Ensuring automatic detection of ventricular fibrillation

Comparison of bipolar and integrated sensing for redetection of ventricular fibrillation

BACKGROUND

Implantable cardioverter-defibrillator function is critically dependent on reliable sensing of intracardiac signals. Lead systems that use integrated sensing, in which the distal shocking coil is part of both the sensing and shocking pathways, may be prone to undersensing of ventricular fibrillation, especially during redetection after a failed first shock. To assess the effect of endocardial lead system on redetection, we compared a dedicated rate-sensing lead and 2 generations of integrated sensing defibrillator leads with a uniform testing algorithm and pulse generator.

METHODS

The study group consisted of 72 patients after implantable cardioverter-defibrillator implantation. Three transvenous rate-sensing leads were evaluated: a standard pacing lead, incorporating true bipolar sensing without ventricular coils, or an integrated shocking and sensing lead (Endotak C) with either 6-mm (60 series) or 12-mm (70 series) spacing between the sensing tip and shocking coil. Redetection was assessed from a failed first shock just below defibrillation threshold.

RESULTS

Compared with the dedicated bipolar lead, redetection was prolonged with the 60 series lead (8.3 +/- 3.6 vs 6.6 +/- 2.3 seconds, P =.04). Moreover, prolonged redetection (>8 seconds) was observed in 41% of patients with 60 series leads compared with only 11% with dedicated bipolar leads (P <.01). No significant effects on redetection were noted with an integrated lead with greater spacing between the tip and coil (70 series).

CONCLUSIONS

Delayed redetection is frequently noted with an integrated lead with close spacing between the tip and coil. Detailed evaluation of detection and redetection of these leads should be performed at the time of pulse generator replacement.

Comparison of single- and dual-coil active pectoral defibrillation lead systems

OBJECTIVES

The purpose of this study was to compare defibrillation thresholds with lead systems consisting of an active left pectoral electrode and either single or dual transvenous coils.

BACKGROUND

Lead systems that include an active pectoral pulse generator reduce defibrillation thresholds and permit transvenous defibrillation in nearly all patients. A further improvement in defibrillation efficacy is desirable to allow for smaller pulse generators with a reduced maximal output.

METHODS

This prospective study was performed in 50 consecutive patients. Each patient was evaluated with two lead configurations with the order of testing randomized. Shocks were delivered between the right ventricular coil and either an active can alone (single coil) or an active can with the proximal atrial coil (dual coil). The right ventricular coil was the cathode for the first phase of the biphasic defibrillation waveform.

RESULTS

Delivered energy at the defibrillation threshold was 10.1+/-5.0 J for the single-coil configuration and 8.7+/-4.0 J for the dual-coil configuration (p < 0.02). Moreover, 98% of patients had low (<15 J) thresholds with the dual-coil lead system, compared with 88% of patients with the single-coil configuration (p=0.05). Leading edge voltage (p < 0.001) and shock impedance (p < 0.001) were also decreased with the dual-coil configuration, although peak current was increased (p < 0.001).

CONCLUSIONS

A dual-coil, active pectoral lead system reduces defibrillation energy requirements compared with a single-coil, unipolar configuration.

Distortion of intracardiac electrograms following defibrillator shocks for atrial tachyarrhythmias

In three patients with a defibrillator system consisting of a Ventak P2 pulse generator and an Endotak C transvenous lead, we observed distortion of intracardiac electrograms following defibrillator shocks for atrial arrhythmias. There was a transient marked widening of the intracardiac ventricular complexes resembling ventricular tachycardia. This phenomenon should be recognized when evaluating arrhythmic episodes.

Inappropriate management of self-terminating ventricular arrhythmias by implantable cardioverter defibrillators despite a specific reconfirmation algorithm: a report of two cases

Algorithms that attempt to reconfirm the presence of an arrhythmia prior to definite treatment have been implemented in ICDs to prevent inappropriate shock therapy due to self-terminating ventricular arrhythmias. Nevertheless, in two patients, clinically inappropriate shocks were delivered after spontaneous conversion of the arrhythmia despite the use of a specific reconfirmation algorithm. Reconfirmation criteria were met due to a premature ventricular complex causing a short cycle in the first patient and a long postextrasystolic pause in the second patient. To avoid inappropriate shock therapy due to self-terminating ventricular arrhythmias, further improvement of detection algorithms is required.

Changes in the amplitude of endocardial electrograms following defibrillator discharge: comparison of two lead systems

Changes in the amplitude of endocardial electrograms after an unsuccessful shock attempt have been demonstrated to cause failure of redetection of ventricular fibrillation in patients using an integrated sense-pace defibrillating lead system. Thus, the objective of this study was to compare the effects of defibrillator shocks on the amplitude of endocardial electrograms in 26 patients using two different nonthoracotomy systems, a previous lead (model 0062) or a redesigned version (model 0072). At implant, bipolar endocardial electrograms were obtained before each shock application, during initial detection and redetection of ventricular fibrillation in case the applied shock was unsuccessful, and during intervals of 5, 10, 20, 30, 60, and 120 seconds after each shock delivery. No significant difference was noted in endocardial amplitudes between the lead models 0062 and 0072 during baseline sinus rhythm (12.2 +/- 4.6 mV vs 11.4 +/- 3.8 mV), and during initial ventricular fibrillation (7.0 +/- 2.4 mV vs 7.6 +/- 2.3 mV). During redetection of ventricular fibrillation, however, there was a significant difference (P = 0.0006) in endocardial amplitudes (3.4 +/- 1.9 mV vs 6.6 +/- 2.3 mV) between both leads tested. Comparing lead models 0062 and 0072, marked differences were found in endocardial amplitudes during sinus rhythm 5, 10, and 20 seconds after successful arrhythmia termination: 2.8 +/- 1.9 mV vs 8.6 +/- 2.9 mV (P < 0.0001), 4.6 +/- 2.9 mV vs 9.2 +/- 3.2 mV (P = 0.0007), and 6.4 +/- 4.0 mV vs 10.5 +/- 3.6 mV (P = 0.01). At predischarge testing, failure of redetection of ventricular fibrillation was documented in two patients with the lead model 0062 requiring external defibrillation to restore sinus rhythm. These findings demonstrate a significant less postshock attenuation of the endocardial electrogram amplitudes during persistent ventricular fibrillation after an unsuccessful shock attempt as well as during sinus rhythm immediately following an effective shock delivery using the redesigned lead system model 0072 compared to the electrogram amplitudes obtained in patients using the previous lead model 0062.

The pacer-cardioverter-defibrillator: function and clinical experience

Pacer-Cardioverter-Defibrillator. This article reviews the function of the pacer-cardioverter-defibrillator (PCD). Detection of ventricular arrhythmias occurs in two programmable zones, with onset and stability modifiers available to diminish overdetection of sinus tachycardia and atrial fibrillation, respectively. The sensing circuitry utilizes an auto-adjusting sensitivity with exponential decay to allow detection of low-amplitude ventricular fibrillation electrograms without T wave oversensing. Treatment can be accomplished by tiered therapy with two types of antitachycardia pacing, cardioversion and defibrillation. Cardioversion and defibrillation shocks are programmable between single pathway when two leads are used and simultaneous or sequential shock delivery when a three-lead system is used. A telemetered marker channel and electrogram aid in assessing device function during implantation and follow-up. Previously published literature is cited to expand on various aspects of PCD function and programming.