Data extraction and quality assessment
The retrieved articles were initially reviewed by two independent
reviewers (SJ and AD). They screened titles and abstracts and removed
the duplicates using the EndNote X9 software. The extracted data were
further verified by the reviewers. The third investigator (MM) was then
consulted to address any discrepancies concerning the evaluation of
studies. The study design, baseline characteristics, and various
outcomes were extracted. For the quality assessment of the included
randomized control trials (RCTs) (13, 14), the Revised Cochrane Risk of
Bias tool (ROB-2) was used. The modified Newcastle Ottawa scale was used
for quality assessment of the remaining non-randomized trial (15).
Interventions
Operators performed PVI under fluoroscopic guidance by advancing an
inflated cryoballoon (CB) catheter (Medtronic Inc., Minneapolis, MN) to
each pulmonary vein antrum and freezing the tissue.
PWI was performed by delivery of at least two cryo-balloon freezes
applied to each quadrant of the left atrial posterior wall (LAPW) under
fluoroscopic guidance. This was accomplished by clocking/counter
clocking of the sheath and balloon catheter after positioning the
cryo-balloon in the individual pulmonary veins supported by pushing in
the Achieve catheter (Medtronic Inc., Minneapolis, MN) to apply pressure
to the LAPW. The cryo-balloon position was monitored on intracardiac
ultrasound. Post ablation 3-dimensional (3D) voltage maps were created
after each procedure.
Study definitions and end points
The primary outcome of interest was the recurrence of AF after the
90-day blanking period. Recurrence of any type of atrial tachyarrhythmia
was defined as >30 seconds on any cardiac rhythm recording
following the specified blanking period after the index CBA procedure.
Secondary outcomes included recurrence of all atrial arrhythmias (AF,
atrial flutter, and atrial tachycardia), total ablation time, and
adverse events.
Statistical analysis
We used the Review Manager (RevMan) computer program, version 5.4, to
perform statistical analysis. A random effects model with
Mantel-Haenszel weighting was then used to analyze our primary and
secondary endpoints. The outcomes were reported as risk ratios (RR) and
mean difference (MD) with a 95% confidence interval (CI). For
assessment of study heterogeneity, the Higgins-I-squared
(I2) model was used with values < 25%,
25–50%, 50–75%, and > 75% corresponding to no, low,
moderate, and high degrees of heterogeneity, respectively. (16) A
p-value of <0.05 was considered statistically significant. The
publication bias was depicted graphically using funnel plots