Measurement bias in activation-recovery intervals from unipolar electrograms

Activation recovery interval as an electrocardiographic repolarization index to detect doxorubicin-induced cardiotoxicity

BACKGROUND

It has been reported that early detection and treatment of cancer therapy- related cardiac dysfunction (CTRCD) improves its prognosis. The detailed relationships between electrocardiographic repolarization indices and decreased left ventricular function in CTRCD have not been elucidated. We closely assessed such relationships in patients with doxorubicin (DOX)-induced CTRCD.

METHODS

This retrospective, single-center, cohort study included 471 consecutive patients with malignant lymphoma who received chemotherapy including DOX. Of them, 17 patients with CTRCD and 68 patients without CTRCD who underwent 12‑lead electrocardiogram and an echocardiogram before and after chemotherapy were eventually analyzed. The fluctuations of the following electrocardiographic repolarization indices were evaluated in lead V5: QT, JT, T peak to T end interval (Tp-e), and activation recovery interval (ARI). These indices were corrected by heart rate with the Fridericia formula.

RESULTS

The median period from the end of chemotherapy to the diagnosis of the CTRCD group was 346 days (IQR 170-1283 days). After chemotherapy, the QT interval was significantly prolonged in both with and without CTRCD groups compared with that before chemotherapy (pre QTc vs. post QTc in CTRCD group, 386 ± 27 ms vs. 411 ± 37 ms, p = 0.03, pre QTc vs. post QTc in non-CTRCD group, 388 ± 24 ms vs. 395 ± 25 ms, p = 0.04, respectively). ARIc after chemotherapy was characteristically observed only in the CTRCD group (pre ARIc vs. post ARIc in CTRCD group, 258 ± 53 ms vs. 211 ± 28 ms, p = 0.03, pre ARIc vs. post ARIc in non-CTRCD group, 221 ± 19 ms vs. 225 ± 23 ms, NS, respectively) and had negative correlations with left ventricular ejection fraction (r = -0.56, p < 0.001). Using the receiver-operating characteristic curve, the relationship between ARIc and CTRCD morbidity was examined. The optimal cut-off point of ARIc prolongation between before and after chemotherapy was 18 ms (sensitivity 75 %, specificity 79 %, area under the curve 0.76).

CONCLUSIONS

ARIc prolongation may be useful in the early detection of developing late-onset chronic DOX-induced CTRCD and lead to early treatment for cardiac protection.

Understanding repolarization in the intracardiac unipolar electrogram: A long-lasting controversy revisited

Background: The optimal way to determine repolarization time (RT) from the intracardiac unipolar electrogram (UEG) has been a topic of debate for decades. RT is typically determined by either the Wyatt method or the "alternative method," which both consider UEG T-wave slope, but differently. Objective: To determine the optimal method to measure RT on the UEG. Methods: Seven pig hearts surrounded by an epicardial sock with 100 electrodes were Langendorff-perfused with selective cannulation of the left anterior descending (LAD) coronary artery and submersed in a torso-shaped tank containing 256 electrodes on the torso surface. Repolarization was prolonged in the non-LAD-regions by infusing dofetilide and shortened in the LAD-region using pinacidil. RT was determined by the Wyatt (t_Wyatt) and alternative (t_Alt) methods, in both invasive (recorded with epicardial electrodes) and in non-invasive UEGs (reconstructed with electrocardiographic imaging). t_Wyatt and t_Alt were compared to local effective refractory period (ERP). Results: With contact mapping, mean absolute error (MAE) of t_Wyatt and t_Alt vs. ERP were 21 ms and 71 ms, respectively. Positive T-waves typically had an earlier ERP than negative T-waves, in line with theory. t_Wyatt -but not t_Alt-shortened by local infusion of pinacidil. Similar results were found for the non-invasive UEGs (MAE of t_Wyatt and t_Alt vs. ERP were 30 ms and 92 ms, respectively). Conclusion: The Wyatt method is the most accurate to determine RT from (non) invasive UEGs, based on novel and historical analyses. Using it to determine RT could unify and facilitate repolarization assessment and amplify its role in cardiac electrophysiology.

Electrophysiology and Arrhythmogenesis in the Human Right Ventricular Outflow Tract

BACKGROUND

Right ventricular outflow tract (RVOT) is a common source of ventricular tachycardia, which often requires ablation. However, the mechanisms underlying the RVOT's unique arrhythmia susceptibility remain poorly understood due to lack of detailed electrophysiological and molecular studies of the human RVOT.

METHODS

We conducted optical mapping studies in 16 nondiseased donor human RVOT preparations subjected to pharmacologically induced adrenergic and cholinergic stimulation to evaluate susceptibility to arrhythmias and characterize arrhythmia dynamics.

RESULTS

We found that under control conditions, RVOT has shorter action potential duration at 80% repolarization relative to the right ventricular apical region. Treatment with isoproterenol (100 nM) shortened action potential duration at 80% repolarization and increased incidence of premature ventricular contractions (P=0.003), whereas acetylcholine (100 μM) stimulation alone had no effect on action potential duration at 80% repolarization or premature ventricular contractions. However, acetylcholine treatment after isoproterenol stimulation reduced the incidence of premature ventricular contractions (P=0.034) and partially reversed action potential duration at 80% repolarization shortening (P=0.029). Immunolabeling of RVOT (n=4) confirmed the presence of cholinergic marker VAChT (vesicular acetylcholine transporter) in the region. Rapid pacing revealed RVOT susceptibility to both concordant and discordant alternans. Investigation into transmural arrhythmia dynamics showed that arrhythmia wave fronts and phase singularities (rotors) were relatively more organized in the endocardium than in the epicardium (P=0.006). Moreover, there was a weak but positive spatiotemporal autocorrelation between epicardial and endocardial arrhythmic wave fronts and rotors. Transcriptome analysis (n=10 hearts) suggests a trend that MAPK (mitogen-activated protein kinase) signaling, calcium signaling, and cGMP-PKG (protein kinase G) signaling are among the pathways that may be enriched in the male RVOT, whereas pathways of neurodegeneration may be enriched in the female RVOT.

CONCLUSIONS

Human RVOT electrophysiology is characterized by shorter action potential duration relative to the right ventricular apical region. Cholinergic right ventricular stimulation attenuates the arrhythmogenic effects of adrenergic stimulation, including increase in frequency of premature ventricular contractions and shortening of wavelength. Right ventricular arrhythmia is characterized by positive spatial-temporal autocorrelation between epicardial-endocardial arrhythmic wave fronts and rotors that are relatively more organized in the endocardium.

Evaluation of a Fully Automatic Measurement of Short-Term Variability of Repolarization on Intracardiac Electrograms in the Chronic Atrioventricular Block Dog

Background: Short-term variability (STV) of repolarization of the monophasic action potential duration (MAPD) or activation recovery interval (ARI) on the intracardiac electrogram (EGM) increases abruptly prior to the occurrence of ventricular arrhythmias in the chronic AV-block (CAVB) dog model. Therefore, this parameter might be suitable for continuous monitoring of imminent arrhythmias using the EGM stored on an implanted device. However, 24/7 monitoring would require automatic STV_ARI measurement by the device.

Objective: To evaluate a newly developed automatic measurement of STV_ARI for prediction of dofetilide-induced torsade de pointes (TdP) arrhythmias in the CAVB-dog.

Methods: Two retrospective analyses were done on data from recently performed dog experiments. (1) In seven anesthetized CAVB-dogs, the new automatic STV_ARI method was compared with the gold standard STV_MAPD at baseline and after dofetilide administration (0.025 mg/kg in 5 min). (2) The predictive value of the automatic method was compared to currently used STV_ARI methods, i.e., slope method and fiducial segment averaging (FSA) method, in 11 inducible (≥3 TdP arrhythmias) and 10 non-inducible CAVB-dogs.

Results: (1) The automatic measurement of STV_ARI had good correlation with STV_MAPD (r² = 0.89; p < 0.001). Bland-Altman analysis showed a small bias of 0.06 ms with limits of agreement between −0.63 and 0.76 ms. (2) STV_ARI of all three methods was significantly different between inducible and non-inducible dogs after dofetilide. The automatic method showed the highest predictive performance with an area under the ROC-curve of 0.93, compared to 0.85 and 0.87 of the slope and FSA methods, respectively. With a threshold of STV set at 1.69 ms, STV_ARI measured with the automatic method had a sensitivity of 0.91 and specificity of 0.90 in differentiating inducible from non-inducible subjects.

Conclusion: We developed a fully-automatic method for measurement of STV_ARI on the intracardiac EGM that can accurately predict the occurrence of ventricular arrhythmias in the CAVB-dog. Future integration of this method into implantable devices could provide the opportunity for 24/7 monitoring of arrhythmic risk.

Non-invasive electrocardiographic imaging in patients with idiopathic premature ventricular contractions from the right ventricular outflow tract: New insights into arrhythmia substrate

AIMS

The aim of this study was to use non-invasive electrocardiographic imaging (ECGI) to study the electrophysiological properties of right ventricular outflow tract (RVOT) in patients with frequent premature ventricular contractions (PVCs) from the RVOT and in controls.

METHODS

ECGI is a combined application of body surface electrocardiograms and computed tomography or magnetic resonance imaging data. Unipolar electrograms are reconstructed on the epicardial and endocardial surfaces. Activation time (AT) was defined as the time of maximal negative slope of the electrogram (EGM) during QRS, recovery time (RT) as the time of maximal positive slope of the EGM during T wave, Activation recovery interval (ARI) was defined as the difference between RT and AT. ARI dispersion (Δ ARI) and RT dispersion (Δ RT) were calculated as the difference between maximal and minimal ARI and RT respectively. We evaluated those parameters in patients with frequent PVCs from the RVOT, defined as >10.000 per 24 h, and in a control group.

RESULTS

We studied 7 patients with frequent RVOT PVCs and 17 controls. Patients with PVCs from the RVOT had shorter median RT than controls, in the endocardium and in the epicardium, respectively 380 (239-397) vs 414 (372-448) ms, p = 0.047 and 275 (236-301) vs 330 (263-418) ms, p = 0.047. The dispersion of ARI and of RT in the epicardium was higher than in controls, Δ ARI of 145 (68-216) vs 17 (3-48) ms, p = 0.001 and Δ RT of 201 (160-235) vs 115 (65-177), p = 0.019.

CONCLUSION

In this group of patients we found a shorter median RT in the endocardium and in the epicardium of the RVOT and a higher dispersion of the ARI and RT across the epicardium in patients with PVCs from the RVOT when comparing to controls.

Unipolar electrogram-guided radiofrequency catheter ablation in paroxysmal atrial fibrillation: electrogram patterns and outcomes

BACKGROUND

Transmural lesions (TLs) are the crucial point for radiofrequency catheter ablation (RFCA) in atrial fibrillation (AF) patients. Previous studies have reported that complete positive unipolar electrogram (UP-EGM) after ablation is associated with transmural lesions. However, UP-EGM patterns may differ in different regions of continuous circular lesions (CCLs) around the pulmonary vein ostia after ablation. We aimed to analyze the different UP-EGM patterns in different CCL regions after ablation and the effectiveness of UP-EGM guided RFCA in paroxysmal atrial fibrillation (PAF).

METHODS

A total of 43 patients with PAF (aged 59 ± 11 years; 65% male) were consecutively included. Pulmonary vein isolation was achieved by contiguous point-by-point RFCA. UP-EGM was recorded by the ablation catheter. Both CCLs were divided into six regions. Two points were randomly chosen from each region to analyze UP-EGM type after ablation. All the patients were followed for atrial arrhythmias recurrence.

RESULTS

All pulmonary veins were isolated with complete bidirectional block. A total of 1032 RFCA points with complete positive UP-EGM were collected. UP-EGM morphology after ablation was divided into four different types defined as R, rR', Rr', and M. M patterns mostly appeared in anterosuperior (65%) and roof (49%) regions of left CCLs. In the remaining regions, the percentage of non-M patterns (R, rR', and Rr') ranged from 63% in posteroinferior regions of right CCLs to 88% in anteroinferior regions of right CCLs. After a mean follow-up time of 19 months, 37 (86%) patients remained in sinus rhythm.

CONCLUSION

Most (72%) UP-EGM types after ablation are non-M patterns. Pulmonary vein isolation guided by UP-EGM with a complete positive pattern in PAF patients is reliable.

Activation recovery interval imaging of premature ventricular contraction

Dispersion of ventricular repolarization due to abnormal activation contributes to the susceptibility to cardiac arrhythmias. However, the global pattern of repolarization is difficult to assess clinically. Activation recovery interval (ARI) has been used to understand the properties of ventricular repolarization. In this study, we developed an ARI imaging technique to noninvasively reconstruct three-dimensional (3D) ARI maps in 10 premature ventricular contraction (PVC) patients and evaluated the results with the endocardial ARI maps recorded by a clinical navigation system (CARTO). From the analysis results of a total of 100 PVC beats in 10 patients, the average correlation coefficient is 0.86±0.05 and the average relative error is 0.06±0.03. The average localization error is 4.5±2.3 mm between the longest ARI sites in 3D ARI maps and those in CARTO endocardial ARI maps. The present results suggest that ARI imaging could serve as an alternative of evaluating global pattern of ventricular repolarization noninvasively and could assist in the future investigation of the relationship between global repolarization dispersion and the susceptibility to cardiac arrhythmias.

In vivo human sock-mapping validation of a simple model that explains unipolar electrogram morphology in relation to conduction-repolarization dynamics

INTRODUCTION

The unipolar electrogram (UEG) provides local measures of cardiac activation and repolarization and is an important translational link between patient and laboratory. A simple theoretical model of the UEG was previously proposed and tested in silico.

METHOD AND RESULTS

The aim of this study was to use epicardial sock-mapping data to validate the simple model's predictions of unipolar electrogram morphology in the in vivo human heart. The simple model conceptualizes the UEG as the difference between a local cardiac action potential and a position-independent component representing remote activity, which is defined as the average of all action potentials. UEGs were recorded in 18 patients using a multielectrode sock containing 240 electrodes and activation (AT) and repolarization time (RT) were measured using standard definitions. For each cardiac site, a simulated local action potential was generated by adjusting a stylized action potential to fit AT and RT measured in vivo. The correlation coefficient (cc) measuring the morphological similarity between 13,637 recorded and simulated UEGs was cc  =  0.89 (0.72-0.95), median (Q₁ -Q₃ ), for the entire UEG, cc  =  0.90 (0.76-0.95) for QRS complexes, and cc  =  0.83 (0.58-0.92) for T-waves. QRS and T-wave areas from recorded and simulated UEGs showed cc> 0.89 and cc> 0.84, respectively, indicating good agreement between voltage isochrones maps. Simulated UEGs accurately reproduced the interaction between AT and QRS morphology and between RT and T-wave morphology observed in vivo.

CONCLUSIONS

Human in vivo whole heart data support the validity of the simple model, which provides a framework for improving the understanding of the UEG and its clinical utility.

Scalable and Accurate ECG Simulation for Reaction-Diffusion Models of the Human Heart

Realistic electrocardiogram (ECG) simulation with numerical models is important for research linking cellular and molecular physiology to clinically observable signals, and crucial for patient tailoring of numerical heart models. However, ECG simulation with a realistic torso model is computationally much harder than simulation of cardiac activity itself, so that many studies with sophisticated heart models have resorted to crude approximations of the ECG. This paper shows how the classical concept of electrocardiographic lead fields can be used for an ECG simulation method that matches the realism of modern heart models. The accuracy and resource requirements were compared to those of a full-torso solution for the potential and scaling was tested up to 14,336 cores with a heart model consisting of 11 million nodes. Reference ECGs were computed on a 3.3 billion-node heart-torso mesh at 0.2 mm resolution. The results show that the lead-field method is more efficient than a full-torso solution when the number of simulated samples is larger than the number of computed ECG leads. While the initial computation of the lead fields remains a hard and poorly scalable problem, the ECG computation itself scales almost perfectly and, even for several hundreds of ECG leads, takes much less time than the underlying simulation of cardiac activity.

Analytical description of the slope of the APD-restitution curve to assess the interacting contribution of conduction and repolarization dynamics

The restitution of the action potential duration (APDR) is a mechanism whereby cardiac excitation and relaxation adapt to changes in heart rate. Several studies, mainly carried out in-vitro and in-silico, have demonstrated that a steep APDR curve is associated with increased vulnerability to fatal arrhythmias. However, the mechanisms that link the steepness of the APDR curve to arrhythmogenesis remain undetermined. Although APDR is known to interact with conduction dynamics, few studies have focused on these interactions. In this paper, an analytical expression of the slope of the APDR is derived. This expression explicitly describes the dependency of the slope of the APDR curve on the activation time and/or conduction velocity changes. The study of this expression shows that conduction dynamics are among the main determinants of the slope of the APDR curve. A small absolute increment in the steepness of the activation time restitution slope can cause the steepness of the APDR slope to dramatically increase. Theoretically, the APDR slope quickly diverges to infinity when the increase in activation time matches the decrease in the pacing interval. High density epicardial mapping performed in a patient undergoing open heart surgery, shows excellent agreement between measures of the slope of the APDR curve and its analytical prediction (linear correlation > 0.95). The in-vivo recordings suggest that activation time restitution is the main determinant of the slope of the APDR curve.

On how 2∶1 conduction block can induce T-wave alternans in the unipolar intracavitary electrogram: Modelling in-vivo human recordings from an ischemic heart

Repolarization alternans is a marker of increased vulnerability to fatal arrhythmias. At the tissue level, in unipolar electrograms (UEGs) recorded on the myocardium, repolarization alternans is often measured as an alternating change of the T-wave, so called T-wave alternans (TWA). During ischemia, UEG-TWA is used as a marker of cardiac instability and is considered as a key parameter to assess pharmacological strategies. However, during ischemia it is not clear whether UEG-TWA is a sign of repolarization alternans which may promote 2:1 conduction block, or whether it is induced by ongoing regional 2:1 conduction block. In this study, we first show in-vivo human data recorded during an ischemic event that suggest that 2:1 conduction block induces UEG-TWA beyond the region of 2:1 conduction block. We then develop an analytical forward model of the UEG by coupling an analytical description of the cardiac action potential with a theoretical expression of the UEG, where each UEG is the combination of a local and a remote component and noise. With this model, we were able to generate signals that closely resemble UEGs recorded in-vivo, with a maximum correlation ρ > 0.94. Finally, we interrogate the model and demonstrate that whenever 2:1 conduction block is present, UEG-TWA arises as a consequence of alternating imbalance of both the local and remote components of the UEG. The statistical significance of UEG-TWA depends on the interactions between local and remote dynamics and noise.We conclude that in an ischemic model, UEG-TWA is likely to be a sign of 2:1 conduction block, either proximal or distal from the recording site.

Effect of autonomic blocking agents on the respiratory-related oscillations of ventricular action potential duration in humans

Ventricular action potential repolarization is critical to electrical stability and arrhythmogenesis. Oscillations at the respiratory frequency were investigated in humans by combining endocardial electrophysiological recordings, controlled respiration with adrenergic blocking agents. Results are consistent with a partial role of the sympathetic nervous system combined with additional mechanisms, possibly involving mechano-electric feedback.

Ventricular action potential duration (APD) is an important component of many physiological functions including arrhythmogenesis. APD oscillations have recently been reported in humans at the respiratory frequency. This study investigates the contribution of the autonomic nervous system to these oscillations. In 10 patients undergoing treatment for supraventricular arrhythmias, activation recovery intervals (ARI; a conventional surrogate for APD) were measured from multiple left and right ventricular (RV) endocardial sites, together with femoral artery pressure. Respiration was voluntarily regulated and heart rate clamped by RV pacing. Sympathetic and parasympathetic blockade was achieved using intravenous metoprolol and atropine, respectively. Metroprolol reduced the rate of pressure development (maximal change in pressure over time): 1,271 (± 646) vs. 930 (± 433) mmHg/s; P < 0.01. Systolic blood pressure (SBP) showed a trend to decrease after metoprolol, 133 (± 21) vs. 128 (± 25) mmHg; P = 0.06, and atropine infusion, 122 (± 26) mmHg; P < 0.05. ARI and SBP exhibited significant cyclical variations (P < 0.05) with respiration in all subjects with peak-to-peak amplitudes ranging between 0.7 and 17.0 mmHg and 1 and 16 ms, respectively. Infusion of metoprolol reduced the mean peak-to-peak amplitude [ARI, 6.2 (± 1.4) vs. 4.4 (± 1.0) ms, P = 0.008; SBP, 8.4 (± 1.6) vs. 6.2 (± 2.0) mmHg, P = 0.002]. The addition of atropine had no significant effect. ARI, SBP, and respiration showed significant coupling (P < 0.05) at the breathing frequency in all subjects. Directed coherence from respiration to ARI was high and reduced after metoprolol infusion [0.70 (± 0.17) vs. 0.50 (± 0.23); P < 0.05]. These results suggest a role of respiration in modulating the electrophysiology of ventricular myocardium in humans, which is partly, but not totally, mediated by β-adrenergic mechanisms.

Accuracy of measurements derived from intracardiac unipolar electrograms: A simulation study

The ventricular action potential duration (APD) is a fundamental determinant of cardiac electrical stability and can be estimated by measuring the activation recovery interval (ARI) from the unipolar electrogram (UEG), which represents the electrical activity of the heart at the tissue level. Under experimental conditions, automatic estimation of ARIs is challenging due to non-related interferences and low signal-to-noise ratios (SNRs). In this simulation study, we investigated how the reliability of ARI estimates is affected by noise and artefacts in the UEG. Real-like electrograms were generated using a 257-node whole heart model to synthesize 20 real-like UEGs exhibiting constant and dynamic ARI patterns. Controlled degrees of noise and contamination (ectopic beats) were added to obtain a range of signal qualities. The generated recordings were automatically analyzed using a proposed standard method to estimate the ARI. The performance was compared with two improvements of the standard method including a narrow search window and a correlation filter. The results show that the robustness of automatic ARI analysis was dramatically improved by using the proposed improvement methods. For typical recordings with a SNR of 10dB and filtered with often used cutoff frequency of 30Hz to measure repolarization, the average mean absolute error of the estimations was reduced from 16.2ms (range:12.2-29.0ms) for the standard method to 11.6ms (range:6.0-13.4ms) for the improved method. The standard deviation was reduced from 38.2ms (range:26.8- 58.5ms) to 14.6ms (range:7.6-16.9ms). Detection of cyclical variation of ARI was also improved by using the improvement strategy: for 0.2Hz ARI oscillations with an amplitude of 5ms, the highest average detection rate increased from 41% for the standard method to 100% using the improved method for recordings with a SNR of 10dB.