Usefulness of ventricular repolarization dynamicity in predicting arrhythmic deaths in patients with ischemic cardiomyopathy (from the European Myocardial Infarct Amiodarone Trial)

Differential diagnosis between LQT1 and LQT2 by QT/RR relationships using 24-hour Holter monitoring: A multicenter cross-sectional study

BACKGROUND

The clinical course and therapeutic strategies in the congenital long QT syndrome (LQTS) are genotype-specific. However, accurate estimation of LQTS genotype is often difficult from the standard 12-lead ECG.

OBJECTIVES

This study aims to evaluate the utility of QT/RR slope analysis by the 24-hour Holter monitoring for differential diagnosis of LQTS genotype between LQT1 and LQT2.

METHODS

This cross-sectional study enrolled 54 genetically identified LQTS patients (29 LQT1 and 25 LQT2) recruited from three medical institutions. The QT-apex (QTa) interval and the QT-end (QTe) interval at each 15-second were plotted against the RR intervals, and the linear regression (QTa/RR and QTe/RR slopes, respectively) was calculated from the entire 24-hour and separately during the day or night-time periods of the Holter recordings.

RESULTS

The QTe/RR and QTa/RR slopes at the entire 24-hour were significantly steeper in LQT2 compared to those in LQT1 patients (0.262 ± 0.063 vs. 0.204 ± 0.055, p = .0007; 0.233 ± 0.052 vs. 0.181 ± 0.040, p = .0002, respectively). The QTe interval was significantly longer, and QTe/RR and QTa/RR slopes at daytime were significantly steeper in LQT2 than in LQT1 patients. The receiver operating curve analysis revealed that the QTa/RR slope of 0.211 at the entire 24-hour Holter was the best cutoff value for differential diagnosis between LQT1 and LQT2 (sensitivity: 80.0%, specificity: 75.0%, and area under curve: 0.804 [95%CI = 0.68-0.93]).

CONCLUSION

The continuous 24-hour QT/RR analysis using the Holter monitoring may be useful to predict the genotype of congenital LQTS, particularly for LQT1 and LQT2.

Fibrosis and wall thickness affect ventricular repolarization dynamics in hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is characterized by ventricular repolarization abnormalities and risk of ventricular arrhythmias. Our aim was to study the association between the phenotype and ventricular repolarization dynamics in HCM patients.

METHODS

HCM patients with either the MYBPC3-Q1061X or TPM1-D175N mutation (n = 46) and control subjects without mutation and hypertrophy (n = 35) were studied with 24-hr ambulatory ECG recordings by measuring time intervals of rate-adapted QT (QTe), maximal QT, and T-wave apex to wave end (TPE) intervals and the QTe/RR slope. Findings were correlated to specified echocardiographic and cardiac magnetic resonance imaging (CMRI) findings.

RESULTS

Rate-adapted QTe interval was progressively longer in HCM patients with decreasing heart rates compared to control subjects (p = 0.020). The degree of hypertrophy correlated with measured QTe values. HCM patients with maximal wall thickness higher than the mean (20.6 mm) had longer maximum QTe and median TPE intervals compared to control subjects and HCM patients with milder hypertrophy (p < 0.001 and p = 0.014, respectively). HCM patients with late gadolinium enhancement (LGE) on CMRI had steeper QTe/RR slopes compared to HCM patients without LGE and control subjects (p = 0.044 and p = 0.001, respectively). LGE was an independent predictor of QTe/RR slope (p = 0.023, B = 0.043).

CONCLUSION

Dynamics of ventricular repolarization in HCM are affected by hypertrophy and fibrosis. LGE may confer an independent effect on QT dynamics which may increase the arrhythmogenic potential in HCM.

Late Gadolinium Enhancement on Cardiac MRI Correlates with QT Dynamicity Represented by QT/RR Relationship in Patients with Ventricular Arrhythmias

BACKGROUND

The distribution of late gadolinium enhancement (LGE) on the cardiac MRI (CMR) indicates myocardial fibrosis and provides information of possible reentry substrates. QT dynamicity reflecting repolarization abnormalities has gained attention as a potential prognostic predictive factor.

OBJECTIVE

To clarify the correlation between the LGE distribution on CMR and QT dynamicity represented by the QT/RR relationship.

METHODS

CMR and QT/RR analyses using Holter monitoring were performed in 34 patients (24 males, 60 ± 11 years) with ventricular tachycardia (VT) and/or ventricular fibrillation (VF). The LGE on CMR was scored using a 4-point score in 17 left ventricular segments. The sum of the LGE scores was calculated for each patient. The QT/RR slope and daytime/nighttime QT/RR ratio (day/night ratio) were calculated. The correlation between the slope or the day/night QT/RR ratio and late enhancement findings was analyzed.

RESULTS

All patients were divided into 23 LGE positive (LGE(+)) and 11 LGE negative (LGE(-)) patients. The slopes of the QTe/RR and QTa /RR were significantly steeper in the LGE(+) than in LGE(-) patients (0.21 ± 0.03 vs 0.13 ± 0.02; P < 0.001, 0.19 ± 0.03 vs 0.13 ± 0.02; P < 0.001, respectively), and both slopes were significantly correlated with the total LGE scores (r = 0.83, P < 0.001; r = 0.71, P < 0.001, respectively). In the LGE(+) patients, the QTe day/night (1.37 ± 0.38 vs 0.91 ± 0.33; P = 0.002) and QTa day/night ratios (1.33 ± 0.26 vs 1.06 ± 0.30; P = 0.011) were significantly greater than those in the LGE(-) patients.

CONCLUSION

The LGE distribution was closely related to the QT dynamicity, suggesting that a combination of these markers can be a powerful tool for understanding the background pathophysiology.

Effect of weight loss on sympatho-vagal balance in subjects with grade-3 obesity: restrictive surgery versus hypocaloric diet

Few and mostly uncontrolled studies indicate that weight loss improves heart rate variability (HRV) in grade-3 obesity. The aim of this study was to compare in grade-3 obesity surgery and hypocaloric diet on clinical and metabolic variables and on autonomic indices of HRV. Twenty-four subjects (body mass index, BMI 45.5 ± 9.13 kg/m(2)) underwent surgery (n = 12, gastric banding, LAGB) or received hypocaloric diet (n = 12, 1,000-1,200 kg/day). Clinical [BMI, systolic blood pressure (SBP) and diastolic blood pressure (DBP), heart rate] and metabolic variables [glucose, cholesterol, HDL- and LDL-cholesterol, triglycerides, AST and ALT transaminases] and 24-h Holter electrocardiographic-derived HRV parameters [R-R interval, standard deviation of R-R intervals (SDNN); low/high-frequency (LF/HF) ratio, and QT interval] were measured at baseline and after 6 months. The two groups were identical at baseline. BMI (-7.5 ± 3.57 kg/m(2), mean ± SD), glucose (-24.1 ± 26.77 mg/dL), SBP (-16.7 ± 22.19 mmHg) and DBP (-6.2 ± 8.56 mmHg) decreased in LAGB subjects (p < 0.05) and remained unchanged in controls. At 6 months, SDNN increased in LAGB subjects (+25.0 ± 37.19 ms, p < 0.05) and LF/HF ratio diminished (2.9 ± 1.84 vs. 4.9 ± 2.78; p = 0.01), with no change in controls; LF (daytime) and HF (24 h and daytime) increased in LAGB subjects, with no change in controls. Decrease in BMI correlated with SBP and DBP decrease (p < 0.05), and DBP decrease correlated with HR decrease (p < 0.05) and QT shortening (p < 0.05). Weight loss is associated with improvement of glucose metabolism, of blood pressure, and with changes in time and frequency domain parameters of HRV; all these changes indicate recovery of a more physiological autonomic control, with increase in parasympathetic and reduction in sympathetic indices of HRV.

The detection of T-wave variation linked to arrhythmic risk: an industry perspective

Although the scientific literature contains ample descriptions of peculiar patterns of repolarization linked to arrhythmic risk, the objective quantification and classification of these patterns continues to be a challenge that impacts their widespread adoption in clinical practice. To advance the science, computerized algorithms spawned in the academic environment have been essential in order to find, extract and measure these patterns. However, outside the strict control of a core lab, these algorithms are exposed to poor quality signals and need to be effective in the presence of different forms of noise that can either obscure or mimic the T-wave variation (TWV) of interest. To provide a practical solution that can be verified and validated for the market, important tradeoffs need to be made that are based on an intimate understanding of the end-user as well as the key characteristics of either the signal or the noise that can be used by the signal processing engineer to best differentiate them. To illustrate this, two contemporary medical devices used for quantifying T-wave variation are presented, including the modified moving average (MMA) for the detection of T-wave Alternans (TWA) and the quantification of T-wave shape as inputs to the Morphology Combination Score (MCS) for the trending of drug-induced repolarization abnormalities.

The association of premature ovarian failure with ventricular repolarization dynamics evaluated by QT dynamicity

AIMS

The association between premature ovarian failure (POF) and cardiovascular diseases has been investigated in a few studies, but none have looked at ventricular repolarization abnormalities in these patients. In this study, we aimed to evaluate the ventricular repolarization by QT dynamicity in patients with POF.

METHODS AND RESULTS

We enrolled 26 female patients (mean age 37.5 ± 10.1 years) with primary POF and 31 healthy female subjects (mean age 37.5 ± 9.0 years). The linear regression slopes of the QT interval measured to the apex and to the end of the T-wave plotted against RR intervals (QTapex/RR and QTend/RR slopes, respectively) were calculated from 24 h Holter recordings using a standard algorithm. QTapex/RR and QTend/RR slopes were more steeper in the POF patients in contrary to healthy control subjects (QTapex/RR = 0.184 ± 0.022 vs. 0.131 ± 0.019, P < 0.001; QTend/RR = 0.164 ± 0.021 vs. 0.128 ± 0.018, P < 0.001). Pearson's correlation analyses revealed a stronger negative correlation between oestradiol (E2) and QTapex/RR (r = -0.715, P < 0.001). There was also a moderate negative correlation between E2 and QTend/RR (r = -0.537, P < 0.001). Serum follicle-stimulating hormone level was positively correlated with QTapex/RR (r = 0.681, P < 0.001) and QTend/RR (r = 0.531, P < 0.001).

CONCLUSIONS

Our study results suggest that QT dynamicity is impaired in patients with POF despite the absence of overt cardiovascular involvement. Further studies are needed to elucidate the prognostic significance and clinical implications of impaired ventricular repolarization in patients with POF.

Methodologies to characterize the QT/corrected QT interval in the presence of drug-induced heart rate changes or other autonomic effects

This White Paper, written collaboratively by members of the Cardiac Safety Research Consortium from academia, industry, and regulatory agencies, discusses different methods to characterize the QT effects for drugs that have a substantial direct or indirect effect on heart rate. Descriptions and applications are provided for individualized QT-R-R correction, Holter bin, dynamic QT beat-to-beat, pharmacokinetic-pharmacodynamic modeling, and QT assessment at constant heart rate. Most of these techniques are optimally performed using continuous electrocardiogram data obtained in clinical studies designed to characterize a drug's effect on the QT interval. An important study design element is the collection of drug-free data over a range of heart rates seen on treatment. The range of heart rates is increased at baseline by using ambulatory electrocardiogram recordings in addition to those collected under semisupine, resting conditions. Discussions in this study summarize areas of emerging consensus and other areas in which consensus remains elusive and provide suggestions for additional research to further increase our knowledge and understanding of this topic.

Isoprenaline increases the slopes of restitution trajectory in the conscious rabbit with ischemic heart failure

Roughly speaking, restitution is the dependence of recovery time of cardiac electrical activity on heart rate. Increased restitution slope is theorized to be predictive of sudden death after heart injury such as from coronary artery occlusion (ischemia). Adrenaline analogs are known to increase restitution slope in normal hearts, but their effects in failing hearts are unknown. Twenty-six rabbits underwent coronary ligation (n = 15) or sham surgery (n = 11) and implantation of a lead in the heart for recording electrocardiograms. Eight weeks later, unanesthetized rabbits were given 0.25-2.0 ml of 1 μmol/L isoprenaline intravenously, which increased heart rate. Heart rate was quantified by time between QRS peaks (RR) and heart activity duration by R to T peak time (QTp). Ligated rabbits (n = 6) had lower ejection fraction than sham rabbits (n = 7, p < 0.0001) indicative of heart failure, but similar baseline RR (269 ± 15 vs 292 ± 23 ms, p = 0.07), QTp (104 ± 17 vs 91 ± 9 ms, p = 0.1), and isoprenaline-induced minimum RR (204 ± 11 vs 208 ± 6 ms, p = 0.4). The trajectory of QTp vs TQ plots displayed hysteresis and regions of negative slope. The slope of the positive slope region was >1 in ligated rabbits (1.27 ± 0.66) and <1 in sham rabbits (0.35 ± 0.14, p = 0.004). The absolute value of the negative slope was greater in ligated rabbits (- 0.81 ± 0.52 vs - 0.35 ± 0.14, p = 0.04). Isoprenaline increased heart rate and slopes of restitution trajectory in failing hearts. The dynamics of restitution trajectory may hold clues for sudden death in heart failure patients.

QT dynamics early after exercise as a predictor of mortality

BACKGROUND

Exercise and QT dynamics during ambulatory monitoring impact mortality in a variety of populations. Heart rate recovery (HRR) after exercise is a known strong predictor of mortality.

OBJECTIVE

This study assessed the independent prognostic significance of the QT response to changing heart rate (QT dynamics) during recovery from exercise.

METHODS

The cohort included patients referred for treadmill exercise stress testing over a 5-year period. Patients had to have at least 4 electrocardiographic tracings within 5 minutes of peak exercise. One had to be recorded 60 seconds into recovery to calculate the HRR. Linear regression of the QT-RR relation during recovery was used to predict the QT interval at cycle lengths of 500 and 600 ms (QT-500 and QT-600). Only studies with an R(2) > or = 0.9 (72%) were retained. Optimal binary cut points were chosen. All-cause mortality was determined from either the Social Security Death Index or hospital records.

RESULTS

A total of 2,994 patients met inclusion criteria; 228 (7.6%) died during an average follow-up of 7.6 +/- 1.9 years. Abnormal QT-500 (>316 ms) was the strongest univariate QT dynamics predictor in a Cox proportional hazards model (hazard ratio = 2.13, P <.001). It remained an independent predictor of mortality after adjustment for age, exercise capacity, medications, single photon emission computed tomography defects, and abnormal (<12 beats/min) HRR (hazard ratio = 1.46, P = .014).

CONCLUSION

An abnormal predicted QT interval at 500 ms (120 beats/min) during recovery from exercise independently predicts all-cause mortality. Because QT dynamics in recovery incorporate information on both repolarization and autonomic responsiveness, its role in risk prediction for sudden cardiac death should be further explored.

QT/RR relationship in patients after remote anterior myocardial infarction with left ventricular dysfunction and different types of ventricular arrhythmias

BACKGROUND

QT/RR relationship was found to be both rate-dependent and rate-independent, what suggests the influence of autonomic drive and other not-autonomic related factors on it. The steeper QT/RR slope in patients after acute myocardial infarction (MI) was described, but the relationship to ventricular arrhythmias is unknown. The purpose of this study was to calculate differences in QT/RR relationship in patients after remote anterior MI with left ventricular dysfunction and different types of ventricular arrhythmias.

METHODS

The cohort of 95 patients (age: 63 +/- 11 years, LVEF: 35 +/- 9%) with previous anterior MI (mean 1.1 years) was divided into two well-matched groups-50 patients without episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF) (NoVT/VF: 39 males, 64 +/- 12 years, LVEF 37 +/- 8%) and 45 patients with VT and/or VF (all with ICD implanted) (VT/VF: 35 males, 62 +/- 10 years, LVEF 34 +/- 10%). No true antiarrhythmics were used. QT/RR slope was calculated from 24-hour Holter ECG for the entire recording (E), daytime (D) and nighttime (N) periods.

RESULTS

Groups did not differ in basic clinical data (age, LVEF, treatment). QT/RR slopes were steeper in VT/VF than in NoVT/VF group in all analyzed periods: E - 0.195 +/- 0.03 versus 0.15 +/- 0.03 (P < 0.001), N - 0.190 +/- 0.03 versus 0.138 +/- 0.03 (P < 0.001) and D - 0.200 +/- 0.04 versus 0.152 +/- 0.03 (P < 0.001). No significant day-to-night differences were found in both groups.

CONCLUSIONS

Steeper QT/RR slope and complete lack of day-to-night differences in VT/VF patients show inappropriate QT adaptation to the heart rate changes. The prognostic significance of this parameter needs prospective studies.

The electrocardiogram as a prognostic tool for predicting major cardiac events

Among patients with cardiac disease, the identification of those who are at low risk and those who are at high risk for major cardiac events is crucial for a rational clinical management of individual patients. A correct noninvasive risk stratification of cardiac patients, in particular, has relevant clinical implications because it would avoid unnecessary exposure to potentially risky invasive diagnostic or interventional procedures in low-risk patients, whereas it would allow an appropriate aggressive diagnostic and therapeutic approach in high-risk patients. Furthermore, the appropriate identification of low- and high-risk patients would also have social and economic implications by favoring optimization of resource distribution and costs. A large number of studies in previous decades provided evidence that several methods and variables derived from the analysis of the electrocardiogram (ECG) are powerful predictors of major cardiac events in several clinical conditions. Despite that, there has been limited attention about how several of these findings can be used in clinical practice. Furthermore, in recent years, most studies about risk stratification of cardiac patients have mainly been focused on the use of a number of serum/plasma biomarkers with reduced attention to ECG variables. Surprisingly, however, there have been few attempts to establish whether the various proposed risk markers add any significant information to that obtainable from ECG methods. In this article, the evidence for the prognostic value of variables derived from the assessment of the ECG signal by several methods and techniques will be briefly reviewed. Because of the largeness of the topic, this review will be necessarily incomplete. Because most of the clinical research in this field concerned risk stratification of patients with coronary artery disease, the article will be largely focused on this population of patients. The role of ECG methods in specific cardiac diseases and, in particular, in the general population of asymptomatic subjects will be briefly discussed when believed appropriate and helpful. Furthermore, only major clinical events (ie, cardiac death, arrhythmic events, acute myocardial infarction) will be taken into account as end points in this article. Minor clinical events (eg, coronary revascularization procedures, coronary artery restenosis, recurrences of symptoms) are indeed less robust as end points because they are widely biased by subjective judgments.

Impaired ventricular electrical stability and sympathetic hyperactivity in patients with multivessel coronary artery disease

OBJECTIVES

The extent of atherosclerotic disease is identified as one of the most important predictors of long-term cardiac events in patients with coronary artery disease. Heart rate variability and QT dynamicity have been used as independent predictors for sudden death in coronary artery disease. Heart rate variability and QT dynamicity, however, have never been investigated in multivessel coronary artery disease. The aim of this study was to identify autonomic nervous system activity and ventricular vulnerability in multivessel coronary artery disease.

METHODS

We examined 204 patients who underwent coronary angiography. According to the number of the three major coronary vessels with significant stenosis (>70%), we divided the patients into three groups: normal coronary arteries (n=61), single-vessel coronary artery disease (n=53) and the multivessel coronary artery disease (n=90). Twenty-four-hour ambulatory electrocardiographic recording was performed by a three-channel recorder. Heart rate variability and QT dynamicity parameters were obtained by ELA TEC software.

RESULTS

Baseline characteristics were similar in multivessel coronary artery disease, single-vessel coronary artery disease and controls. SDNN (90+/-35, 117+/-52, 134+/-53, respectively; P<0.001) and HFnu (9.6+/-8.2, 8.9+/-3.7, 12.2+/-7.4, respectively; P=0.011) were significantly lower, whereas LFnu (27.2+/-11.3, 26.1+/-8.4, 22.0+/-13.4, respectively; P=0.014) and LF/HF ratio (4.4+/-3.2, 3.3+/-1.4, 2.1+/-1.6, respectively; P<0.001) were significantly higher in multivessel coronary artery disease. QTend/RR and QTapex/RR slopes were more significantly increased in multivessel coronary artery disease than in single-vessel coronary artery disease and control participants [QTend/RR: 0.15 (0.04-0.66), 0.12 (0.02-0.33), 0.12 (0.01-0.22), respectively; P=0.002; QTapex/RR: 0.16 (0.06-0.30), 0.12 (0.02-0.29), 0.11 (0.01-0.19), respectively; P<0.001].

CONCLUSIONS

Heart rate variability and QT dynamicity are impaired in patients with multivessel coronary artery disease. Our results may indicate that heart rate variability and QT dynamicity parameters can be useful noninvasive methods that may detect autonomic nervous system activity and ventricular vulnerability in multivessel coronary artery disease.

Effects of exercise training on heart rate and QT interval in healthy young individuals: are there gender differences?

AIMS

The aim of the present study was to assess the effects of exercise training on heart rate, QT interval, and on the relation between ventricular repolarization and heart rate in men and women.

METHODS AND RESULTS

A 24 h Holter recording was obtained in 80 healthy subjects (40 males) who differed for the degree of physical activity. Trained individuals showed a lower heart rate and a higher heart rate variability than sedentary subjects, independent of the gender difference in basal heart rate. Mean 24 h QTc was similar in trained and non-trained men, while a significant difference was observed between trained and non-trained women. Exercise training reduced the QT/RR slope in both genders. This effect on the QT/RR relation was more marked in women; in fact, the gender difference in the ventricular repolarization duration at low heart rate observed in sedentary subjects was no longer present among trained individuals.

CONCLUSION

The results of this study suggest that the cardiovascular response to exercise training may be different in men and women. Women may benefit more from interventions aimed to increase physical activity as a tool for prevention of cardiovascular morbidity and mortality.

[Clinical significance of dynamic QT-interval-analyses]

Dynamic parameters of ventricular repolarization as Holter derived parameters expressed as QT-interval adaptation to heart rate changes (QT/RR-slope) and QT-interval-variability are being more and more frequently used to identify patients with increased risk for ventricular arrhythmias. Steep QT-RR-slopes, reflecting inadequate adaptation of ventricular repolarization to heart rate changes, as well as increased QT-interval-variability, reflecting temporal inhomogeneity of ventricular repolarization duration, are frequently observed in patients at risk for sudden cardiac death. Additionally, there is strong evidence for significant alterations in the dynamics of action potential duration restitution in patients with structural heart disease. This review gives an up-to-date overview about the current research in methods of assessment and clinical relevance of dynamic parameters of ventricular repolarization.