Comparing the relationship between QT/RR slope and basal QTc in LQT1 patients and healthy subjects

The dependency of the QT interval to the previous RR intervals has been widely studied, QT/RR slope and other modeling techniques revealed individual-specific relationship. In this work we studied the relationship between QT/RR slope and a basal QTc interval in 154 healthy subjects and in 97 patients with the inherited long QT syndrome type-1 (LQT1) to provide insights into the effect of the impairment of the outwardly directed delayed rectifier potassium current on the dynamic QT-RR coupling. QT/RR slope values show strong relationship to basal QTc interval in healthy (R=0.65; p<0.00001) and in LQT1 patients (R=0.56; p<0.00001). The dependency of QT/RR slope on QTc is steeper in healthy (a1=0.0016 ± 0.0002) than in LQT1 (a1=0.0010 ± 0.0002), p<0.0001. The steeper dependency on QTc in healthy preserves proper shortening of QT intervals during increased heart rate in healthy while in LQT1 patients the QT intervals does not adapt to increased heart rate sufficiently (lack of QT adaptation to heart rate acceleration). This observation is consistent with current clinical mechanism associated with the triggering of life-threatening arrhythmias in the LQTS type-1 patients.