Temporal decline in defibrillation thresholds with an active pectoral lead system

OBJECTIVES

The objective of this study was to characterize temporal changes in defibrillation thresholds (DFTs) after implantation with an active pectoral, dual-coil transvenous lead system.

BACKGROUND

Ventricular DFTs rise over time when monophasic waveforms are used with non-thoracotomy lead systems. This effect is attenuated when biphasic waveforms are used with transvenous lead systems; however, significant increases in DFT still occur in a minority of patients. The long-term stability of DFTs with contemporary active pectoral lead systems is unknown.

METHODS

This study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pectoral lead system. Thresholds were measured at implantation, before discharge and at long-term follow-up (70 +/- 40 weeks) in 50 patients.

RESULTS

The DFTs were 9.2 +/- 5.4 J at implantation, 8.3 +/- 5.8 J before discharge and 6.9 +/- 3.6 J at long-term follow-up (p < 0.01 by analysis of variance; p < 0.05 for long-term follow-up vs. at implantation or before discharge). The effect was most marked in a prespecified subgroup with high implant DFTs (> or =15 J). No patient developed an inadequate safety margin (< 9 J) during follow-up.

CONCLUSIONS

The DFTs declined significantly after implantation with an active pectoral, dual-coil transvenous lead system, and no clinically significant increases in DFT were observed. Therefore, routine defibrillation testing may not be required during the first two years after implantation with this lead system, in the absence of a change in the cardiac substrate or treatment with antiarrhythmic drugs.

Acute hemodynamic effects of right ventricular pacing site and pacing mode in patients with congestive heart failure secondary to either ischemic or idiopathic dilated cardiomyopathy

The hemodynamic effects of pacing in patients with congestive heart failure (CHF) remain controversial. Early studies reported that pacing from the right ventricular (RV) apex improved acute hemodynamic parameters in patients with left ventricular systolic dysfunction, but these findings were not confirmed in subsequent controlled studies. More recently, it has been proposed that pacing from the RV side of the ventricular septum improves hemodynamic function compared with intrinsic conduction or apical pacing. Either dual-chamber or ventricular pacing have been evaluated, again with inconsistent findings. To assess the effects of pacing site and mode on acute hemodynamic function, we evaluated 21 subjects with CHF and intrinsic conduction disease. Hemodynamics were compared in AAI, VVI, and DDD modes with pacing from the RV apex or high septum. The pacing rate was constant in each patient and the order of testing was randomized. In the absence of ventricular pacing (AAI mode), the mean systemic arterial pressure was 85 +/- 11 mm Hg, the right atrial pressure was 11 +/- 4 mm Hg, the pulmonary capillary wedge pressure was 18 +/- 8 mm Hg and the cardiac index was 2.4 +/- 0.7 L/min/m(2). Compared with AAI pacing, there were no improvements in any hemodynamic parameter with DDD pacing from either RV site. Hemodynamic function worsened with VVI pacing from both RV sites. Subgroup analyses of patients with dilated cardiomyopathy, with prolonged PR interval, or with significant mitral regurgitation also failed to demonstrate an improvement with pacing. We conclude that pacing mode but not RV pacing site affects acute hemodynamic function. Pacing in the DDD mode prevents the deleterious effects of VVI pacing in this patient population.

Optimization of transvenous coil position for active can defibrillation thresholds

INTRODUCTION

Lead systems that include an active pectoral pulse generator are now standard for initial defibrillator implantations. However, the optimal transvenous lead system and coil location for such active can configurations are unknown. The purpose of this study was to evaluate the benefit and optimal position of a superior vena cava (SVC) coil on defibrillation thresholds with an active left pectoral pulse generator and right ventricular coil.

METHODS AND RESULTS

This prospective, randomized study was performed on 27 patients. Each subject was evaluated with three lead configurations, with the order of testing randomized. Biphasic shocks were delivered between the right ventricular coil and an active can alone (unipolar), or an active can in common with the proximal coil positioned either at the right atrial/SVC junction (low SVC) or in the left subclavian vein (high SVC). Stored energies at defibrillation threshold were higher for the single-coil, unipolar configuration (11.2 +/- 6.6 J) than for the high (8.9 +/- 4.2 J) or low (8.5 +/- 4.2 J) SVC configurations (P < 0.01). Moreover, 96% of subjects had low (< or = 15 J) thresholds with the SVC coil in either position compared with 81% for the single-coil configuration. Shock impedance (P < 0.001) was increased with the unipolar configuration, whereas peak current was reduced (P < 0.001).

CONCLUSION

The addition of a proximal transvenous coil to an active can unipolar lead configuration reduces defibrillation energy requirements. The position of this coil has no significant effect on defibrillation thresholds.

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways

OBJECTIVES

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

BACKGROUND

Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown.

METHODS

This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial).

RESULTS

Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002).

CONCLUSIONS

These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.

Intravenous amiodarone suppression of electrical storm refractory to chronic oral amiodarone

We report the case of an electrical storm in a cardiac arrest survivor with an ICD, in whom chronic oral amiodarone failed to suppress ventricular arrhythmias, and in whom intravenous amiodarone resulted in stability for 6 weeks prior to successful cardiac transplantation. Intravenous amiodarone can be successful in suppressing life-threatening ventricular arrhythmias, even when chronic oral amiodarone is unsuccessful.

The effect of shock configuration and delivered energy on defibrillation impedance

Shock impedance is an important determinant of defibrillation efficacy. Lead configuration, shock polarity, and delivered energy can affect shock impedance, but these variables have not been studied in active can lead systems. The present study was a prospective evaluation of 25 patients undergoing initial transvenous defibrillator implantation. In all patients, a dual coil lead and pectoral emulator were placed and three lead configurations were tested in random order: Lead (distal to proximal coil), unipolar (distal coil to can), and triad (distal coil to can + proximal coil). Shock energies of 0.1- to 15-J shock were evaluated. Impedance increased a mean of 21% as delivered energy was decreased (P < 0.001), an effect independent of lead configuration. At all delivered energies, impedances in the unipolar configuration were about 40% higher than triad, while the lead configuration was about 20% higher than triad (ps < 0.001). Polarity did not affect impedance. These results indicate that transvenous lead configurations and delivered energy, but not polarity, significantly influence shock impedance. The magnitude of the increase of impedance at low energies is independent of the shocking pathway. This effect has important implications for low energy shocks used to terminate atrial fibrillation or ventricular tachycardia.

A new defibrillator discrimination algorithm utilizing electrogram morphology analysis

Inappropriate therapies delivered by implantable cardioverter defibrillators (ICDs) for supraventricular arrhythmias remain a common problem, particularly in the event of rapidly conducted atrial fibrillation or marked sinus tachycardia. The ability to differentiate between ventricular tachycardia and supraventricular arrhythmias is the major goal of discrimination algorithms. Therefore, we developed a new algorithm, SimDis, utilizing morphological features of the shocking electrograms. This algorithm was developed from electrogram data obtained from 36 patients undergoing ICD implantation. An independent test set was evaluated in 25 patients. Recordings were made in sinus rhythm, sinus tachycardia, and following the induction of ventricular tachycardia and atrial fibrillation. The arrhythmia complex is defined as wide if the duration is at least 30% greater than the template in sinus rhythm. For narrow complexes, four maximum and minimum values were measured to form a 4-element feature vector, which was compared with a representative feature vector during normal sinus rhythm. For each rhythm, any wide complex was classified as ventricular tachycardia. For narrow complexes, the second step of the algorithm compared the electrogram with the template, computing similarity and dissimilarity values. These values were then mapped to determine if they fell within a previously established discrimination boundary. On the independent test set, the SimDis algorithm correctly classified 100% of ventricular tachycardias (27/27), 98% of sinus tachycardias (54/55), and 100% of episodes of atrial fibrillation (37/37). We conclude that the SimDis algorithm yields high sensitivity (100%) and specificity (99%) for arrhythmia discrimination, using the computational capabilities of an ICD system.

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.

Effect of shock polarity on biphasic defibrillation thresholds using an active pectoral lead system

INTRODUCTION

The downsizing of implantable defibrillator pulse generators has made pectoral placement routine. A further reduction of defibrillation thresholds (DFTs) may simplify implantation defibrillation testing and allow for smaller, lower output pulse generators while maintaining an adequate defibrillation safety margin. One factor that may affect defibrillation efficacy is shock polarity.

METHODS AND RESULTS

Sixty consecutive patients undergoing dual-coil, active left pectoral defibrillator implantation were evaluated. Paired, biphasic DFTs were measured in normal (RV apex = cathode) and reverse (RV apex = anode) polarity with order of testing randomized. Reverse polarity conferred a 15% reduction of mean DFTs (8.5 +/- 5.0 J normal, 7.2 +/- 4.6 J reverse polarity, P = 0.02). The effect of polarity appeared most pronounced among the patients with a high DFT (> or = 15 J) resulting in a 31% reduction with reverse polarity (16.7 +/- 2.5 J normal, 11.5 +/- 5.9 J reverse, P = 0.03).

CONCLUSION

Reversing shock polarity results in significantly lower biphasic DFTs with an active pectoral lead system, particularly in the subgroup of patients with a high normal polarity threshold. Reversing polarity in these patients may simplify acute defibrillation testing and allow for lower output devices.

Temporal stability of defibrillation thresholds with an active pectoral lead system

INTRODUCTION

Monophasic defibrillation thresholds rise over time with a variety of lead systems. These chronic changes are attenuated or eliminated by biphasic waveforms, although the effect appears dependent upon the lead system. With the downsizing of pulse generator size to allow for routine pectoral implantation, active can lead systems have now become standard. However, the temporal stability of such lead systems has not been evaluated previously.

METHODS AND RESULTS

This study was a prospective assessment of the changes of active pectoral defibrillation thresholds over time. Thresholds were measured at implant, predischarge, and at a mean follow-up of 50 days in 46 patients with a uniform testing protocol and shock polarity. The lead system was a dual-coil Endotak DSP lead with an active pectoral pulse generator. Defibrillation thresholds were 9.9+/-5.5 J at implantation, 8.5+/-6.0 J predischarge, and 7.6+/-5.5 J at follow-up (ANOVA, P = 0.007). Moreover, only two patients developed an increased threshold > 5 J, and no patient had an inadequate safety margin at follow-up.

CONCLUSION

These results indicate that active pectoral defibrillation thresholds are stable over the first 2 months postimplantation and question the need for routine serial defibrillation threshold testing.

Effect of biphasic waveforms on transvenous defibrillation thresholds in patients with coronary artery disease

This study is a prospective, randomized comparison of monophasic and biphasic defibrillation thresholds in 19 patients with a single transvenous lead. Despite using reverse polarity and optimal tilts for the monophasic waveform, the defibrillation threshold was reduced with biphasic shocks from 15.8 +/- 11.3 to 11.5 +/- 6.1 (p <0.05) with comparable reductions of leading edge voltage and current.

Cardiac trauma. Diagnosis, management, and current therapy

In cardiac trauma the two main mechanisms of injury are blunt and penetrating trauma. Common cardiac effects of trauma include myocardial rupture, contusion, laceration, pericardial insult, coronary injury, valvular damage, arrhythmias, and conduction abnormalities. Hemodynamic instability can develop rapidly and pose marked risk to patient survival. An adequate level of clinical awareness and timely use of diagnostic techniques such as echocardiography, aortography, and cardiac angiography are essential for rapid identification of cardiac trauma. Once the diagnosis is made, prompt surgical intervention is often the key to survival.

Selective slow pathway ablation does not alter enhancement of vagal tone on sinus and atrioventricular nodal function

We studied the effects of edrophonium on sinus cycle length, atrioventricular (AV) nodal fast pathway refractoriness, and AV nodal Wenckebach cycle length in 21 patients with AV nodal reentrant tachycardia (AVNRT) who received edrophonium, and 8 patients who received phenylephrine before and after selective slow pathway ablation. Changes in sinus cycle length, fast pathway conduction, and refractoriness were not altered by radiofrequency ablation of the slow pathway, suggesting that parasympathetic denervation does not occur after slow pathway ablation of AVNRT.