Department of Cardiology, Oslo University Hospital, Oslo, Norway.
Circulation. 2010 Oct 5;122(14):1355-63. doi: 10.1161/CIRCULATIONAHA.110.960377. Epub 2010 Sep 20.
Long-QT syndrome (LQTS) is characterized by prolonged myocardial action potential duration. The longest action potential duration is reported in the endomyocardium and midmyocardium. Prolonged action potential duration in LQTS may cause prolonged cardiac contraction, which can be assessed by strain echocardiography. We hypothesized that myocardial contraction is most prolonged in subendocardial myofibers in LQTS patients and that inhomogeneous transmural contraction is related to the risk of spontaneous arrhythmia.
We included 101 genotyped LQTS mutation carriers and 35 healthy individuals. A history of cardiac arrhythmias was present in 48 mutations carriers, and 53 were asymptomatic. Myocardial contraction duration was assessed by strain echocardiography as time from the ECG Q wave to peak strain in 16 LV segments. Strain was assessed along the longitudinal axis, predominantly representing subendocardial fibers, and along the circumferential axis, representing midmyocardial fibers. Mean contraction duration was longer in LQTS mutation carriers compared with healthy individuals (445 ± 45 versus 390 ± 40 milliseconds; P<0.001) and longer in symptomatic compared with asymptomatic LQTS mutation carriers (460 ± 40 versus 425 ± 45 milliseconds; P<0.001). Contraction duration by longitudinal strain was longer than by circumferential strain in symptomatic LQTS patients (460 ± 45 versus 445±45 milliseconds; P=0.008) but not in asymptomatic patients and healthy individuals, indicating transmural mechanical dispersion. This time difference was present in a majority of LV segments and was most evident in patients with LQT2 and the Jervell and Lange-Nielsen syndrome.
Contraction duration in symptomatic LQTS mutation carriers was longer in the subendocardium than in the midmyocardium, indicating transmural mechanical dispersion, which was not present in asymptomatic and healthy individuals.
长 QT 综合征（LQTS）的特征是心肌动作电位时程延长。目前报道的心内膜和中层的动作电位时程最长。LQTS 中的动作电位时程延长可能导致心脏收缩延长，这可以通过应变超声心动图来评估。我们假设 LQTS 患者的心内膜下肌纤维收缩时间最长，并且不均匀的跨壁收缩与自发性心律失常的风险相关。
我们纳入了 101 名经基因分型的 LQTS 突变携带者和 35 名健康个体。48 名突变携带者有心脏心律失常病史，53 名无心律失常病史。通过应变超声心动图评估心肌收缩时间，即从心电图 Q 波到 16 个左心室节段峰值应变的时间。应变沿长轴评估，主要代表心内膜下纤维，沿环向轴评估，代表中层心肌纤维。与健康个体相比，LQTS 突变携带者的平均收缩时间更长（445±45 与 390±40 毫秒；P<0.001），有症状的 LQTS 突变携带者比无症状的更长（460±40 与 425±45 毫秒；P<0.001）。与无症状 LQTS 患者相比，有症状的 LQTS 患者的纵向应变收缩时间长于环向应变（460±45 与 445±45 毫秒；P=0.008），但在无症状患者和健康个体中没有这种差异，表明存在跨壁机械弥散。这种时间差异存在于大多数左心室节段，在 LQT2 和 Jervell 和 Lange-Nielsen 综合征患者中最为明显。
有症状的 LQTS 突变携带者的心内膜下收缩时间比中层长，表明存在跨壁机械弥散，而无症状和健康个体中则没有。
