Underdetection of ventricular fibrillation despite ICD testing and high sinus R wave

Failure to Treat Ventricular Tachycardia or Ventricular Fibrillation by Implantable Cardioverter-Defibrillators

BACKGROUND

Normally-functioning implantable cardioverter-defibrillators (ICDs) with intact lead systems occasionally fail to deliver therapy for ventricular tachycardia/ fibrillation (VT/VF) or deliver it only after clinically-significant delays ("failure-to-treat").

OBJECTIVE

To investigate ICD failure-to-treat VT/VF in a large patient cohort.

METHODS

We searched the United States (US) Food and Drug Association's online Manufacturer and User Facility Device Experience (MAUDE) database from 2019 to 2023 for manufacturer-verified reports in which normally-functioning ICDs failed to treat VT/VF.

RESULTS

We identified 854 reports classified as deaths (n=96, 11.2%), injuries (n=585, 68.5%), or malfunctions (n=173, 20.4%) for normally-functioning ICDs. The most common causes were misclassification as supraventricular tachycardia (SVT) or atrial fibrillation (AF) (54.8%), undersensing (21.1%), and failure to satisfy programmed rate/duration criteria (8.7%). Most events caused by misclassification as SVT/AF (89.5%) and failure to satisfy rate/duration criteria (70.3%) were VT; most caused by undersensing were either VF (54.4%) or not specified as VT or VF (19.4%). Undersensing caused 65.6% of deaths, although it comprised only 21.1% of reports. In the United States, the number of reports increased faster than that of ICD patients.

CONCLUSIONS

In the largest reported series of failure-to-treat VT/VF by normally-functioning ICDs, the most common cause was misclassification of VT as SVT/AF; the most common cause of death was undersensing of VF. Although relatively few patients with normally-functioning ICDs experience failure-to-treat VT/VF, the absolute number of verified MAUDE reports suggests that more work is needed to quantify the magnitude of the problem, identify root causes, and develop solutions.

Sensing and Detection Functions in Implantable Cardioverter Defibrillators: The Good, the Bad and the Ugly

Implantable cardioverter defibrillators are small devices that have been proven to be beneficial by preventing sudden cardiac death, whether in primary or secondary prevention. Appropriate functioning of implantable cardioverter defibrillators is mainly dependent on the "good" sensing of ventricular electrogram waves, allowing for the adequate detection of ventricular arrhythmias in order to deliver appropriate therapy of either antitachycardia pacing or by delivering a shock according to the detected rhythm. Basic sensing function in defibrillators is based on detection rate and detection duration; additional parameters that are involved in the process of adequate detection include ventricular electrogram sensing, auto-adjusting sensitivity, supraventricular arrhythmia discrimination criteria, noise detection, and various dedicated algorithms. Defective sensing may result in the delivery of inappropriate therapy (oversensing) or inappropriate withholding of therapy (undersensing); the latter of which may lead to sudden cardiac death. This paper describes different clinical scenarios and programming tips to avoid abnormal or critical clinical situations.

Sinus rhythm R-wave amplitude as a predictor of ventricular fibrillation undersensing in patients with implantable cardioverter-defibrillator

BACKGROUND

Ventricular fibrillation (VF) is induced during implantable cardioverter-defibrillator (ICD) implantation to ensure that the ICD will sense, detect, and defibrillate VF. ICD implant guidelines state that the amplitude of the sinus rhythm R wave recorded from the ventricular electrogram should have amplitude ≥5 mV. No study has tested the relationship between sinus rhythm R-wave amplitude and VF sensing using modern, transvenous sensing electrodes.

OBJECTIVE

The goal of this study was to determine whether there is a sinus rhythm R-wave amplitude cutoff that can be used to determine which patients are not at risk of VF undersensing.

METHODS

A retrospective analysis of induced and spontaneous VF episodes from 2 clinical trials with 2022 patients was performed. Episodes with undersensing during the initial detection of VF were identified, and the distribution of sinus rhythm R-wave amplitudes for patients with and without VF undersensing was analyzed.

RESULTS

Only 3% of analyzed induced VF episodes were considered to have VF undersensing, and none had clinically significant detection delays. There was no correlation between device-measured, rectified sinus rhythm R-wave amplitude and VF undersensing at the time of implantation or during follow-up, although <4% of patients had sinus rhythm R-waves with amplitude <3 mV.

CONCLUSION

We analyzed true bipolar sensing of induced VF or spontaneous ventricular tachycardia/VF detected in the ICD VF zone. Sensing of VF was so reliable that clinically significant undersensing did not occur. Our findings do not support any recommended minimum sinus rhythm R wave to ensure reliable sensing of VF or the necessity of inducing VF to verify sensing for rectified sinus rhythm R-waves with amplitude ≥3 mV.