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| Journal of the New Zealand Medical Association,
23-September-2011, Vol 124 No 1343
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Prediction of cardiac rhythm 1 year following
cardioversion for atrial fibrillation
Amjad K Hamid, A Mark Richards, Ian G Crozier, John G
Lainchbury, Iain Melton, Paul G Bridgman, Suetonia C Palmer, Chris M Frampton, M
Gary Nicholls
Atrial fibrillation (AF) affects 0.4-1% of the general
population. Prevalence increases with age to 8% in those over 80
years.1–3 AF is associated with increased
risk of stroke, heart failure and all-cause mortality. The significant costs of
management are driven largely by
hospitalisation.1,4 Treatment consists of
either ventricular rate control combined with anticoagulation, or attempts at
restoring sinus rhythm (SR).
Robust randomised controlled trials suggest rate control is
not inferior to attempted rhythm control regarding survival and morbidity, and
is appropriate for many patients with recurrent or persistent
AF.1,5,6 Similar findings were observed in
patients with congestive heart failure.7
Accurate case selection for cardioversion (CV) is required to offer the best
chance of sustained SR.
Whilst CV for AF has been used for over 40 years, follow-up
periods have often been brief with reported rates of sustained SR of 44 to 69%
at 4 weeks and 23 to 79% at 1 year.8-14 Factors
predicting atrial fibrillation recurrence include duration of
arrhythmia,9,10,13,14,16-19 type of arrhythmia
(AF or flutter),14 echocardiographic
indices,9,10,18,20
age,1,13,14,17
gender,1,12 underlying cardiac
disease,5,11,12,17 frequency of paroxysmal AF
and previous CV attempts,1,16,17 the use of
rate-controlling or anti-arrhythmic
drugs,11,17,18 functional status (NYHA
Class),13,14,19 hypertension or pulmonary
disease,5,11,12 the initial energy used to
achieve CV21 and restoration of SR with drug
therapy.9
We report findings from a large consecutive cohort of
patients with AF/flutter presenting over a 2-year period regarding maintenance
of SR over 1 year, predictors of rhythm outcomes, and mortality and
cardiovascular morbidity.
MethodsThe study, approved by the Regional Ethics Committee,
was carried out in Burwood and Christchurch Hospitals which serve a population
of 481,431 (2001 population census). All patients with AF/flutter undergoing CV
between December 2000 and December 2002 were included. Patients were categorised
into those who underwent immediate CV within 72 hours from AF/flutter onset (IC)
and elective CV after receiving warfarin for at least 4 weeks with an INR at 2
to 4 for 2 weeks prior to CV (EC).
A transoesophageal echocardiogram was first performed
on patients with AF duration of more than 48 hours, IC group, or they had not
been on Warfarin long enough; EC group. Warfarin was continued for at least 6
weeks post CV. Demographics, known duration of arrhythmia, presenting symptoms,
comorbid conditions, medications and the number of DC shocks and Joules
delivered were recorded.
In preparation for CV, all patients had a 12 lead
electrocardiograph (ECG), routine blood tests and echocardiography according to
American Society of Echocardiography
Guidelines22. Using a monophasic defibrillator,
CV was performed following the intravenous administration of propofol and
remifentanil or midazolam with the defibrillator paddles placed on the chest in
the anterior and posterior positions. The standard energy selection was 200
Joules for the first shock followed, if required, by 2 shocks each at 360
Joules. CV was considered successful if the patient maintained SR for more than
20 minutes. Cardiac rhythm and medical status were recorded at 6 weeks and 1
year following CV.
Apart from 38 patients, all CV in the EC group were
performed by one of the authors (AH). The primary end point of the study was
cardiac rhythm at 6 weeks and 1 year. Secondary outcomes included total and
cardiovascular mortality and cardiovascular morbidity as determined from the
hospital electronic Patient Management System records.
Statistics—Data are shown as
mean (± SD or SEM), median (interquartile range) when non-parametric, or
frequency (%). Comparisons of categorical and continuous variables between the
IC and EC groups were conducted using Chi-square and independent
t-tests or Mann-Whitney U tests respectively. Univariable regression
analysis was used to determine predictors of SR at 6 weeks and 1 year after
cardioversion. Within the EC group only, in view of adequate sample size for
robust results, the independent predictive power of atrial flutter,
hypertension, medications, requirement for >1 shock, duration of AF/atrial
flutter and LA diameter>40 mm to predict SR at 6 weeks and 1 year after EC
was tested using multivariable logistic regression. P<0.05 indicated
statistical significance. Analyses were conducted using SPSS version 13.
ResultsOver 2 years, 53 patients underwent IC and 508 patients EC.
One IC patient and 12 in the EC group were lost to follow up leaving 52 and 496
respectively. Patients in the IC group underwent CV while receiving low
molecular weight heparin. None of the IC group had undergone prior CV. Seventy
EC patients (15%) had one and 17 (4%) had two or more previous cardioversions.
Patient characteristics are shown in Table 1. Males
presented with AF/atrial flutter at a younger age than females (statistically
significant within EC group, P<0.001).
Table 1. Clinical, treatment &
echocardiography data (mean ± SEM, median [interquartile range] or number
[%])
P<0.001, † P<0.01,
‡ P<0.05 for comparisons among groups using
independent t-test, Mann-Whitney U tests and Chi-square tests as appropriate.
All percentages are given to the nearest whole percent.
Initial success rates were similar in both groups regardless
of the presenting rhythm. In the EC group, 86.3% were successfully cardioverted
(87.4% in AF and 86.1% in atrial flutter). In the IC group 94.2% were
cardioverted (94.4% in AF and 93.8% in atrial flutter patients). A significantly
higher percentage of IC patients were in SR at both 6 weeks and 1 year than in
the EC group (65.4% versus 43.3 % and 57.7% versus 30% respectively—Figure
1).
Table 2 illustrates the significant
predictors of SR maintenance at 6 weeks and 1 year. Combining known duration of
AF/flutter with the requirement for >1 shock to achieve SR provided a graded
prediction regarding outcome at 6 weeks and 1 year (Figure 2) which was superior
to the prediction using either factor alone. Neither previous CV nor CHADS2
score predicted rhythm outcome at 6 weeks or 1 year on either univariable or
multivariable analysis.
Figure 1. The percentage of patients in SR at 6
weeks and 1 year according to the number of shocks required to achieve SR in
both Immediate and Elective Cardioversion groups combined, n=477
 Morbidity and mortality—At 1 year,
there was no difference in mortality between groups (IC one death; 1.9%, EC 11
patients; 2.2%) or new-onset heart failure (2 patients; 3.8% compared with 14
patients; 2.8%). Combined cardiovascular events including fatal and non-fatal
acute coronary syndromes, stroke (1 patient in the IC; 1.9%, 7 patients in the
EC; 1.4%), hospitalisation due to recurrence of AF/flutter and heart failure
affected a higher percentage of patients in the IC group (24.7%) than in the EC
group (14.8%; P=0.025).
Figure 2. Maintenance of SR at 6 weeks and 1
year according to a combination of known duration of AF/atrial flutter and
number of shocks required for successful cardioversion
DiscussionOnly 43.3% and 30% of the EC group remained in SR at 6 weeks
and 1 year respectively. The success rate was significantly higher in the IC
cohort (65.4% and 57.7% respectively). We have documented, for the first time,
that initial resistance to electrical CV, reflected in the number of shocks
required to restore SR, is one indicator of the likelihood of reverting to AF.
Along with
others,9,13,14,16,18-20 we identified
arrhythmia duration as an independent predictor of rhythm outcome. With
long-established AF/flutter, electrical remodelling becomes established
rendering the atria resistant to resynchronisation and vulnerable to early
return of AF or flutter. Our results, along with earlier
reports,9,10,13,14,16-20 suggest that every
effort should be made to ensure patients are referred early for CV.
The ability of echocardiographic indices to predict outcome
following CV is controversial. In our patients, as reported
elsewhere,9,20 left atrial dilatation was
predictive of return to AF/flutter – but on univariate analysis
only.
Higher rates of sustained SR in IC compared with EC patients
presumably reflect younger age, a higher proportion in atrial flutter, shorter
duration of arrhythmia, less prior cardiovascular disease and more frequently
normal cardiac structure.
The role of amiodarone in preventing atrial fibrillation
post cardiac surgery and post CV is well
established.23-26 Accordingly, we noted
pre-treatment with amiodarone appeared protective against recurrence of
AF/atrial flutter. IC and EC patients on beta-blockers were more likely to
remain in SR, although statistically not significant, similar to earlier
findings suggesting that at least some beta-blockers improve rates of sustained
SR after CV25-27 and for patients with heart
failure beta-blockers reduce the incidence of new AF
onset.28
Despite evidence that the renin-angiotensin system promotes
arrhythmogenesis15 whereas blockade of the
system (with ACE inhibitors or angiotensin II receptor blockers) can be
inhibitory, we found ACE inhibitors had no impact on post CV outcome. Those on
ACE inhibitors, however, were more likely to have impaired cardiac function.
Accordingly, it is likely that any protective effect of ACE inhibitors against
return of AF was masked by the underlying cardiac disorders for which they were
prescribed. Similarly in our group of patients, being on statins did not seem to
influence SR maintenance.
Hypertensive cardiovascular disease is the most common
antecedent of AF29,30. Accordingly, one might
have anticipated hypertension to be a negative, rather than positive predictor
of outcome. However, hypertension did not predict outcome at 1 year, and did not
retain independent predictive power on multivariate analysis. Similar to earlier
findings,14 the presence of atrial flutter
rather than AF was a positive predictor of sustained SR.
Limitations—The effect of medications
on cardiac rhythm cannot be ascertained with confidence from our data. Beyond
the factors we have evaluated, a variety of medications and chromosomal variants
may have played a role in determining success or failure in maintaining SR.
A monophasic defibrillator was utilised in all patients
undergoing cardioversion in this study. Current guidelines and recent robust
papers recommend the use of biphasic shocks and the extrapolation of our
findings to biphasic defibrillators may not be appropriate.
In summary, in a large consecutive cohort from a single
referral centre, 57.7% of patients requiring immediate cardioversion for
AF/atrial flutter remained in SR after CV at 1 year whereas the figure was only
30% in patients undergoing elective cardioversion. The number of shocks required
to achieve SR, and the known duration of AF/atrial flutter are independent
additive predictors of rhythm at 6 weeks and 1 year after elective CV.
Competing interests: None.
Author information: Amjad K Hamid, SMO, PhD
Student*; A Mark Richards, Professor*; Ian G Crozier, Cardiologist†; John
G Lainchbury, Cardiologist†; Iain Melton, Cardiologist†; Paul G
Bridgman, Cardiologist†; Suetonia C Palmer, Nephrologist*; Chris M
Frampton, Biostatistician*; M Gary Nicholls, Professor*
*Department of Medicine, Otago University –
Christchurch
†Department of Cardiology, Christchurch Hospital,
Christchurch
Acknowledgement: This research was funded
by a grant from the National Heart Foundation of New Zealand.
Correspondence: Amjad K Hamid, Cardiology
Department, Christchurch Hospital, Private Bag 4710, Riccarton Avenue,
Christchurch, New Zealand. Fax: +64 (0)3 3648303; email: amjadh@cdhb.govt.nz
References:
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