Background <p>Acute myocardial infarction (AMI) remains a significant cause of morbidity and mortality despite advancements in percutaneous coronary intervention (PCI). This study investigates whether 24-hour QT interval variability (QTV) and heart rate variability (HRV) can predict major adverse cardiovascular events (MACE) post-PCI.</p> Methods <p>We conducted a retrospective case-control study involving 238 AMI patients undergoing PCI between June 2021 and January 2023. Patients were divided into MACE (<i>n</i> = 96) and non-MACE (<i>n</i> = 142) groups. Variability in QT interval and HRV was assessed via continuous ECG monitoring pre- and post-PCI using a Holter recorder with a sampling rate of 1000&#xa0;Hz. QT variability index (QTVI) and other QT measures were evaluated for their predictive power regarding MACE occurrence. All QT interval measurements were corrected using the Fridericia formula (QTcF).</p> Results <p>Analysis revealed that the corrected QT interval (QTcF) was significantly prolonged in the MACE group compared with the non-MACE group (425.34 ± 42.15 ms vs. 410.28 ± 33.47 ms, <i>P</i> = 0.004). Additionally, the standard deviation of QT intervals (QT-SD) was significantly greater in the MACE group (7.80 ± 1.07 ms vs. 7.54 ± 0.33 ms, <i>P</i> = 0.023).The QTVI was higher in the MACE group (-0.60 ± 0.11 vs. -0.65 ± 0.21, <i>P</i> = 0.007), as was the normalized QT variance (QTVN, calculated as QTv/QTm²)(0.38 ± 0.07 vs. 0.36 ± 0.04, <i>P</i> = 0.010). There was a significant correlation between hypertension and MACE occurrence (<i>P</i> = 0.006), and elevated pulmonary artery systolic pressure was more prominent in the MACE group (25.66 ± 3.14 mmHg vs. 23.77 ± 6.58 mmHg, <i>P</i> = 0.003). ROC analysis showed that combining QTVI with clinical variables achieved an AUC of 0.78 (95% CI: 0.72–0.84).</p> Conclusion <p>QTV is a significant predictor of MACE post-PCI in AMI patients, underscoring its potential utility in post-procedural monitoring and risk stratification.</p>