QRS complex and T wave planarity for the efficacy prediction of automatic implantable defibrillators

OBJECTIVE

To test the hypothesis that in recipients of primary prophylactic implantable cardioverter-defibrillators (ICDs), the non-planarity of ECG vector loops predicts (a) deaths despite ICD protection and (b) appropriate ICD shocks.

METHODS

Digital pre-implant ECGs were collected in 1948 ICD recipients: 21.4% females, median age 65 years, 61.5% ischaemic heart disease (IHD). QRS and T wave three-dimensional loops were constructed using singular value decomposition that allowed to measure the vector loop planarity. The non-planarity, that is, the twist of the three-dimensional loops out of a single plane, was related to all-cause mortality (n=294; 15.3% females; 68.7% IHD) and appropriate ICD shocks (n=162; 10.5% females; 87.7% IHD) during 5-year follow-up after device implantation. Using multivariable Cox regression, the predictive power of QRS and T wave non-planarity was compared with that of age, heart rate, left ventricular ejection fraction, QRS duration, spatial QRS-T angle, QTc interval and T-peak to T-end interval.

RESULTS

QRS non-planarity was significantly (p<0.001) associated with follow-up deaths despite ICD protection with HR of 1.339 (95% CI 1.165 to 1.540) but was only univariably associated with appropriate ICD shocks. Non-planarity of the T wave loop was the only ECG-derived index significantly (p<0.001) associated with appropriate ICD shocks with multivariable Cox regression HR of 1.364 (1.180 to 1.576) but was not associated with follow-up mortality.

CONCLUSIONS

The analysed data suggest that QRS and T wave non-planarity might offer distinction between patients who are at greater risk of death despite ICD protection and those who are likely to use the defibrillator protection.

QRS micro-fragmentation as a mortality predictor

AIMS

Fragmented QRS complex with visible notching on standard 12-lead electrocardiogram (ECG) is understood to represent depolarization abnormalities and to signify risk of cardiac events. Depolarization abnormalities with similar prognostic implications likely exist beyond visual recognition but no technology is presently suitable for quantification of such invisible ECG abnormalities. We present such a technology.

METHODS AND RESULTS

A signal processing method projects all ECG leads of the QRS complex into optimized three perpendicular dimensions, reconstructs the ECG back from this three-dimensional projection, and quantifies the difference (QRS 'micro'-fragmentation, QRS-μf) between the original and reconstructed signals. QRS 'micro'-fragmentation was assessed in three different populations: cardiac patients with automatic implantable cardioverter-defibrillators, cardiac patients with severe abnormalities, and general public. The predictive value of QRS-μf for mortality was investigated both univariably and in multivariable comparisons with other risk factors including visible QRS 'macro'-fragmentation, QRS-Mf. The analysis was made in a total of 7779 subjects of whom 504 have not survived the first 5 years of follow-up. In all three populations, QRS-μf was strongly predictive of survival (P < 0.001 univariably, and P < 0.001 to P = 0.024 in multivariable regression analyses). A similar strong association with outcome was found when dichotomizing QRS-μf prospectively at 3.5%. When QRS-μf was used in multivariable analyses, QRS-Mf and QRS duration lost their predictive value.

CONCLUSION

In three populations with different clinical characteristics, QRS-μf was a powerful mortality risk factor independent of several previously established risk indices. Electrophysiologic abnormalities that contribute to increased QRS-μf values are likely responsible for the predictive power of visible QRS-Mf.

Intra-subject stability of different expressions of spatial QRS-T angle and their relationship to heart rate

Three-dimensional angle between the QRS complex and T wave vectors is a known powerful cardiovascular risk predictor. Nevertheless, several physiological properties of the angle are unknown or poorly understood. These include, among others, intra-subject profiles and stability of the angle relationship to heart rate, characteristics of angle/heart-rate hysteresis, and the changes of these characteristics with different modes of QRS-T angle calculation. These characteristics were investigated in long-term 12-lead Holter recordings of 523 healthy volunteers (259 females). Three different algorithmic methods for the angle computation were based on maximal vector magnitude of QRS and T wave loops, areas under the QRS complex and T wave curvatures in orthogonal leads, and weighted integration of all QRS and T wave vectors moving around the respective 3-dimensional loops. These methods were applied to orthogonal leads derived either by a uniform conversion matrix or by singular value decomposition (SVD) of the original 12-lead ECG, giving 6 possible ways of expressing the angle. Heart rate hysteresis was assessed using the exponential decay models. All these methods were used to measure the angle in 659,313 representative waveforms of individual 10-s ECG samples and in 7,350,733 individual beats contained in the same 10-s samples. With all measurement methods, the measured angles fitted second-degree polynomial regressions to the underlying heart rate. Independent of the measurement method, the angles were found significantly narrower in females (p &lt; 0.00001) with the differences to males between 10o and 20o, suggesting that in future risk-assessment studies, different angle dichotomies are needed for both sexes. The integrative method combined with SVD leads showed the highest intra-subject reproducibility (p &lt; 0.00001). No reproducible delay between heart rate changes and QRS-T angle changes was found. This was interpreted as a suggestion that the measurement of QRS-T angle might offer direct assessment of cardiac autonomic responsiveness at the ventricular level.

Short-Term Beat-to-Beat QT Variability Appears Influenced More Strongly by Recording Quality Than by Beat-to-Beat RR Variability

Increases in beat-to-beat variability of electrocardiographic QT interval duration have repeatedly been associated with increased risk of cardiovascular events and complications. The measurements of QT variability are frequently normalized for the underlying RR interval variability. Such normalization supports the concept of the so-called immediate RR effect which relates each QT interval to the preceding RR interval. The validity of this concept was investigated in the present study together with the analysis of the influence of electrocardiographic morphological stability on QT variability measurements. The analyses involved QT and RR measurements in 6,114,562 individual beats of 642,708 separate 10-s ECG samples recorded in 523 healthy volunteers (259 females). Only beats with high morphology correlation (r &gt; 0.99) with representative waveforms of the 10-s ECG samples were analyzed, assuring that only good quality recordings were included. In addition to these high correlations, SDs of the ECG signal difference between representative waveforms and individual beats expressed morphological instability and ECG noise. In the intra-subject analyses of both individual beats and of 10-s averages, QT interval variability was substantially more strongly related to the ECG noise than to the underlying RR variability. In approximately one-third of the analyzed ECG beats, the prolongation or shortening of the preceding RR interval was followed by the opposite change of the QT interval. In linear regression analyses, underlying RR variability within each 10-s ECG sample explained only 5.7 and 11.1% of QT interval variability in females and males, respectively. On the contrary, the underlying ECG noise contents of the 10-s samples explained 56.5 and 60.1% of the QT interval variability in females and males, respectively. The study concludes that the concept of stable and uniform immediate RR interval effect on the duration of subsequent QT interval duration is highly questionable. Even if only stable beat-to-beat measurements of QT interval are used, the QT interval variability is still substantially influenced by morphological variability and noise pollution of the source ECG recordings. Even when good quality recordings are used, noise contents of the electrocardiograms should be objectively examined in future studies of QT interval variability.

Sex and Rate Change Differences in QT/RR Hysteresis in Healthy Subjects

While it is now well-understood that the extent of QT interval changes due to underlying heart rate differences (i.e., the QT/RR adaptation) needs to be distinguished from the speed with which the QT interval reacts to heart rate changes (i.e., the so-called QT/RR hysteresis), gaps still exist in the physiologic understanding of QT/RR hysteresis processes. This study was designed to address the questions of whether the speed of QT adaptation to heart rate changes is driven by time or by number of cardiac cycles; whether QT interval adaptation speed is the same when heart rate accelerates and decelerates; and whether the characteristics of QT/RR hysteresis are related to age and sex. The study evaluated 897,570 measurements of QT intervals together with their 5-min histories of preceding RR intervals, all recorded in 751 healthy volunteers (336 females) aged 34.3 ± 9.5 years. Three different QT/RR adaptation models were combined with exponential decay models that distinguished time-based and interval-based QT/RR hysteresis. In each subject and for each modelling combination, a best-fit combination of modelling parameters was obtained by seeking minimal regression residuals. The results showed that the response of QT/RR hysteresis appears to be driven by absolute time rather than by the number of cardiac cycles. The speed of QT/RR hysteresis was found decreasing with increasing age whilst the duration of individually rate corrected QTc interval was found increasing with increasing age. Contrary to the longer QTc intervals, QT/RR hysteresis speed was faster in females. QT/RR hysteresis differences between heart rate acceleration and deceleration were not found to be physiologically systematic (i.e., they differed among different healthy subjects), but on average, QT/RR hysteresis speed was found slower after heart rate acceleration than after rate deceleration.

Polyscore of autonomic parameters for risk stratification of the elderly general population: the Polyscore study

Aims

Present society is constantly ageing and elderly frequently suffer from conditions that are difficult and/or costly to treat if detected late. Effective screening of the elderly is therefore needed so that those requiring detailed clinical work-up are identified early. We present a prospective validation of a screening strategy based on a Polyscore of seven predominantly autonomic, non-invasive risk markers.

Methods and results

Within a population-based survey in Germany (INVADE study), participants aged ≥60 years were enrolled between August 2013 and February 2015. Seven prospectively defined Polyscore components were obtained during 30-min continuous recordings of electrocardiogram, blood pressure, and respiration. Out of 1956 subjects, 168 were excluded due to atrial fibrillation, implanted pacemaker, or unsuitable recordings. All-cause mortality over a median 4-year follow-up was prospectively defined as the primary endpoint. The Polyscore divided the investigated population (n = 1788, median age: 72 years, females: 58%) into three predefined groups with low (n = 1405, 78.6%), intermediate (n = 326, 18.2%), and high risk (n = 57, 3.2%). During the follow-up, 82 (4.6%) participants died. Mortality in the Polyscore-defined risk groups was 3.4%, 7.4%, and 17.5%, respectively (P < 0.0001). The Polyscore-based mortality prediction was independent of Framingham score, diabetes, chronic kidney disease, and major stroke and/or myocardial infarction history. It was particularly effective in those aged <75 years (n = 1145).

Conclusion

The Polyscore-based mortality risk assessment from short-term non-invasive recordings is effective in the elderly general population, especially those aged 60–74 years. Implementation of a comprehensive Polyscore screening of this age group is proposed to advance preventive medical care.

Influence of heart rate correction formulas on QTc interval stability

Monitoring of QTc interval is mandated in different clinical conditions. Nevertheless, intra-subject variability of QTc intervals reduces the clinical utility of QTc monitoring strategies. Since this variability is partly related to QT heart rate correction, 10 different heart rate corrections (Bazett, Fridericia, Dmitrienko, Framingham, Schlamowitz, Hodges, Ashman, Rautaharju, Sarma, and Rabkin) were applied to 452,440 ECG measurements made in 539 healthy volunteers (259 females, mean age 33.3 ± 8.4 years). For each correction formula, the short term (5-min time-points) and long-term (day-time hours) variability of rate corrected QT values (QTc) was investigated together with the comparisons of the QTc values with individually corrected QTcI values obtained by subject-specific modelling of the QT/RR relationship and hysteresis. The results showed that (a) both in terms of short-term and long-term QTc variability, Bazett correction led to QTc values that were more variable than the results of other corrections (p < 0.00001 for all), (b) the QTc variability by Fridericia and Framingham corrections were not systematically different from each other but were lower than the results of other corrections (p-value between 0.033 and < 0.00001), and (c) on average, Bazett QTc values departed from QTcI intervals more than the QTc values of other corrections. The study concludes that (a) previous suggestions that Bazett correction should no longer be used in clinical practice are fully justified, (b) replacing Bazett correction with Fridericia and/or Framingham corrections would improve clinical QTc monitoring, (c) heart rate stability is needed for valid QTc assessment, and (d) development of further QTc corrections for day-to-day use is not warranted.

In Comparison to Pathological Q Waves, Selvester Score is a Superior Diagnostic Indicator of Increased Long-Term Mortality Risk in ST Elevation Myocardial Infarction Patients Treated with Primary Coronary Intervention

The development of pathological Q waves has long been correlated with worsened outcome in patients with ST elevation myocardial infarction (STEMI). In this study, we investigated long-term mortality of STEMI patients treated by primary percutaneous coronary intervention (PPCI) and compared predictive values of Q waves and of Selvester score for infarct volume estimation. Data of 283 consecutive STEMI patients (103 females) treated by PPCI were analysed. The presence of pathological Q wave was evaluated in pre-discharge electrocardiograms (ECGs) recorded ≥72 h after the chest pain onset (72 h Q). The Selvester score was evaluated in acute ECGs (acute Selvester score) and in the pre-discharge ECGs (72 h Selvester score). The results were related to total mortality and to clinical and laboratory variables. A 72 h Q presence and 72 h Selvester score ≥6 was observed in 184 (65.02%) and 143 (50.53%) patients, respectively. During a follow-up of 5.69 ± 0.66 years, 36 (12.7%) patients died. Multivariably, 72 h Selvester score ≥6 was a strong independent predictor of death, while a predictive value of the 72 h Q wave was absent. In high-risk subpopulations defined by clinical and laboratory variables, the differences in total mortality were highly significant (p < 0.01 for all subgroups) when stratified by 72 h Selvester score ≥6. On the contrary, the additional risk-prediction by 72 h Q presence was either absent or only borderline. In contemporarily treated STEMI patients, Selvester score is a strong independent predictor of long-term all-cause mortality. On the contrary, the prognostic value of Q-wave presence appears limited in contemporarily treated STEMI patients.

Heart Rate Dependency and Inter-Lead Variability of the T Peak - T End Intervals

The electrocardiographic (ECG) assessment of the T peak–T end (Tpe) intervals has been used in many clinical studies, but several related physiological aspects have not been reported. Specifically, the sources of the Tpe differences between different ECG leads have not been systematically researched, the relationship of Tpe duration to underlying heart rate has not been firmly established, and little is known about the mutual correspondence of Tpe intervals measured in different ECG leads. This study evaluated 796,620 10-s 12-lead ECGs obtained from long-term Holters recorded in 639 healthy subjects (311 female) aged 33.8 ± 9.4 years. For each ECG, transformation to orthogonal XYZ lead was used to measure Tpe in the orthogonal vector magnitude (used as a reference for lead-to-lead comparisons) and to construct a three-dimensional T wave loop. The loop roundness was expressed by a ratio between its circumference and length. These ratios were significantly related to the standard deviation of Tpe durations in different ECG leads. At the underlying heart rate of 60 beats per minute, Tpe intervals were shorter in female than in male individuals (82.5 ± 5.6 vs 90.0 ± 6.5 ms, p < 0.0001). When studying linear slopes between Tpe intervals measured in different leads and the underlying heart rate, we found only minimal heart rate dependency, which was not systematic across the ECG leads and/or across the population. For any ECG lead, positive Tpe/RR slope was found in some subjects (e.g., 79 and 25% of subjects for V2 and V4 measurements, respectively) and a negative Tpe/RR slope in other subjects (e.g., 40 and 65% for V6 and V5, respectively). The steepest positive and negative Tpe/RR slopes were found for measurements in lead V2 and V4, respectively. In all leads, the Tpe/RR slope values were close to zero, indicating, on average, Tpe changes well below 2 ms for RR interval changes of 100 ms. On average, longest Tpe intervals were measured in lead V2, the shortest in lead III. The study concludes that the Tpe intervals measured in different leads cannot be combined. Irrespective of the measured ECG lead, the Tpe interval is not systematically heart rate dependent, and no heart rate correction should be used in clinical Tpe investigations.

Heart Rate Influence on the QT Variability Risk Factors

QT interval variability, mostly expressed by QT variability index (QTVi), has repeatedly been used in risk diagnostics. Physiologic correlates of QT variability expressions have been little researched especially when measured in short 10-second electrocardiograms (ECGs). This study investigated different QT variability indices, including QTVi and the standard deviation of QT interval durations (SDQT) in 657,287 10-second ECGs recorded in 523 healthy subjects (259 females). The indices were related to the underlying heart rate and to the 10-second standard deviation of RR intervals (SDRR). The analyses showed that both QTVi and SDQT (as well as other QT variability indices) were highly statistically significantly (p < 0.00001) influenced by heart rate and that QTVi showed poor intra-subject reproducibility (coefficient of variance approaching 200%). Furthermore, sequential analysis of regression variance showed that SDQT was more strongly related to the underlying heart rate than to SDRR, and that QTVi was influenced by the underlying heart rate and SDRR more strongly than by SDQT (p < 0.00001 for these comparisons of regression dependency). The study concludes that instead of QTVi, simpler expressions of QT interval variability, such as SDQT, appear preferable for future applications especially if multivariable combination with the underlying heart rate is used.

Problems with Bazett QTc correction in paediatric screening of prolonged QTc interval

Background

Bazett formula is frequently used in paediatric screening for the long QT syndrome (LQTS) and proposals exist that using standing rather than supine electrocardiograms (ECG) improves the sensitivity of LQTS diagnosis. Nevertheless, compared to adults, children have higher heart rates (especially during postural provocations) and Bazett correction is also known to lead to artificially prolonged QTc values at increased heart rates. This study assessed the incidence of erroneously increased QTc values in normal children without QT abnormalities.

Methods

Continuous 12-lead ECGs were recorded in 332 healthy children (166 girls) aged 10.7 ± 2.6 years while they performed postural manoeuvring consisting of episodes (in the following order) of supine, sitting, standing, supine, standing, sitting, and supine positions, each lasting 10 min. Detailed analyses of QT/RR profiles confirmed the absence of prolonged individually corrected QTc interval in each child. Heart rate and QT intervals were measured in 10-s ECG segments and in each segment, QTc intervals were obtained using Bazett, Fridericia, and Framingham formulas. In each child, the heart rates and QTc values obtained during supine, sitting and standing positions were averaged. QTc durations by the three formulas were classified to < 440 ms, 440–460 ms, 460–480 ms, and > 480 ms.

Results

At supine position, averaged heart rate was 77.5 ± 10.5 beat per minute (bpm) and Bazett, Fridericia and Framingham QTc intervals were 425.3 ± 15.8, 407.8 ± 13.9, and 408.2 ± 13.1 ms, respectively. At sitting and standing, averaged heart rate increased to 90.9 ± 10.1 and 100.9 ± 10.5 bpm, respectively. While Fridericia and Framingham formulas showed only minimal QTc changes, Bazett correction led to QTc increases to 435 ± 15.1 and 444.9 ± 15.9 ms at sitting and standing, respectively. At sitting, Bazett correction identified 51, 4, and 0 children as having the QTc intervals 440–460, 460–480, and > 480 ms, respectively. At sitting, these numbers increased to 118, 11, and 1, while on standing these numbers were 151, 45, and 5, respectively. Irrespective of the postural position, Fridericia and Framingham formulas identified only a small number (< 7) of children with QT interval between 440 and 460 ms and no children with longer QTc.

Conclusion

During screening for LQTS in children, the use of Bazett formula leads to a high number of false positive cases especially if the heart rates are increased (e.g. by postural manoeuvring). The use of Fridericia formula can be recommended to replace the Bazett correction not only for adult but also for paediatric ECGs.

Automated electrocardiographic quantification of myocardial scar in patients undergoing primary prevention implantable cardioverter-defibrillator implantation: Association with mortality and subsequent appropriate and inappropriate therapies

BACKGROUND

Myocardial scarring from infarction or nonischemic fibrosis forms an arrhythmogenic substrate. The Selvester QRS score has been developed to estimate myocardial scar from the 12-lead electrocardiogram.

OBJECTIVE

We aimed to assess the value of an automated version of the Selvester QRS score for the prediction of implantable cardioverter-defibrillator (ICD) therapy and death in patients undergoing primary prevention ICD implantation.

METHODS

Unselected patients undergoing primary prevention ICD implantation were included in this retrospective, observational, multicenter study. The QRS score was calculated automatically from a digital standard preimplantation 12-lead electrocardiogram and was correlated to the occurrence of death and appropriate and inappropriate shocks during follow-up. Analyses were performed in groups defined by QRS duration < 130 ms vs ≥ 130 ms.

RESULTS

Overall, 1047 patients (872 [83%] men; median age 64 years IQR [55-71]) with ischemic (648, 62%) or nonischemic (399, 38%) cardiomyopathy were included. The median QRS duration was 123 ms (interquartile range [IQR] 111-157 ms), and the median QRS score was 5 (IQR 2-8). The QRS duration was <130 ms in 59% and ≥130 ms in 41%. During a median follow-up of 45 months (IQR 24-72 months), a QRS score of ≥5 was independently associated with a significantly higher risk of mortality (hazard ratio [HR] 1.67; 95% confidence interval [CI] 1.05-2.66; P = .031) and appropriate (HR 1.83; 95% CI 1.07-3.14; P = .028) and inappropriate (HR 2.32; 95% CI 1.04-5.17; P = .039) shocks in patients with QRS duration ≥ 130 ms. No association of the QRS score and outcome was observed in patients with QRS duration < 130 ms (P > .05).

CONCLUSION

The automatically calculated Selvester QRS score, an indicator of myocardial scar burden, predicts mortality and appropriate and inappropriate shocks in patients undergoing primary prevention ICD implantation with a prolonged QRS duration.

Physiologic heart rate dependency of the PQ interval and its sex differences

On standard electrocardiogram (ECG) PQ interval is known to be moderately heart rate dependent, but no physiologic details of this dependency have been established. At the same time, PQ dynamics is a clear candidate for non-invasive assessment of atrial abnormalities including the risk of atrial fibrillation. We studied PQ heart rate dependency in 599 healthy subjects (aged 33.5 ± 9.3 years, 288 females) in whom drug-free day-time 12-lead ECG Holters were available. Of these, 752,517 ECG samples were selected (1256 ± 244 per subject) to measure PQ and QT intervals and P wave durations. For each measured ECG sample, 5-minute history of preceding cardiac cycles was also obtained. Although less rate dependent than the QT intervals (36 ± 19% of linear slopes), PQ intervals were found to be dependent on underlying cycle length in a highly curvilinear fashion with the dependency significantly more curved in females compared to males. The PQ interval also responded to the heart rate changes with a delay which was highly sex dependent (95% adaptation in females and males after 114.9 ± 81.1 vs 65.4 ± 64.3 seconds, respectively, p < 0.00001). P wave duration was even less rate dependent than the PQ interval (9 ± 10% of linear QT/RR slopes). Rate corrected P wave duration was marginally but significantly shorter in females than in males (106.8 ± 8.4 vs 110.2 ± 7.9 ms, p < 0.00001). In addition to establishing physiologic standards, the study suggests that the curvatures and adaptation delay of the PQ/cycle-length dependency should be included in future non-invasive studies of atrial depolarizations.

Sex and race differences in J-Tend, J-Tpeak, and Tpeak-Tend intervals

To facilitate the precision of clinical electrocardiographic studies of J-to-Tpeak (JTp) and Tpeak-to-Tend (Tpe) intervals, the study investigated their differences between healthy females and males, and between subjects of African and Caucasian origin. In 523 healthy subjects (254 females; 236 subjects of African origin), repeated Holter recordings were used to measure QT, JT, JTp, and Tpe intervals preceded by both stable and variable heart rates. Subject-specific curvilinear regression models were used to obtain individual QTc, JTc, JTpc and Tpec intervals. Rate hysteresis, i.e., the speed with which the intervals adapted after heart rate changes, was also investigated. In all sex-race groups, Tpe intervals were not systematically heart rate dependent. Similar to QTc intervals, women had JTc, and JTpc intervals longer than males (difference 20–30 ms, p < 0.001). However, women had Tpec intervals (and rate uncorrected Tpe intervals) shorter by approximately 10 ms compared to males (p < 0.001). Subjects of African origin had significantly shorter QTc intervals than Caucasians (p < 0.001). Gradually diminishing race-difference was found for JTc, JTpc and Tpec intervals. JTc and JTpc were moderately increasing with age but Tpe/Tpec were not. Rate hysteresis of JTp was approximately 10% longer compared to that of JT (p < 0.001). In future clinical studies, Tpe interval should not be systematically corrected for heart rate and similar to the QT interval, the differences in JT, JTp and Tpe intervals should be corrected for sex. The differences in QT and JT, and JTp intervals should also be corrected for race.

Sources of QTc variability: Implications for effective ECG monitoring in clinical practice

Pharmaceuticals that prolong ventricular repolarization may be proarrhythmic in susceptible patients. While this fact is well recognized, schemes for sequential QTc interval monitoring in patients receiving QT‐prolonging drugs are frequently overlooked or, if implemented, underutilized in clinical practice. There are several reasons for this gap in day‐to‐day clinical practice. One of these is the perception that serially measured QTc intervals are subject to substantial variability that hampers the distinction between potential proarrhythmic signs and other sources of QTc variability. This review shows that substantial part of the QTc variability can be avoided if more accurate methodology for electrocardiogram collection, measurement, and interpretation is used. Four aspects of such a methodology are discussed. First, advanced methods for QT interval measurement are proposed including suggestion of multilead measurements in problematic recordings such as those in atrial fibrillation patients. Second, serial comparisons of T‐wave morphologies are advocated instead of simple acceptance of historical QTc measurements. Third, the necessity of understanding the pitfalls of heart rate correction is stressed including the necessity of avoiding the Bazett correction in cases of using QTc values for clinical decisions. Finally, the frequently overlooked problem of QT‐heart rate hysteresis is discussed including the possibility of gross QTc errors when correcting the QT interval for simultaneously measured short‐term heart rate.

Sex differences in heart rate responses to postural provocations

Sex differences are known in several facets of cardiac electrophysiology, mostly concerning myocardial repolarisation. In this study, heart rate and heart rate variability (HRV) responses to postural provocations were compared in 175 and 176 healthy females and males, respectively (aged 33.1 ± 9.1 years). Two different postural provocative tests with position changes supine→sitting→standing→supine and supine→standing→sitting→supine (15-min standing, 10-min other positions) were performed up to 4 times in each subject. Heart rate and heart rate variability spectral indices were measured in 5-min windows before positional changes. At supine position, females had averaged heart rate approximately 5 beats per minute (bpm) faster than males and this sex difference was practically constant during the postural changes. In both sexes, change supine→sitting and supine→standing increased heart rate by approximately 10 and 30 bpm, respectively, with no statistical differences between the sex groups. At supine baseline, females had normalised high frequency components (nHF) of HRV approximately 7% larger compared to males (p < 0.001). While the same difference in nHF was found at sitting, the change to standing position lead to significantly larger nHF reduction in females compared to males (mean changes 22.5 vs 17.2%, p < 0.001). This shows that despite similar heart rate increase, females respond to standing by more substantial shifts in cardiac sympatho-vagal modulations. This makes it plausible to speculate that the differences in autonomic reactions to stress contribute to the known sex-differences in psychosocial responses to stressful situations and to the known difference in susceptibility to ventricular fibrillation between females and males.

Individually Rate Corrected QTc Intervals in Children and Adolescents

Accurate evaluation of the appearance of QTc sex differences during childhood and adolescence is intricate. Inter-subject differences of individual QT/RR patterns make generic heart rate corrections inaccurate because of fast resting heart rates in children. The study investigated 527 healthy children and adolescents aged 4–19 years (268 females, 50.9%). All underwent continuous ECG 12-lead monitoring while performing postural changes during a 70-min investigative protocol to obtain QT interval measurements at different heart rates. On average, more than 1200 ECG measurements (QT interval and its 5-min history of preceding RR intervals) were made in each subject. Curvilinear QT/RR regression involving intra-individual correction for QT/RR hysteresis were calculated in each subject. The projection of the QT/RR regressions to the heart rate of 60 beats per minute defined individually corrected QTc intervals. In males, gradual QTc shortening by about 15 ms appeared during the ages of 13–19 years synchronously with the incidence of secondary sex signs (p = 0.016). On the contrary, whilst gradual QTc prolongation by about 10 ms appeared in females, it occurred only during ages 16–19 years and was not related to the incidence of secondary sex signs (p = 0.18). The study also showed that in children and adolescents, linear QT/RR models fit the intra-subject data significantly more closely than the log-linear models (p < 0.001). The study speculates that hormonal shifts during puberty might be directly responsible for the QTc shortening in males but that QTc prolongation in females is likely more complex since it was noted to follow the appearance of secondary sex signs only after a considerable delay.

Detection of T Wave Peak for Serial Comparisons of JTp Interval

Electrocardiogram (ECG) studies of drug-induced prolongation of the interval between the J point and the peak of the T wave (JTp interval) distinguished QT prolonging drugs that predominantly block the delayed potassium rectifier current from those affecting multiple cardiac repolarisation ion channel currents. Since the peak of the T wave depends on ECG lead, a “global” T peak requires to combine ECG leads into one-dimensional signal in which the T wave peak can be measured. This study aimed at finding the optimum one-dimensional representation of 12-lead ECGs for the most stable JTp measurements. Seven different one-dimensional representations were investigated including the vector magnitude of the orthogonal XYZ transformation, root mean square of all 12 ECG leads, and the vector magnitude of the 3 dominant orthogonal leads derived by singular value decomposition. All representations were applied to the median waveforms of 660,657 separate 10-s 12-lead ECGs taken from repeated day-time Holter recordings in 523 healthy subjects aged 33.5 ± 8.4 years (254 women). The JTp measurements were compared with the QT intervals and with the intervals between the J point and the median point of the area under the T wave one-dimensional representation (JT50 intervals) by means of calculating the residuals of the subject-specific curvilinear regression models relating the measured interval to the hysteresis-corrected RR interval of the underlying heart rate. The residuals of the regression models (equal to the intra-subject standard deviations of individually heart rate corrected intervals) expressed intra-subject stability of interval measurements. For both the JTp intervals and the JT50 intervals, the curvilinear regression residuals of measurements derived from the orthogonal XYZ representation were marginally but statistically significantly lower compared to the other representations. Using the XYZ representation, the residuals of the QT/RR, JTp/RR and JT50/RR regressions were 5.6 ± 1.1 ms, 7.2 ± 2.2 ms, and 4.9 ± 1.2 ms, respectively (all statistically significantly different; p < 0.0001). The study concludes that the orthogonal XYZ ECG representation might be proposed for future investigations of JTp and JT50 intervals. If the ability of classifying QT prolonging drugs is further confirmed for the JT50 interval, it might be appropriate to replace the JTp interval since with JT50 it appears more stable.

Errors of Fixed QT Heart Rate Corrections Used in the Assessment of Drug-Induced QTc Changes

The accuracy of studies of drug-induced QTc changes depends, among others, on the accuracy of heart rate correction of QT interval. It has been recognized that when a drug leads to substantial heart rate changes, fixed universal corrections cannot be used and that alternative methods such as subject-specific corrections established for each study participant need to be considered. Nevertheless, the maximum heart rate change that permits use of fixed correction with reasonable accuracy has not been systematically investigated. We have therefore used full QT/heart-rate profiles of 751 healthy subjects (mean age 34.2 ± 9.6, range 18–61 years, 335 females) and compared their subject-specific corrections with 6 fixed corrections, namely Bazett, Fridericia, Framingham, Hodges, Rautaharju, and Sarma formulae. The comparison was based on statistical modeling experiments which simulated clinical studies of N = 10 or N = 50 female or male subjects. The experiments compared errors of ΔQTc intervals calculated as differences between QTc intervals at an initial heart rate (in the range of 40 to 120 beats per minute, bpm) and after a heart rate change (in the range from −20 to +20 bpm). The experiments also investigated errors due to spontaneous heart rate fluctuation and due to omission of correction for QT/RR hysteresis. In each experiment, the absolute value of the single-sided 90th percentile most remote from zero was used as the error estimate. Each experiment was repeated 10,000 times with random selection of modeled study group. From these repetitions, median and upper 80th percentile was derived and graphically displayed for all different combinations of initial heart rate and heart rate change. The results showed that Fridericia formula might be reasonable (with estimated errors of ΔQTc below 8 ms) in large studies if the heart rate does not change more than ± 10 bpm and that the errors by fixed corrections and the errors due to omission of QR/RR hysteresis are additive. Additionally, the results suggest that the variability introduced into QTc data by not correcting for the underlying heart rate accurately might have a greater impact in smaller studies. The errors by Framingham formula were practically the same as with the Fridericia formula. Other investigated fixed heart rate corrections led to larger ΔQTc errors.

Clinical value of different QRS-T angle expressions

Aims

Increased spatial angle between QRS complex and T wave loop orientations has repeatedly been shown to predict cardiac risk. However, there is no consensus on the methods for the calculation of the angle. This study compared the reproducibility and predictive power of three most common ways of QRS-T angle assessment.

Methods and results

Electrocardiograms of 352 healthy subjects, 941 survivors of acute myocardial infarction (MI), and 605 patients recorded prior to the implantation of automatic defibrillator [implantable cardioverter defibrillator (ICD)] were used to obtain QRS-T angle measurements by the maximum R to T (MRT), area R to T (ART), and total cosine R to T (TCRT) methods. The results were compared in terms of physiologic reproducibility and power to predict mortality in the cardiac patients during 5-year follow-up. Maximum R to T results were significantly less reproducible compared to the other two methods. Among both survivors of acute MI and ICD recipients, TCRT method was statistically significantly more powerful in predicting mortality during follow-up. Among the acute MI survivors, increased spatial QRS-T angle (TCRT assessment) was particularly powerful in predicting sudden cardiac death with the area under the receiver operator characteristic of 78% (90% confidence interval 63-90%). Among the ICD recipients, TCRT also predicted mortality significantly among patients with prolonged QRS complex duration when the spatial orientation of the QRS complex is poorly defined.

Conclusion

The TCRT method for the assessment of spatial QRS-T angle appears to offer important advantages in comparison to other methods of measurement. This approach should be included in future clinical studies of the QRS-T angle. The TCRT method might also be a reasonable candidate for the standardization of the QRS-T angle assessment.

Correction to: Implications of Individual QT/RR Profiles-Part 1: Inaccuracies and Problems of Population-Specific QT/Heart Rate Corrections

The Open Access license, which previously read.

Correction to: Implications of Individual QT/RR Profiles-Part 2: Zero QTc/RR Correlations Do Not Prove QTc Correction Accuracy in Studies of QTc Changes

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License which permits unrestricted use.

Sudden Cardiac Death in Dialysis: Arrhythmic Mechanisms and the Value of Non-invasive Electrophysiology

Sudden Cardiac Death (SCD) is the leading cause of cardiovascular death in dialysis patients. This review discusses potential underlying arrhythmic mechanisms of SCD in the dialysis population. It examines recent evidence from studies using implantable loop recorders and from electrophysiological studies in experimental animal models of chronic kidney disease. The review summarizes advances in the field of non-invasive electrophysiology for risk prediction in dialysis patients focusing on the predictive value of the QRS-T angle and of the assessments of autonomic imbalance by means of heart rate variability analysis. Future research directions in non-invasive electrophysiology are identified to advance the understanding of the arrhythmic mechanisms. A suggestion is made of incorporation of non-invasive electrophysiology procedures into clinical practice. Key Concepts: - Large prospective studies in dialysis patients with continuous ECG monitoring are required to clarify the underlying arrhythmic mechanisms of SCD in dialysis patients. - Obstructive sleep apnoea may be associated with brady-arrhythmias in dialysis patients. Studies are needed to elucidate the burden and impact of sleeping disorders on arrhythmic complications in dialysis patients. - The QRS-T angle has the potential to be used as a descriptor of uremic cardiomyopathy. - The QRS-T angle can be calculated from routine collected surface ECGs. Multicenter collaboration is required to establish best methodological approach and normal values. - Heart Rate Variability provides indirect assessment of cardiac modulation that may be relevant for cardiac risk prediction in dialysis patients. Short-term recordings with autonomic provocations are likely to overcome the limitations of out of hospital 24-h recordings and should be prospectively assessed.

QRS-T Angle Predicts Cardiac Risk and Correlates With Global Longitudinal Strain in Prevalent Hemodialysis Patients

Background: Cardiovascular disease is the commonest cause of death in hemodialysis (HD) patients but accurate risk prediction is lacking. The spatial QRS – T angle is a promising electrophysiological marker for sudden cardiac death risk stratification. The aim of this study was to assess the prognostic value of spatial QRS-T angle derived from standard 12 lead electrocardiograms (ECG) and its association with echocardiographic parameters in HD patients.

Methods: This prospective study of 178 prevalent HD patients (aged 67 ± 14 years, 72% men) collected ECG and echocardiographic data on an annual basis. Baseline echocardiograms at study entry were used for cross-sectional comparisons with ECGs. Study endpoints were all-cause mortality, cardiovascular mortality, and major adverse cardiac events (MACE). The QRS – T angle was calculated from standard 10-s ECG as the total cosine R to T (TCRT) using singular value decomposition and expressed in degrees. TCRT above 100° was defined as abnormal.

Results: During a follow-up period of 36 ± 19 months, 74 patients died, including 17 cardiac deaths, and 54 suffered from MACE. In multivariate Cox regression analysis, QRS-T angle by TCRT at baseline was associated with increased cardiovascular mortality both as a continuous value and dichotomized below or above 100° (HR 1.016, p = 0.029, CI: 1.002–1.030 and HR 3.506, CI: 1.118–10.995, p = 0.031 respectively) and with MACE dichotomized at 100° (HR 1.902, CI: 1.046–3.459; p = 0.035). In multivariate regression analysis including baseline parameters, echocardiographic global longitudinal strain (GLS) was significantly correlated with TCRT (F 9.648, r² = 0.192, standardized β = 0.331, unstandardized β = 3.567, t = 4.4429, CI: 1.976–5.157, p < 0.001).

Conclusion: TCRT correlates with GLS and is independently associated with cardiac deaths and MACE in HD patients.

Polyscore of Non-invasive Cardiac Risk Factors

Non-invasive risk stratification of cardiac patients has been the subject of numerous studies. Most of these investigations either researched unique risk predictors or compared the predictive power of different predictors. Fewer studies suggested a combination of a small number of non-invasive indices to increase the accuracy of high-risk group selection. To advance non-invasive risk assessment of cardiac patients, we propose a combination score (termed the Polyscore) of seven different cardiac risk stratifiers that predominantly quantify autonomic cardiovascular control and regulation, namely the slope of heart rate turbulence, deceleration capacity of heart rate, non-invasively assessed baroreflex sensitivity, resting respiration frequency, expiration triggered sinus arrhythmia, post-ectopic potentiation of systolic blood pressure, and frequency of supraventricular and ventricular ectopic beats. These risk stratification tests have previously been researched and their dichotomies defining abnormal results have been derived from previous reports. The Polyscore combination was defined as the number of positive tests among these seven risk predictors, giving a numerical scale which ranges from 0 (all tests normal) to 7 (all tests abnormal). The Polyscore was tested in a population of 941 contemporarily treated survivors of acute myocardial infarction (median age 61 years, 182 females) of whom 72 (7.65%) died during a 5-year follow-up. In these patients, all the risk predictors combined in the Polyscore were assessed during in-hospital 30-min simultaneous non-invasive recordings of high-frequency orthogonal electrocardiogram, continuous blood pressure and respiration. Compared to Polyscore 0 stratum, the hazard ratios of mortality during follow-up increased almost exponentially in strata 1 through 7 (vs. stratus 0, the hazard ratios were 1.37, 1.96, 7.03, 15.0, 35.7, 48.2, and 114, in strata 1 to 7, respectively; p < 0.0001). This allowed selecting low-risk (Polyscore ≤ 2), intermediate risk (Polyscore 3 or 4) and high-risk (Polyscore ≥ 5) sub-groups of the population that differed greatly in the Kaplan–Meier probabilities of mortality during follow-up. Since the Polyscore was derived from recordings of only 30-min duration, it can be reasonably applied in different clinical situations including population-wide screening. We can therefore conclude that the Polyscore is a reasonable method for cardiac risk stratification that is ready for prospective validation in future independent studies.

Risk stratifiers for arrhythmic and non-arrhythmic mortality after acute myocardial infarction

The effective discrimination between patients at risk of Arrhythmic Mortality (AM) and Non-Arrhythmic Mortality (NAM) constitutes one of the important unmet clinical needs. Successful risk assessment based on Electrocardiography (ECG) records is greatly improved by the combination of different indices reflecting not only the pathological substrate but also the autonomic regulation of cardiac electrophysiology. This study assesses the cardiac risk stratification capacity of two new Heart Rate Variability (HRV) parameters, Breath Concurrence 6 (BC6) -sinusoidal RR variability of 6 heart beats per breath cycle- and Primary Ectopia (PE) -presence of early ventricular contractions of any etiology- together with the Deceleration Capacity (DC). While BC6 characterizes the response to physiological and pathophysiological stimuli, PE qualifies autonomic cardiac electrophysiology. The analysis of the European Myocardial Infarct Amiodarone Trial (EMIAT) database indicates that BC6 is related with the risk of Arrhythmic Mortality (AM) and PE with the risk of Non-Arrhythmic Mortality. BC6 is the only single parameter that significantly discriminates between AM and NAM. While the combination of BC6 and DC contributes to the identification of AM risk, PE together with DC improves the prediction of NAM in patients with severe ischemic heart disease.

Association of QRS-T angle and heart rate variability with major cardiac events and mortality in hemodialysis patients

INTRODUCTION

Mortality in hemodialysis (HD) patients is high with significant proportion attributed to fatal arrhythmias. In a pilot study, we showed that intradialytic electrocardiographic (ECG) monitoring can yield stable profiles of selected repolarisation descriptors and heart rate variability (HRV) parameters. This study investigated the relationship of these ECG markers with major adverse cardiac events (MACE) and mortality.

METHODS

Continuous ECGs were obtained during HD and repeated five times at 2-week intervals. The QRS-T angle calculated as Total Cosine R to T (TCRT) and T-wave morphology dispersion (TMD) were calculated in overlapping 10 s ECG segments. High- (HF) and low (LF)-frequency components and the LF/HF ratio of HRV were calculated every 5 min. These indices were averaged during the first hour of dialysis and subsequently overall recordings in each subject.

RESULTS

All ECG parameters were available in 72 patients aged 61 ± 15, 23 (31.9%) females and 26 (36.1%) diabetics. After a median follow up of 54.8 months, 16 patients died, 20 were transplanted, and 9 suffered MACE. TCRT (in degrees) was higher and LF/HF was lower in patients who died compared to survivors (112 ± 30 vs. 73 ± 35, p = 0.000 and 0.222 ± 0.418 vs. 0.401 ± 0.274, p = 0.000, respectively) and in MACE positive compared to negative (117 ± 40 vs. 77 ± 34, p = 0.017 and 0.125 ± 0.333 vs.0.401 ± 0.274, p = 0.007 respectively). In multivariate Cox regression analysis of mortality risk adjusted for age, diabetes mellitus, and coronary artery disease, TCRT and LF/HF remained significant predictors (p < 0.05).

CONCLUSION

QRS-T angle and HRV may serve risk assessment in future prospective studies in HD patients.

Electrocardiographic and Cardiac Autonomic Indices - Implications of Sex-Specific Risk Stratification in Women After Acute Myocardial Infarction

BACKGROUND

The debate on whether sex-specific predictive models improve risk stratification after myocardial infarction is ongoing.

METHODS

This review summarises the current clinical knowledge on sex-specific differences in post-infarction risk stratification parameters. Particular focus is given to electrocardiographic risk factors and indices of cardiac autonomic status.

RESULTS

Differences in the underlying pathophysiology between men and women are known. However, clinical findings often lead to uncertain conclusions for a number of risk predictors including, among others, resting heart rate, heart rate variability, heart rate turbulence, QT interval duration, and QRS-T angle. The review links recent findings in prognostic parameters with successful approaches in sex-specific non-invasive risk stratification.

CONCLUSION

Disparities are described in the current clinical opinions on the relevance of investigated parameters in women and possible directions for further research in the field are given.

Sex differences in long-term mortality among acute myocardial infarction patients: Results from the ISAR-RISK and ART studies

BACKGROUND

Mortality rates in females who survived acute myocardial infarction (AMI) exceed those in males. Differences between sexes in age, cardiovascular risk factors and revascularization therapy have been proposed as possible reasons.

OBJECTIVE

To select sets of female and male patients comparable in respect of relevant risk factors in order to compare the sex-specific risk in a systematic manner.

METHODS

Data of the ISAR-RISK and ART studies were investigated. Patients were enrolled between 1996 and 2005 and suffered from AMI within 4 weeks prior to enrolment. Patients of each sex were selected with 1:1 equivalent age, previous AMI history, sinus-rhythm presence, hypertension, diabetes mellitus, smoking status, left ventricular ejection fraction (LVEF), and revascularization therapy. Survival times were compared between sex groups in the whole study cohort and in the matched cohort.

RESULTS

Of 3840 consecutive AMI survivors, 994 (25.9%) were females and 2846 (74.1%) were males. Females were older and suffered more frequently from hypertension and diabetes mellitus. In the whole cohort, females showed an increased mortality with a hazard ratio (HR) of 1.54 compared to males (p<0.0001). The matched cohort comprised 802 patients of each sex and revealed a trend towards poorer survival in females (HR for female sex 1.14; p = 0.359). However, significant mortality differences with a higher risk in matched females was observed during the first year after AMI (HR = 1.61; p = 0.045) but not during the subsequent years.

CONCLUSION

Matched sub-groups of post-AMI patients showed a comparable long-term mortality. However, a female excess mortality remained during first year after AMI and cannot be explained by differences in age, cardiovascular risk factors, and modes of acute treatment. Other causal factors, including clinical as well as psychological and social aspects, need to be considered. Female post-AMI patients should be followed more actively particularly during the first year after AMI.

Expiration-Triggered Sinus Arrhythmia Predicts Outcome in Survivors of Acute Myocardial Infarction

BACKGROUND

Respiratory sinus arrhythmia (RSA), a measure of cardiac vagal modulation, provides cardiac risk stratification information. RSA can be quantified from Holter recordings as the high-frequency component of heart rate variability or as the variability of RR intervals in individual respiratory cycles. However, as a risk predictor, RSA is neither exceptionally sensitive nor specific.

OBJECTIVES

This study aimed to improve RSA determination by quantifying the amount of sinus arrhythmia related to expiration (expiration-triggered sinus arrhythmia [ETA]) from short-term recordings of electrocardiogram and respiratory chest excursions, and investigated the predictive power of ETA in survivors of acute myocardial infarction.

METHODS

Survivors of acute myocardial infarction (N = 941) underwent 30-min recordings of electrocardiogram and respiratory chest excursions. ETA was quantified as the RR interval change associated with expiration by phase-rectified signal averaging. Primary outcome was 5-year all-cause mortality. Univariable and multivariable Cox regression was used to investigate the association of ETA with mortality.

RESULTS

ETA was a strong predictor of mortality, both in univariable and multivariable analysis. In a multivariable model including respiratory rate, left ventricular ejection fraction, diabetes mellitus, and GRACE score, ETA ≤0.19 ms was associated with a hazard ratio of 3.41 (95% confidence interval: 1.10 to 5.89, p < 0.0001). In patient subgroups defined by abnormal left ventricular ejection fraction, increased respiratory rate, high GRACE score, or presence of diabetes mellitus, patients were classified as high or low risk on the basis of ETA.

CONCLUSIONS

Expiration-triggered sinus arrhythmia (ETA) is a potent and independent post-infarction risk marker.

Higher incidence of hypotension episodes in women during the sub-acute phase of ST elevation myocardial infarction and relationship to covariates

OBJECTIVE

The introduction of primary percutaneous coronary intervention (PPCI) has modified the profile of ST elevation myocardial infarction (STEMI) patients. Occurrence and prognostic significance of hypotension episodes are not known in PPCI treated STEMI patients. It is also not known whether and/or how the hypotension episodes correlate with the degree of myocardial damage and whether there are any sex differences.

METHODS

Data of 293 consecutive STEMI patients (189 males) treated by PPCI and without cardiogenic shock were analyzed. Blood pressure was measured noninvasively. A hypotensive episode was defined as a systolic blood pressure below 90 mmHg over a period of at least 30 minutes.

RESULTS

A hypotensive episode was observed in 92 patients (31.4%). Female sex was the strongest independent predictor of hypotension episodes (p < 0.0001), while there was no relationship to electrocardiographic STEMI localization. Hypotensive patients had significantly higher levels of troponin T and brain natriuretic peptide; hypotensive episodes were particularly frequent in women with increased troponin T. Treatment with angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB) and betablockers was less frequent in hypotensive patients. After a mean 20-month follow-up, all-cause mortality did not differ between hypotensive patients and others. However, mortality in hypotensive patients who did not tolerate ACEI/ARB therapy was significantly higher compared to other hypotensive patients (p = 0.016).

CONCLUSION

Hypotension episodes are not uncommon in the sub-acute phase of contemporarily treated STEMI patients with a striking difference between sexes-female sex was the strongest independent predictor of hypotension episodes. Hypotensive episodes may lead to a delay in pharmacotherapy which influences prognosis. Higher incidence of hypotension in women could at least partially explain the sex-related differences in the use of cardiovascular pharmacotherapy which was repeatedly observed in various studies.

Inappropriate ICD shocks do not induce pro-arrhythmic electrocardiographic changes in men

OBJECTIVES

Longer-term electrocardiographic effects of multiple inappropriate ICD shocks were investigated to study their hypothesized pro-arrhythmic potential.

DESIGN

Thirteen male patients with ischemic cardiomyopathy who received ≥2 inappropriate shocks within 24 h and for whom 12-lead ECGs were available both before and within 72h after the inappropriate shocks were analyzed. Exclusion criteria included continuous ventricular pacing, underlying AF, events within 6 weeks after lead implantation and concomitant acute medical problems.

RESULTS

A total of 149 inappropriate shocks (mean 11 ± 19) were received. There were no significant differences in any of the measured intervals or morphological indices, nor was there a correlation between the "before-after" differences and the number of shocks received. Non-significant changes showed Percentage of Loop Area increase and relative T-wave Residuum decrease while the opposite changes have previously been associated with arrhythmic risk.

CONCLUSIONS

No potentially pro-arrhythmic electrocardiographic changes were found 19 h after multiple inappropriate shocks.

Sex and race differences in QRS duration

AIMS

The study investigated healthy subjects to study sex and race differences in QRS durations and the dependency of QRS durations on heart rates and other physiologic correlates.

METHODS AND RESULTS

QRS duration and its heart rate dependency were evaluated in 420 615 electrocardiograms obtained in 523 healthy subjects including 111 females of African origin, 130 Caucasian females, 125 males of African origin, and 129 Caucasian males. The distributions of QRS/RR slopes and QRS durations at RR intervals of 1 and 0.5 s were compared between sex- and race-defined subgroups. At high heart rates, QRS duration was increased in ∼35% of all subjects, while in the others, QRS was shortened (no differences between the subgroups). At RR interval of 1 s, the QRS duration was 97.4 ± 4.6, 99.8 ± 6.0, 101.6 ± 5.3, and 104.8 ± 6.3 ms in African females, Caucasian females, African males, and Caucasian males, respectively (all differences P < 0.001). Similar statistical differences were found at an RR of 0.5 s. When accounting for the differences in lean body mass, the difference between African and Caucasian subjects was as large as the difference between females and males. Within each subgroup, the normal QRS durations differed by 15-20 and 18-25 ms at RR intervals of 1 and 0.5 s, respectively.

CONCLUSION

The QRS widths are heart rate dependent and different not only between women and men but also between African and Caucasian individuals. Difference in cardiac resynchronization therapy efficacy might be expected between patients of African and Caucasian origin stratified by QRS duration.

ICH E14-compatible holter bin method and its equivalence to individual heart rate correction in the assessment of drug-induced QT changes

INTRODUCTION

The Holter bin method evaluates QT interval changes in the presence of heart rate changes without correcting the QT interval. However, the method does not allow time-matched comparisons, thus contradicting available guidance and good practice. We report a modification of the methods that allows time-matched comparisons without any heart rate correction.

METHODS AND RESULTS

The modified Holter bin method (a) finds matching baseline heart rates for each QT reading on treatment and (b) calculates ΔQT values from the QT intervals on baseline and on treatment that match in heart rates. The difference between ΔQT values on active treatment and placebo provides the ΔΔQT value. The method was compared with the individual correction method in the data of the mirabegron thorough QT study in which supratherapeutic doses of this β3-adrenoceptor agonist led to substantial heart rate changes. The modified Holter bin method reproduced closely the results obtained with the individual heart rate correction. At all time points of the mirabegron study, the differences between the mean ΔΔQT values by the Holter bin method and the individual correction method were below 1 millisecond. Compared to the individual correction, the Holter bin method led to slight increases in the standard deviations of ΔΔQT values, but these were on average below 0.25 millisecond.

CONCLUSIONS

The Holter bin methodology can be modified to make it compatible with the available guidance and with good practice of clinical investigations. The results obtained with the modified Holter bin method are practically the same as with individualized heart rate corrected QT intervals. The close correspondence between the 2 methods demonstrates that the present possibilities of comparing QT interval duration in the presence of experiment-induced heart rate differences are not influenced by methodological artifacts.

P-wave abnormality predicts recurrence of atrial fibrillation after electrical cardioversion: a prospective study

BACKGROUND

Maintenance of atrial fibrillation (AF) is related to atrial electrical inhomogeneity and resultant chaotic reentry. Our aim was to test the hypothesis that abnormalities of P morphology on the surface electrocardiogram (ECG) predict recurrent AF following electrical cardioversion (ECV).

METHODS

A 12-lead ECG was recorded after ECV for persistent AF in 77 patients (51 men, 65 ± 10 years) and repeated 1 month later. P-wave duration was obtained in each lead using blinded on-screen measurement. Maximum P-wave duration (P-max) was defined as the longest measurable P-wave duration in any lead. P-wave dispersion (PWd) was calculated as the maximum-minimum P-wave duration.

RESULTS

One month after ECV, 29 (38%) patients maintained sinus rhythm. Compared with the sinus rhythm group, those with recurrent AF had significantly greater PWd (66 ± 19 vs 57 ± 16 ms, P = 0.024) and included more patients with P-max ≥142 ms (65% vs 38%, P = 0.023). Using a cutoff of ≥62 ms for PWd and ≥142 ms for P-max, both indices had similar predictive value (sensitivity 66.7 and 64.6%, specificity 58.6 and 62.1%, respectively). In multiple regression analysis, including established clinical predictors, P-max ≥142 ms was the only independent predictor of AF recurrence (P = 0.025).

CONCLUSION

A prolonged P-wave duration measured by 12-lead ECG predicts recurrent AF within 1 month after ECV.

QT/RR curvatures in healthy subjects: sex differences and covariates

Data of a large clinical study were used to investigate how much are the QT/RR patterns in healthy subjects curved and whether these curvatures differ between women and men. Daytime drug-free 12-lead Holter recordings were repeated 4 times in each of 176 female healthy subjects and 176 male healthy subjects aged 32.7 ± 9.1 yr. In each of the subjects, up to 1,440 carefully verified QT interval measurements were obtained with QT/RR hysteresis-corrected RR intervals. Individual subject data were used to fit the following regression equation: QT = χ + (δ/γ)(1 - RR(γ)) + ε, where QT and RR are QT and RR measurements (in s), χ is regression intercept, δ is the QT/RR slope, γ is the QT/RR curvature and provides the lowest regression residual, and ε represents normally distributed zero-centered errors. The bootstrap technique showed the intrasubject reproducibility of QT/RR slopes and curvatures. In women and men, QT/RR curvatures were 0.544 ± 0.661 and 0.797 ± 0.706, respectively (P = 0.0006). The corresponding QT/RR slopes were 0.158 ± 0.030 and 0.139 ± 0.023, respectively (P < 0.0001). QT/RR curvatures were related to QT/RR slopes but not to individually corrected mean QTc intervals or individual QT/RR hysteresis profiles. The individual heart rate correction formula derived from the curvilinear regression provided a significantly lower intrasubject variability of QTc interval than individual optimisation of linear or log-linear QT/RR heart rate corrections. The QT/RR curvature can be reliable measured and expressed numerically. The corresponding heart rate correction formula provides more compact data than the previously proposed approaches. There are substantial sex differences in QT/RR patterns. Women have a QT/RR pattern that is not only steeper than men but also more curved.

Relationship of QT interval variability to heart rate and RR interval variability

The study investigated whether the beat-to-beat QT interval variability relationship to the mean heart rate and the RR interval variability depended on the cardiovascular autonomic status changed by postural positioning. Repeated long-term 12-lead Holter recordings were obtained from 352 healthy subjects (mean age 32.7 ± 9.1 years, 176 females) while they underwent postural provocative tests involving supine, unsupported sitting and unsupported standing positions. Each recording was processed as a sequence of overlapping 10-second segments. In each segment, the mean RR interval, the coefficients of variance of the RR intervals (RRCV) and the QT intervals (QTCV) were obtained. In each subject, these characteristics, corresponding to different postural positions, were firstly averaged and secondly used to obtain within-subject correlation coefficients between the different characteristics at different postural positions. While the within-subject means of RRCV generally decreased when changing the position from supine to sitting and to standing (4.53 ± 1.95%, 4.12 ± 1.51% and 3.26 ± 1.56% in females and 3.99 ± 1.44%, 4.00 ± 1.24% and 3.53 ± 1.32% in males respectively), the means of QTCV systematically increased during these position changes (0.96 ± 0.40%, 1.30 ± 0.56% and 1.88 ± 1.46% in females and 0.85 ± 0.30%, 1.13 ± 0.41% and 1.41 ± 0.59% in males, respectively). The intra-subject relationship between QTCV, RRCV and mean RR intervals was highly dependent on postural positions. The study concludes that no universally applicable normalization of the QT interval variability for the heart rate and/or the RR interval variability should be assumed. In future studies of the QT variability, it seems preferable to report on the absolute values of QT variability, RR variability and mean heart rate separately.

Importance of subject-specific QT/RR curvatures in the design of individual heart rate corrections of the QT interval

OBJECTIVE

A statistical modelling study investigated whether incorporating the curvatures of QT/RR patterns into the individual-specific QT heart rate correction increases QTc data accuracy.

METHODS

Repeated ECG readings were available from 4 different drug-free recordings made in 176+176 healthy female and male subjects (aged 32 ± 10 and 33 ± 8 years, respectively). In each subject, up to 1440 ECG readings were made of QT intervals and of the corresponding QT/RR hysteresis corrected RR intervals. The QT/RR patterns of each study participant was fitted with 12 different regression formulae that corresponded to differently curved physiologically plausible QT/RR profiles. In each subject, each of the regression fits was converted into a QT heart rate correction formula and the optimum model that fitted the data of the subject best was identified. Correction formulae were applied to modelled QT/RR data with RR intervals between 400 ms and 1600 ms. Differences in QTc intervals calculated by the correction formulae corresponding to the individually optimum QT/RR regression models and by the same type of regression in all study subjects were statistically summarised in females and males.

RESULTS

Compared to the individually curvature optimised QTc heart rate correction formulae, formulae of the different regression models overestimated or underestimated the QTc values when applied on all study subjects. At RR of 500 ms, the model assuming linear QT/RR relationship led to errors of -5.01 ± 6.63 ms and of -4.80 ± 7.23 ms in females and males, respectively. At the same RR interval level, the model assuming the linear relationship between the logarithms of QT and RR intervals led to errors of +11.51 ± 6.36 ms and of +15.09 ± 7.61 ms in females and males, respectively.

CONCLUSION

The differences in the curvatures of QT/RR patterns should be considered in the optimisation of subject-specific heart rate corrections. Forcing an arbitrary simple regression model on the QT/RR patterns of different subjects may lead to appreciable errors in QTc estimates. The frequently used linear and log-linear regression models were among the least precise if used without checking their appropriateness in individual subjects.