Construction of intracardiac vectorcardiogram from implantable cardioverter-defibrillator intracardiac electrograms

We constructed an intracardiac vectorcardiogram from 3 configurations of intracardiac cardiovertor defibrilator (ICD) electrograms (EGMs). Six distinctive 3 lead combinations were selected out of five leads: can to right ventricular coil (RVC); RVC to superior vena cava coil (SVC); atrial lead tip (A-tip) to right ventricular (RV)-ring; can to RV-ring; RV-tip to RVC, in a patient with dual chamber ICD. Surface spatial QRS-T angle (119.8°) was similar to intracardiac spatial QRS-T angle derived from ICD EGMs combination A (101.3°), B (96.1°), C (92.8°), D (95.2), E (99.0), F (96.2) and median (101.5). Future validation of the novel method is needed.

Modelling the heart as a communication system

Electrical communication between cardiomyocytes can be perturbed during arrhythmia, but these perturbations are not captured by conventional electrocardiographic metrics. We developed a theoretical framework to quantify electrical communication using information theory metrics in two-dimensional cell lattice models of cardiac excitation propagation. The time series generated by each cell was coarse-grained to 1 when excited or 0 when resting. The Shannon entropy for each cell was calculated from the time series during four clinically important heart rhythms: normal heartbeat, anatomical reentry, spiral reentry and multiple reentry. We also used mutual information to perform spatial profiling of communication during these cardiac arrhythmias. We found that information sharing between cells was spatially heterogeneous. In addition, cardiac arrhythmia significantly impacted information sharing within the heart. Entropy localized the path of the drifting core of spiral reentry, which could be an optimal target of therapeutic ablation. We conclude that information theory metrics can quantitatively assess electrical communication among cardiomyocytes. The traditional concept of the heart as a functional syncytium sharing electrical information cannot predict altered entropy and information sharing during complex arrhythmia. Information theory metrics may find clinical application in the identification of rhythm-specific treatments which are currently unmet by traditional electrocardiographic techniques.

Intracardiac J-point elevation before the onset of polymorphic ventricular tachycardia and ventricular fibrillation in patients with an implantable cardioverter-defibrillator

BACKGROUND

The clinical importance of the J-point elevation on electrocardiogram is controversial.

OBJECTIVE

To study intracardiac J-point amplitude before ventricular arrhythmia.

METHODS

Baseline 12-lead electrocardiogram and far-field right ventricular intracardiac implantable cardioverter-defibrillator electrograms were recorded at rest in 494 patients (mean age 60.4 ± 13.1 years; 360 [72.9%] men) with structural heart disease (278 [56.3%] ischemic cardiomyopathy) who received primary (463 [93.9%] patients) or secondary prevention implantable cardioverter-defibrillator. Ten-second intracardiac far-field electrograms before the onset of arrhythmia were compared with the baseline. The J-point amplitude was measured on the baseline 12-lead surface electrocardiogram and the intracardiac far-field electrogram. The relative J-point amplitude was calculated as the ratio of J-point amplitude to peak-to-peak R-wave.

RESULTS

The paired t test showed that the relative intracardiac J-point amplitude was significantly higher before polymorphic ventricular tachycardia/ventricular fibrillation (VF) onset (0.28 ± 0.08 vs -0.19 ± 0.39; P = .012) than at baseline. In a mixed-effects logistic regression model, adjusted for multiple episodes per patient, each 10% increase in relative J-point amplitude increased the odds of having ventricular tachycardia/VF by 13% (odds ratio 1.13 [95% confidence interval 1.07-1.19]; P < .0001) and increased the odds of having polymorphic ventricular tachycardia/VF by 27% (odds ratio 1.27 [95% confidence interval 1.11-1.46]; P = .001).

CONCLUSIONS

The relative intracardiac J-point amplitude is augmented immediately before the onset of polymorphic ventricular tachycardia/VF in patients with structural heart disease.

Intracardiac QT integral on far-field ICD electrogram predicts sustained ventricular tachyarrhythmias in ICD patients

BACKGROUND

Prediction of sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) could help to guide preventive interventions in at-risk patients. The QRST integral (∫QT) reflects intrinsic repolarization properties.

OBJECTIVE

The objective of this study was to determine whether intracardiac ∫QT predicts VT/VF in the next few months in patients with implantable cardioverter defibrillators (ICDs).

METHODS

Far-field (FF) and near-field (NF) right ventricular intracardiac electrograms (EGMs) were recorded via telemetry in 46 patients with structural heart disease and ICDs implanted for secondary prevention of sudden cardiac death. Epochs of 4.9 ± 0.4 minutes during sinus rhythm (mean heart rate 70.9 ± 15.2 beats/min) and ventricular pacing at 105 beats/min were analyzed. Mean ∫QT was calculated on FF and NF EGMs as the algebraic sum of areas under the QRST curve and adjusted by mean heart rate. Patients were followed up for at least 3 months. True VT/VF events treated by the ICD served as the end point.

RESULTS

During a mean follow-up of 4.6 months, 22 patients (48%) were treated for VT/VF. Unadjusted and adjusted by heart rate, FF EGM ∫QT in sinus rhythm was a significant predictor of VT/VF (unadjusted ∫QT hazard ratio 1.007; 95% confidence interval 1.002 to 1.0013; P = .007; adjusted ∫QT hazard ratio 1.68; 95% confidence interval 1.19 to 2.36; P = .002). The highest quartile of intracardiac ∫QT predicted VT/VF (log-rank test P = .042) and identified patients at risk with a specificity of 86% and positive predictive value of 73%.

CONCLUSION

Increased intracardiac FF EGM ∫QT predicts VT/VF in patients with structural heart disease and secondary prevention ICDs.