Conclusions
In the present study, both types of cardioplegia were similar in
mortality and major postoperative complications. However, DNC was
associated with significantly shorter CPB and aortic cross clamp times.
Importantly, DNC was also independently associated with lower levels of
postoperative Troponin release which may indicate less myocardial
injury. Moreover, the duration of inotropic support and ICU stay were
significantly lower in the DNC group (Graphical summary is depicted inFigure 2 ).
DNC seems to reduce postoperative troponin release which may indicates
less myocardial damage. This is perhaps related to one or more
components of the solution. The DNC has an electrolyte composition that
mimics extracellular fluids with addition of potassium chloride, sodium
bicarbonate, mannitol, magnesium sulphate and
lidocaine.1 Lidocaine act as a sodium channel blocker
and magnesium act as a calcium competing agent which results in
reduction of intracellular calcium level. As such, myocardial
excitability, cellular metabolism, and energy consumption are
reduced.2,16 This is one potential explanation for the
extended period of myocardial protection with the DNC and perhaps the
reduced myocardial injury as indicated by significantly lower Troponin
leak in the present study which was independent of aortic cross clamp
time.
Additionally, DNC may have a better distribution throughout the coronary
bed due to the vasodilatory effect of Lidocaine.17This may provide more myocardial preservation and lessen myocyte injury.
Furthermore, the shorter cross clamp time with DNC (p < .0001)
is potentially another factor that may have contributed to lower
postoperative troponin levels in the DNC group. Indeed, Erkut et al.
found a direct and linear relationship between aortic cross clamp
duration and postoperative Troponin levels in patients undergoing
isolated CABG.18
Nonetheless, the lower level of postoperative troponin in our study was
independent of the aortic cross clamp time. In addition, since all
procedures were performed by a single surgeon, the potential confounding
effect of differences in surgical and myocardial protection techniques
is likely minimized. This include factors such as the degree of systemic
hypothermia, use of topical ice, cardioplegia route, coronary surgery
techniques among others which were similar between the groups in the
present study. Therefore, the observed advantage of lower Troponin
release with DNC in the present study is perhaps related to one or more
components of the DNC solution itself.
The findings from our study, which included a wide range of simple and
complex, low and high risk adult cardiac surgery procedures, are
consistent with a recent randomized controlled trial (RCT) that included
primarily low risk patients with first-time coronary artery bypass
grafting and/or first-time single valve procedures. In this RCT, Ad and
associates found several advantages with use of DNC which has led them
to prematurely end the study after the data safety interim analyses.
They found a higher return to spontaneous rhythm (97.7% vs 81.6%; P =
.023) and fewer patients required inotropic support (65.1% vs 84.2%; P
= .050), with the use of DNC. They also found a trend of lower Troponin
levels with DNC which did not reach a statistical significance (P= .04).
In their study, an alpha level of P < .001 was determined to
be required for statistical significance because of the effect of early
ending of study on alpha level.12
In another RCT which also included relatively low risk patients, Sanerta
and coauthors randomized 150 patients who underwent isolated aortic
valve replacement to DNC or cold blood cardioplegia. They also found a
trend of lower Troponin values in the DNC that did not reach a
statistical significance. Their study however was not powered to detect
such a difference.13
Similarly, safety and potential advantages of DNC in adult cardiac
surgery has been reported in several observational
studies.5-11 In a large systematic review and
meta-analysis included more than 2000 patients (mostly isolated CABG and
single valve procedures), An et al found no difference between DNC and
BC in mortality or major morbidity. However, DNC
reduced cardioplegia volume requirements (P <
0.001), aortic cross-clamp (P < 0.001), and CPB times (P =
0.03). Likewise, and similar to our findings, DNC was associated with
reduced Troponin release (P = 0.001).19
In contrast to aforementioned studies that included mostly low risk and
relatively simple adult cardiac surgery procedures. Reports on use of
DNC for more complex procedures have been
limited.14,15 deLenoir and associates20 compared DNC to blood cardioplegia in 283 patients
undergoing complex aortic root procedures. Similar to our findings and
findings of others, aortic cross-clamp and CPB times were shorter with
DNC (P=0.006). Interestingly, in contrast to findings by us and others,
they found a non-significant trend toward higher troponin T levels with
DNC (P=0.07) and in patients with myocardial ischemia longer than 180
minutes, median CK-MB was higher in DNC group (75.1 (59.3-300) μg/L than
in BCS 60.5 (16.5-116) μg/L (P=0.01). In view of findings by deLenoir
and colleagues, we performed a post-hoc sub-group analyses to examine
the trend in postoperative Troponin T levels in patients with ischemia
time longer than 180 minutes (n= 32) and we found a trend of lower peak
Troponin T level in the DNC group that did not reach a statistical
significance with the limited sample size (1.5 ± .8 ng/ml vs. 1.8 ± .7
ng/ml, P = 0.2).
Similar to our findings, Hamad and associates 15compared DNC to blood cardioplegia in patients undergoing combined CABG
and aortic valve replacement and found that postoperative creatine
kinase, MB isotype (P = 0.011) and troponin T levels \sout(P = 0.028)
were significantly lower in the DNC group compared to BC. Additionally,
our findings regarding lower Troponin T level is in line with findings
from a recent important meta-analysis by Gambardella and
associates.21
In conclusion, DNC was associated with significantly shorter CPB and
cross clamp time, significantly lower post-operative troponin release
and shorter duration of inotropic support and ICU length of stay. These
benefits were observed for all categories of adult cardiac surgery
including high risk procedures.