Overactive bladder (OAB) is a complex of symptoms such as urgency, frequency, nocturia and urgency incontinence which can significantly affect the quality of life. The overall prevalence of OAB syndrome in women is reported at about 16.9% and it incomparably increases with age. Ageing also affects the cardiovascular system and leads to heart disorders and arrhythmia, i.e. supraventricular premature beats are observed in 5–10% of all individuals older than 60 years, while atrial fibrillation can affect 6% of those > 65 years.Therefore, prescribing pharmacotherapy for OAB treatment should include the potential influence on the cardiovascular system.
Intradetrusor injections of onabotulinumtoxinA are considered to be highly effective in the treatment of OAB. Unfortunately, systemic side effects, including cardiac function, following the injection are not sufficient investigated. 
The aim of the study was to evaluate the influence of intravesical onabotulinumtoxinaA on cardiac function in patients with cardiac arrhythmia. This was based on changes in heart rate and QTc interval on electrocardiograms.

This is a prospective, case-controlled, single centre study. The study protocol was approved by our local institutional ethical committee. Before inclusion into the study, all patients, who were women of European descent, gave written informed consent. From June 2016 to October 2017, seventy-one patients with idiopathic OAB were approached to participate in this study. Patients were divided into two age-matched sub-groups: with diagnosis of cardiac arrhythmia (extra beats, supraventricular tachycardia, ventricular arrhythmia) and without cardiac arrhythmia. 
Patient with cardiac arrhythmia were on stable doses of antiarrhythmic drugs.
In the final analysis were included data collected from sixty-two OAB female patients - 31 women with cardiac arrhythmia and 31 age-matched participants without cardiac arrhythmia who were enrolled into the control group to enable additional comparisons.
During the study, 12-lead electrocardiograms were performed according to the schedule: 2 hours before onabotulinumtoxinA injection procedure, 1 hour after treatment (or later if a patient reported the feeling of an unpleasant sensation in their bladder) and 2 weeks after the day of treatment.
The following parameters were measured: heart rate; PR, PQ, QT, QTc intervals and QRS duration.
Prolonged PQ and QTc intervals were determined as ≥200 ms and ≥460 ms, respectively. 
After 6 weeks, the patients were asked during a phone-call survey about any abnormalities.
OnabotulinumtoxinA injections were performed with rigid cystoscopy under local anaesthesia. 
Sixty-two age-matched patients completed the study, including the follow-up visit conducted by phone-call at week 6.
Statistical analysis was performed with Statistica Statsoft, version 12 package, using the χ2 test, ANOVA with post-hoc tests and the Student t test, as appropriate. A p value<0.05 was defined as statistically significant.

Baseline demographic characteristics were similar between groups and are summarized in Table 1.
A slight increase of the mean heart rate (from 71 bpm to 74.7 bpm, p<0.05) was observed in the control group when baseline and post-procedure ECG measurements were compared. This alteration, however, is unlikely to be relevant from the clinical point of view.
None of the patients in either study sub-group developed tachycardia or prolonged QTc interval. In 4 patients (2 in each subgroup), prolonged PQ interval was observed, however, this alteration was present before intravesical onabotulinumtoxinA administration. The only statistically findings was a slight increase in HR in the control group when comparing ECG performed 1 hour after injections and at week 2 follow-up visit (Figure 1). However, these results still remained within the normal range. We did not observe any significant differences in analyzed ECG intervals or QRS complex within each subgroup at subsequent measurements, as well as when cardiac arrhythmia and control group were compared.
During the phone-call survey at week 6, none of the patients reported any subjective disturbances in heart rate or other cardiologic complaints.

It has been already proposed that intravesical onabotulinumtoxinA injection might be an attractive, alternative option for elderly OAB patients because of the lack of many adverse events associated with oral antimuscarinics therapy. In our study we did not observe any clinically, significant changes in analysed ECG measurements. The only one finding was an increase the mean heart rate observed between pre- and post-injections ECGs, however HR was still within normal range. We can speculate that this issue could be incidental or associated with some psychological factors

This observational study provides reassurance that intravesical onabotulinumtoxinA injections are safe for patients with cardiac arrhythmia and do not trigger any changes in heart rate or electrocardiographic abnormalities.