What is the QTc?
The QTc is the corrected QT interval. It is usually calculated using Leads II, V5, or V6. The QT interval varies with heart rate and must be corrected to the QTc to accurately measure the QT interval and assess the risk. The QT interval is prolonged at slower heart rates and shortened at faster heart rates.
How does one calculate the QTc using Lead II from a 6 lead mobile ECG?
Click here for the Inpatient Informational Handout to capture and submit for QTc calculation of a KardiaMobile 6L recording. To manually calculate the QTc we recommend either using an EKG ruler and following the instructions provided with the ruler, or you can use ECG calipers to manually measure the QT and RR intervals, which will be needed to calculate the QTc.
Will the QTc analysis include a wide QRS adjustment?
No, the QTc analysis will not include a wide QRS adjustment. For patients with a wide QRS from either ventricular pacing or left/right bundle branch block, a wide-QRS QTc adjustment should be made. Clinicians who are managing COVID-19 patients and are unsure whether this adjustment should be made if their QTc is >= 500ms should consult with cardiology before making a medication decision.
How were the threshold QTc values in the Mayo protocol determined?
Mayo protocol QTc threshold values were based on the average values observed in their patients with long QT syndrome (LQTS).
Average, QTc values (ms) 99th percentile value Potential Increased Risk (ms) Healthy, postpubertal MALE 410 470 Healthy, postpubertal FEMALE 420 480 Prepubertal MALE/FEMALE 460
Patients with a resting QTc³ 500ms have a significantly greater risk for drug-induced Torsades de Pointes (DI-TdP) and drug-induced sudden cardiac death (DI-SCD). Therefore, these values were used to define risk in the Mayo protocol.