Several medicines, including cancer therapies, are known to alter the electrophysiological function of ventricular myocytes resulting in abnormal prolongation and dispersion of ventricular repolarization (quantified by multi-lead QTc measurement). This effect could be amplified by other concomitant factors (e.g., combination with other drugs affecting the QT, and/or electrolyte abnormalities, such as especially hypokalemia, hypomagnesaemia, and hypocalcemia). Usually, this condition results in higher risk of torsade de point and other life-threatening arrhythmias, related to unrecognized unpaired cardiac ventricular repolarization reserve (VRR). Being VRR a dynamic phenomenon, QT prolongation might often not be identified during the 10-s standard 12-lead ECG recording at rest, leaving the patient at increased risk for life-threatening event. We report the case of a 49-year woman, undergoing tamoxifen therapy for breast cancer, which alteration of ventricular repolarization reserve, persisting also after correction of concomitant recurrent hypokalemia, was evidenced only after manual measurements of the corrected QT (QTc) interval from selected intervals of the 12-lead ECG Holter monitoring. This otherwise missed finding was fundamental to drive the discontinuation of tamoxifen, shifting to another “safer” therapeutic option, and to avoid the use of potentially arrhythmogenic antibiotics when treating a bilateral pneumonia in recent COVID-19.

已知包括癌症疗法在内的几种药物会改变心室肌细胞的电生理功能，导致心室复极异常延长和离散（通过多导联 QTc 测量量化）。这种作用可能会被其他伴随因素放大（例如，与其他影响 QT 的药物和/或电解质异常，例如特别是低钾血症、低镁血症和低钙血症）的组合。通常，这种情况会导致发生点扭转和其他危及生命的心律失常的风险更高，这些心律失常与未识别的未配对心室复极储备 (VRR) 相关。由于 VRR 是一种动态现象，在 10 秒的标准 12 导联心电图记录期间通常无法识别出 QT 延长，从而使患者面临危及生命的事件的风险增加。我们报告了一名 49 岁女性的病例，她接受他莫昔芬治疗乳腺癌，其心室复极储备的改变，在纠正伴随的复发性低钾血症后也持续存在，只有在手动测量选定的校正 QT (QTc) 间期后才能证实。 12 导联心电图动态监测的间隔。这一否则被遗漏的发现对于推动他莫昔芬停药、转向另一种“更安全”的治疗选择以及在最近的 COVID-19 中治疗双侧肺炎时避免使用潜在的致心律失常抗生素至关重要。仅在从 12 导联心电图动态监测的选定间隔手动测量校正后的 QT (QTc) 间隔后证实。这一否则被遗漏的发现对于推动他莫昔芬停药、转向另一种“更安全”的治疗选择以及在最近的 COVID-19 中治疗双侧肺炎时避免使用潜在的致心律失常抗生素至关重要。仅在从 12 导联心电图动态监测的选定间隔手动测量校正后的 QT (QTc) 间隔后证实。这一否则被遗漏的发现对于推动他莫昔芬停药、转向另一种“更安全”的治疗选择以及在最近的 COVID-19 中治疗双侧肺炎时避免使用潜在的致心律失常抗生素至关重要。