From the Guidelines

A recent electrocardiogram (EKG) for anesthesia preoperative (preop) evaluation is generally considered to be within 30 days of surgery.

The optimal time interval between obtaining a 12-lead ECG and elective surgery is unknown, but general consensus suggests that an ECG within 30 days of surgery is adequate for those with stable disease 1.
A preoperative 12-lead ECG is likely to be more valuable for patients planned for elevated-risk surgical procedures, particularly for patients with known coronary heart disease, arrhythmias, peripheral arterial disease, cerebrovascular disease, or other significant structural heart disease 1.
The prognostic significance of numerous electrocardiographic abnormalities has been identified in observational studies, including arrhythmias, pathological Q-waves, LV hypertrophy, ST depressions, QTc interval prolongation, and bundle-branch blocks 1.
Routine preoperative resting 12-lead ECG is not useful for asymptomatic patients undergoing low-risk surgical procedures 1.

Preoperative resting 12-lead ECG is reasonable for patients with known coronary heart disease or other significant structural heart disease, except for low-risk surgery 1.
Preoperative resting 12-lead ECG may be considered for asymptomatic patients, except for low-risk surgery 1.

From the Research

There is no specific definition of a "recent" EKG for anesthesia preoperative evaluation. However, the following points can be considered:

The American Society of Anesthesiologists (ASA) does not provide a specific timeframe for a recent EKG 2.
The decision to obtain a preoperative EKG is typically based on the patient's medical history, physical examination, and the type of surgery being performed 3, 4, 5, 6.
Some studies suggest that a preoperative EKG may be useful in patients with certain risk factors, such as cardiovascular disease, diabetes, or kidney disease 5, 6.
The usefulness of a preoperative EKG in predicting postoperative cardiac complications is debated, with some studies suggesting that it may not be a reliable predictor 3, 4, 6.

The following factors may influence the decision to obtain a preoperative EKG:

Patient's medical history, including cardiovascular disease, diabetes, or kidney disease 5, 6
Physical examination findings, such as hypertension or heart murmurs 5
Type of surgery being performed, with high-risk surgeries potentially requiring a preoperative EKG 3, 6
Patient's age, with older patients potentially requiring a preoperative EKG 5, 6
ASA physical status classification, with patients classified as ASA III-V potentially requiring a preoperative EKG 5

Preoperative EKG abnormalities are common, but their predictive value for postoperative cardiac complications is debated:

Some studies suggest that certain EKG abnormalities, such as bundle branch blocks, may be associated with an increased risk of postoperative cardiac complications 6
Other studies suggest that preoperative EKG abnormalities are not reliable predictors of postoperative cardiac complications 3, 4