New quantitative methods for evaluation of dynamic changes in QT interval on 24 hour Holter ECG recordings: QT interval in idiopathic ventricular fibrillation and long QT syndrome

Improving the management of patients with chronic cardiac and respiratory diseases by extending pulse-oximeter uses: the dynamic pulse-oximetry

Respiratory and cardio-vascular chronic diseases are among the most common noncommunicable diseases (NCDs) worldwide, accounting for a large portion of health-care costs in terms of mortality and disability. Their prevalence is expected to rise further in the coming years as the population ages. The current model of care for diagnosing and monitoring NCDs is out of date because it results in late medical interventions and/or an unfavourable cost-effectiveness balance based on reported symptoms and subsequent inpatient tests and treatments. Health projects and programs are being implemented in an attempt to move the time of an NCD's diagnosis, as well as its monitoring and follow up, out of hospital settings and as close to real life as possible, with the goal of benefiting both patients' quality of life and health system budgets. Following the SARS-CoV-2 pandemic, this implementation received additional impetus. Pulseoximeters (POs) are currently used in a variety of clinical settings, but they can also aid in the telemonitoring of certain patients. POs that can measure activities as well as pulse rate and oxygen saturation as proxies of cardio-vascular and respiratory function are now being introduced to the market. To obtain these data, the devices must be absolutely reliable, that is, accurate and precise, and capable of recording for a long enough period of time to allow for diagnosis. This paper is a review of current pulse-oximetry (POy) use, with the goal of investigating how its current use can be expanded to manage not only cardio-respiratory NCDs, but also acute emergencies with telemonitoring when hospitalization is not required but the patients' situation is debatable. Newly designed devices, both "consumer" and "professional," will be scrutinized, particularly those capable of continuously recording vital parameters on a 24-hour basis and coupling them with daily activities, a practice known as dynamic pulse-oximetry.

Polymorphic Ventricular Tachycardia: Terminology, Mechanism, Diagnosis, and Emergency Therapy

Polymorphic ventricular tachyarrhythmias are highly lethal arrhythmias. Several types of polymorphic ventricular tachycardia have similar electrocardiographic characteristics but have different modes of therapy. In fact, medications considered the treatment of choice for one form of polymorphic ventricular tachycardia, are contraindicated for the other. Yet confusion about terminology, and thus diagnosis and therapy, continues. We present an in-depth review of the different forms of polymorphic ventricular tachycardia and propose a practical step-by-step approach for distinguishing these malignant arrhythmias.

Normative Heart-Rate Corrected Values for Repolarisation Length From Holter Recordings in Children and Adults

BACKGROUND

Normative values for heart-rate corrected repolarisation length are not available in children and are scarce in adults. We wished to define repeatability and normative values of Holter recording measurements of repolarisation length in healthy individuals using a commercially available system, and compare measurements with those from 12-lead electrocardiograms (ECGs).

METHODS

Twenty-four-hour (24-) Holter recordings were made on 99 Healthy volunteers: 52 children (7 months to 14 years) and 47 adults (≥15 yrs). Mean and peak values of QTc, and RTPc (R-wave to peak T-wave) were assessed. Bazett heart rate correction was employed for each measurement and only heart rates between 40 and 120 bpm were analysed. The end of the T-wave was defined from the zero-crossing point. QTc was also determined from 12-lead ECGs from the same population by manual measurement recording the longest QTc of leads 2 and V5. The tangent technique was used to define the end of the T-wave.

RESULTS

Interobserver repeatability: mean QTc ±15 ms (CI 3.5%), peak QTc ±25 ms (CI 4.5%), mean RTPc ±3 ms (CI 1%), peak RTPc ±44 ms (CI 11%). Mean values were very similar for <15 years and all females and were therefore amalgamated: mean (±2 SD); mean QTc 424 ms (394-454), mean RTPc 291ms (263-319). Values were lower in males ≥15 years; (mean QTc 408 ms (370-446), p<0.01; mean RTPc 274 ms (234-314), p<0.01. The highest mean QTc value was 467 ms in an adult female. QTc from 12-lead ECG: females <15 years 409 ms (384-434) males <15 years 408 ms (383-433), females ≥15 years 426 ms (401-451), males ≥15 years 385 ms (362-408).

CONCLUSIONS

Holter measurements of mean QTc and RTPc are highly repeatable. Males ≥15 years have shorter mean repolarisation length over 24 hours than males <15 years and all females. Mean QTc Holter values were on average 15-17 ms longer than QTc from 12-lead ECGs except in females >15 years.

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.

Abnormal repolarization dynamics in a patient with KCNE1(G38S) who presented with torsades de pointes

Risk of G38S, major KCNE1 polymorphism [KCNE1(G38S)], for long QT syndrome (LQTS) remains unclear. A 72-year-old woman was admitted with recurrent torsades de pointes (TdP). She had remarkable QT prolongation (corrected QT interval 568 ms) under conditions of hypokalemia and hypomagnesemia. After correction of this electrolytic imbalance, TdP was suppressed and metoprolol was started. The QT-RR slope in 24-hour Holter electrocardiogram was steep and this enhanced bradycardia-dependent QT prolongation was similar to that in LQTS. She carried KCNE1(G38S). Patients with KCNE1(G38S) could have similar potential risk of ventricular arrhythmia as with LQTS. Analysis of QT-RR relationship could also evaluate the latent arrhythmogenicity of KCNE1(G38S).

Time-Dependent Changes in QT Dynamics after Initiation and Termination of Paroxysmal Atrial Fibrillation

BACKGROUND

Little is known about time-dependent changes in QT dynamics after initiation of atrial fibrillation (AF) and after restoration of sinus rhythm (SR) in patients with paroxysmal AF.

METHODS

Beat-to-beat QT and RR intervals in CM5 lead were measured automatically in 13 patients with both AF and SR on the single 24-hour Holter electrocardiology recording. QT-RR relation was analyzed at six periods of time: 1 hour before AF onset (Pre(0-1h)), 0-1 hour and 4-5 hours after AF onset (AF(0-1h) and AF(4-5h)), and 0-1 hour, 2-3 hours, and 4-5 hours after the restoration of SR (SR(0-1h), SR(2-3h), and SR(4-5h)).

RESULTS

QT-RR slope was gradually decreased after AF onset and gradually returned to the baseline level after restoration of SR. The slope became greater at SR(4-5h) than at AF(4-5h) and AF(0-1h). In patients receiving antiarrhythmic drugs (AADs; n = 5), QT-RR slope was greater at SR(4-5h) than in those not receiving AADs (n = 8).

CONCLUSION

In patients with paroxysmal AF, bradycardia-dependent QT prolongation was attenuated during AF, and was corrected and gradually augmented along with continuation of SR, especially in patients receiving AADs. This could increase the risk of developing torsade de pointes.

CYP2C19 variation, not citalopram dose nor serum level, is associated with QTc prolongation

Recently, a FDA Safety Communication warned of a dose-dependent risk for QTc prolongation with citalopram, which is metabolized by CYP2C19 of the cytochrome P450 system. We investigate associations between citalopram and escitalopram dose, serum concentration, CYP2C19 phenotype, and QTc. We undertook a retrospective chart review of citalopram or escitalopram patients with the inclusion criteria of consistent medication dose, CYP2C19 phenotype (extensive metabolizers [EM], intermediate metabolizers [IM], poor metabolizers [PM]), and QTc interval on ECG. We further identified 42 citalopram users with citalopram serum concentration measurements and ECG. Regression and one-way ANOVA were used to examine the relationship between citalopram dose, citalopram serum concentration, CYP2C19 phenotype, and QTc interval. Of 75 citalopram patients, the EM group had significantly shorter QTc intervals than a combined IM+PM group (427.1±23.6 ms vs. 440.1±26.6 ms, one-tailed t-test, p=0.029). In the 80 escitalopram cohort, there was no significant difference in QTc between phenotype groups. There was no statistical correlation between citalopram (p=0.62) or escitalopram (p=0.30) dose and QTc. QTc was not associated with citalopram serum level (p=0.45). In contrast to the FDA warning, this study found no association between citalopram/escitalopram dose and QTc. However, PM of the drug tended to have longer QTc intervals. Our findings suggest cytochrome P450 genotyping in select patients may be helpful to guide medication optimization while limiting harmful effects.

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

QT-RR linear regression consists of two parameters, slope and intercept, and the aim of this study was to evaluate repolarization dynamics using the QT-RR linear regression slope and intercept relationship during 24-h Holter ECG. This study included 466 healthy subjects (54.6 ± 14.6 years; 200 men and 266 women) and 17 patients with ventricular arrhythmias, consisted of 10 patients with idiopathic ventricular fibrillation (IVF) and 7 patients with torsades de pointes (TDP). QT and RR intervals were measured from ECG waves based on a 15-s averaged ECG during 24-h 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). The slope of the QT-RR regression line in healthy subjects was significantly greater in women than in men (0.185 ± 0.036 vs. 0.161 ± 0.033, p < 0.001) and the intercept was significantly smaller in women than in men (0.229 ± 0.028 vs. 0.240 ± 0.027, p < 0.001). A scatter diagram of the QT-RR regression line slope and intercept among healthy subjects demonstrated a statistically significant negative correlation (B = -0.62A + 0.34, r = -0.79). Distribution of both scatter diagrams of the slope and the intercept of the QT-RR regression line in patients with IVF and TDP was different from healthy subjects (left corner for IVF and upward shift for TDP). The slope and intercept relationship of the QT-RR linear regression line based on 24-h Holter ECG may become a simple useful marker for abnormality of ventricular repolarization dynamics.

Increased risk of antipsychotic-related QT prolongation during nighttime: a 24-hour holter electrocardiogram recording study

Most antipsychotic agents can cause QT prolongation, which causes torsades de pointes. The QT interval in healthy subjects is longer during nighttime than during daytime. The QT interval of patients treated with antipsychotics may be prolonged during nighttime, and the effects of antipsychotics on the QT interval may differ between antipsychotics. This study investigated the circadian dynamics of the QT interval in patients treated with antipsychotics and healthy controls, using a 24-hour Holter electrocardiogram in a clinical setting. Sixty-six patients with a diagnosis of schizophrenia that were treated with risperidone or olanzapine and 40 healthy volunteers were enrolled. The QT intervals were corrected using the Fridericia formula (QTcF = QT / RR). Mean ± SD nighttime QTcFs were 411.6 ± 29.0, 395.9 ± 21.2, and 387.8 ± 19.0 milliseconds (ms) in the risperidone, olanzapine, and control groups, respectively. The mean daytime QTcFs were 397.7 ± 23.4, 392.4 ± 18.9, and 382.6 ± 17.3 ms, respectively. The mean nighttime QTcF of the risperidone group was significantly longer than that of the olanzapine and control groups, although there was no significant difference in the mean daytime QTcF between the risperidone and olanzapine groups. The current study used 24-hour Holter electrocardiograms to reveal significantly longer QT intervals in the risperidone group especially during nighttime. In clinical practices, evaluations of the QT interval have been conducted over short periods in the daytime, but it is believed that such methods may not be able to fully elucidate the effects of antipsychotics on the QT interval.

QT/RR relation during atrial fibrillation based on a single beat analysis in 24-h Holter ECG: the role of the second and further preceding RR intervals in QT modification

BACKGROUND

During atrial fibrillation (AF) irregularity of RR intervals may modify QT/RR relation differently from sinus rhythm. The purpose of this study was to compare QT/RR relation based on a single-beat analysis using the first preceding RR interval with the modified RR interval reflecting not only the first preceding but also the second and further preceding RR intervals during AF.

METHODS

QT and RR intervals were measured using an automatic QT analyzing system in 32 patients who had both AF and sinus rhythm on the same 24-h Holter ECG recording. In 12 patients antiarrhythmic drugs (AADs) were administered. To reflect irregularity of the preceding RR intervals during AF, a modified RR (mRR) using a weighted average of five successive RR intervals: (5RR(1)+2RR(2)+RR(3)+RR(4)+RR(5))/10 was adopted. Linear regression analyses between QT and RR intervals were performed using the preceding RR(1) (QT/RR) and the modified RR (QT/mRR) during AF.

RESULTS

During AF the slope of QT/RR was lower than that of QT/mRR and was also lower than that of QT/RR during sinus rhythm in patients with and without AAD. Slopes of regression line in QT/RR during sinus rhythm, QT/RR and QT/mRR during AF were steeper in patients with AAD than those in patients without. Slopes of QT/RR during sinus rhythm correlated with those of QT/mRR (r=0.79, p<0.01) better than those of QT/RR (r=0.64, p<0.05) during AF. QT interval at an RR interval of 1.20s or 1.00 s obtained from QT/RR during AF was significantly smaller than that during sinus rhythm in patients with and without AAD.

CONCLUSIONS

The slope of QT/mRR during AF became closer to that of QT/RR during sinus rhythm compared with that of QT/RR during AF. QT interval during sinus rhythm could be estimated better using QT/mRR than using QT/RR during AF.

Comparison of QT/RR relation based on a 15-s averaged ECG and a single beat ECG during atrial fibrillation

BACKGROUND

The aim of this study was to compare QT/RR relation based on a 15-s averaged beat ECG with a single beat ECG during atrial fibrillation (AF) and to determine which was better to estimate the QT interval after sinus restoration.

METHODS AND RESULTS

QT and RR intervals were measured using an automatic QT analyzing system in 33 patients who had both AF and sinus rhythm on the same 24-h Holter ECG recording. In 14 patients, antiarrhythmic drugs (AAD) were administered. QT/RR relations were analyzed from ECG waves obtained by the summation of consecutive QRS-T complexes during each 15-s period (QT/RR-average) and a single beat QRS-T (QT/RR-single). During sinus rhythm, the slope of QT/RR-average did not differ from that of QT/RR-single in patients with and without AAD. On the other hand, during AF, the slope of QT/RR-average was significantly greater than that of QT/RR-single (without AAD: 0.12±0.06 vs. 0.06±0.03, P<0.001; with AAD: 0.15±0.05 vs. 0.08±0.04, P<0.001). During AF, the QT interval at an RR interval of 1.2-s (QT-1.2) determined from QT/RR-average was significantly greater than QT-1.2 from QT/RR-single in patients with and without AAD. QT-1.2 in QT/RR-single during AF was significantly smaller than that during sinus rhythm but QT-1.2 in QT/RR-average during AF was not.

CONCLUSIONS

The QT interval after sinus restoration could be estimated better using QT/RR-average than using QT/RR-single during AF.

The role of the epinephrine test in the diagnosis and management of children suspected of having congenital long QT syndrome

The epinephrine test has been shown to be a powerful tool to predict the genotype of congenital long QT syndrome (LQTS). The aim of this study was to evaluate its role in the diagnosis and management of LQTS in children. The test (using the Shimizu protocol) was conducted in patients with some evidence of LQTS but in whom clinical and management decisions were challenging (n = 41, age 9.6 +/- 3.9 years, 19 female). LQT1, LQT2, and negative responses to epinephrine were obtained in 16, 5, and 20 subjects, respectively. LQTS gene positivity was obtained in two subjects. Beta-blocker therapy was started in all subjects with a positive epinephrine response (n = 21) and in some negative responders because of their strong LQTS phenotype (n = 10). No therapy was given to the subset with less convincing features of LQTS who had also responded negatively to epinephrine (n = 10). Follow-up for 3.0 +/- 2 years was uneventful in both management groups. Due to the discordance with genotyping, the epinephrine test cannot be used to diagnose genotype-positive LQTS but when used in combination with phenotype assessment and genetic screening, it could enable better management decisions.

Drug-induced QT interval shortening: potential harbinger of proarrhythmia and regulatory perspectives

ATP-dependent potassium channel openers such as pinacidil and levcromakalim have long been known to shorten action potential duration and to be profibrillatory in non-clinical models, raising concerns on the clinical safety of drugs that shorten QT interval. Routine non-clinical evaluation of new drugs for their potential to affect cardiac repolarization has revealed that drugs may also shorten QT interval. The description of congenital short QT syndrome in 2000, together with the associated arrhythmias, suggests that drug-induced short QT interval may be proarrhythmic, and an uncanny parallel is evolving between our appreciation of the short and the long QT intervals. Epidemiological studies report an over-representation of short QT interval values in patients with idiopathic ventricular fibrillation. Therefore, as new compounds that shorten QT interval are progressed further into clinical development, questions will inevitably arise on their safety. Arising from the current risk-averse clinical and regulatory environment and concerns on proarrhythmic safety of drugs, together with our lack of a better understanding of the clinical significance of short QT interval, new drugs that substantially shorten QT interval will likely receive an unfavourable regulatory review unless these drugs fulfil an unmet clinical need. This review provides estimates of parameters of QT shortening that may be of potential clinical significance. Rufinamide, a recently approved anticonvulsant, illustrates the current regulatory approach to drugs that shorten QT interval. However, to further substantiate or confirm the safety of these drugs, their approval may well be conditional upon large-scale post-marketing studies with a focus on cardiac safety.

Not another formula for heart rate correction of QT interval

BACKGROUND

Normal limits for QT and heart rate were developed in a Japanese population undergoing 24 hour recordings of the electrocardiogram (ECG). The purpose of this study is to validate these normal limits in a West London population having 12-lead ECGs.

METHODS

A retrospective observational cohort of 10,099 patients aged 20-79 attending a hospital ECG department was studied. From the Japanese data z-scores were calculated for men under 50, for men over 50, for women under 50 and for women over 50. z-scores were used to compare the West London and Japanese populations.

RESULTS

Cardiac infarction injury scores (CIIS) for all four groups were less than zero indicating a population at low risk of cardiovascular disease. From the Japanese data a z-score of 1 is roughly 20 ms. West London mean (SD) z-scores for men under 50, for men over 50, for women under 50 and for women over 50 were 0.20 (0.85), -0.02 (0.86), 0.14 (0.93), and -0.45 (0.88), respectively.

CONCLUSIONS

The distributions of the QT and heart rate data of a West London population at low risk of cardiovascular disease are comparable to the Japanese data. The Japanese QT normal limits for women over the age of 50 are about 9 ms higher regardless of heart rate. The QT normal limits for Afro-Caribbeans are about 5 ms lower than other ethnic groups. The Japanese normal limits are applicable elsewhere, albeit adjusting for women over the age of 50 and for Afro-Caribbeans.

Pharmacological Cardioversion of Long-Lasting Atrial Fibrillation

Pharmacological therapy for atrial fibrillation (AF) is difficult because AF induces atrial remodeling. Randomized prospective studies using amiodarone could not show the superiority of rhythm control strategy to rate control strategy for treatment of AF. Bepridil is a multichannel blocker like amiodarone and expected to be effective for termination of AF without exacerbation of extracardiac adverse effects. Efficacy and safety of bepridil in pharmacological cardioversion of long-lasting AF (≥3 months) was assessed. To avoid the risk of excessive QT prolongation, bepridil dosage was limited to ≤200 mg/day and aprindine (class Ib) was added if necessary. Bepridil alone or in combination with aprindine restored sinus rhythm in 69% of patients. No adverse effects necessitating drug termination occurred. The average time to conversion after starting bepridil was 30 days and cardioversion was associated with significant increase in fibrillation cycle length. After cardioversion, atrial contraction recovered faster within 1 week and sinus rhythm was maintained better than conventional electrical cardioversion. The history of drug-resistant AF did not affect efficacy of bepridil. These observations suggest that pharmacological cardioversion of long-lasting AF could become a new therapeutic option. Although the precise mechanism of cardioversion by bepridil is not clear, reversal of the remodeled atria may play an important role.

Evaluation of a 12-Lead Digital Holter System for 24-Hour QT Interval Assessment

BACKGROUND

Drug induced QT prolongation may precipitate life threatening cardiac arrhythmias. Evaluation of the QT prolonging effect of new pharmaceutical agents in a 'thorough QT/QTc study' is being mandated by FDA. The purpose of this study was to evaluate an automated 12-lead digital Holter system for a thorough QT/QTc study.

METHODS

Five healthy volunteers underwent 24-hour digital Holter monitoring. Each recording underwent a fully automated QT analysis (AQA) followed by an onscreen complete manual over read (MOR). Each recording was analyzed twice at least 2 weeks apart. The effect of data sampling (5-min segment/hour), the system sensitivity to detect 5-ms increase in QT, and the ability to assess circadian variation were evaluated.

RESULTS

The AQA resulted in identical QT for the first and second analyses, but with obvious errors in QT measurements. Compared to the complete onscreen MOR, the mean QT was longer with AQA (416 +/- 41 vs. 387 +/- 30 ms, p < 0.001), correlation; r = 0.3. The reproducibility of AQA with complete MOR was very good (QT: 387 +/- 30 vs. 387 +/- 30 ms, coefficient of variation: 0.2%, r = 0.986. The 5-min mean QT intervals correlated well with the hourly mean QT intervals (r = 0.994, p < 0.001, coefficient of variation = 1 ms) and both showed a similar circadian variation. The system was sensitive to detect a 5-ms change in QT intervals (5 +/- 2 ms, coefficient of variation = 0.6%, r = 0.998, p < 0.001).

CONCLUSIONS

The AQA is not an acceptable method, while the automatic analysis with complete MOR is a highly sensitive and reproducible method. Data sampling by analyzing 5-min segments per hour is sensitive and reproducible.