Measure of the QT–RR Dynamic Coupling in Patients with the Long QT Syndrome

Abstract

Background The patients with the long QT syndrome type-1 (LQT-1) have an impaired adaptation of the QT interval to heart rate changes. Yet, the description of the dynamic QT/RR coupling in genotyped LQT-1 has never been thoroughly investigated. Method We propose a method to model the dynamic QT/RR coupling by defining a transfer function characterizing the relationship between a QT interval and its previous RR intervals measured from ambulatory Holter recordings. Three parameters are used to characterize the QT/RR coupling: a fast gain (GainF), a slow gain (GainL), and a time constant (τ). We investigated the values of these parameters across genders, and in genotyped LQT-1 patients with normal QTc interval duration (QTc<470 ms). Results The QT/RR dynamic profiles are significantly different between LQT-1 patients (97) and controls (154): LQT-1 have longer QTc interval (453±35 vs. 384±26 ms, p<0.0001), and an increased dependency of the QT interval to previous RR changes revealed by a larger GainL (0.22±0.06 vs. 0.18±0.07, p<0.0001) and GainF (0.05±0.02 vs. 0.03±0.01, p<0.0001). Importantly, LQT-1 patients have a faster QT dynamic response to previous RR changes described by τ: 122±44 vs. 172±92 beats (p<0.0001). This faster QT dynamic response of the QT-RR dynamic coupling remained in LQT-1 patients with QTc in a normal range (<430 ms). Conclusions The measurement of QT/RR dynamic coupling could be used in patients suspected to carry a concealed form of the LQT-1 syndrome, or to provide insights into the types of arrhythmogenic triggers a patient may be prone to.

Clinical applications of QT/RR hysteresis assessment: A systematic review

“…Our review also points out that it remains unknown if QT‐hys is a time invariant individual characteristic that could be lastingly impaired in response to aging and disease, or a marker of time‐varying and short‐lived conditions that are involved in the initiation of an arrhythmic event. While QT‐hys appears to be increased concurrently with exercise‐induced myocardial ischemia (Lauer et al., ; Zhang et al., ) or in the minutes preceding onset of torsades de pointes (Chen & Trayanova, ); QT‐hys from long ECG recordings (such as 24 hr Holter) is impaired in some conditions (Halamek et al., ; Malik et al., ; Pueyo et al., ), implying that QT‐hys could be durably altered. Condition‐specific studies using repeated or adaptive QT‐hys assessment from continuous ECG recordings would be beneficial to clarify this question.…”

“…To our knowledge, a single study investigated QT-hys in LQTS based on the estimation of the optimal RR memory in a dynamic QT/ RR model (Halamek et al, 2012). In a relatively large sample of LQT1 patients, they reported a significantly decreased QT-hys in LQT1 patients compared to controls, seemingly contradicting aforementioned studies which reported either increased QT-hys in ungenotyped LQTS samples (most likely including a significant proportion of LQT1 patients) (Chauhan et al, 2004;Gao et al, 2007;Krahn et al, 1997;Krahn et al, 2002) or similar QT-hys in LQT1 and controls (Chattha et al, 2010;Wong et al, 2010).…”

Information transfer in QT-RR dynamics: Application to QT-correction

“…In the literature, other attempts have been made to quantify the dynamic QT-RR coupling 4,22,[36][37][38] . These approaches rely on statistical models of the given form and, thus, have assumptions behind the models.…”

Repolarization parameters in heart transplant subjects

“…Very little is known about the physiological background of repolarization and QT/RR coupling. It is well known that women have longer QTc and a steeper QT/RR slope compared to men [2][3][4], though the physiological explanation for such differences is not clear. These differences may be the result of genetic differences in the myocardium (heart properties, the distribution of action potentials) or genetic differences not originating in the heart (hormones, different concentration or distribution of ions).…”