Beat-to-beat QT dynamics in paroxysmal atrial fibrillation

Children and Adolescent Patients with Variants in the ATP1A3 -encoded Sodium-Potassium ATPase Alpha-3 Subunit Demonstrate an Impaired QT Response to Bradycardia and Predisposition to Sinus Node Dysfunction

Background

Alternating hemiplegia of childhood (AHC) is a rare disorder with both neurologic and cardiac manifestations. The ATP1A3-D801N variant is associated with a pathologically short QT interval and risk of ventricular arrhythmia following bradycardia; however, the mechanism of this remains unknown. We investigated the relationship between heart rate (HR), QT, and QTc, hypothesizing that individuals with ATP1A3-D801N have abnormal, impaired shortening of QT and QTc at lower HR leading to arrhythmia predisposition.

Methods

We performed a retrospective observational study of individuals who underwent clinical evaluation, Holter monitoring, and genetic testing for AHC at Duke University Hospitals. We also compiled a group of healthy individuals as a control cohort. A larger, worldwide cohort of individuals with ATP1A3 - related phenotypes was compiled to investigate sinus node dysfunction. Linear regression analysis was then performed.

Results

The cohort consisted of 44 individuals with ATP1A3 -related phenotypes with 81 Holter recordings (52.27% female; mean age at first Holter 8.04 years, range 0.58 - 33 years), compared to 36 healthy individuals with 57 Holter recordings (52.78% female; mean age at first Holter 9.84 years, range 0.08 - 38 years). Individuals with ATP1A3-D801N had reduced prolongation of QT at lower HR, manifest as a significantly lower slope for HR vs QT compared to healthy (P<0.0001). This resulted in a significantly higher slope of the relationship for HR vs QTc compared to healthy (P<0.0001). Individuals with ATP1A3 - related phenotypes and baseline QTc <350 milliseconds (ms) had increased shortening of QT and QTc at lower HR compared to those with normal QTc (P=0.003; P=0.001). Among worldwide cases, 3 out of 131 individuals with ATP1A3 -related phenotypes required device implantation and/or had sinus pauses >4 seconds.

Conclusions

Individuals with the ATP1A3-D801N variant exhibit paradoxical shortening of QT and QTc at lower HR, which contribute to an increased risk of arrhythmias during bradycardia. This is exacerbated by an underlying risk of sinus node dysfunction.

Clinical Perspective

What is Known: Individuals with ATP1A3-D801N have a short baseline QTc.Two individuals with AHC experienced ventricular fibrillation following bradycardia. What the Study Adds: The QT and QTc shorten to a greater extent at lower heart rate in individuals with ATP1A3-D801N than in healthy individuals. Individuals with ATP1A3 -related phenotypes and QTc <350ms show greater impairment of QT and QTc dynamics than those with normal QTc. There is low prevalence of device implantation and significant sinus pauses in individuals with ATP1A3 -related phenotypes, with a relatively greater prevalence in those with ATP1A3-D801N.

QT interval Adaptation to Heart Rate Changes in Atrial Fibrillation as a Predictor of Sudden Cardiac Death

OBJECTIVE

The clinical significance of QT interval adaptation to heart rate changes has been poorly investigated in atrial fibrillation (AF), since QT delineation in the presence of f-waves is challenging. Therefore, the objective of the present study is to investigate new techniques for QT adaptation estimation in permanent AF.

METHODS

A multilead strategy based on generalized periodic component analysis is proposed for QT delineation, involving a spatial, linear transformation which emphasizes Twave periodicity and attenuates f-waves. QT adaptation is modeled by a linear, time-invariant filter, whose impulse response describes the dependence between the current QT interval and the preceding RR intervals, followed by a memoryless, possibly nonlinear, function. The QT adaptation time lag is determined from the estimated impulse response.

RESULTS

Using simulated ECGs in permanent AF, the transformed lead was found to offer more accurate QT delineation and time lag estimation than did the original ECG leads for a wide range of f-wave amplitudes (the time lag estimation error was found to be -0.2+/-0.6 s for SNR = 12 dB). In a population with chronic heart failure and permanent AF, the time lag estimated from the transformed lead was found to have the strongest, statistically significant association with sudden cardiac death (SCD) (hazard ratio = 3.49), whereas none of the original, orthogonal leads had any such association.

CONCLUSIONS

Periodic component analysis provides more accurate QT delineation and improves time lag estimation in AF. A prolonged adaptation time of the QT interval to heart rate changes is associated with a high risk for SCD.

SIGNIFICANCE

This study demonstrates that SCD risk markers, originally developed for sinus rhythm, can also be used in AF, provided that Twave periodicity is emphasized. The time lag is a potentially useful marker for identifying patients at high risk for SCD, guiding clinicians in adopting effective therapeutic decisions.

Recent heart rate history affects QT interval duration in atrial fibrillation

QT interval prolongation is associated with a risk of polymorphic ventricular tachycardia. QT interval shortens with increasing heart rate and correction for this effect is necessary for meaningful QT interval assessment. We aim to improve current methods of correcting the QT interval during atrial fibrillation (AF). Digitized Holter recordings were analyzed from patients with AF. Models of QT interval dependence on RR intervals were tested by sorting the beats into 20 bins based on corrected RR interval and assessing ST-T variability within the bins. Signal-averaging within bins was performed to determine QT/RR dependence. Data from 30 patients (29 men, 69.3±7.3 years) were evaluated. QT behavior in AF is well described by a linear function (slope ~0.19) of steady-state corrected RR interval. Corrected RR is calculated as a combination of an exponential weight function with time-constant of 2 minutes and a smaller “immediate response” component (weight ~ 0.18). This model performs significantly (p<0.0001) better than models based on instantaneous RR interval only including Bazett and Fridericia. It also outperforms models based on shorter time-constants and other previously proposed models. This model may improve detection of repolarization delay in AF. QT response to heart rate changes in AF is similar to previously published QT dynamics during atrial pacing and in sinus rhythm.

QT interval variability in body surface ECG: measurement, physiological basis, and clinical value: position statement and consensus guidance endorsed by the European Heart Rhythm Association jointly with the ESC Working Group on Cardiac Cellular Electrophysiology

This consensus guideline discusses the electrocardiographic phenomenon of beat-to-beat QT interval variability (QTV) on surface electrocardiograms. The text covers measurement principles, physiological basis, and clinical value of QTV. Technical considerations include QT interval measurement and the relation between QTV and heart rate variability. Research frontiers of QTV include understanding of QTV physiology, systematic evaluation of the link between QTV and direct measures of neural activity, modelling of the QTV dependence on the variability of other physiological variables, distinction between QTV and general T wave shape variability, and assessing of the QTV utility for guiding therapy. Increased QTV appears to be a risk marker of arrhythmic and cardiovascular death. It remains to be established whether it can guide therapy alone or in combination with other risk factors. QT interval variability has a possible role in non-invasive assessment of tonic sympathetic activity.

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.

Anti-KCNQ1 K⁺ channel autoantibodies increase IKs current and are associated with QT interval shortening in dilated cardiomyopathy

AIMS

Autoimmune-associated proarrhythmia in dilated cardiomyopathy (DCM) is poorly understood. Given the significance of KCNQ1 potassium channels in heart rhythm disorders, we hypothesized that circulating anti-KCNQ1 autoantibodies directly modulate cardiac electrophysiology in DCM patients. The purpose of this pilot study was to characterize ion channel autoantibodies in DCM targeting the cardiac repolarizing K(+) current, IKs, and the underlying KCNQ1 potassium channel.

METHODS AND RESULTS

One hundred and fifty DCM patients were screened for anti-KCNQ1 autoantibodies using an enzyme-linked immunosorbent assay. Autoantibodies targeting the extracellular pore domain of the KCNQ1 channel were detected in 6% of study patients. Seropositive individuals exhibited significantly shorter corrected QT intervals when compared with seronegative patients (371 ± 39.9 ms vs. 408 ± 47.9 ms; P = 0.036). There was no difference in clinical severity of heart failure between groups. The functional significance of anti-KCNQ1 antibodies was determined in human embryonic kidney 293 cells expressing KCNQ1/KCNE1 using the whole-cell patch clamp technique. IKs recordings demonstrated a 2.7-fold increase in mean current density on exposure to patients' sera containing anti-KCNQ1 antibodies in contrast to seronegative controls (8.74 ± 1.44 pA/pF vs. 3.26 ± 0.36 pA/pF; P = 0.003). IKs enhancement was not associated with increased KCNQ1 protein levels or altered cell surface expression of the channel.

CONCLUSION

Anti-KCNQ1 autoantibodies found in a subgroup of DCM patients are associated with QT interval shortening and increased IKs current.

Time dependent history improves QT interval estimation in atrial fibrillation

PURPOSE

It is not recommended to perform QTc estimation in patients with atrial fibrillation (AF). We evaluated multiple QT interval correction formulas, including a novel time-dependent history approach, in an effort to identify the best method for correcting the QT interval in patients with AF. The ideal correction results in independence between the QTc estimate and HR.

METHODS

Per-beat characteristics were derived using SuperECG (Mortara Instrument). Offline beat-to-beat QTc interval estimates were constructed using standard formulae and averaged (2-10) groups constructed.

RESULTS

Seventy-one patients were included, age 67 ± 10 years, 69% men. Mean-mean QTc intervals varied by correction (range 394-459 ms). Averaging resulted in the same mean-mean QTc estimate, but significantly reduced variability by up to 55%. Time-dependent RR interval history reduced variability the most (Δ 80%), increased QT/RR dynamics (m=.03 vs .17), and was independent with HR (m = 0.0008).

CONCLUSIONS

Our data suggests that QTc interval estimation in patients with AF can be performed reliably using time-dependent history (RRc) outperforming other correction methods.

Estimation and modeling of QT-interval adaptation to heart rate changes

This paper introduces a new method for QT-interval estimation. It consists in a batch processing mode of the improved Woody's method. Performance of this methodology is evaluated using synthetic data. In parallel, a new model of QT-interval dynamics behavior related to heart rate changes is presented. Since two kinds of QT response have been pointed out, the main idea is to split the modeling process into two steps: 1) the modeling of the fast adaptation, which is inspired by the electrical behavior at the cellular level relative to the electrical restitution curve, and 2) the modeling of the slow adaptation, inspired by experimental works at the cellular level. Both approaches are based on a low-complexity autoregressive process whose parameters are estimated using an unbiased estimator. This new modeling of QT adaptation, combined with the presented QT-estimation process, is applied to several ECG recordings with various heart rate variability dynamics. Its potential is then illustrated on ECG recorded during rest, atrial fibrillation episodes, and exercise. Meaningful results in agreement with physiological knowledge at the cellular level are obtained.

Metabolic syndrome in an Hispanic population–cardiovascular complications

The metabolic syndrome (MetS) is presently one of the main medical problems in developing countries. This syndrome was studied in Puerto Rico at the Cardiovascular Center of Puerto Rico and the Caribbean with emphasis on understanding the cardiovascular complications.

The medical records of patients admitted between 1999 to 2005 were evaluated for three or more MetS diagnostic criteria.

One hundred and seventy-three patients met the consensus criteria of metabolic syndrome (MetS). The mean age of those diagnosed with MetS was 60 years of age. Fifty-seven percent were males and 42 percent females. The mean body mass was 30 kg/m. The ejection fraction was found to be subnormal ( 49±8%) and the end systolic dimension of the left atrium was increased ( 45±10 mm) in comparison to a group of diabetic patients without MetS used for comparison. The incidence of atrial fibrillation was found to be 16% higher in the MetS group than in the comparison group.

The number of cases of metabolic syndrome recorded within the Hispanic population of Puerto Rico showed a higher incidence of atrial fibrillation without ventricular tachycardia. This is thought to be as a result of the abnormal left ventricular and atrial function.

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.

Low-complexity autoregressive modeling of the fast and slow QT adaptation to heart rate changes

The aim is to develop a new model of the QT interval dynamics behavior related to heart rate changes. Since two kinds of QT response have been pointed out, the main idea is to split the modeling process into two steps: 1) the modeling of the "fast" adaptation, which is inspired by the electrical behavior at the cellular level relative to the electrical restitution curve, 2) the modeling of the "slow" adaptation, inspired by experiments works at the cellular level. Both are modeled as low-complexity autoregressive process whose parameters are computed using an unbiased estimator. The relevance of this approach is illustrated on several ECG recordings where the variations of the heart rate are various (rest, atrial fibrillation episodes, exercise). Significant results are obtained in agreement with the physiological knowledge at the cellular level.

Regadenoson, a novel pharmacologic stress agent for use in myocardial perfusion imaging, does not have a direct effect on the QT interval in conscious dogs

Our goal was to determine the effect of regadenoson (a novel A2A adenosine receptor agonist) on the QT interval in conscious dogs. Sixteen mongrel dogs were chronically instrumented for measurements of blood pressure and ECG. Regadenoson (2.5, 5, and 10 microg/kg, IV) caused a dose-dependent QT interval shortening (DeltaQT: 14 +/- 3, 24 +/- 5, and 27 +/- 5 ms, mean +/- SEM; n = 7 to 11; all P < 0.05) associated with significant increases in HR (Peak HR: 114 +/- 9, 125 +/- 6, and 144 +/- 7 bpm). Atrial pacing (135, 150, and 165 bpm) also caused a frequency-dependent shortening of the QT interval (DeltaQT: 15 +/- 3, 22 +/- 3, and 39 +/- 5 ms; n = 6 to 7; all P < 0.05). Regadenoson- and pacing-induced shortenings in the QT interval were significantly correlated with the R-R interval (r = 0.67 and 0.8, both P < 0.05). Regadenoson at 5 and 10 microg/kg did not cause a significant change in HR or QT interval either during atrial pacing at 165 bpm or after administration of propranolol and atropine to prevent HR from changing or after treatment of dogs with hexamethonium to block autonomic ganglia. Regadenoson (5 to 10 microg/kg) caused no significant changes of QT interval in the heart in which HR was kept constant via physiological or pharmacological procedures, indicating that regadenoson has no direct effect on the QT interval.

An Improved QT Correction Method for use in Atrial Fibrillation and a Comparison with the Assessment of QT in Sinus Rhythm

BACKGROUND

Conventional QT corrections may be inappropriate inatrial fibrillation (AF) due to RR variability and QT lag. Existing formulashave been modified by the formula RRmod to account for this lag. Wedeveloped a novel correction formula for use in AF (QTAF) based onthe slope ∆QT/∆RRmod and report its performance in AF.We also compare QTAF obtained in AF with rate-independentcorrections in NSR.

MATERIALS AND METHODS

A total of 3063 RR/QT pairs from 28 patients with AFwere measured, 22 of whom also had measurements during sinus rhythm. QTc (theBazett equation), QTLC (the Framingham linear correction), and QTAFwere calculated utilizing RRmod, and the rate-independence of eachformula in AF tested. Mean QTAF values in AF were compared to QTintervals corrected with QTLC in normal sinus rhythm.

RESULTS

∆QTc/∆RRmod and∆QTLC/∆RRmod slopes were significantlynon-zero whereas ∆QTAF/∆RRmod was not. QTLCand QTc corrections were imperfect at extremes of RRmod whileQTAF was constant. QTAF corrections in AF were shorterthan QTc or QTLC corrections in NSR.

CONCLUSIONS

QTAF is a novel QT correction with adefined relationship to correction in NSR that performs better than existingstrategies.