Atrial fibrillation (AF) poses a significant challenge to patients, physicians and healthcare systems globally. AF is the most prevalent arrhythmia in clinical practice, with an estimated global prevalence of 46.3 million (Choi and Kwon, 2022). It is more common in males than females, with ageing, ethnicity and genetics all factors affecting likelihood of AF (Hindricks et al, 2021). AF progression is associated with a decline in quality of life, which in time becomes irreversible and less amenable to treatment, consequently leading to a requirement for further interventions including pacemakers, costly heart failure treatment and a significant burden on the healthcare system.
Cardioversion is a rhythm control therapy that is recommended in symptomatic patients with persistent AF (Hindricks et al, 2021) to improve symptoms and quality of life (QoL). Indications for elective cardioversion are symptom management of AF, improving heart failure symptoms (tachycardia-mediated cardiomyopathy) and an intervention for failed pharmacological cardioversion. Boodhoo et al (2004) suggested that direct current cardioversion is the most effective method for restoring sinus rhythm in patients with persistent AF. It has been reported that cardioversion successfully terminates AF in 90% of cases (Brandes et al, 2020).
Synchronised direct current cardioversion involves the patient being fasted and the use of a short-acting anaesthetic agent for sedation. An electric current - electric shock - is delivered from a biphasic defibrillator via pads attached to the patient (Piccini and Fauchier, 2016).
Aims
The aim of this evaluation was to review patient demographics and retrospectively evaluate the success of cardioversion at specified time frames. It included a subset analysis on cardioversion patients who had a background of heart failure and obesity to assess whether cardioversion was successful in this population.
Data collection
Ethical approval for data collection was obtained from the local trust. Inclusion criteria for data analysis were all patients who had been referred for elective cardioversion via a formal referral process. The exclusion criteria were patients who were in sinus rhythm before cardioversion or patients who had a medical reason that made them unsuitable for cardioversion. In total 194 patients met the inclusion criteria.
The specified time frames to evaluate the success of cardioversion were:
- Initial success on day of cardioversion
- Patient remained in sinus rhythm at 8-week follow-up and
- Long-term review of outcome of patients' records at 6 months for all patients (classed as end of follow-up).
The long-term outcome of successful cardioversion was defined as no evidence of return to AF on review of electronic clinical notes or through hospital admissions or correspondence. Data were collected from July 2020 until December 2021, and analysed using Microsoft Excel.
Analysis and discussion – overall
Table 1 shows the characteristics of the patients included in the overall analysis. The evaluation here found a predominantly male population (64.4%), the average age was 65 years, average weight was 92 kg, and average BMI was 30.56.
Table 1. Demographics of cardioversion patients (n=194)
| Gender | Male n=125 | Female n=69 |
| Parameter | Range | Mean |
|---|---|---|
| Age (years) | 32–87 | 68.5 |
| Weight (kg) | 46–151 | 92 |
| BMI | 30.56 |
Rochlani et al (2016) suggested that the predominant age range for patients undergoing elective cardioversion would be 40–64 years old and patients would be predominantly male. Norton et al (2016) discussed the biographical demographics of a cardioversion service: they found that the mean age of patients was 65 years, mean BMI was 28.95 and the majority of patient were male. This would suggest that the cardioversion population is very similar in demographic detail to the previous studies mentioned, although the age range may point towards an older population in the area.
The initial success rate of cardioversions (Table 2) was high (94%), with a decline in success (63%) at 8-week follow up. Long-term success rates for the remaining population (n=115) remained positive (73%), with cardioversion unsuccessful in one-quarter of patients (25%). The data would suggest that following the initial high success rate of cardioversions there is a significant drop-off in success in one-third of patients in the 8 weeks following cardioversion. In the remaining population (n=115), there was a further drop in success rate but only by one-quarter of the remaining population. Of the 194 patients who had cardioversion, 84 remained in sinus rhythm at 6 months, indicating a 43% chance of cardioversion success in the long term (Figure 1). Complication rates of the cardioversions were low, with bradycardia being the main complication at 27% out of the 194 participants, which was likely related to medications.
Table 2. Success rates of cardioversion: overall
| Initial success rates (n=194) | |||
|---|---|---|---|
| Successful | Unsuccessful | ||
| 183 (94.3%) | 11 (5.7%) | ||
| Success rate after 8-week follow-up (n=183)* | |||
| Successful | Unsuccessful | No follow up | Deceased |
| 115 (62.8%) | 57 (31.1%) | 10 | 1 |
| Long-term follow-up success rates (n=115)† | |||
| Successful | Unsuccessful | No follow up | Deceased |
| 84 (73.0%) | 29 (25.2%) | 0 | 2 |
Defined as no evidence of return to AF on review of electronic clinical notes, or through hospital admissions, or correspondence at 6-month end point
Note: The 3 deceased patients involved in this study did not die as a result of cardioversion
For comparison, Toso et al's (2017) study, with more than 1000 participants, found a 99% initial success rate of cardioversion (99%) with a drop-off in success to 55% at 1-year follow-up and then an overall success rate at the end of follow-up of 45%.
Atrial fibrillation and obesity
This section of the service evaluation will concentrate on obese patients who underwent cardioversion, to determine success rates on patients with a BMI of 30 or more – using the National Institute for Health and Care Excellence (2023) definition of obesity.
Data were collected retrospectively from the hospital electronic record system. The inclusion criteria were patients who had been referred for cardioversion with BMI ≥30, aged over 18 years; both male and female patients were included. The position of defibrillator pads for this set of patients was anterior and posterior.
A total of 101 patients were identified from the available resources with an average weight of 101 kg, lowest BMI 30, highest BMI 67; 59 patients were male and 42 were female.
Background
Obesity is a risk factor for the development of new-onset AF (Grönberg et al, 2015) and has been described as a major modifiable risk factor for cardiovascular diseases with a dramatic increase in AF coinciding with a rise in obesity (Vyas and Lambiase, 2019). The relationship between AF and obesity has been debated. Fenger-Grøn et al (2019) concluded that high BMI independently presents an increased risk of AF regardless of gender. Tsang et al (2008) found that obesity was associated with AF independent of age, diabetes, hypertension and gender. The pathophysiology of AF in obese patients is thought to include hypertension-induced diastolic dysfunction, sleep apnoea/obesity hypoventilation syndrome, haemodynamic changes that alter cardiac structure, epicardial fat, adipose tissue distribution, and anti-inflammatory reactions, which can diffuse directly into the myocardium and can cause fibrosis (Vyas and Lambiase, 2019). Voskoboinik et al (2019) summarised that obesity is associated with higher electrical cardioversion failure in persistent AF due to transthoracic impedance (TTI), but it was mentioned that anterior/posterior pad placement was more successful in populations with obesity. Lacoste et al (2023) advised that patients with a BMI of 50 or more have lower success than patients with a BMI of over 30 (but below 50). Lip et al (2019) advised that success rates for cardioversion are lower in patients with a BMI of over 30 in comparison with a BMI of under 30. Cichoń et al (2021) researched the success of cardioversion patients with BMI of over 30, reporting that initial success was high (92%) and that after 1-month follow-up success rates had dropped (38%).
Data review and discussion
The initial success rate in this group of patients was high (97%) with only a small number of procedures unsuccessful on the day (3%) (Table 3). Success of cardioversion at 8-week follow-up then dropped (60.2%) with an increase in failure to maintain sinus rhythm (34.6%). The long-term outcomes from the records demonstrated that of the remaining patients (n=59) there was only a small reduction in failure to remain in sinus rhythm.
Table 3. Success rates of cardioversion: obesity
| Initial success rates (n=101) | |||
|---|---|---|---|
| Successful | Unsuccessful | ||
| 98 (97%) | 3 (3%) | ||
| Success rate after 8-week follow-up (n=98)* | |||
| Successful | Unsuccessful | No follow up | Deceased |
| 59 (60.2%) | 33 (34.6%) | 5 (5.1%) | 1 (1%) |
| Long-term follow-up success rates (n=59)† | |||
| Successful | Unsuccessful | No follow up | Deceased |
| 41 (69.4%) | 17 (28.8%) | 1 | 0 |
Defined as no evidence of return to AF on review of electronic clinical notes, or through hospital admissions, or correspondence at 6-month end point
In comparison with previous studies on success rates (Cichoń et al, 2021), there is a correlation with initial high success rates The trend at 8-week follow-up of the remaining patients does show a drop in success rates, but not as steep as that documented by Cichoń et al (2021) at 1-month follow-up. The long-term follow-up results show that a significant proportion (69.4%) of the remaining patients remained in sinus rhythm.
There is an indication from the data that there was a significant success rate (69.4%) in the obesity population under review. However, out of the total group of patients with a BMI of over 30 who underwent cardioversion, the long term success rate was calculated at 40.6% (Figure 2).
Atrial fibrillation and heart failure
This section of the service review assessed whether patients who had cardioversion for AF-related heart failure, defined as heart failure with reduced ejection fraction (HFrEF), had an improvement in heart function following cardioversion at post-cardioversion echocardiogram follow-up. Heart failure is classified according to the European Society of Cardiology/Heart Failure Association of European Society of Cardiology guidelines (McDonagh et al, 2022) (Table 4).
Table 4. Different types of heart failure
| Classification | Ejection fraction* (%) | |
|---|---|---|
| Heart failure with reduced ejection fraction (HFrEF) | ≤40 | Also referred to as systolic HF |
| Heart failure with preserved ejection fraction (HFpEF) | ≥50 | Diastolic HF |
| Heart failure with mildly reduced ejection fraction (HFmrEF) | 41–49 | Treatment patterns and outcomes similar to HFpEF |
| Heart failure with improved ejection fraction | >40 | In patients who previously had HFrEF |
The patients' records were assessed for 6 months post cardioversion for evidence of an echocardiogram being performed to assess heart function. All patients who attended for elective cardioversion were taking heart failure, rhythm and/or rate-controlling medications. Graby et al (2019) stressed the importance of rhythm-controlling strategies to return patients to sinus rhythm in HFrEF to improve heart function and heart failure symptoms. Cardioversion in heart failure patients can be used as a strategy to confirm whether tachycardia-induced cardiomyopathy (which includes AF-related heart failure) is the primary cause, which would guide future strategies including ablation and pacemaker insertion.
Patients were included in the data review if they had been electively referred for cardioversion and had a pre-cardioversion echocardiogram identifying HFrEF. Patients were excluded if they had a did not have a diagnosis of HFrEF or no follow up echocardiogram available on the hospital system. A total of 38 patients were identified with HFrEF.
Analysis and discussion
The initial success rate of cardioversion was high (Table 5) but the improvement from HFrEF to a left ventricular ejection fraction of more than 40% was seen only in just over half of the cohort of patients.
Table 5. Success rates of cardioversion: heart failure
| Initial success rates (n=38) | ||
|---|---|---|
| Successful | Unsuccessful | |
| 36 (94.7%) | 2 (5.3%) | |
| Result on follow-up echocardiogram (n=36) | ||
| HFrEF | HF with improved EF | No echocardiogram |
| 19 (52.7%) | 14 (38.8%) | 3 (8.3%) |
Graby et al (2019) retrospectively analysed 103 AF patients with significant left ventricular systolic dysfunction, classified as moderate (EF 35-45%) or severe (EF <35%) who underwent elective cardioversion. They found that 90% of patients had an improvement in ejection fraction. Zimmermann et al (2015) enrolled patients with a background of tachycardia-induced cardiomyopathy to evaluate left heart changes following electrical cardioversion. They found that there was a significant increase in ejection fraction on follow-up and thereafter, summarising that cardioversion will result in an increase in left ventricular function due to widening of diastolic filling time, recovery of atrial filling time and decreased heart rate.
It is debatable whether cardioversion can be considered a success based only on the numbers of patients who responded to the cardioversion and had an improvement in their ejection fraction. Ideally, heart failure symptoms should be assessed using the New York Heart Association functional classification for heart failure to see if this can be considered an intervention that resolves heart failure symptoms, as well as heart function on echocardiogram. Of the group of heart failure patients who underwent cardioversion, there was a 53% success rate at end-point follow-up.
Limitations with the data
There were restrictions with the data, such as only being able to analyse the electronic hospital data to establish whether there had been any entries confirming a return to AF. If there were no entries, it was presumed patients remained in sinus rhythm.
The low numbers of patients involved – 101 patients in the obesity subgroup, 38 patients in the heart failure subgroup – should be taken into account when considering whether generalisations can be made from the results.
Conclusion
AF represents a significant treatment challenge for health professionals, with limited treatment options, and is becoming more prevalent. Cardioversion has a role to play when AF becomes less amenable to pharmacological treatment. Although initially the success rate of cardioversion in this evaluation was high there was a decline in success within a short period, followed by a more sustained success long term at the 6-month end point. Comparison with another study by Toso et al (2017) showed a slight reduction in success rates; there is a prediction from the data that there is around a 41% chance of cardioversion success in the long term (based on the available data records) – this is slightly lower than the success rates of Toso et al (2017) at 45%, although that was a study with more participants, which may have enhanced the results.
The group of patients with AF and obesity followed a similar pattern to the larger group initially, but based on the literature it could be said that the actual pathophysiology of obese patients with AF appears to be a barrier to long-term success of cardioversion. The data gathered for this evaluation suggest that there was only a 41% success rate of patients remaining in sinus rhythm over the long term, compared with 43% in the wider group. It could be suggested that treating the underlying cause of AF (ie obesity) would be a more appropriate treatment.
Patients with AF and heart failure again showed high initial success rates of cardioversion, then a reduction to just above half experiencing long-term success, measured by heart function improving on follow-up echocardiogram. There is a future option to review patients in the different heart failure categories to question their symptoms to see whether there was a true response to cardioversion, rather than relying only on imaging, by assessing symptoms using the New York Heart Association heart failure classification. There was only a small number of patients for this category to enable a clear view on success or failure to improve symptoms following cardioversion, and a more qualitative approach should be sought in the future.
KEY POINTS
- Atrial fibrillation (AF) is becoming more prevalent and will require a more patient-focused approach to achieve outcomes
- Cardioversion is a safe intervention in AF alongside the appropriate medications with a low complication rate. It has been shown to be a successful rhythm control strategy and should be considered to achieve short- and long-term goals (symptom management and an initial strategy in the management of AF)
- The demographic data from this study seem to be comparable with other studies, suggesting common themes among AF patients
- In the category of patients with obesity, there was less than 50% success rate over the long term (6 months). The literature suggests that there is a pathophysiological cause of AF in these patients, and more effort should be made to understand the underlying cause of AF to guide management
CPD reflective questions
- Reflect on current medical management of atrial fibrillation (AF) and the role of cardioversion. What do you think are the key approaches to ensuring high success rates for cardioversion?
- Do you feel that cardioversion in heart failure patients should be considered, bearing in mind the success rates from this service evaluation?
- How would you offer patients more tailored treatment, involving weight management goals to improve AF symptoms?