Discussion
3D-RV FWS analysis is an innovative instrument for assessment of
longitudinal RV function. In the present study we described
intraoperativ normal values for 3D-RV FWS that can be expected in
onpump CABG patient with preoperative preserved LV and RV function and
an uneventful perioperative course, and compared them to conventional
parameters of RV function assessment. Although, 3D-RV FWS assessment was
already described as feasible, intraoperativ data are
sparse.11, 12, 18 Intraoperative evaluation RV strain
and decision making is ambitious since there are no established
reference values for anesthetized and ventilated cardiac surgery
patients as there are for awake, spontaneously breathing patients in the
non-operative setting.5, 9 Therefore, our study has
important findings.
In our group of CABG patients, with preserves LV and RV function and an
uneventful intraoperative course we were able to measure 3D-RV FWS after
induction of anesthesia, under stable hemodynamics, a predefined fluid
management and without the influence of vasoactive support or pacing, in
about 95% of our patients. These measured values for RV FWS are notnormal values as it would be expected for healthy volunteers
without cardiac disease, but normal values that can be expected
in CABG patients with preserved LV and RV function, and a
complication-free intraoperative course. In our opinion normal
values from individuals without cardiac disease are not helpful in
intraoperative decision making in cardiac surgery patients with
different cardiac states (e.g., ischemia or subclinical myocardial
dysfunction beside normal conventional parameters). Regarding existing
literature, we are unaware of published reports on 3D-RV FWS in onpump
CABG patients, beside our own pilot study.12 Other
authors report about 3D-RV FWS in different patient populations and
clinical scenarios. Keller et al.18 reported in a
retrospective chart review about left-sided cardiac valve surgery
patients with different grades of LV and RV function and different
pulmonary pressure profiles. They described prebypass values of 3D-RV
FWS of -19.4 ± 6 (95%-CI -20.9; -17.9) in 59 patients with normal
pulmonary artery pressure profiles, but heterogenous LV function, and of
-20.5 ± 7.3 (95%-CI -22.4; -18.6) in 60 patients with normal LV
function, but different pulmonary pressure profiles. Patients in this
group were treated with norepinephrine as clinical necessary. In another
retrospective study Keller and colleagues11 observed
presternotomy TEE-assessed 3D-RV FWS values of -19.6 ± 6.9 in
twenty-three off-pump CABG patients and -20.1 ± 7.1 in twenty mitral
valve surgery patients, both groups again treated with vasoactive
therapy as clinical necessary. In a huge retrospective study including
496 patients, Keller et al.19 report about a
heterogenous cardiac surgery patient population with different LV and RV
function constellations including CABG and/or valve surgery procedure
and even left ventricular assist device (LVAD) implantations in elective
and urgent scenarios. Using a custom-made 3D mesh-derived software they
were able to measure three-dimensional RV FWS. In their report they
present values of this 3D mesh-derived RV FWS of -17.7 ± 6.9, assessed
after induction of anesthesia and before sternotomy by TEE. Their
patient population was supported by vasopressors and/or inotropes as
clinically necessary. The presented data for 3D-RV FWS of our study
patients could be considered as normal because our patient
collection was less heterogeneous than the above-mentioned studies, not
supported by vasopressor and/or inotropes and had no serious
perioperative complications. However, 3D-RV FWS in our study was more
declined than the normal values of TTE-assessed 2D-RV FWS
reported by ASE / EACVI guidelines on chamber
quantification5 of -29±4.5, or normal values of 2D-RV
FWS from World Alliance of Societies of Echocardiography
Study20 of -28.3±4.3, or from a metanalysis from Fine
et al.9 of -27±2, described for all ages and genders
in healthy individuals. Although all of our patients were preoperatively
evaluated having preserved RV function by conventional parameters, 3D-RV
EF was reduced (<45%) in 56 patients. Therefore, we evaluated
3D-RV-FWS also in a subgroup of our patients with 3D-RV EF ≥45%.
Differences in the altered described normal values might be
explained by the more declined RV function in heart valve surgery and
mixed populations of the retrospective studies from Keller and
colleagues compared to our relatively healthy CABG population with
preserved LV and RV function and without more than mild heart valve
disease and without elevated pulmonary pressure. Our data are comparable
to observed values for 2D-RV FWS measured by TTE after induction of
anesthesia in non-cardiac surgery patients without myocardial disease
reported by Dalla21 et al. (-26.5±3.9). Prospective
observations of 2D-RV FWS by Donauer et al.22 and
Gronlykke et al.,23 each with 30 CABG patients
included, revealed higher mean values, which means a more declined RV
function, in their patient populations of -22±4 and -19.9±7.2,
respectively. This may be explained by differences in used assessment
technique, different vendors of echo machines and probes, or by
initially more declined RV function beside stated normal or preserved RV
function, as evaluated preoperatively by conventional echocardiographic
parameters. Our own pilot trial12 showed a median
3D-RV FWS of -24.35 with an interquartile range (IQR) of -29.8 to -20.6.
The fact that we measured RV function under stable hemodynamic
conditions after induction of anesthesia, without influence of
vasopressors or any other intravenous vasoactive therapy and in the
absence of rhythm disorder may help to explain our data.
We have strengthened our trial in choosing a homogenous group of
patients with preserved LV and RV function, homogenous procedures
without influence of vasoactive support on echocardiographic evaluation,
a predefined infusion regime and sinus rhythm, used only one vendor and
type of echo machine and probes and used three-dimensional full-volume
multi-beat acquisition that captures all essential structures through
the entire cardiac cycle.
Our study has limitations. It is a single-center observational study
including 150 patients. Evaluation of 3D-RV FWS is an “offline”
analysis and mostly not incorporated in the echo machines at the moment.
However, we suppose that this novel parameter will be included on the
echo machines in the near future and become available for intraoperative
“online” evaluation. We did not analyze regional differences of 3D-RV
FWS and did not evaluate for a correlation with localization of coronary
heart disease. But most of our patients had triple vessel disease. Most
of our patients were men older than 60 years, which might influence
generalization of the results. Finally, we did not evaluate intra- or
interobserver variability. Since our trial is a prospective single
center observational study, the results need to be confirmed in further
well-designed multicenter trials. Our data might help in to find
reference values for intraoperative decision making in on-pump CABG
surgery patients and could serve as a basis for further research.