The digital journey: 25 years of digital development in electrophysiology from an Europace perspective

AIMS

Over the past 25 years there has been a substantial development in the field of digital electrophysiology (EP) and in parallel a substantial increase in publications on digital cardiology.In this celebratory paper, we provide an overview of the digital field by highlighting publications from the field focusing on the EP Europace journal.

RESULTS

In this journey across the past quarter of a century we follow the development of digital tools commonly used in the clinic spanning from the initiation of digital clinics through the early days of telemonitoring, to wearables, mobile applications, and the use of fully virtual clinics. We then provide a chronicle of the field of artificial intelligence, a regulatory perspective, and at the end of our journey provide a future outlook for digital EP.

CONCLUSION

Over the past 25 years Europace has published a substantial number of papers on digital EP, with a marked expansion in digital publications in recent years.

Basic Properties And Clinical Applications Of The Intracardiac

The electric signals detected by intracardiac electrodes provide information on the occurrence and timing of myocardial depolarization, but are not generally helpful to characterize the nature and origin of the sensed event. A novel recording technique referred to as intracardiac ECG (iECG) has overcome this limitation. The iECG is a multipolar signal, which combines the input from both atrial and ventricular electrodes of a dual-chamber pacing system in order to assess the global electric activity of the heart. The tracing resembles a surface ECG lead, featuring P, QRS and T waves. The time-course of the waveform representing ventricular depolarization (iQRS) does correspond to the time-course of the surface QRS with any ventricular activation modality. Morphological variants of the iQRS waveform are specifically associated with each activity pattern, which can therefore be diagnosed by evaluation of the iECG tracing. In the event of tachycardia, SVTs with narrow QRS can be distinguished from other arrhythmia forms based upon the preservation of the same iQRS waveform recorded in sinus rhythm. In ventricular capture surveillance, real pacing failure can be reliably discriminated from fusion beats by the analysis of the area delimited by the iQRS signal. Assessing the iQRS waveform correspondence with a reference template could be a way to check the effectiveness of biventricular pacing, and to discriminate myocardial capture alone from additional His bundle recruitment in para-Hisian stimulation. The iECG is not intended as an alternative to conventional intracavitary sensing, which remains the only tool suitable to drive the sensing function of a pacing device. Nevertheless, this new electric signal can add the benefits of morphological data processing, which might have important implications on the quality of the pacing therapy.

Detection and discrimination of tachycardia in ICDs manufactured by St. Jude Medical

Modern implantable cardioverter/defibrillator (ICD) systems offer a multitude of algorithms to optimize performance in sensing and tachycardia detection even in difficult circumstances (e. g., ventricular tachycardia during supraventricular tachycardia, fine ventricular fibrillation with intermittent undersensing), to reliably discriminate sustained ventricular tachyarrhythmia from noise, nonsustained and supraventricular tachyarrhythmia, and to limit shock therapy only to those arrhythmias that definitely need to be treated by a shock. A disadvantage of these multiple algorithms is the complexity of annotated tracings that makes it sometimes difficult to understand why the ICD did what it did. If a tachycardia classification was wrong, it may be thus difficult to find the best way to reprogram the device to avoid another misclassification. This review explains in detail the algorithms used for tachycardia detection, discrimination, and prevention of inappropriate therapy in single- and dual-chamber ICDs manufactured by St. Jude Medical. Knowledge of these features may help to optimize ICD treatment in patients fitted with these devices.

Advances in implantable cardioverter defibrillator therapy

Since the first implant in 1980, implantable cardioverter defibrillator (ICD) technology has progressed rapidly. Modern ICD's have hundreds of programmable options with the general goal of preventing inappropriate shocks and providing shocks for truly life threatening symptomatic ventricular arrhythmias. New studies on ICD programming have shown the benefits of prolonged detection intervals in reaching this goal. Anti-tachycardia pacing (ATP) therapy has become an important adjunct to defibrillator shocks. Remote monitoring technologies have surfaced which have been shown to identify arrhythmias and problems with the device in an expedient fashion. The subcutaneous ICD offers the advantage of avoiding intravascular leads and their inherent risks. Lastly, the current understanding of the effects of MRI in ICD patients has advanced creating new opportunities to provide MRI safely to such patients.

Electrical And Hemodynamic Evalution Of Ventricular And Supraventricular Tachycardias With An Implantable Dual-Chamber Pacemaker

The discrimination between ventricular (VT) and supraventricular tachycardia (SVT) and the evaluation of their hemodynamic impact are essential issues in the arrhythmia management. A new pacing device features a tachycardia diagnostic system relying on simultaneous recording of the transvalvular impedance (TVI) and a special integrated electric signal derived by the whole set of endocardial electrodes (iECG). The iECG waveform is sensitive to the pattern of ventricular activation, similarly to the surface ECG. The TVI increases in systole and decreases in diastole and the amplitude of this cyclic fluctuation is an expression of the effectiveness of the pump function. In order to test the value of these signals in the analysis of a tachycardia, we have assessed the iECG and TVI modifications induced by different SVTs and tolerated and non-tolerated VTs, during electrophysiological (EP) studies. In case of SVT, the ventricular component of the iECG maintained the same morphology as in sinus rhythm. The peak-peak amplitude of the TVI fluctuation was reduced to 66 ± 11 % of the individual sinus rhythm reference, but the signal was present at every beat and showed a remarkable stability (variation coefficient 0.19 ± 0.01). In case of VT, the ventricular component of the iECG was strikingly different than in sinus rhythm. Regular TVI fluctuation was observed with tolerated VTs (peak-peak amplitude 74 ± 6 %; variation coefficient 0.21 ± 0.04). In contrast, with non-tolerated VTs the TVI amplitude was depressed below 40%, and the signal was virtually absent in the event of very fast VT or VF. Our results confirm that the iECG is a reliable tool to quickly discriminate VTs from SVTs and that TVI can provide information on the severity of the hemodynamic impairment produced by a tachycardia, with potential clinical benefit in the follow-up of pacemaker patients. Furthermore, the application of these signals to automatic algorithms of arrhythmia recognition might improve the specificity of therapy administration by an implantable defibrillator (ICD).

ICD programming

BACKGROUND

Appropriate ICD programming is the key to prevent inappropriate shock delivery, that is closely associated to a negative patients' outcome.

METHODS

Review of the literature on ICD therapy to generate ICD programmings that can be applied to the broad population of ICD and CRT-D carriers.

RESULTS

Arrhythmia detection should occur with a detection time ranging 9″-12″ in the VF zone, and 15″-60″ in the VT zone. Discriminator should be applied at least up to 200 bpm. ATP therapy is applied to all VTs up to 250 bpm, with a success rate of 70%. Inappropriate shocks should occur in <3.6% of patients.

CONCLUSION

Tailored ICD programming can be achieved following evidence from large ICD trials. Pre-defined settings that are saved on the programmer and that can be uploaded at device implantation help to ensure optimal programming and to avoid random errors.

Identification of recurring patterns in fractionated atrial electrograms using new transform coefficients

Background

Identification of recurrent patterns in complex fractionated atrial electrograms (CFAE) has been used to differentiate paroxysmal from persistent atrial fibrillation (AF). Detection of the atrial CFAE patterns might therefore be assistive in guiding radiofrequency catheter ablation to drivers of the arrhythmia. In this study a technique for robust detection and classification of recurrent CFAE patterns is described.

Method

CFAE were obtained from the four pulmonary vein ostia, and from the anterior and posterior left atrium, in 10 patients with paroxysmal AF and 10 patients with longstanding persistent AF (216 recordings in total). Sequences 8.4 s in length were analyzed (8,192 sample points, 977 Hz sampling). Among the 216 sequences, two recurrent patterns A and B were substituted for 4 and 5 of the sequences, respectively. To this data, random interference, and random interference + noise were separately added. Basis vectors were constructed using a new transform that is derived from ensemble averaging. Patterns A and B were then detected and classified using a threshold level of Euclidean distance between spectral signatures as constructed with transform coefficients.

Results

In the presence of interference, sensitivity to detect and distinguish two patterns A and B was 96.2%, while specificity to exclude nonpatterns was 98.0%. In the presence of interference + noise, sensitivity was 89.1% while specificity was 97.0%.

Conclusions

Transform coefficients computed from ensemble averages can be used to succinctly quantify synchronized patterns present in AF data. The technique is useful to automatically detect recurrent patterns in CFAE that are embedded in interference without user bias. This quantitation can be implemented in real-time to map the AF substrate prior to and during catheter ablation.

Health care utilisation after defibrillator implantation for primary prevention according to the guidelines in 2 Dutch academic medical centres

Background

The benefit of implantable defibrillators (ICDs) for primary prevention remains debated. We analysed the implications of prophylactic ICD implantation according to the guidelines in 2 tertiary hospitals, and made a healthcare utilisation inventory.

Methods

The cohort consisted of all consecutive patients with coronary artery disease (CAD) or dilated cardiomyopathy (DCM) receiving a primary prophylactic ICD in a contemporary setting (2004–2008). Follow-up was obtained from hospital databases, and mortality checked at the civil registry. Additional data came from questionnaires sent to general practitioners.

Results

There were no demographic differences between the 2 centres; one had proportionally more CAD patients and more resynchronisation therapy (CRT-D). The 587 patients were followed over a median of 28 months, and 50 (8.5%) patients died. Appropriate ICD intervention occurred in 123 patients (21%). There was a small difference in intervention-free survival between the 2 centres. The questionnaires revealed 338 hospital admissions in 52% of the responders. Device-related admissions happened on 68 occasions, in 49/276 responders. The most frequently reported ICD-related admission was due to shocks (20/49 patients); for other cardiac problems it was mainly heart failure (52/99). Additional outpatient visits occurred in 19%.

Conclusion

Over a median follow-up of 2 years, one fifth of prophylactic ICD patients receive appropriate interventions. A substantial group undergoes readmission and additional visits. The high number of admissions points to a very ill population. Overall mortality was 8.5%. The 2 centres employed a similar procedure with respect to patient selection. One centre used more CRT-D, and observed more appropriate ICD interventions.