Influence of Thoracic Paravertebral Block on Atrioventricular Conduction

Inclusion Criteria: * woman above 18 years of age, legally able of giving informed consent * participants previously qualified for elective breast surgery due to neoplasm, with or without axillary node dissection * physical status corresponding to class I or II in American Society of Anaesthesiologist classification Exclusion Criteria: * lack of consent to participation or to regional anaesthesia for planned surgery * bilateral operation planned * symptomatic circulatory disease at the time of qualification, artificial heart pacemaker presence, positive history of arrythmia * allergy to amide local anaesthetics * severe deformation of thoracic spine * use of medications with "known" or "possible" potential of QT prolongation, according to Arizona Center for Education and Research on Therapeutics \[AZCERT\] Inc. list, in 5 days preceding the intervention * use of beta-adrenolytic medications in 5 days preceding the intervention All exclusion criteria except the last one are based on the original study protocol (NCT05822076).