Temporary stimulation on the RVDS with epicardial electrodes after CBP is a common practice in cardiac surgery. Different studies, investigating the sites of pacing to optimize CO including: RVP at, apical, diaphragmatic surface, paraseptal and outflow tract; LVP: posterobasal, mid free-wall, apical and paraseptal, have generated controversial results
Vaughan et al.
 performed an extreme search on the subject. They concluded that only 9 of the 13 publications, resulted in significant increases of cardiac index,up to 22% with BiVP or AR-LVP. Tanaka et al. and others
[18, 22, 23] observed greatest benefits in patients with low EF and wide QRS complex. Whereas others, report no significant hemodynamic improvement with these pacing modes or even no adverse effects with RA-RVP in populations with normal ventricular function
The strategy for perioperative optimization, by means of LVP or BiVP using a LV basal cathodal electrode and adequate adjustments of AVD and VVD if feasible, is gaining progressive acceptance, to improve CO perioperatively, particularly in cases with depressed EF and LBBB
[11, 13, 18, 23]
In our study, in an heterogeneous population, RA-LVP,LVP or BiVP effectiveness, was validated by MAP and CO monitoring, proving to be beneficial in almost 80% of the whole population, with significant improvements of MAP and CO in the low EF and LBBB subgroups, being highest in the AF group with depressed EF. The increments obtained may appear rather modest but simultaneously avoid the adverse effects of RVP. Similar positive results with RA-LVP have been obtained by Flynn et al.
In the average population, RA-RVP decreases CO and MAP and this effects also occurs in the different subgroups studied. Similar adverse observations have been reported in cases undergoing CABG surgery
[8, 18]. Besides, it has been noticed that with low EF, systolic dyssynchrony with RA-RVP is significantly higher compared with RA-LVP or BiVP
,except in cases with RBBB
. From our study, no conclusions can be reached as there were only two cases with such alteration.
Our investigation, shows a 20% of non responders. They were tested only by RA-RVP or RA-LVP modes with AVD adjustments. The most delayed site on the inferolateral LV wall was not established by echocardiography and BiVP was not applied in the SR group, lacking a possible optimization of synchronicity with VVD.
In the setting of postoperative CPB, there is very limited experience reported with AF, generally due to the established exclusion criteria. In an acute HD study in CHF, including AF cases, Blanc et al.
 observed a significant increase of systolic blood pressure with both LVP and BiVP.
Mixed venous oxygen saturation, only showed favourable significant differences, in the group of AF with EF < 35%, using LVP or BiVP. Eberhardt el al
 in CABG patients, did not found differences in SvO2 among the various pacing modalities. Our results seem to indicate that SvO2, may not be a suitable parameter to validate the effectiveness of the different postoperative TS modes, when ventricular function is preserved.
Due to the nonexistence of an external triple chamber pacemaker, we employed only in AF cases, a biventricular dual cathodal pacing system
, which implies two independent activated circuits, with a cathode in each ventricle, allowing VVD adjustments. To our knowledge the present study, using dual cathodal BiVP is the only clinical experience reported, in cases with AF, during the postoperative CPB period.
Few reports provide a precise description of the BiVP configuration used, accomplished either with the split bipole or the dual cathodal split system, but always with the drawback of not been able to adjust the VVD, to maximize the optimization benefit
[11, 12]. Fernandez et al. (30) questioned the assessment of the potential hemodynamic benefits of TS, based on the fact, that different authors have used distinct terminology for the pacing configurations of left anocathodal system, versus biventricular left cathodal split bipole.
Our study,in AF cases with EF < 35%, both LVP and BiVP significantly increased MAP and CO, accompanied by significant improvements of dP/dt max, without statistical differences between them. Flynn et al.
 in a subset of five cases of AF submitted to CABG, placing an active lead on the LV posterobasal area, did not observed significant changes in MAP.
A recent study
 under acute RV and LV failure conditions, has demonstrated using BiVP, that the dP/dt max of the failing ventricle, is maximized when interventricular contraction is close to synchronous. During acute ventricular failure, BiVP parameters like LVP site and the correct VVD, can recruit the unstressed ventricle to support function of the failing one by “interventricular assist”.
Right acute ventricular failure after CPB is an important hemodynamic complication difficult to treat effectively. BiVP with VVD adjustments, could be very helpful in that setting stressing the relevance of this pacing mode.
Wang et al.
 in a substudy of the BiPACS trial (mean LVEF < 35%), have reported an increase of 14% in CO after AVD optimization compared with the worst value and 7% mean increase from an AVD of 120 ms. The optimum VVD differed from the nominal value, in 5% CO improvement. Overall, optimized BiVP resulted in a CO increase of 10% versus SR. Schmidt and co-workers
,pointed out the limitation of not using AVD and VVD optimization with BiVP, after not obtaining any HD improvement in CBPG cases.
These results, further stress the relevance of optimizing AVD and VVD in the perioperative CPB setting, particularly, in cases with preexisting LV dysfunction, at high risk of developing acute low-output state. Nevertheless, the mechanisms by which pacing optimization improves hemodynamics in this setting, are still not fully defined
 and require further dedicated studies.
Future investigations using TS to improve cardiac function, will be more feasible using external triple chamber generators with adjustable VVD and should contribute to establish pacing optimization as a routine step of perioperative protocols.