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\begin{document}

\title{The behavior of residual pulmonary artery gradient after arterial switch
operation: A longitudinal data analysis}



\author[1]{HANI ALKATTAN}%
\author[1]{Obayda M Diraneyya}%
\author[1]{Hatem Elmontaser}%
\author[1]{Joohum Jaweed}%
\author[1]{Abdulsalam Alsayad}%
\author[1]{Ahmed Arifi}%
\author[2]{Abdullah A. Alghamdi}%
\affil[1]{National Guard Health Affairs}%
\affil[2]{King Abdulaziz Cardiac Center}%


\vspace{-1em}



  
  \date{May 25, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
{}Objective: The arterial switch operation is the standard treatment for
the transposition of the great arteries. The timely variation in the
residual pressure gradient across the pulmonary arteries is ill-defined.
This work is aimed to study the progressive changes in the pressure
gradient across the pulmonary valve and pulmonary arteries after
arterial switch operation (ASO). Methods: All eligible patients for this
study who underwent arterial switch operation between 2000 and 2019 were
reviewed. Transthoracic echocardiography (TTE), was used to estimate the
peak pressure gradient across the pulmonary artery and its branches. The
primary outcome was the total peak pressure gradient (TPG) which is the
sum of peak pressure gradients across the main pulmonary artery and
pulmonary artery branches. Furthermore, a longitudinal data analyses
with mixed effect modeling were used to determine the independent
predictors for the changes in pressure gradient. Results: 309 patients
were included in the study. Over 17-year follow up, the freedom from
pulmonary stenosis reintervention was 95\% (16 out of the 309 patients
underwent reintervention = 5\%). the Longitudinal data analyses of
serial 1844 echocardiographic studies for the included patients revealed
that the TPG recorded in the first postoperative echocardiogram across
pulmonary valve, right and left pulmonary artery branches was the most
significant predictor for reintervention. Conclusion: The total peak
gradient measured in the first postoperative echocardiogram is the most
important predictor for reintervention. We propose that a total peak
gradient in the first postoperative echocardiography of 55 mmHg or more
is a predictor for reintervention%
\end{abstract}%



\sloppy




\textbf{The behavior of residual pulmonary artery gradient after
arterial switch operation:}

\textbf{A longitudinal data analysis}

\textbf{ABSTRACT}

\textbf{Objective:} The arterial switch operation is the standard
treatment for the transposition of the great arteries. The timely
variation in the residual pressure gradient across the pulmonary
arteries is ill-defined. This work is aimed to study the progressive
changes in the pressure gradient across the pulmonary valve and
pulmonary arteries after arterial switch operation (ASO).

\textbf{Methods:} All eligible patients for this study who underwent
arterial switch operation between 2000 and 2019 were reviewed.
Transthoracic echocardiography (TTE), was used to estimate the peak
pressure gradient across the pulmonary artery and its branches. The
primary outcome was the total peak pressure gradient (TPG) which is the
sum of peak pressure gradients across the main pulmonary artery and
pulmonary artery branches. Furthermore, a longitudinal data analyses
with mixed effect modeling were used to determine the independent
predictors for the changes in pressure gradient.

\textbf{Results:} 309 patients were included in the study. Over 17-year
follow up, the freedom from pulmonary stenosis reintervention was 95\%
(16 out of the 309 patients underwent reintervention = 5\%). the
Longitudinal data analyses of serial 1844 echocardiographic studies for
the included patients revealed that the TPG recorded in the first
postoperative echocardiogram across pulmonary valve, right and left
pulmonary artery branches was the most significant predictor for
reintervention.

\textbf{Conclusion:} The total peak gradient measured in the first
postoperative echocardiogram is the most important predictor for
reintervention. We propose that a total peak gradient in the first
postoperative echocardiography of 55 mmHg or more is a predictor for
reintervention.

\emph{Main Document}

\textbf{INTRODUCTION:}

Transposition of the great arteries (TGA) is a common cyanotic
congenital heart disease either in isolation or as a part of more
complex congenital cardiac anomalies. Since its inception in 1975 by
Jatene, the arterial switch operation (ASO) has become the standard
method for surgical repair of the TGA\textsuperscript{1,2}.

The goal of surgical repair is to have an anatomical correction. Part of
the surgical treatment is performing the Lecompte procedure where the
pulmonary arteries are relocated anteriorly\textsuperscript{4}.
Furthermore, the neo-pulmonary artery is reconstructed, most often using
a pericardial patch. Although the current operative mortality is low and
the mid and late outcomes are satisfactory, there are still some
complications, one of which is the residual pressure gradient across the
pulmonary valve and reconstructed pulmonary
arteries\textsuperscript{3-6}.

The pressure gradient across the neo-pulmonary artery (especially in the
supra-valvular area) is the most crucial determinant for reintervention,
though modifications of arterial switch operation have reduced the
occurrence of pulmonary stenosis\textsuperscript{4,5,7}.

The reported incidence of reoperation related to pulmonary stenosis
after the arterial switch operation ranges from
5-30\%\textsuperscript{5,8-10}. Because the pulmonary artery pressure
gradient can vary with the somatic growth, we sought to examine the
behavior of the pulmonary artery pressure gradient over time and to
determine the contributing factors and its relationship with the need
for reintervention.

\textbf{MATERIAL AND METHODS:}

\textbf{Study Population:}

After approval of the research ethics board, all consecutive patients
who underwent ASO between 2000 and 2019 were reviewed. Exclusion
criteria were: double outlet right ventricle (DORV), congenitally
corrected transposition of the great arteries (CCTGA), specific
pathology forms of transpositions (e.g., isomerism, posterior
transposition), late presenting patients (age more than 3-months) and
patients who died early (in-hospital death). These exclusion criteria
were applied to yield a homogenous group of patients.

\textbf{Institutional Surgical Technique:}

Our institutional repair strategy for the transposition of the great
arteries includes performing LeCompte maneuver and reconstruction of the
neo-pulmonary artery using quadrangular fresh autologous pericardial
patch. The pulmonary reconstruction technique includes mobilization of
both pulmonary artery branches into the hila, direct suturing of the
patch to 2/3 of the annulus of the neo-pulmonary trunk, and
re-suspension of the neo-pulmonary valve inside the patch. An
anastomosis without tension is then performed, using the reconstructed
pulmonary tract to fit out the expected size of the distal-pulmonary
artery (Figure 1).

\textbf{Echocardiographic follow up:}

All included patients underwent Intraoperative transesophageal
echocardiogram (TEE) as well as a routine pre-discharge TTE (first
post-operative echocardiogram). Patient follow-up and need for
reintervention were determined from the outpatient clinic charts. The
TTE was performed regularly in the outpatient setting to assess the
pressure gradient across the main pulmonary artery and the pulmonary
artery branches. In our center the follow up protocol is to do TTE after
6 weeks, 3 months, 6 months, 1 year of discharge, then once yearly
unless there are pathologic changes in first year of follow up. Follow
up was available for all patients at a mean duration of 9.3 years. the
follow-up included for the purpose of this study, the valvular function
and the pulmonary artery pressure gradient.

\textbf{Outcomes:}

The primary outcome was the total peak gradient across the main
pulmonary artery (MPA), right pulmonary artery (RPA), and left pulmonary
artery (LPA); thereby, total peak gradient (TPG)= MPA+RPA+LPA measured
by echocardiography in the postoperative period (pre-discharge
echocardiogram). The secondary outcome was the reintervention by means
of percutaneous or surgical intervention.

\textbf{Statistics:}

Continuous data were presented as means with standard deviation and
categorical data were presented as proportions. Kaplan-Meier statistics
were used to display time to reintervention. A multivariable
proportional hazard modeling was used to identify the influence of
preoperative and operative variables on the need for reintervention.
Longitudinal data analyses with mixed effect modeling were used to
display and identify predictors of the progressive changes in the
pressure gradient following repair. The statistical software system SAS,
version 9.4, Cary, USA, was used for all statistical analyses.

\textbf{Results:}

Study patients

A total of 411 patients who underwent arterial switch operations between
2000 and 2019 were reviewed. The inclusion/exclusion criteria were
applied, 67 patients had specific pathology requiring arterial switch
operation were excluded because this pathology had innate pulmonary
arteries disease, the rest are 344 patients, 24 of them who were older
than 90 days were also excluded due to basic significant pulmonary
hypertension in this population. There were 11 early mortalities. There
were no late mortalities. Most of the mortalities were in the early era
of the study. None of those (mortality group of patients) underwent
reintervention for residual pulmonary artery stenosis. Therefore, the
final study cohort included 309 patients (Figure 2).

Baseline characteristics:

35\% of patients are male, 65\% of patients had simple transposition and
35\% had complex

transposition, balloon atrial septostomy (BAS) was done for 55\% of
patients, mean age of the

population was 20\selectlanguage{ngerman}±17 days, mean weight was 3.2±0.5 kg, mean height was
51±5 cm, mean body surface area (BSA) was 0.2±0.02, mean
cardio-pulmonary bypass (CPB) time was 160±39 minutes, mean cross clamp
(CC) time was 95±27 minutes. Mean PG across the main pulmonary artery,
left PA, Right PA are 9±7, 14±11, 17±13 mmHg Respectively. The baseline
characteristics are summarized in table 1 and 2.

\par\null

Comparison based on reintervention and preoperative variables

A univariable comparison was performed to identify the significant
preoperative variables between those who underwent reintervention and no
intervention group, (Table 3\&4).

Age, weight, height, BSA, CPB time, CC time, gender, and surgeon there
were not statistically different between both groups. However, the
estimated PG across left PA, right PA, and TPG were statistically
different.

Time to reintervention analysis

Time to reintervention using Kaplan-Meier statistics for the entire
cohort of 309 patients showed 16 events (re-interventions) with freedom
from re-intervention along the span of the study of 17-year was 95 \%.
The mean follow-up time was 9.3 years (Figure 3). Survival analysis with
stratification by the sex, surgeon, type of transposition and balloon
atrial septostomy using log-rank statistics showed no significant
differences.

Serial Transthoracic Echocardiographic Measurements:

All patients underwent serial transthoracic echocardiographic
evaluations. The minimum number of echocardiograms done for each patient
(excluding the intraoperative TEE) was 1, and the maximum was
17(mean=6±4), Figure 4.

Reintervention group (N=16):

Of the 16 patients who underwent reintervention due to pulmonary
stenosis, there was no

mortality and nine patients (56\%) had the intervention within two years
following the surgery

(Figure 5). 14 patients had one Intervention, one patient underwent two
interventions, and one

patient underwent three interventions.

Furthermore, 6 out of the 16 patients had simple TGA, and 10 had complex
TGA.

The common type of pulmonary stenosis was supra-valvular and was
observed in (14 out of 16),

and only two patients had valvar and sub-valvar pulmonary stenosis. In
the supra-valvular

group, three patients had main pulmonary artery stenosis, three patients
had right pulmonary

artery stenosis, one patient had left Pulmonary artery stenosis and
seven patients had bilateral

pulmonary artery stenosis. The clinical decision to perform the
reintervention was based on the

multidisciplinary (heart-team) meeting.

Out of the 19 reinterventions performed (19 reinterventions for 16
patients), 12 were surgical, Figure 6.

Longitudinal Data Analysis

All serial transthoracic echocardiographic studies, excluding the
intraoperative TEE for all

patients, were included (N=1844). Longitudinal graphical data display
was used, respecting the

different timing of the echocardiographic measurements.

The averaged longitudinal data for the total gradient showed that most
of the changes happen in

the first two years following surgery (Figure 7).

Longitudinal Data Analysis with stratification:

Stratification by the sex, type of transposition, balloon atrial
septostomy and the operating surgeon did not show significant
differences. The most notable finding in the stratified longitudinal
data display was the rate of drop of the pressure gradient between those
who underwent reintervention and those who did not (Figure 8).
Longitudinal data analysis with mixed effect modeling showed that the
significant variables in relation to the peak pressure gradient
following arterial switch operation included: younger age at surgery,
complex transposition, and longer bypass time.

As the rate of change of pressure gradient immediately after surgery was
the most notable difference between patients based on reintervention.
Further testing with proportional hazard modeling for all variables with
time-to-reintervention as an outcome with stepwise selection methodology
showed that the only predictive preoperative variable for reintervention
was the total peak gradient (MPA+RPA+LPA) (p\textless{}0.0001). Further
analysis with the area under the receiver operating characteristics
curve showed that a total peak gradient 55 mmHg or more was a predictor
for reintervention with a hazard ratio of 12.

\textbf{Discussion:}

There has been attention to the neo-pulmonary artery stenosis after
arterial switch operation as it is the commonest reason for
reintervention\textsuperscript{3-5}. Therefore, several techniques to
reconstruct the pulmonary artery during arterial switch procedures have
been developed, including pantaloon pericardial patch, limited buttons
resection, and extended pericardial patch to pulmonary branches.

The use of pantaloon pericardial patch compared to synthetic patch was
associated with lower neo-pulmonary artery stenosis (7\% versus 40\%)
and reintervention rate (4\% versus 14\%), respectively. However,
complex anatomy increased risk for neo-pulmonary
reintervention\textsuperscript{4}.

Regarding Limited buttons resection technique, a data of 120 patients
and follow up 66±46

Months revealed that (5\%) of the patients required neo-pulmonary
reintervention\textsuperscript{5}.

A report by Wervovsky and colleagues was in favor of extended
pericardial patch technique due to the result of gradual recognition of
the necessity to avoid tension on the anastomosis of the neo-pulmonary
artery. This led to the more extensive mobilization of the distal
pulmonary arteries and the use of more generous pericardial patches
(single or double), not only for filling in the defects created by
coronary arteries dissection but also to add length to the proximal
neo-pulmonary root\textsuperscript{7}.

Pulmonary artery reconstruction with quadrangular fresh autologous
pericardial patch represents a practical, simple and reproducible option
during the arterial switch operation with all positions of the great
vessels. The incidence of postoperative pulmonary stenosis is low, and
there may be considerable potential for unlimited tissue growth. The
peak pressure gradient across the neo-pulmonary valve and pulmonary
artery branches as determined by transthoracic echocardiography is the
most common clinical tool to assess the outcome of the surgical repair.
Ideal results would show laminar flow across the proximal pulmonary tree
with no significant pressure gradient. However, there is almost always
an element of flow acceleration and measured pressure gradient that
could be attributed to stretching of the pulmonary arteries secondary to
Lecompte maneuver and the reconstruction technique of the neo-pulmonary
artery. The value of that residual pressure gradient is ill-defined in
the literature. This paper is focused on examining the value of the
residual pressure gradient, its behavior over time, and its relationship
with the need for reintervention.

In this report, 309 patients were included with all echocardiographic
measurements that were performed in standardized fashion (n=1844). The
rate of reintervention was 5\%, which is at the lowest part of the
published ranges\textsuperscript{5,8-11}. There was no difference in the
pressure gradient in the presence or absence of an associated
ventricular septal defect. It was not surprising to find the residual
pressure gradient more in patients with complex anatomy and longer
bypass time as compared to those without.

Our institutional repair strategy is based on using a fresh autologous
redundant pericardial patch for the reconstruction of the neo-pulmonary
artery. Furthermore, the impact of the surgeon was not significant in
predicting the pressure gradient or reintervention in multivariable
testing. The most notable difference in pressure gradient was seen in
the first postoperative transthoracic echocardiogram (pre-discharge).
Using the longitudinal data analysis with stratification based on
intervention, it showed clear demarcation of the behavior of the
pressure gradient. We propose if the pressure gradient as measured in
the first postoperative transthoracic echocardiogram is 55 mmHg or more
will likely increase over time and subsequently require re-intervention.
The threshold for reintervention was a clinical decision was based on
the observed increase in the pressure gradient across the pulmonary
arteries. The sustainability of laminar flow in the main pulmonary
artery and its branches is the main component of maintaining low
longitudinal averaged mean line of the total peak gradient following
surgery for the entire follow up time (17-year), and we believe that
enough dissection of right and left pulmonary arteries and tension-free
anastomosis with redundant fresh pericardial patch for the
reconstruction of the neo-pulmonary artery are crucial to achieving this
result.

Additional statistical techniques were used to determine the best
cut-off point of the ``high gradient'' that will persist, get higher and
predict reintervention. The best cut-off point was a total peak gradient
across the neo-pulmonary artery, right pulmonary artery and left
pulmonary artery as measures in the first postoperative echocardiography
of 55 mmHg or higher.

The association between the transposition of the great arteries and
pulmonary artery growth has been suggested in published reports relating
it to accelerated pulmonary vasculopathy and asymmetric distribution of
the pulmonary blood flow\textsuperscript{12,13}.

\textbf{Conclusion:}

The total peak gradient (across pulmonary valve, right and left
pulmonary artery branches) measured in the early postoperative
echocardiogram is the most significant predictor for reintervention
after arterial switch operation. Furthermore, we propose that the total
peak gradient in the early postoperative echocardiogram of 55 mmHg or
more is a predictor for reintervention.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Figure 1: Illustration of the surgical technique\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2: Patients' selection based on inclusion/exclusion
criteria}

\textbf{Table 1: The general characteristics of the entire cohort of
patients N=309}\selectlanguage{english}
\begin{longtable}[]{@{}ll@{}}
\toprule
\textbf{Variable} & \textbf{Number (Proportion)}\tabularnewline
Sex Male Female & 109 (35\%) 200 (65\%)\tabularnewline
Type Simple transposition Complex transposition & 201 (65\%) 108
(35\%)\tabularnewline
Balloon atrial septostomy & 171 (55\%)\tabularnewline
Reintervention for residual pulmonary artery stenosis & 16
(5\%)\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 2: The general characteristics of the entire cohort of
patients N=309}\selectlanguage{english}
\begin{longtable}[]{@{}ll@{}}
\toprule
\textbf{Variable} & \textbf{Mean}\tabularnewline
Age (day) & 20\selectlanguage{ngerman}±17\tabularnewline
Weight (kg) & 3.2\selectlanguage{ngerman}±0.5\tabularnewline
Height (cm) & 51\selectlanguage{ngerman}±5\tabularnewline
Body surface area (\(m^{2})\) & 0.2\selectlanguage{ngerman}±0.02\tabularnewline
Cardiopulmonary bypass time (min) & 160\selectlanguage{ngerman}±39\tabularnewline
Cross clamp time (min) & 95\selectlanguage{ngerman}±27\tabularnewline
Peak pressure gradient across the neo-pulmonary valve (mmHg) &
9\selectlanguage{ngerman}±7\tabularnewline
Peak pressure gradient across the left pulmonary artery (mmHg) &
14\selectlanguage{ngerman}±11\tabularnewline
Peak pressure gradient across the right pulmonary artery (mmHg) &
17\selectlanguage{ngerman}±13\tabularnewline
Total Peak Gradient* & 40\selectlanguage{ngerman}±24\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}

* the total peak pressure gradient measured simultaneously across the
main pulmonary artery +the right and left pulmonary artery

\textbf{Table 3: Univariable comparison based on reintervention}\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
\textbf{Variable} & \textbf{No Intervention (N=293)} &
\textbf{Intervention (N=16)} & \textbf{p-Value}\tabularnewline
Age (day) & 20\selectlanguage{ngerman}±17 & 22\selectlanguage{ngerman}±21 & 0.7\tabularnewline
Weight (Kg) & 3.2\selectlanguage{ngerman}±0.5 & 3.3\selectlanguage{ngerman}±0.6 & 0.6\tabularnewline
Height (cm) & 51\selectlanguage{ngerman}±5 & 51\selectlanguage{ngerman}±4 & 0.8\tabularnewline
Body surface area (\(m^{2})\) & 0.2\selectlanguage{ngerman}±0.02 & 0.2\selectlanguage{ngerman}±0.03 &
0.7\tabularnewline
Cardiopulmonary bypass time (min) & 160\selectlanguage{ngerman}±39 & 182\selectlanguage{ngerman}±48 & 0.1\tabularnewline
Cross clamp time (min) & 96\selectlanguage{ngerman}±27 & 101\selectlanguage{ngerman}±28 & 0.5\tabularnewline
Peak pressure gradient across the neo-pulmonary valve (mmHg) & 9\selectlanguage{ngerman}±6 &
14\selectlanguage{ngerman}±13 & 0.1\tabularnewline
Peak pressure gradient across the left pulmonary artery (mmHg) & 13\selectlanguage{ngerman}±9 &
28\selectlanguage{ngerman}±25 & 0.03\tabularnewline
Peak pressure gradient across the right pulmonary artery (mmHg) & 16\selectlanguage{ngerman}±11
& 33\selectlanguage{ngerman}±24 & 0.01\tabularnewline
Total Peak Gradient* & 38\selectlanguage{ngerman}±20 & 76\selectlanguage{ngerman}±46 & 0.004\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 4: Univariable comparison based on reintervention}\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
\textbf{Variable} & \textbf{No Intervention (N=293)} &
\textbf{Intervention (N=16)} & \textbf{p-value}\tabularnewline
Male & 104 (35\%) & 5 (31\%) & 0.7\tabularnewline
Complex transposition & 100 (93\%) & 8 (7\%) & 0.2\tabularnewline
Balloon atrial septostomy & 160 (94\%) & 11 (6\%) & 0.3\tabularnewline
Surgeon A & 97 (96\%) & 4 (4\%) & 0.8\tabularnewline
Surgeon B & 158 (94\%) & 10 (6\%) & 0.8\tabularnewline
Surgeon C & 38 (95\%) & 2 (5\%) & 0.8\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3: Kaplan-Meier Curves for the entire cohort
(time-to-reintervention)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4: Histogram displaying the number of transthoracic
echocardiograms in relation to patients}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 5: Time to reintervention (N=16)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure (6): Re-intervention group of patients}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 7: Longitudinal averaged a mean line of the total
gradient following surgery for the entire follow up time (17-year)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\textbf{Figure 8: Longitudinal averaged the mean line of the peak
pressure gradient following surgery for the re-intervention group.}

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