This prospective observational study aims to compare the effects of spinal and general anesthesia on frontal QRS axis in patients undergoing elective total knee arthroplasty. Adult patients aged 18 years and older with ASA physical status I to III will be included. Participants will be grouped according to the anesthesia technique applied in routine clinical practice. Standard 12-lead electrocardiography will be obtained preoperatively and postoperatively, and frontal QRS axis values will be recorded using the automatic measurements of the ECG device. The primary objective is to evaluate the preoperative-to-postoperative change in frontal QRS axis and to compare this change between patients receiving spinal anesthesia and those receiving general anesthesia. Demographic and perioperative variables, including comorbidities, intraoperative fluid administration, blood pressure, oxygen saturation, heart rate, and tourniquet time, will also be recorded. This study is designed to provide clinical information about the potential effects of anesthesia technique on cardiac electrical activity in patients undergoing total knee arthroplasty.

This is a single-center, prospective, observational, non-interventional clinical study to be conducted in the Department of Anesthesiology and Reanimation at Elazig Fethi Sekin City Hospital. The study population consists of adult patients scheduled for elective total knee arthroplasty under either spinal anesthesia or general anesthesia in routine clinical practice. Patients will not be assigned to an intervention by protocol; instead, they will be observed according to the anesthesia technique selected during standard care.

Eligible participants will be patients aged 18 years or older with ASA physical status I to III who undergo elective total knee arthroplasty under spinal or general anesthesia. Exclusion criteria include the presence of a pacemaker, known cardiac conduction abnormalities, technically inadequate preoperative electrocardiograms, active preoperative electrolyte abnormalities, acute coronary syndrome, heart failure, and bilateral knee arthroplasty performed in the same session.

For each participant, demographic and perioperative data will be collected, including age, sex, ASA class, comorbidities, intraoperative fluid volume, arterial blood pressure, oxygen saturation, heart rate, and tourniquet duration. Standard 12-lead electrocardiography will be recorded before surgery and again in the postoperative period before mobilization. Frontal QRS axis values will be obtained from the automatic measurements reported by the ECG device.

The primary outcome measure is the preoperative-to-postoperative change in frontal QRS axis. The main analysis will compare this change between the spinal anesthesia group and the general anesthesia group. Secondary analyses will examine perioperative and demographic factors that may be associated with changes in frontal QRS axis. According to the protocol, approximately 140 to 150 patients are planned for inclusion, taking into account possible loss to follow-up or incomplete data.

Statistical analyses will be performed using IBM SPSS Statistics version 25. Descriptive statistics will be presented as mean and standard deviation, median, or percentage, as appropriate. Between-group comparisons will be performed using the independent samples t test or Mann-Whitney U test depending on data distribution. Within-group preoperative and postoperative comparisons will be assessed using the paired samples t test or Wilcoxon signed-rank test. A p value below 0.05 will be considered statistically significant.

Inclusion Criteria:

• Adults aged 18 years and older
• Patients scheduled for elective total knee arthroplasty
• ASA physical status I to III
• Patients undergoing surgery under spinal anesthesia or general anesthesia

Exclusion Criteria:

• Presence of a pacemaker
• Known cardiac conduction abnormality
• Technically inadequate preoperative electrocardiogram
• Active preoperative electrolyte abnormality
• Acute coronary syndrome
• Heart failure
• Bilateral knee arthroplasty performed in the same session

Adult patients undergoing elective total knee arthroplasty at a single center and managed with either spinal anesthesia or general anesthesia in routine clinical practice.

Individual participant data will not be shared because no formal data-sharing plan has been established for this single-center observational study.