(Circulation. 1999;99:262-270.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Johns Hopkins University School of Medicine, Baltimore, Md, and the Departments of Health Research and Policy and Medicine (D.A.B.), Stanford University School of Medicine, Stanford, Calif.
Correspondence and reprint requests to Hugh Calkins, MD, the Johns Hopkins University School of Medicine, Carnegie 592, 600 N Wolfe St, Baltimore, MD 21287. E-mail hcalkins{at}welchlink.welch.jhu.edu
| Abstract |
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Methods and ResultsThe patient population included 1050 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia (AVNRT), an accessory pathway (AP), or the atrioventricular junction (AVJ). Ablation was successful in 996 patients. The probability of success was highest among patients who had undergone ablation of the AVJ, lowest in patients who had undergone ablation of an AP, and in between for patients who had undergone ablation of AVNRT. A major complication occurred in 32 patients. Four variables predicted ablation success (AVJ, AVNRT, or left free wall AP ablation and an experienced center). Four factors predicted arrhythmia recurrence (right free wall, posteroseptal, septal, and multiple APs). Two variables predicted development of a complication (structural heart disease and the presence of multiple targets), and 3 variables predicted an increased risk of death (heart disease, lower ejection fraction, and AVJ ablation).
ConclusionsThese findings may serve as a guide to clinicians considering therapeutic options in patients who are candidates for ablation.
Key Words: catheter ablation Wolff-Parkinson-White syndrome atrioventricular node complications
| Introduction |
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| Methods |
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Patient Evaluation, Electrophysiology Testing, and Catheter
Ablation
Before the ablation procedure, each patient gave informed
consent. A history and physical examination, ECG, and echocardiogram
were also obtained. Catheter ablation of AVNRT was performed with the
posterior approach. An initial attempt at catheter ablation was made
with the investigational ablation system (RF Ablatr or RF Marinr,
Medtronic CardioRhythm) as previously reported.23 If
successful ablation was not achieved, an alternate system could be
used. Pacemaker implantation was performed in all patients who had
undergone successful ablation of the AVJ. The programmed pacing rate
after the procedure was at the discretion of the physician.
Follow-Up Evaluation
Each patient was evaluated 1, 3, 6, 12, and 24 months after
ablation. Patients who experienced palpitations underwent
transtelephonic monitoring. Of the 776 patients enrolled in this study
who underwent successful ablation of AVNRT or an AP with the
investigational ablation system, 457 (59%) underwent a follow-up
electrophysiological study a mean of
2.5±0.9 months after ablation. The median duration of follow-up was
6.3 months.
Outcomes
There were 5 predetermined outcomes: ablation success,
development of major complications, development of new
echocardiographic abnormalities, arrhythmia
recurrence, and death. Catheter ablation procedures were
classified at the completion of the procedure as acutely successful or
unsuccessful on the basis of whether all ablation targets had been
successfully eliminated.
Complications were classified as major or minor. Major complications
were defined as those that resulted in permanent injury or death,
required an intervention for treatment, or prolonged the duration of
hospitalization. An asymptomatic increase in the degree of
valvular regurgitation by 2 or more
echocardiographic grades (ie, mild to severe) was also
classified as a major complication. Paired echocardiograms (before and
after the procedure) were requested as part of the clinical protocol in
all patients and were available for analysis in 972 patients
(93%).Differences in the echocardiograms were classified as
demonstrating a major change if a thrombus, new wall-motion
abnormality,
15% change in estimated ejection fraction, an increase
in valvular regurgitation by
2 grades, or the
presence of a pericardial effusion was detected. A minor change in the
findings on echocardiography was determined to be
present if there was a 5% to 15% change in the estimated ejection
fraction or if a 1-grade increase in valvular
regurgitation was observed.
With the use of long-term follow-up data, patients were further classified as having a recurrence or not and as dead or alive. Analysis of arrhythmia recurrence was confined to the 887 patients in whom successful ablation was achieved with the investigational ablation system.
Statistical Methods
All tests were 2-sided, and P values <0.05 were
considered significant. Regression models were used to identify
variables associated with the acute result of the ablation
procedure and the development of major complications (as defined
above). Variables that were evaluated as potential predictors of
outcome are shown in Table 1
.
Repeated analyses were also performed with the ablation centers
grouped as high- or low-volume centers on the basis of whether
40
patients had been enrolled in the protocol, and also with the centers
classified either as predominantly a pediatric center or predominantly
an adult center. Each variable was tested by generation of a
logistic regression model to predict outcome, with only 1 variable
being incorporated at a time. Variables were jointly assessed for
predictive power with a forward-selection multivariate,
stepwise logistic regression model.
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Recurrence survival rates were estimated with the Kaplan-Meier method. Cox proportional hazards models were used to assess which factors were associated with the risk of recurrence and the risk of death.
| Results |
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Five hundred patients underwent ablation of a single AP, 373 underwent
ablation of AVNRT, and 121 underwent ablation of the AVJ. An additional
56 patients had >1 type of ablation target. Among those patients who
underwent ablation of a single AP, 270 procedures involved the left
free wall, 92 involved the right free wall, 98 were
posteroseptal, and 40 were septal. Patients who underwent
ablation of an AP were significantly younger (mean age, 27±17 years)
than patients with AVNRT (44±18 years) or patients who underwent
ablation of the AVJ (64±15 years; P<0.0001; Figure 1
). Patients who underwent ablation of
AVNRT were more likely to be female (70%) than were patients who
underwent ablation of an AP (42%) or the AVJ (52%;
P<0.001).
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Acute Success of Catheter Ablation
Catheter ablation was acutely successful with either the
investigational or noninvestigational ablation system in 996 patients
(95%; Table 2
). The median number of RF
applications was 6 (range, 1 to 98). Two ablation sessions were
required in 42 patients. The success rate of catheter ablation was
lower among patients who underwent ablation of an AP (93%) and highest
among patients who underwent catheter ablation of the AVJ (100%), with
the success rate for AVNRT falling in between (97%;
P<0.001). Among patients with an AP, success rates were
lower during ablation of right free wall and posteroseptal
APs (90% and 88%, respectively) than during ablation of left free
wall APs (95%; P=0.03). It is interesting to note that the
greater difficulty of ablation of APs, particularly
posteroseptal and right free wall APs, is also reflected in
an increased proportion of patients who required a second ablation
procedure (Table 2
). Success with the investigational ablation
system was achieved in 889 patients (85%; Table 2
).
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When separate logistic regression models were used to assess the odds
of success among the variables of interest, 9 predictors of
ablation success were individually significant (P<0.05):
the ablation target (AVNRT, right free wall AP,
posteroseptal AP, multiple accessory APs, or AVJ), the
ejection fraction, whether or not a center had
40 patients enrolled
in the study, and several specific ablation centers (Table 1
).
Table 3
presents the results of
multivariate logistic regression analysis.
Catheter ablation of the AVJ was 100% successful. Because it was a
perfect predictor, it could not be included in the statistical model.
Three additional factors were identified as jointly predictive of
successful ablation, including the ablation target (AVNRT and left free
wall APs) and the experience of the ablation center.
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Complications
A major complication occurred within 1 month after ablation in 32
patients (3%), and minor complications developed in 87 patients
(8.2%). The type and distribution of complications are shown in Table 4
. The most significant complications
included 3 patient deaths, 2 strokes, 1 myocardial infarction, and 10
cases of complete AV block that required placement of a permanent
pacemaker.
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The most common complications were the development of transient first- or second-degree AV block in 21 patients (2%) and development of complete heart block, which required pacemaker implantation, in 10 patients (1%). The development of complete heart block was related to the type of ablation procedure and occurred in 5 of 373 patients who had undergone ablation of AVNRT (1.3%) compared with 5 (1%) of 500 patients who underwent ablation of an AP. The development of complete heart block during ablation of an AP was most commonly observed after ablation of septal (1 of 40, 2.5%) and posteroseptal (3 of 98, 3%) APs but also occurred in 1 (0.3%) of 270 patients who undergone ablation of a left free wall AP. Two patients had a stroke (0.2%), 1 after ablation of a left-side AP with a transeptal approach and the second after ablation of the AVJ with a retrograde aortic approach. There were 3 deaths (within 30 days of the procedure). One patient died on the day of the ablation procedure; this 56-year-old woman, who had known coronary artery disease and an ejection fraction of 38% with a left lateral AP, died during the procedure as a result of a dissected left main coronary artery. A second patient died on the seventh day after the procedure; this 74-year-old man with an ischemic dilated cardiomyopathy (ejection fraction, 17%) had undergone an AVJ ablation and placement of a pacemaker. He died suddenly 1 week later. Ventricular fibrillation was documented by the emergency medical technicians. The third patient was a 49-year-old woman with a dilated cardiomyopathy who had undergone an AVJ ablation and pacemaker implantation after a failed attempt at ablation of atrial flutter. She died on the 14th day after the procedure. The patient was reported to be choking and was found to be in electromechanical dissociation on the arrival of paramedics. It is presumed that the patient died of a pulmonary embolus.
As identified with separate logistic regression analyses, the 3
predictors that influenced the odds of a major complication were
patient age, the presence of structural heart disease, and the presence
of multiple ablation targets. Table 5
presents the results of multivariate logistic
regression analysis. The 2 factors found to be jointly
associated with the development of a major complication were the
presence of multiple ablation targets and the presence of structural
heart disease.
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Echocardiographic Findings
Echocardiograms were performed before and after catheter ablation
in 972 patients. Six of these patients developed clinical evidence of
tamponade during the ablation procedure that was subsequently confirmed
with echocardiography. Among the 966 patients in
whom an echocardiogram was performed solely for the purposes of this
study, there was no significant change in 805 patients, a minor change
in 139 patients (13%), and a major change in 22 patients (2%). The
type of ablation target associated with these
echocardiographic findings is shown in Table 6
. Little correlation was noted between
changes in valvular function and the specific ablation target
and approach used for ablation. For example, although an increase in
aortic insufficiency was observed in 20 patients, only 4 had undergone
ablation via the retrograde aortic approach.
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Arrhythmia Recurrence
After a successful ablation procedure, 56 (6%) of the 889
patients in whom success was achieved with the investigational ablation
system developed a recurrence: 31 patients (7.8%) who had
undergone ablation of an AP, 16 (4.6%) who had undergone ablation of
AVNRT, and 2 (1.9%) who had undergone ablation of the AVJ
(P<0.01; Table 2
). The median time to
recurrence was 35 days (range, 0 to 244 days). Figure 2
shows Kaplan-Meier curves for
recurrence based on the ablation target and also on AP
location. When separate Cox proportional hazards models were used to
assess the risk of a recurrence, 8 predictors were individually
significant (P<0.05): whether the ablation center was
pediatric or adult, patient age, the ablation target (left free wall,
right free wall, septal, or multiple APs), and 2 specific ablation
centers (Table 1
). Table 7
presents the results of the stepwise Cox proportional hazards
multivariate regression analysis. The 4 factors
found to be jointly predictive of the risk of recurrence were
the presence of a septal, posteroseptal, or right free wall
AP and the presence of multiple APs.
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Long-Term Survival
Twenty-three patients died either in the periprocedural
period or during a median follow-up of 6.3 months. Of the 23 deaths, 9
had a noncardiac cause, 8 were classified as cardiac nonarrhythmic
death, 5 were classified as sudden cardiac death (including the patient
who died on day 7), and 1 was due to a presumed pulmonary
embolus (as described above). Of the 5 sudden deaths, 4 were known to
be due to ventricular fibrillation, and the fifth was
unwitnessed. The ablation target was the AVJ in each of these
patients. One of these patients died suddenly 7 days after the
ablation procedure, another died suddenly 10 weeks after ablation, and
the remaining 3 died suddenly >5 months after ablation.
Total survival was estimated by the Kaplan-Meier method. Overall, 98%
of patients were alive at 1 year of follow-up. Significant differences
were observed in patient survival when analyzed according to
their ablation target. Patients who had undergone ablation of the AVJ
had a lower 1-year survival (86%) compared with patients who had
undergone ablation of an AP or AVNRT (99% 1-year survival,
P<0.001, Figure 3
). As
identified with separate Cox proportional hazards regressions, the 4
predictors of risk of death were patient age, the presence of
structural heart disease, the ejection fraction percentage
(analyzed as a continuous variable or dichotomized on the
basis of a cutoff of 35%), and the AVJ as the ablation target (Table 1
). The 3 factors found to be jointly predictive of the risk of
death were the ejection fraction, the presence of structural heart
disease, and the AVJ as the ablation target (Table 8
).
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| Discussion |
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Factors Affecting Ablation Success and Recurrence
Successful ablation of tissue responsible for an
arrhythmia with RF energy requires accurate mapping and
adequate tissue heating. Catheter ablation of the AVJ was associated
with the highest efficacy, followed by ablation of AVNRT and then by
ablation of APs. Among APs, greater success was achieved during
ablation of left free wall APs than ablation of multiple APs,
posteroseptal APs, and right free wall APs. These findings
can be understood if one considers the increasingly well-recognized
target-dependent differences that exist in the ease of mapping and the
effectiveness of tissue heating.23 24 25 26 27 Given the technical
expertise required to map arrhythmias accurately and to
maintain adequate catheter-tissue contact to achieve adequate tissue
heating, it is perhaps not unexpected that success was more likely at
more experienced ablation centers. It is also important to note that no
age-related differences in ablation success were observed.
The probability of arrhythmia recurrence after a successful ablation procedure was strongly influenced by the ablation target, with recurrence being more likely after ablation of right free wall, posteroseptal, and septal APs and with multiple APs. These differences in the likelihood of arrhythmia recurrence can be explained, in large part, by the target-dependent differences in the effectiveness of tissue heating noted above.23 24 25
Complications
The incidence of major complications in this study was 3%, and
the incidence of less serious complications was 8%. The most
significant major complications included 3 patient deaths, 2 stroke, 1
myocardial infarction, and 10 cases of complete heart block that
required placement of a permanent pacemaker. Of the 3 patient deaths,
only 1 occurred as an immediate result of the ablation procedure;
sudden death occurred in the other 2 patients after hospital discharge
as a result of ventricular fibrillation or a presumed
massive pulmonary embolus. The finding that heart block was at
least as common during ablation of posteroseptal and septal
APs as during ablation of AVNRT is an important reminder that ablation
anywhere along the septal aspect of the tricuspid valve may result in
heart block.28 The 2 factors that were identified as
independent predictors of a major complication were structural heart
disease and multiple ablation targets. Although the importance of
structural heart disease is not surprising, the basis for the link
between multiple ablation targets and complication cannot be readily
explained but may reflect longer procedures, greater catheter
manipulation, and physician fatigue. The results of the present
study also provide evidence that catheter ablation does not result in
significant valvular damage and that echocardiograms do not
need to be routinely performed after ablation procedures.
Survival
The 1-year survival rate after catheter ablation was 98%.
Patients who underwent ablation of the AVJ had a much lower 1-year
survival rate (86%) than patients who underwent ablation of AVNRT or
an AP (99%). The 3 factors identified as independent predictors of
increased risk of death included ablation of the AVJ, the presence of
structural heart disease, and a lower ejection fraction. The importance
of ablation of the AVJ as an independent predictor of mortality is
consistent with the findings of prior studies that have
reported on the development of sudden cardiac death after ablation of
the AVJ.20 29 30 31 It is notable that the prevalence of
sudden cardiac death after ablation of the AVJ with the use of RF
energy in the present study (5 of 121, 4%) was somewhat higher
than was originally reported with the use of DC shock energy in the
Percutaneous Cardiac Mapping and Ablation Registry (8
of 499, 1.6%).29 These findings suggest
that the development of sudden cardiac death after ablation of the AVJ
cannot be attributed solely to proarrhythmic effects of DC shock
ablation but extend also to RF ablation. A better understanding of the
specific cause of this type of complication and identification of
methods to prevent late sudden cardiac death are needed before AVJ
ablation becomes more widely performed. The findings from several
recent studies31 32 33 suggest that the early development of
malignant ventricular arrhythmias after ablation of
the AVJ are pause or bradycardia dependent. Geelen and
colleagues31 reported a 6% incidence of
ventricular fibrillation or sudden cardiac death within 1
month after RF ablation of the AVJ when pacing rates were set to 60 bpm
compared with a 0% incidence of sudden cardiac death when pacing rates
were programmed to 90 bpm for the first 1 to 3 months after the
procedure, with subsequent reductions of the pacing rate to 70 bpm.
Although pacing rates were left to the physician's discretion in the
present study and are unavailable for analysis, it is
important to note that sudden cardiac death occurred within 1 month of
the ablation procedure in only 1 of the 5 patients who died suddenly
after ablation of the AVJ in this series.
Role of Temperature Monitoring
Because patients were not randomized to either power or
temperature control, we were unable to determine whether closed-loop
temperature control per se results in improved efficacy or a lower
incidence of complications than catheter ablation with power control
alone. However, we previously reported that applications of RF energy
delivered with closed-loop temperature control are associated with a
3-fold reduction in the incidence of coagulum development compared with
those delivered with the power-control mode.23 We suspect
that this reduction in the likelihood of coagulum development would
translate to a decrease in the incidence of thromboembolic
complications.
The 95% overall success rate in the present study reflects an 85% success rate with the investigational ablation system and a need for an alternate ablation system in 10% of patients. This finding is consistent with the well-recognized clinical observation that a variety of ablation catheters are often required to achieve catheter stability and ablation success because of differences in heart size and shape and depending on the ablation target.
Comparison With Prior Reports
During the past several years, a number of studies have been
published reporting the results of catheter ablation of
supraventricular arrhythmias. The success,
frequency of arrhythmia recurrence, and incidence of
major complications reported in the present study are similar to
results from prior reports of catheter ablation in
adults.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 In contrast, the success rates reported in
the present study are higher than have previously been reported in
children and adolescents according to the pediatric ablation
registry.34 This difference may reflect the learning curve
involved with ablation procedures as well as the vast experience of the
2 pediatric centers that participated in the present study.
Clinical Implications
The results of this study may serve as a guide to clinicians
considering therapeutic options in patients who are candidates for
ablation. Because we identified factors that are predictive of outcome,
this study also identifies subgroups of patients most likely to have a
favorable result in whom it would be reasonable for clinicians to
recommend catheter ablation as first-line therapy. It is hoped that the
identification of a group of patients at increased risk of death after
catheter ablation will stimulate further investigation of the potential
mechanisms of this important complication and lead to its resolution.
The absence of a difference in the outcome of catheter ablation in
children and adults provides further evidence that ablation should be
considered an important therapeutic tool in children and
adults34 35 36 ; however, infants are an exception, because a
body weight <15 kg has been demonstrated to be associated with a
higher incidence of complications.34
| Acknowledgments |
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| Footnotes |
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| Appendix 1 |
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Received April 15, 1998; revision received September 10, 1998; accepted October 1, 1998.
| References |
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