Evaluation of QTc before and after exercise testing in a population of patients with severe obesity: possible association with obstructive sleep apnoea

openObesity is associated with QT interval prolongation. Obesity is also associated with OSA (obstructive sleep apnoea). OSA as well is associated with prolongation of the QT interval. The purpose of this study is to evaluate the QTc before and after exercise testing in a population of patients with severe obesity, and a possible association between QTc prolongation and OSA

Methods of Assessment and Clinical Relevance of QT Dynamics

The dependence on heart rate of the QT interval has been investigated for many years and several mathematical formulae have been proposed to describe the QT interval/heart rate (or QT interval/RR interval) relationship. While the most popular is Bazett’s formula, it overcorrects the QT interval at high heart rates and under-corrects it at slow heart rates. This formulae and many others similar ones, do not accurately describe the natural behaviour of the QT interval. The QT interval/RR interval relationship is generally described as QT dynamics. In recent years, several methods of its assessment have been proposed, the most popular of which is linear regression. An increased steepness of the linear QT/RR slope correlates with the risk of arrhythmic death following myocardial infarction. It has also been demonstrated that the QT interval adapts to heart rate changes with a delay (QT hysteresis) and that QT dynamics parameters vary over time. New methods of QT dynamics assessment that take into account these phenomena have been proposed. Using these methods, changes in QT dynamics have been observed in patients with advanced heart failure, and during morning hours in patients with ischemic heart disease and history of cardiac arrest. The assessment of QT dynamics is a new and promising tool for identifying patients at increased risk of arrhythmic events and for studying the effect of drugs on ventricular repolarisation

An Overview of QT Dispersion Finding in Cardiac Patients,Review Article

Background: QT duration represents the time of the whole summated electric cardiac ventricular activity involving stepwise depolarization followed by repolarization. There has been a long history of using the surface electrocardiogram (ECG) to identify ventricular repolarization problems. The 1960s were a turning point for precise mathematical methodologies. It has been customary in clinical practice to use only the QT interval and the polarity and shape of the T wave when evaluating cardiac repolarization using an electrocardiogram (ECG). This terminology, such as "non-specific ST segment and T wave variations are widely used. An earlier theory on interlead disparities in QTI length was resurrected in a 1990 report by the group led by Professor John Campbell. The "QT dispersion" range of durations was proposed as a measure of ventricular recovery time spatial dispersion. Objective: Determine the relevance of QTd in prediction of myocardial and its severity. Conclusion: For cardiac patients, QTd is an easy-to-use, rapid, affordable, and helpful tool for helping with study interpretation, clinical management, and therapeutic orientation

Weightlessness and Cardiac Rhythm Disorders: Current Knowledge from Space Flight and Bed-Rest Studies

Isolatedepisodesofheartrhythmdisordershavebeenreportedduring40yearsofspaceflight,triggeringresearchtoevaluatetheriskofdevelopinglife-threateningarrhythmiasinducedbyprolongedexposuretoweightlessness.Infact,theseeventscouldcompromiseastronautperformanceduringexploratorymissions,aswellasposeatrisktheastronauthealth,duetolimitedoptionsofcareonboardtheInternationalSpaceStation.Startingfromoriginalobservations,thisminireviewwillexplorethelatestresearchinthisfield,consideringresultsobtainedbothduringspaceflightandonEarth,thelatterbysimulatinglong-termexposuretomicrogravitybyhead-downbedrestmaneuverinordertoelicitcardiovasculardeconditioningonnormalvolunteers

Regional differences in APD restitution can initiate wavebreak and re-entry in cardiac tissue: A computational study

Background Regional differences in action potential duration (APD) restitution in the heart favour arrhythmias, but the mechanism is not well understood. Methods We simulated a 150 × 150 mm 2D sheet of cardiac ventricular tissue using a simplified computational model. We investigated wavebreak and re-entry initiated by an S1S2S3 stimulus protocol in tissue sheets with two regions, each with different APD restitution. The two regions had a different APD at short diastolic interval (DI), but similar APD at long DI. Simulations were performed twice; once with both regions having steep (slope > 1), and once with both regions having flat (slope < 1) APD restitution. Results Wavebreak and re-entry were readily initiated using the S1S2S3 protocol in tissue sheets with two regions having different APD restitution properties. Initiation occurred irrespective of whether the APD restitution slopes were steep or flat. With steep APD restitution, the range of S2S3 intervals resulting in wavebreak increased from 1 ms with S1S2 of 250 ms, to 75 ms (S1S2 180 ms). With flat APD restitution, the range of S2S3 intervals resulting in wavebreak increased from 1 ms (S1S2 250 ms), to 21 ms (S1S2 340 ms) and then 11 ms (S1S2 400 ms). Conclusion Regional differences in APD restitution are an arrhythmogenic substrate that can be concealed at normal heart rates. A premature stimulus produces regional differences in repolarisation, and a further premature stimulus can then result in wavebreak and initiate re-entry. This mechanism for initiating re-entry is independent of the steepness of the APD restitution curve

Direct in-vivo assessment of global and regional mechano-electric feedback in the intact human heart

BACKGROUND: Inhomogeneity of ventricular contraction is associated with sudden cardiac death, but the underlying mechanisms are unclear. Alterations in cardiac contraction impact electrophysiological parameters through mechano-electric feedback. This has been shown to promote arrhythmias in experimental studies, but its effect in the in-vivo human heart is unclear. OBJECTIVE: The aim of this study was to quantify the impact of regional myocardial deformation provoked by a sudden increase in ventricular loading (aortic occlusion) on human cardiac electrophysiology. METHODS: In ten patients undergoing open-heart cardiac surgery, left ventricular (LV) afterload was modified by transient aortic occlusion. Simultaneous assessment of whole-heart electrophysiology and LV deformation was performed using an epicardial sock (240 electrodes) and speckle-tracking transoesophageal echocardiography. Parameters were matched to six AHA LV model segments. The association between changes in regional myocardial segment length and in the activation-recovery interval (ARI, a conventional surrogate for action potential duration) was studied using mixed-effect models. RESULTS: Increased ventricular loading reduced longitudinal shortening (P=0.01) and shortened the ARI (P=0.02), but changes were heterogeneous between cardiac segments. Increased regional longitudinal shortening was associated with ARI shortening (effect size 0.20, 0.01 - 0.38, ms/% P=0.04) and increased local ARI dispersion (effect size -0.13, -0.23 - -0.03) ms/%, P=0.04). At the whole organ level, increased mechanical dispersion translated into increased dispersion of repolarization (correlation coefficient, r=0.81, P=0.01). CONCLUSIONS: Mechano-electric feedback can establish a potentially pro-arrhythmic substrate in the human heart and should be considered to advance our understanding and prevention of cardiac arrhythmias

Techniques for ventricular repolarization instability assessment from the ECG

Instabilities in ventricular repolarization have been documented to be tightly linked to arrhythmia vulnera- bility. Translation of the information contained in the repolar- ization phase of the electrocardiogram (ECG) into valuable clinical decision-making tools remains challenging. This work aims at providing an overview of the last advances in the pro- posal and quantification of ECG-derived indices that describe repolarization properties and whose alterations are related with threatening arrhythmogenic conditions. A review of the state of the art is provided, spanning from the electrophysio- logical basis of ventricular repolarization to its characteriza- tion on the surface ECG through a set of temporal and spatial risk markers

Dynamic spatial dispersion of repolarization is present in regions critical for ischemic ventricular tachycardia ablation

Background: The presence of dynamic substrate changes may facilitate functional block and reentry in ventricular tachycardia (VT). Objective: We aimed to study dynamic ventricular repolarization changes in critical regions of the VT circuit during sensed single extrastimulus pacing known as the Sense Protocol (SP). Methods: Twenty patients (aged 67 ± 9 years, 17 male) underwent VT ablation. A bipolar voltage map was obtained during sinus rhythm (SR) and right ventricular SP pacing at 20 ms above ventricular effective refractory period. Ventricular repolarization maps were constructed. Ventricular repolarization time (RT) was calculated from unipolar electrogram T waves, using the Wyatt method, as the dV/dtmax of the unipolar T wave. Entrainment or pace mapping confirmed critical sites for ablation. Results: The median global repolarization range (max-min RT per patient) was 166 ms (interquartile range [IQR] 143-181 ms) during SR mapping vs 208 ms (IQR 182-234) during SP mapping (P = .0003 vs intrinsic rhythm). Regions of late potentials (LP) had a longer RT during SP mapping compared to regions without LP (mean 394 ± 40 ms vs 342 ± 25 ms, P < .001). In paired regions of normal myocardium there was no significant spatial dispersion of repolarization (SDR)/10 mm2 during SP mapping vs SR mapping (SDR 11 ± 6 ms vs 10 ± 6 ms, P = .54). SDR/10 mm2 was greater in critical areas of the VT circuit during SP mapping 63 ± 29 ms vs SR mapping 16 ± 9 ms (P < .001). Conclusion: Ventricular repolarization is prolonged in regions of LP and increases dynamically, resulting in dynamic SDR in critical areas of the VT circuit. These dynamic substrate changes may be an important factor that facilitates VT circuits