Prevention of inappropriate therapy in implantable defibrillators: A meta-analysis of clinical trials comparing single-chamber and dual-chamber arrhythmia discrimination algorithms

Single- Versus Dual-Chamber Implantable Cardioverter-Defibrillator for Primary Prevention of Sudden Cardiac Death in the United States

Background Routine addition of an atrial lead during an implantable cardioverter-defibrillator (ICD) implantation for primary prevention of sudden cardiac death, in patients without pacing indications, was not shown beneficial in contemporary studies. We aimed to investigate the use and safety of single- versus dual-chamber ICD implantations in these patients. Methods and Results Using the National Inpatient Sample database, we identified patients with no pacing indications who underwent primary-prevention ICD implantation in the United States between 2015 and 2019. Sociodemographic and clinical characteristics, as well as in-hospital complications, were analyzed. Multivariable logistic regression was used to identify predictors of in-hospital complications. An estimated total of 15 940 patients, underwent ICD implantation for primary prevention of sudden cardiac death during the study period, 8860 (55.6%) received a dual-chamber ICD. The mean age was 64 years, and 66% were men. In-hospital complication rates in the dual-chamber ICD and single-chamber ICD group were 12.8% and 10.7%, respectively (P<0.001), driven by increased rates of pneumothorax/hemothorax (4.6% versus 3.4%; P<0.001) and lead dislodgement (3.6% versus 2.3%; P<0.001) in the dual-chamber ICD group. Multivariable analyses confirmed atrial lead addition as an independent predictor for "any complications" (odds ratio [OR], 1.1 [95% CI, 1.0-1.2]), for pneumo/hemothorax (odds ratio, 1.1 [95% CI, 1.0-1.4]), and for lead dislodgement (odds ratio, 1.3 [95% CI, 1.1-1.6]). Conclusions Despite lack of evidence for clinical benefit, dual-chamber ICDs are implanted for primary prevention of sudden cardiac death in a majority of patients who do not have pacing indication. This practice is associated with increased risk of periprocedural complications. Avoidance of routine implantation of atrial leads will likely improve safety outcomes.

Arrhythmic Storm Due to ICD Atrial Lead Malfunction

We describe the case of a young woman with a dual-chamber implantable cardioverter-defibrillator for long-QT syndrome who was referred to our emergency department (Cardiovascular Research Centre of Aalst, Belgium) because of an “arrhythmic storm” caused by atrial lead fracture. This case highlights the importance of the correct choice of both the device type and the pacing modality. (Level of Difficulty: Intermediate.)

Long-term evaluation of sensing variability of a floating atrial dipole in a single‑lead defibrillator: The mechanistic basis of long-term stability of amplified atrial electrogram

BACKGROUND

A single‑lead implantable cardioverter-defibrillator (ICD) with a floating atrial dipole has been developed to enhance the diagnostic capability of atrial arrhythmias and to facilitate adjudication of arrhythmic events without the additional effort required for atrial lead insertion. However, there have been concerns about the long-term reliability of atrial sensing.

METHODS

We enrolled patients with the single-chamber ICD with atrial-sensing electrodes from 4 tertiary university hospitals in Korea. Minimal, maximal, and mean P wave amplitudes were collected at 3-6 months, 6-12 months, and 12-24 months after implantation. The difference between the minimal and maximal sensing amplitudes was calculated as an indicator of the variability of atrial sensing, while the atrial sensing stability was assessed using the mean amplitude.

RESULTS

A total of 86 patients were included for analysis. The variability of atrial sensing amplitudes significantly decreased at 12-24 months compared to 3-6 months (p = 0.01), while mean atrial amplitudes were stable throughout the mean follow-up duration of 17.4 months. Nine patients (10.5%) experienced inappropriate ICD therapy mostly due to misclassification of supraventricular tachycardia.

CONCLUSIONS

Under the hypothesis that sensing stability can be guaranteed as the variability decreases with time, we suggest that the concern about long-term sensing stability of a floating dipole can be abated with an ICD that has been implanted for over 2 years.

No Association Between T-peak to T-end Interval on the Resting ECG and Long-Term Incidence of Ventricular Arrhythmias Triggering ICD Interventions

Background and Objectives

Potential of using the T-peak to T-end (TpTe) interval as an electrocardiographic parameter reflecting the transmural dispersion of ventricular repolarization (TDR) to identify patients (pts.) with higher risk of malignant ventricular arrhythmias (MVA) for better selection of candidates for implantable cardioverter-defibrillator (ICD) in primary prevention (PP) of sudden cardiac death (SCD) remains controversial. The primary objective of this study was to investigate the relationship between the TpTe interval in patient’s preimplantation resting 12-lead electrocardiogram (ECG) and the incidence of MVA resulting in appropriate ICD intervention (AI). The secondary objective was to assess its relationship to overall mortality.

Methods

A total of 243 consecutive pts. with severe left ventricular (LV) systolic dysfunction after myocardial infarction (MI) with a single-chamber ICD for PP of SCD from one implantation center were included. Excluded were all pts. with any other disease that could interfere with the indication of ICD implantation. Primarily investigated intervals were measured manually in accordance with accepted methodology. Data on ICD interventions were acquired from device interrogation during regular outpatient visits. Survival data were collected from the databases of health insurance and regulatory authorities.

Results

We did not find a significant relationship between the duration of the TpTe interval and the incidence of MVA (71.5 ms in pts. with MVA vs. 70 ms in pts. without MVA; p = 0.408). Similar results were obtained for the corrected TpTe interval (TpTec) and the ratio of TpTe to QT interval (76.3 ms vs. 76.5 ms; p = 0.539 and 0.178 vs. 0.181; p = 0.547, respectively). There was also no significant difference between the duration of TpTe, TpTec and TpTe/QT ratio in pts. groups by overall mortality (71.5 ms in the deceased group vs. 70 ms in the survivors group; HR 1.01; 95% CI, 0.99–1.02; p = 0.715, 76.3 ms vs. 76.5 ms; HR 1.01; 95% CI, 0.99–1.02; p = 0.208 and 0.178 vs. 0.186; p = 0.116, respectively).

Conclusion

This study suggests no significant association of overall or MVA-free survival with ECG parameters reflecting TDR (TpTe, TpTec) in patients with systolic dysfunction after MI and ICD implanted for primary prevention.

Over- and undersensing-pitfalls of arrhythmia detection with implantable devices and wearables

Cardiac implantable electronic devices (CIEDs) are a cornerstone of arrhythmia and heart failure detection as well as management. In recent years new kinds of devices have emerged which can be used subcutaneously or worn on the skin. In particular for large-scale arrhythmia monitoring, small, unobtrusive gadgets seem positioned to upend paradigms and care delivery. However, the performance of CIEDs and wearables is only as good as their sensing and detection capacities. Whether for pacing, defibrillation or diagnostic monitoring, the device must be able to process and filter the sensed signal to reduce noise and to exclude irrelevant physiological signals. The demands on sensing and detection quality will differ depending on how the information is applied. With a pacemaker or implantable cardioverter/defibrillator, withheld or erroneous therapy can have severe consequences and accurate and reliable detection of cardiac function is crucial. Monitoring devices are usually used in risk assessment and management, with greater tolerance for isolated artefacts or lower quality of readings. This review discusses sensing and detection and the performance to date by CIEDs as well as subcutaneous and wearable devices.

Subclinical atrial fibrillation detection with a floating atrial sensing dipole in single lead implantable cardioverter-defibrillator systems: Results of the SENSE trial

INTRODUCTION

Subclinical atrial fibrillation (AF), in the form of cardiac implantable device-detected atrial high rate episodes (AHREs), has been associated with increased thromboembolism. An implantable cardioverter-defibrillator (ICD) lead with a floating atrial dipole may permit a single lead (DX) ICD system to detect AHREs. We sought to assess the utility of the DX ICD system for subclinical AF detection in patients, with a prospective multicenter, cohort-controlled trial.

METHODS AND RESULTS

One hundred fifty patients without prior history of AF (age 59 ± 13 years; 108 [72%] male) were enrolled into the DX cohort and implanted with a Biotronik DX ICD system at eight centers. Age-, sex-, and left ventricular ejection fraction-matched single- and dual-chamber ICD cohorts were derived from a Cornell database and from the IMPACT trial, respectively. The primary endpoint were AHRE detection at 12 months. During median 12 months follow-up, AHREs were detected in 19 (13%) patients in the DX, 8 (5.3%) in the single-chamber, and 19 (13%) in the dual-chamber cohorts. The rate of AHRE detection was significantly higher in the DX cohort compared to the single-chamber cohort (P = .026), but not significantly different compared to the dual-chamber cohort. There were no inappropriate ICD therapies in the DX cohort. At 12 months, only 3.0% of patients in the DX cohort had sensed atrial amplitudes less than 1.0 mV.

CONCLUSION

Use of a DX ICD lead allows subclinical AF detection with a single lead DX system that is superior to that of a conventional single-chamber ICD system.

Reprogramming the tachycardia parameters with long-detection strategy in patients with pre-existing implantable cardioverter-defibrillator

Background: A long-detection interval (LDI) programming has been proved to reduce shock therapy in patients who underwent de novo implantable cardioverter defibrillator (ICD) implantation. We aimed to evaluate effectiveness and safety of this new strategy in old ICD recipients. Methods: We included 147 primary prevention patients with ischaemic and non-ischaemic aetiology. Conventional setting parameters (18 of 24 intervals to detect ventricular arrhythmias (VA's)) were reprogrammed with LDI strategy (30 of 40 intervals to detect VA's). One monitoring zone (between 360 and 330 ms) and two therapy zones were programmed, treating all rhythms of cycle length <330 ms that met the duration criterion of 30/40 intervals and were discriminated as ventricular tachycardia/ventricular fibrillation (VT/VF). The supraventricular tachycardia (SVT) discriminators were used in all patients. Results: At a median follow-up of 24 months, 12.9% (n = 19) of patients received shock therapies (± antitachycardia pacing (ATP)). Appropriate and inappropriate shocks occurred in 7.5 and 5.4% of patients during follow-up, respectively. Only one patient experienced an arrhythmic syncope during the follow-up period. There was no death related to LDI programming. The LDI programming helped to stop unnecessary in 10 patients (6.8%), who otherwise would have been treated in the conventional programming. Conclusions: LDI programming was found safe and effective. Hence, old ICD recipients will benefit from this strategy.

Optimal Strategies to Reduce Inappropriate Implantable Cardioverter-defibrillator Shocks

Since the widespread implementation of implantable cardioverter-defibrillators (ICDs), their effectiveness in various situations has become well-established. However, despite many advances in both the technology and its utilization, inappropriate therapy remains a risk. Here, we review ICD shocks, their effect on outcomes, and current methods to reduce inappropriate therapy, finding overall that inappropriate ICD shocks are common and associated with adverse outcomes. However, strategies do exist to minimize inappropriate shock rates including device selection and programming, medication, catheter ablation, and remote monitoring. Overall, ICDs are useful in reducing the risk of sudden cardiac death, but many patients with an ICD will receive an inappropriate shock. Understanding strategies to prevent inappropriate shocks is crucial to improving the care of patients with ICDs.

Inappropriate ICD Shocks in Pediatric and Congenital Heart Disease Patients

Although implantable cardioverter-defibrillators (ICDs) have proven to be life-saving devices, there are frequent complications associated with their use, especially in the pediatric and congenital heart disease populations. Inappropriate shocks are a particularly frequent complication in these groups. This review discusses the causes and implications of inappropriate ICD shocks, and presents potential interventions that may assist in safely reducing the rates of inappropriate shocks in pediatric and congenital heart disease patients with ICDs.

Incidence of Device-Detected Atrial Fibrillation and Long-Term Outcomes in Patients With Hypertrophic Cardiomyopathy

Atrial fibrillation (AF) is a common complication of hypertrophic cardiomyopathy (HC) and associated with adverse clinical outcomes, such as thromboembolisms. Cardiac implantable electronic devices (CIEDs) enable early detection of AF. The aim of this study was to assess the incidence of device-detected AF and the impact on long-term outcomes in patients with HC. The cohort consisted of 132 patients (63% men, mean age 52 ± 16 years) with a diagnosis of HC and a CIED. Follow-up started at the date of CIED implantation to assess the incidence of device-detected AF. Patients with persistent AF at the time of implantation were excluded from the analysis of the incidence of AF. End points were all-cause and cardiac mortality, device-detected AF, and thromboembolism (stroke, transient ischemic attack, or peripheral arterial embolism). In total, 114 patients were in sinus rhythm at time of CIED implantation. During the median 2.8 (interquartile range 1.2 to 5.4) years of follow-up, device-detected AF occurred in 29 patients (25%), resulting in an annual incidence of 7.0%/year. Device-detected AF led to a change in the clinical management in 22 patients (76%). Anticoagulation therapy was started in 13 (45%), antiarrhythmic medication in 9 (31%), and electrical cardioversion in 8 (28%) patients. Six patients (5%) suffered a thromboembolic complication. All-cause mortality was 27 (20%), and cardiac mortality was 21 (16%). A history of AF at time of implantation was an independent predictor of cardiac death (hazard ratio 4.7, p = 0.003). In conclusion, the incidence of device-detected AF in patients with HC was 7.0%/year, leading to a change in clinical management in the majority (76%) of cases to reduce the risk of thromboembolic complications. These findings stress the importance of AF detection in HC and advocate vigilant interrogation of the device.

Atrial electrograms improve the accuracy of tachycardia interpretation from ICD and pacemaker recordings: The RATE Registry

BACKGROUND

Tachycardia diagnoses from implantable device recordings ultimately depend on the analysis of captured electrograms (EGMs). The degree to which atrial EGMs improve tachycardia discrimination, dependent on the level of expertise of the medical professional involved, remains uncertain.

OBJECTIVE

The purpose of this article was to determine whether atrial EGM recordings improve tachycardia discrimination and whether this improvement, if any, varies for professionals with different levels of training.

METHODS

Expert-adjudicated supraventricular tachycardia (SVT) and ventricular tachycardia (VT) dual-chamber EGMs (DEGMs) from the Registry of Atrial Tachycardia and Atrial Fibrillation Episodes in the Cardiac Rhythm Management Device Population were provided to electrophysiology specialists, electrophysiology fellows (EPF), and nurse practitioners or physician assistants (NPPA). Each participant diagnosed 112 EGM episodes presented in random sequence (61 VTs and 51 SVTs) and independently categorized each as "SVT," "VT," or "uncertain" in 2 stages. First, participants analyzed ventricular EGMs (VEGMs) alone (atrial channel covered). Second, the tracings were randomized and reanalyzed with atrial EGMs exposed. The diagnostic accuracy of VEGMs alone vs DEGMs was assessed for each group.

RESULTS

For all 3 groups, diagnostic accuracy improved significantly (>20% for VTs and >15% for SVTs; P < .01 for all) when DEGMs were provided. Electrophysiology specialists diagnosed VTs more accurately than did EPF and NPPA (VEGM: 73.1%±7.6% vs 58.7%±15.5% and 56.1%±14.1%; P < .01; DEGM: 98.0%±2.7% vs 90.8%±16.0% and 80.3%±7.4%; P < .01). EPF diagnosed VTs more accurately than did NPPA only when DEGMs were provided. There was no significant intergroup difference in SVT diagnoses.

CONCLUSION

DEGMs are superior to VEGMs alone for tachycardia discrimination at all levels of expertise. The level of training affects diagnostic accuracy with and without atrial EGMs.

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.

Low rate of and rapid attention to inappropriate ICD shocks with remote device and rhythm monitoring: a qualitative study

Objectives

Inappropriate shocks are unpleasant and painful. We hypothesise that remote monitoring and careful attention to known and incident atrial fibrillation (AF) can reduce inappropriate shocks to a very low level in clinical praxis.

Methods

Altogether 259 patients with implantable cardioverter defibrillator implanted for secondary (S, n=113) and primary (P, n=146) prevention were followed via remote monitoring. At implant, 42S (37%) and 54P (37%) patients had known AF.

Results

Inappropriate shocks, all but five due to AF, occurred in 7S (6.2%) and 11P (7.5%), and there were only inappropriate shocks in 5/7S and in 8/11P. They occurred in four of 42S (9.5%) with and in three of 71S (4.2%) without known AF, and in seven of 54P (13%) with and in four of 92P (4.3%) without known AF. The median time from shock to action was 5 and 1 day, respectively. Actions were medication with amiodarone, β blockers, β blockers+amiodarone or β blockers+digoxin (n=5), β blockers+insertion of an atrial lead (n=1), replacement of a fractured lead (n=2), reprogramming in combination with β blockers, digoxin or amiodarone (n=4), reprogramming (n=2) and none (n=4). After action, four further inappropriate shocks occurred during more than 2 years of follow-up, all due to AF.

Conclusions

Inappropriate shocks occurred at a low rate and most often because of AF known at implant. Remote monitoring enabled rapid action, after which few inappropriate shocks occurred over more than 2 years. Attention to known and incident AF was the most important action to reduce inappropriate shocks.

Programming implantable cardioverter/defibrillators and outcomes

Implantable cardioverter-defibrillators are complex technical devices with a multitude of programming options for the physician. In recent years, numerous randomized trials have been performed to define the optimal programming strategies and have provided valuable insights, especially in primary prevention patients. This article provides an actual overview on the existing evidence on the most important programming features for accurate detection and therapy of ventricular arrhythmias.

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).

Implantable cardioverter defibrillator system with floating atrial sensing dipole: a single-center experience

BACKGROUND

The concept of a single-lead dual-chamber implantable cardioverter defibrillator (ICD) with floating sensing atrial dipole has been proven safe and functional. We report a single-center experience with this ICD system; the major focus of the work is on the recorded atrial activation and its stability on a medium term follow-up.

METHODS

Thirteen patients received a DX ICD (BIOTRONIK SE & Co, Berlin, Germany) with the Linox Smart S DX(ProMRI) ICD lead; the implantation data were reported. Daily P- and R-wave sensing amplitude was collected and followed up during 200 days; their coefficient of variance (CV) was calculated. In addition, all the atrial and ventricular high-rate episodes were analyzed.

RESULTS

The total x-ray exposure time was 3.9 ± 1.8 minutes. The overall mean sensing was 4.2 ± 1.9 mV for P wave and 12.9 ± 4.5 mV for R wave. The CV was significantly higher for the P-wave amplitude than for the R-wave one (0.25 ± 0.11 vs 0.08 ± 0.06; P < 0.001). A total of 27 high ventricular rate episodes were recorded and correctly discriminated by the device. Fifty-six high atrial rate episodes were recorded, 49 were true arrhythmic events.

CONCLUSIONS

The single-lead ICD system with floating atrial dipole provides reliable atrial sensing amplitude over time. The physician, without the implantation of an additional lead, has the atrial information that may be used for the discrimination of supraventricular tachyarrhythmia/ventricular tachycardia, for the early detection of atrial fibrillation episodes and for the evaluation of changes in the patient's heart status.

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.

Cardiac pacing and defibrillation in children and young adults

The population of children and young adults requiring a cardiac pacing device has been consistently increasing. The current generation of devices are small with a longer battery life, programming capabilities that can cater to the demands of the young patients and ability to treat brady and tachyarrhythmias as well as heart failure. This has increased the scope and clinical indications of using these devices. As patients with congenital heart disease (CHD) comprise majority of these patients requiring devices, the knowledge of indications, pacing leads and devices, anatomical variations and the technical skills required are different than that required in the adult population. In this review we attempt to discuss these specific points in detail to improve the understanding of cardiac pacing in children and young adults.

Prospective comparison of discrimination algorithms to prevent inappropriate ICD therapy: primary results of the Rhythm ID Going Head to Head Trial

BACKGROUND

Inappropriate therapy for supraventricular arrhythmias remains a significant source of morbidity in implantable cardioverter-defibrillator (ICD) recipients.

OBJECTIVE

The Rhythm ID Goes Head to Head Trial (RIGHT) was designed to compare rhythm discrimination and inappropriate therapies among patients with ICDs from 2 manufacturers.

METHODS

Patients with standard ICD indications were randomized to receive a Guidant VITALITY 2 with Rhythm ID or selective Medtronic pulse generators using the Enhanced PR Logic or Wavelet discrimination algorithms. A single- or dual-chamber device was implanted based on clinical indications and programmed in 2 detection zones with detection enhancements enabled for rates between 150 and 200 bpm. Algorithm performance was compared between randomization groups, stratified by single or dual chamber, for the primary end point of first inappropriate therapy (shock or antitachycardia pacing) for supraventricular arrhythmias.

RESULTS

There were 1962 patients enrolled and followed for 18.3 ± 9.2 months, with no difference in all-cause mortality between groups. There were 3973 treated episodes where electrograms were available and adjudicated. The primary end point of inappropriate therapy occurred in 246 of 985 VITALITY 2 patients vs 187 of 977 specific Medtronic ICD patients (hazard ratio = 1.34; confidence interval = 1.11-1.62; P = .003). Differences in inappropriate therapy were confined to single-chamber ICDs. Inappropriate shocks were more frequent in VITALITY 2 ICDs (hazard ratio = 1.63; confidence interval = 1.29-2.06; P < .001), with most therapies and performance differences occurring at slower rhythms (rates < 175 bpm).

CONCLUSION

Rhythm discrimination performed better in the specific Medtronic than in VITALITY 2 ICDs evaluated, particularly for single-chamber devices. Inappropriate therapies, and differences in performance, may be reduced with the use of rate cutoff above 175 bpm.

Early therapy following myocardial infarction: arguments for and against implantable cardioverter-defibrillators

The implantable cardioverter-defibrillator (ICD), when implanted in the late phase of myocardial infarction (MI) in the primary prevention of sudden cardiac death, reduces total mortality by 23-31%. Current guidelines recommend ICD implantation at least 40 days after MI. Despite optimal MI therapy, the risk of sudden cardiac death or cardiac arrest remains highest within the first 30 days after index infarction. Two randomized trials with ICD implantation early after MI failed to show the reduction of total mortality in a long-term follow-up study. The decrease of sudden cardiac death incidence was counterbalanced by an increase of nonsudden deaths, which may have been caused by the augmentation of heart failure deaths in ICD groups, presumably due to ICD interventions. Therefore, optimizing ICD appears to be the most important issue influencing the long-term outcome.

Inappropriate Implantable Cardioverter-Defibrillator Therapy

Although improvements in implantable cardioverter-defibrillator (ICD) therapy have taken place, many challenges do remain. Inappropriate delivery of therapy is a big problem that impacts the quality of life of ICD recipients. Although there is now a clear understanding that atrial arrhythmias are the main cause of inappropriate ICD therapies, physicians have not been very successful in preventing them. Additionally, although many tachycardia detection discriminators have been shown to be helpful, it is not clear that there is a particular combination that is ideal for all patients. Until such an algorithm is developed (which may not be possible), a detailed knowledge and use of all available programming options, guided by special characteristics of each unique patient, are the only foreseeable solutions. Finally, one must face the prospect that this problem cannot be vanquished, but only ameliorated.

Identification of hemodynamically unstable arrhythmias using subcutaneous photoplethysmography

INTRODUCTION

Determination of hemodynamic status is central to arrhythmia management in the inpatient setting. In contrast, therapy decisions in implantable cardioverter defibrillators (ICDs) are based exclusively on the arrhythmia's electrical signature. Hemodynamic sensing in ICDs would allow tailoring of therapy according to perfusion status. Subcutaneous photoplethysmography (PPG) is an attractive technology for this application because it responds to changes in arterial pressure and can be readily incorporated into the housing of implanted devices. This study evaluated the accuracy of PPG in identifying hemodynamically unstable simulated arrhythmias in an animal model.

METHODS AND RESULTS

Rapid atrial and ventricular pacing was used to simulate arrhythmias in an acute preparation of 7 healthy dogs. Aortic pressure and subcutaneous PPG were simultaneously recorded. Simulated arrhythmias were defined as hemodynamically unstable if aortic pressure decreased by >or=15 mmHg, marginally unstable if pressure decreased by 5-15 mmHg, and hemodynamically stable if pressure either increased or decreased by no more than 5 mmHg. An average of 56 arrhythmias were simulated in each animal. Changes in pressure and PPG output were highly correlated, with correlation coefficient of 0.7-0.9. Subcutaneous PPG identified hemodynamically unstable episodes with a sensitivity of 100% for 6 subjects and 80% for 1 subject. Specificity was more than 90% for 6 subjects and was 50% for 1 subject.

CONCLUSIONS

Subcutaneous PPG detects hemodynamically unstable simulated arrhythmias in an acute canine preparation. If successfully validated in humans, this technology may allow ICD therapy to be specifically tailored according to the hemodynamic status of the arrhythmia.