Nemati Shamim, Malhotra Atul, Clifford Gari D
Harvard Medical School, Brigham and Women's Hospital, Boston, MA, USA.
J Electrocardiol. 2011 Mar-Apr;44(2):126-30. doi: 10.1016/j.jelectrocard.2010.10.036. Epub 2010 Dec 15.
T-wave alternans (TWA) activity is known to be a function of heart rate and condition, as well as perhaps physiological state. A recently published nonparametric nonstationary TWA analysis method has been shown to reject nonstationary noise accurately using phase-randomized surrogates and has been shown to estimate TWA accurately. This new method was evaluated on multiple databases over a range of heart rates and in healthy subjects, cardiac disease patients, and obstructive sleep apnea (OSA) patients. We hypothesized that TWA would be lower than previously reported when measured with our new technique and that higher levels of TWA would be observed in OSA patients when compared with healthy subjects.
Five databases were analyzed, as follows: (1) healthy subjects from PhysioNet's Normal Sinus Rhythm Database, (2) arrhythmia patients from PhysioNet's Chronic Heart Failure Database and (3) PhysioNet's Sudden Cardiac Death Database, (4) OSA patients from PhysioNet's MIT-BIH Polysomnographic Database, and (5) 85 subjects from a private Sleep Apnea Database. T-wave alternans magnitudes were calculated for 7 heart rate decades (intervals of 10 beats/min (bpm) between 40 and 110 bpm) for each database. The Mann-Whitney U test and the 2-sample Kolmogorov-Smirnov test were applied to test for significant differences between data from each database in each heart rate decade interval.
In the healthy population, TWA activity level tended to increase with heart rate. Moreover, there appeared to be an unexpected nadir in TWA activity around 60 to 70 bpm and a small but significant rise in TWA above and below these heart rates. The rise in TWA at lower heart rates has not been previously reported, to our knowledge. We also observed that TWA is unexpectedly lower in OSA patients and did not increase with heart rate.
Although the physiological mechanisms underlying our observations are unclear, there may be clinical implications for TWA testing, particularly at low heart rates, a previously overlooked aspect of TWA.
已知T波交替（TWA）活动是心率、身体状况以及可能的生理状态的函数。最近发表的一种非参数非平稳TWA分析方法已被证明可使用相位随机替代物准确地排除非平稳噪声，并且已被证明能准确估计TWA。该新方法在多个数据库中针对一系列心率进行了评估，涉及健康受试者、心脏病患者和阻塞性睡眠呼吸暂停（OSA）患者。我们假设，使用我们的新技术测量时，TWA会低于先前报道的值，并且与健康受试者相比，OSA患者中会观察到更高水平的TWA。
分析了五个数据库，如下所示：（1）来自PhysioNet正常窦性心律数据库的健康受试者；（2）来自PhysioNet慢性心力衰竭数据库和（3）PhysioNet心脏性猝死数据库的心律失常患者；（4）来自PhysioNet麻省理工学院-布列根和妇女医院多导睡眠图数据库的OSA患者；以及（5）来自一个私人睡眠呼吸暂停数据库的85名受试者。针对每个数据库，在7个心率十年（40至110次/分钟（bpm）之间，间隔为10次/分钟（bpm））内计算T波交替幅度。应用曼-惠特尼U检验和双样本柯尔莫哥洛夫-斯米尔诺夫检验来检验每个心率十年间隔内每个数据库的数据之间的显著差异。
在健康人群中，TWA活动水平倾向于随心率增加。此外，在60至70 bpm左右的TWA活动中似乎存在一个意外的最低点，并且在这些心率之上和之下TWA有小幅但显著的上升。据我们所知，先前尚未报道较低心率时TWA的上升情况。我们还观察到，OSA患者中的TWA出人意料地较低，并且不随心率增加。
尽管我们观察结果背后的生理机制尚不清楚，但TWA检测可能具有临床意义，特别是在低心率时，这是TWA一个先前被忽视的方面。
