Brief Reports

QT interval and arrhythmic risk assessment after myocardial infarction

In patients with chronic heart failure (CHF), circadian variability of RR and QT intervals may be altered because of neurohumoral activation and functional and structural remodeling of the heart.

The aim of this study was to evaluate the prognostic significance of circadian variability of the RR and QT intervals and QT dynamicity (QT/RR slope) in CHF patients.

We prospectively enrolled 121 patients with stable CHF in sinus rhythm (age 67 ± 14 years, mean ± SD; range 34 to 87 years). The RR, QT, and rate-corrected QT (QTc) intervals and the QT/RR slope measured from 24-hour Holter electrocardiogram were fitted by cosine curves.

During the follow-up period of 34 ± 17 months, 40 (33%) patients died of cardiac causes, 10 of which were sudden. All patients showed significant circadian rhythms in the RR, QT, and QTc intervals and the QT/RR slope by cosine-curve fitting. In addition to the expected higher heart rate, longer QT interval, and steeper QT/RR slope, we found that patient who died of cardiac causes had reduced circadian variability of QT interval (10 ± 10 ms vs 21 ± 13 ms) and a later maximum RR interval (4.1 ± 0.9 AM vs 2.3 ± 2.1 AM) compared with survivors, among many other statistically significant circadian parameter differences. These 2 parameters were independent predictors of cardiac death in multivariate Cox proportional hazards regression analysis.

Circadian variability analyses of Holter-derived RR and QT intervals may provide prognostic information beyond that provided by 24-hour averages of these parameters.

Obstructive sleep apnea syndrome (OSAS) is characterized by the repeated episodes of upper airway obstruction during sleep, leading to significant hypoxia. Noninvasive evaluation of autonomic nervous system (ANS) and myocardial vulnerability may help determination of OSAS patients who are under high risk of malignant cardiac arrhythmias. The aim of this study was to show the effects of OSAS on predictors of arrhythmias by the evaluation of heart rate turbulence (HRT), heart rate variability (HRV) and QT dynamicity reflecting the ANS balance and myocardial vulnerability.

After polysomnographic study, 80 patients with OSAS and 55 age matched OSAS (−) subjects were included in the study. Twenty-four-hour Holter monitoring was performed in all subjects. HRT, HRV and QT dynamicity parameters were calculated.

Turbulence slope was significantly decreased in OSAS patients whereas turbulence onset was increased (P<0.001). QT/RR slopes were significantly increased for QT end and QT apex (P<0.001). In HRV analysis, autonomic balance changed in favor of sympathetic system at night in OSAS patients. Furthermore, HRT and QT dynamicity parameters are found to be correlated with Apnea-Hypopnea Index (AHI).

OSAS is associated with a significant worsening in HRV, HRT, and QT dynamicity parameters. Our results may indicate that HRV and QT dynamicity parameters can be useful noninvasive methods that may detect autonomic nervous system activity and ventricular vulnerability in OSAS.

The purpose of this study was to compare measures of repolarization dynamics (QT dynamics) with other Holter risk predictors, left ventricular systolic function, and demographic characteristics to establish whether QT dynamics add independent information on risk stratification after myocardial infarction (MI). A novel QT dynamics parameter, the QT/RR variability ratio (VR), was introduced in this study.

Abnormal repolarization contributes to arrhythmogenesis, and quantification of QT dynamics may have prognostic value after MI.

A 24-hour Holter recording was performed in 481 consecutive MI patients. Recordings from 311 patients were included in the analysis. QT/RR slope and intercept, mean and standard deviation of all QT, QTc, and RR intervals, and VR (defined as the ratio between the standard deviation of all QT intervals and the standard deviation of all RR interval) were calculated. Ventricular premature beats and ventricular tachycardia were counted.

During 3-year follow-up, 70 deaths from all causes occurred. All parameters except mean of all QT intervals and standard deviation of all QTc intervals univariately predicted all-cause mortality. In multivariate Cox analysis, only VR per 0.1 (hazard ratio [HR]: 1.9 [1.5–2.4]), left ventricular ejection fraction per 5% (HR: 1.2 [1.1–1.3]), ventricular premature beats per 10 beats/hour (HR: 1.03 [1.002–1.06]), and age per 10 years (HR: 1.6 [1.3–2.0]) independently predicted all-cause mortality.

Measures of QT dynamics univariately predicted total mortality. VR, left ventricular ejection fraction, ventricular premature beats, and age made up the optimal Cox model for risk stratification after MI. VR seems to be a promising risk factor for identifying sudden arrhythmic death.

Severe obstructive sleep apnea is associated with increased QT corrected interval dispersion and continuous positive airway pressure is thought to improve this arrhythmogenic marker.

The aim of the study was to determine the decrease of ratio of cardiovascular risk in patients with obstructive sleep apnea.

The study included 65 patients with severe obstructive sleep apnea who had an apnea-hypopnea index score of >30. Each patient underwent 12-channel electrocardiogram monitoring and polysomnography. Patients with an apnea-hypopnea index score of <5 were used as the control group. The control group also underwent electrocardiogram monitoring and polysomnography testing. The QT corrected interval dispersion levels of both groups were calculated. Three months after continuous positive airway pressure treatment, electrocardiogram recordings were obtained from the 65 patients with severe obstructive sleep apnea again, and their QT corrected interval dispersion values were calculated.

There were 44 male and 21 female patients with severe obstructive sleep apnea syndrome. The age, gender, body mass index, initial saturation, minimum saturation, average saturation, and desaturation index were determined in both groups. The QT corrected intervals of the obstructive sleep apnea patients (62.48 ± 16.29 ms) were significantly higher (p = 0.001) than those of the control group (29.72 ± 6.30 ms). There were statistically significant differences between the QT corrected values before and after the continuous positive airway pressure treatment, with pretreatment QT corrected intervals of 62.48 ± 16.29 ms and 3-month post-treatment values of 41.42 ± 16.96 ms (p = 0.001). There was a positive and significant correlation between QT corrected interval dispersion periods and the apnea-hypopnea index and hypopnea index in obstructive sleep apnea patients (p = 0.001; r = 0.71; p = 0.001; r = 0.679, respectively).

Continuous positive airway pressure treatment reduced the QT corrected interval dispersion in patients with severe obstructive sleep apnea. In addition, shortening the QT corrected interval dispersion periods in patients with severe obstructive sleep apnea may reduce their risk of arrhythmias and cardiovascular disease.

A apneia obstrutiva do sono grave está associada a uma maior dispersão do intervalo QT corrigido e acredita-se que a pressão positiva contínua nas vias aéreas melhore esse marcador arritmogênico.

Determinar a diminuição da razão de risco cardiovascular em pacientes com apneia obstrutiva do sono.

O estudo incluiu 65 pacientes com apneia obstrutiva do sono grave que apresentavam índice de apneia-hipopneia > 30. Cada paciente foi submetido à monitorização por eletrocardiograma de 12 derivações e polissonografia. Os pacientes com escore de índice de apneia-hipopneia < 5 foram utilizados como o grupo de controle. O grupo de controle também foi submetido à monitorização por eletrocardiograma e teste de polissonografia. Os níveis de dispersão do intervalo QT corrigido dos dois grupos foram calculados. Três meses após o tratamento com pressão positiva contínua nas vias aéreas, os registros de eletrocardiograma foram novamente obtidos dos 65 pacientes com apneia obstrutiva do sono grave, e seus valores de dispersão do intervalo QT corrigido foram calculados.

Havia 44 pacientes do sexo masculino e 21 do sexo feminino com síndrome de apneia obstrutiva do sono grave. A idade, sexo, índice de massa corporal, saturação inicial, saturação mínima, saturação média e índice de dessaturação foram determinados em ambos os grupos. Os intervalos QT corrigido dos pacientes com apneia obstrutiva do sono (62,48 ± 16,29 ms) foram significativamente maiores (p = 0,001) do que os do grupo controle (29,72 ± 6,30 ms). Houve diferenças estatisticamente significativas entre os valores de QT corrigido antes e após o tratamento com pressão positiva contínua nas vias aéreas, com intervalos QT corrigido pré-tratamento de 62,48 ± 16,29 ms e 3 meses pós-tratamento, de 41,42 ± 16,96 ms (p = 0,001). Houve uma correlação positiva e significativa entre os períodos de dispersão do intervalo QT corrigido e o índice de apneia-hipopneia e índice de hipopneia em pacientes com apneia obstrutiva do sono (p = 0,001; r = 0,71; p = 0,001; r = 0,679, respectivamente).

O tratamento com pressão positiva contínua nas vias aéreas reduziu a dispersão do intervalo QT corrigido em pacientes com apneia obstrutiva do sono grave. Além disso, o encurtamento de dispersão do intervalo QT corrigido em pacientes com apneia obstrutiva do sono grave pode reduzir o risco de arritmias e doenças cardiovasculares.