Evaluation of repolarization dynamics using the QT-RR regression line slope and intercept relationship during 24-h Holter ECG

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.

Prevalence of early repolarization pattern and its association with sudden cardiac death and arrhythmia over one-year follow-up in an Egyptian cohort

Background and objectives

Early repolarization pattern (ERP) is not uncommon electrocardiography (ECG) finding and could be associated with arrhythmia and sudden cardiac death (SCD). We aimed to prospectively determine the prevalence of ERP and its association with arrhythmia and SCD during one-year follow-up in an outpatient Egyptian cohort.

Methods

Clinical assessment and ECG were performed to 1850 consecutive individuals presented at the outpatient clinic of Suez Canal University Hospital (SCUH). Then, the ERP group and 100 age and gender-matched ERP −ve controls had undergone echocardiography, 24-h Holter ECG and exercise stress ECG.

Results

ERP was found in 124 individuals (6.7%); we excluded 24 patients with structural heart disease. ERP group (No. = 100) were relatively young (80% <50 years-old) and showed male preponderance (60%). ERP frequencies were: inferolateral (50%), antero-lateral (38%), inferior (10%), and global (2%). ERP subjects were leaner than controls (BMI was 25.3 vs. 30 kg/m², P value < 0.001) and achieved more metabolic equivalents (METS) on stress ECG (10.7 vs. 8.5 METS, P value < 0.01). Only 4% in the ERP group had horizontal/descending ST slope, while 8% had ST elevation ≥ 2 ms. No arrhythmia or SCD were reported during 1-year follow-up in both groups. Regression analysis showed that male gender, Sokolow-Lyon criteria and short QTc were significant independent predictors of ERP, P value < 0.05.

Conclusions

In outpatient-based Egyptian cohort, the prevalence of ERP was 6.7%, mostly the inferolateral pattern. Our ERP subjects had low-risk clinical and ECG criteria for malignant ERP. Further epidemiological studies are needed to explore the natural history of ERP.

Latent pathogenicity of the G38S polymorphism of KCNE1 K+ channel modulator

KCNE1 encodes a modulator of KCNQ1 and KCNH2 channels. Although KCNE1(G38S), a single-nucleotide polymorphism (SNP) causing a G38S substitution in KCNE1, is found frequently, whether and how this SNP causes long QT syndrome (LQTS) remains unclear. We evaluated rate-dependent repolarization dynamics using Holter electrocardiogram (ECG) to assess the pathogenicity of KCNE1(G38S). Forty-five patients exhibiting long QT intervals, as assessed by their baseline ECGs, and 16 control subjects were enrolled. KCNE1(G38S) carriers were identified using genome sequencing. LQTS patients were classified into LQT1 or LQT2 using genetic analysis or epinephrine test. QT-RR relations were determined using 24-h Holter ECG recordings. Among the 15 patients (33.3 %) with KCNE1(G38S), four patients without any mutations or amino acid changes in other major cardiac ion channels were categorized as KCNE1(G38S) carriers. In the QT-RR regression lines, the QT-RR slope was greater in the KCNE1(G38S) carriers and the LQT2 patients (0.215 ± 0.021 and 0.207 ± 0.032, respectively) than in the LQT1 patients (0.163 ± 0.014, P < 0.05) and the control subjects (0.135 ± 0.025, P < 0.001). The calculated QT intervals at an RR interval of 1200 ms were longer in the KCNE1(G38S) carriers and LQT1 and LQT2 patients than in the control subjects. Patients with KCNE1(G38S) had a rate-dependent repolarization abnormality similar to patients with LQT2 and, therefore, may have a potential risk to develop lethal arrhythmias.

Differences in the Slope of the QT-RR Relation Based on 24-Hour Holter ECG Recordings between Cardioembolic and Atherosclerotic Stroke

Objective Detecting paroxysmal atrial fibrillation in patients with ischemic stroke presenting in sinus rhythm is difficult because such episodes are often short, and they are also frequently asymptomatic. It is possible that the ventricular repolarization dynamics may reflect atrial vulnerability and cardioembolic stroke. Hence, we compared the QT-RR relation between cardioembolic stroke and atherosclerotic stroke during sinus rhythm. Methods The subjects comprised 62 consecutive ischemic stroke patients including 31 with cardioembolic strokes (71.8±12.7 years, 17 men) and 31 with atherosclerotic strokes (74.8±10.8 years, 23 men). The QT and RR intervals were measured from ECG waves based on a 15-sec averaged ECG during 24-hour Holter recording using an automatic QT analyzing system. The QT interval dependence on the RR interval was analyzed using a linear regression line for each subject ([QT]=A[RR]+B; where A is the slope and B is the y-intercept). Results The mean slope of the QT-RR relation was significantly greater in cardioembolic stroke than in atherosclerotic stroke (0.187±0.044 vs. 0.142±0.045, p<0.001). The mean QT, RR, or QTc during 24-hour Holter recordings did not differ between them. An increased slope (≥0.14) of the QT-RR regression line could predict cardioembolic stroke with 97% sensitivity, 55% specificity and a positive predictive value of 64%. Conclusion The increased slope of the QT-RR linear regression line based on 24-hour Holter ECG in patients with ischemic stroke presenting in sinus rhythm may therefore be a simple and useful marker for cardioembolic stroke.

Can QT/RR relationship differentiate between low- and high-risk patients with hypertrophic cardiomyopathy?

BACKGROUND

Abnormal dynamicity of repolarization is considered to be a marker of myocardial vulnerability contributing to increased risk of arrhythmic events and sudden death. However, little is known about QT dynamics in hypertrophic cardiomyopathy (HCM). In this study, we aimed to evaluate ventricular repolarization by QT dynamicity in patients with HCM, focusing on its value to define if it is able to differentiate among low- and high-risk HCM patients.

METHODS

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-hour Holter recordings using a standard algorithm in 36 HCM patients and 64 control subjects.

RESULTS

QTapex/RR and QTend/RR slopes were significantly steeper in the HCM patients in contrary to healthy control subjects (QTapex/RR = 0.22 + 0.08 vs 0.20 + 0.05, P = 0.0367; QTend/RR = 0.25 + 0.10 vs 0.20 + 0.06, P = 0.023). Moreover, the slopes of QTend/RR and QTapex/RR of high-risk patients were significantly steeper than those of control subjects while no significant differences were found among low-risk HCM patients and control subjects and only QTe/RR of high-risk patients was significantly different between low- and high-risk HCM patients.

CONCLUSIONS

Our study results suggest that QT dynamicity is impaired in patients with HCM and may help to differentiate among low- and high-risk patients. Further studies are needed to elucidate the prognostic significance and clinical implications of impaired ventricular repolarization in patients with HCM.