STANDARDISATION of mathematical formulas assessing heartbeat rhythms with electrocardiograms (ECG) could help optimise the use of chemotherapy. New research shows that when using the wrong formula, oncologists may be inclined to stop chemotherapy inappropriately.
These mathematical formulas are based on the contraction and relaxation of the heart. When the interval between the start of the Q wave and the end of the T wave is prolonged on an ECG, meaning that the heart is taking longer to contract and relax, the risk of developing heart rhythm increases, leading to a risk of sudden cardiac arrest. Before a chemotherapy drug can be approved, it is thoroughly tested to assess whether it causes QT prolongation. This is especially important in the case of targeted therapies, many of which prolong the QT interval. A team at University of North Carolina Lineberger Comprehensive Cancer Center, Chapel Hill, USA, analysed medical records of 6,881 adult patients with cancer, who had received 24 types of chemotherapy and nearly 20,000 ECGs from 2010–2020.
They discovered that the Bazett formula, the default formula for many ECG devices, tripled the corrected QT interval compared to other formulas, and resulted in longer QT prolongations than the Framingham and Fridericia formulas in 40.9% of ECGs. Senior author Joshua F. Zeidner stated: “We initially discovered this problem while treating a patient with acute promyelocytic leukaemia with arsenic trioxide, a drug known to cause QT prolongation. We realised that there was inconsistent guidance about how to assess the QT interval with this drug and what values should lead to dose reductions.”
While this drug had been approved using the Framingham formula, the team used the Bazett formula to guide their treatment decisions. Due to overestimation of the QT interval, the Bazett formula could impact clinical care through misguided chemotherapy modifications. They therefore recommended that the Bazett formula should no longer be used for clinical guidance.
The team now wants to study oncologists’ and pharmacists’ awareness of the formulas, and advocate for standardisation of assessment of patients, as well as better understanding of the effect of formula choice on outcomes.