 22.5, 47.8). But this drawback did not necessarily mean poorer systemic perfusion, which could be vividly reflected by peak serum lactate level after resuscitation [15]. The length of low-flow time did not correlate with the peak serum lactate after resuscitation in our study (R2 = 0.001). (Fig. 2a)
Therefore, the peak serum lactate of our OHCA and IHCA patients were not distinct, implying similar sufficiency of resuscitation was achieved. As a result, our OHCA and IHCA patients put on ECPR shared similar rate of weaning-off from mechanical support, and nearly identical rate of survival to discharge. (32.3% vs. 32.9%, p = 1.0). In our opinion, if high quality CPR could be applied consistently and persistently, patients of cardiac arrest could share the same outcome, in spite of the difference of low-flow time.
The prognostic factors: peak serum lactate and LVEF
The peak serum lactate and LVEF cast significant predictability. Those with higher lactate level or poorer LV function suffered higher mortality rate in our cohort. These two factors have been well reported to tell the prognosis in the literature [16]. In our study, the low-flow time did not differ between those who survived and those who succumbed to (60.0 ± 44.1 vs. 60.4 ± 39.8 mins, p = 0.948). Neither were the peak serum lactate (R2 = 0.001) (Fig. 2) nor the LVEF (R2 = 0.002) correlated with the low-flow time. (Fig. 2b). Furthermore, the peak serum lactate and LVEF were not interactive and no correlation existed (p = 0.956). In addition, the duration of dependence on mechanical support did not influence the outcome (survival vs. mortality 12.2 ± 20.9 vs. 7.1 ± 11.9 days, p = 0.065), but it was the wean-off rate that mattered (93.8 vs. 22.2%, p < 0.001). In other words, as long as the patient could get rid of the indwelled machinery, he or she may be able to survive to discharge, regardless of how long the patient was put on the machine.
The LV decompression/modified LVAD
So far, our study demonstrated comparable and compatible characters with currently available literature, such as diagnosis composition, mortality of ECPR-treated IHCA, prognostic predictability of peak serum lactate and LVEF. This legitimized further extrapolation of our cohort, to explore the efficacy of LV decompression in the care of cardiac arrest patients. In addition to equal distribution of demographics in the two groups of VA-ECMO and modified LVAD, the highly predictive parameter, peak serum lactate, was not distinct among them. Even the low-flow time was similar. LVEF was the only different parameter. But in this category, it should be regarded as the driving factor that rendered urgent indication for LV decompression, rather than the contributor to the outcome. The ration could be, the lower the LVEF, the more the need for LV decompression, and resultantly, the better the survival. Based on the cross-sectional mortality, the modified LVAD offered survival benefit over VA-ECMO by 3 days in our ECPR patients, which was further illustrated by Kaplan-Meyer analysis.
In the study conducted by Chen YS et al., the authors found that ECPR did benefit IHCA patients, but OHCA patients with longer low-flow-time were not enrolled [17]. There was no further delineation of the role of LV decompression then. To our knowledge, there were only 3 individual series that comprised more than 20 cases of LV decompression: Centofanti P et al. 24 cases, Eastaugh LJ et al. 44 cases, Hacking DF et al. 49 cases [18–20]. The latter two were studying pediatric patients, and only Centofanti P et al. addressed the survival benefit of trans-apical LV venting in adults with cardiogenic shock put on VA-ECMO. Moreover, none of the above mentioned cardiac arrest. Our cohort enrolled 45 cases of LV decompression, by direct surgical LV venting, upstream LA drainage either by sternotomy, or peripheral trans-septal approach. In addition, these 45 patients were even more complicated, as they suffered from cardiac arrests and ensuing resuscitation. Our patients of both OHCA and IHCA could have more survival probability, if modified LVAD were appropriately indicated.
Study limitations
This is a prospective cohort study, and inheriting the drawback of selection bias was not inevitable. However, nearly all items of demographic were evenly distributed, which should offset the influences derived from shortcomings of a non-randomized design.