Comparison of fixed tilt and tuned defibrillation waveforms: the PROMISE study.

BACKGROUND: All modern defibrillation systems use biphasic shock waveforms. Typically a fixed tilt waveform is used for implantable defibrillators (ICDs), but a tuned waveform with duration based on shock impedance may be superior based on theoretical calculations. OBJECTIVE: The objective of this study was to compare defibrillation efficacy of fixed tilt and tuned waveforms. METHODS: PROMISE was designed as a prospective, within-patient, randomized study of defibrillation thresholds (DFTs) comparing a tuned (assuming a 3.5 milliseconds membrane time constant) versus a 50/50% tilt waveform. All patients had a left pectoral implant (active can) and testing was performed with a single coil shocking configuration ("SVC coil OFF"). DFTs were measured in random order with a binary search method in 52 patients, using the high-voltage lead impedance to select the pulse widths for both waveforms. RESULTS: At the DFT, the tuned waveform had similar delivered energy (10.5 ± 6.3 vs 9.5 ± 5.5 J, P = 0.47), stored energy (13.6 ± 7.9 vs 11.3 ± 6.3 J, P = 0.06), peak current (7.5 ± 3.0 vs 6.8 ± 2.2 A, P = 0.09), and delivered voltage (451.0 ± 134.5 vs 411.5 ± 120.7 V, P = 0.05) compared with the 50/50% tilt waveform. CONCLUSION: The DFTs for 3.5-millisecond time constant based tuned and 50/50% tilt waveforms are similar using a single coil, left pectoral active can.

Efficacy of tuned waveforms based on different membrane time constants on defibrillation thresholds: primary results from the POWER trial.

BACKGROUND: The efficacy of tuned defibrillation waveforms versus the nominal fixed-tilt waveform has been previously studied. However, the optimal membrane time constant for tuning was not known. The POWER (Pulsewidth Optimized Waveform Evaluation tRial) trial was designed to determine the optimal membrane time constant for programming "tuned" biphasic waveforms. METHODS: This acute, multicenter study included 121 implantable cardioverter-defibrillator/cardiac resynchronization therapy defibrillator patients who were randomized at implant to any two of the three membrane time constant waveforms (2.5, 3.5, and 4.5 ms). Fixed pulse widths were programmed using the measured high voltage shock impedance. The defibrillation threshold (DFT) estimates were obtained using a hybrid protocol starting with an upper limit of vulnerability estimate followed by a step-up/step-down ventricular fibrillation induction process. RESULTS: DFT voltage was significantly lower using 3.5- and 4.5-ms waveforms as compared to the 2.5-ms waveform (P = 0.004 and 0.035, respectively). DFT voltage with both 3.5- and 4.5-ms waveforms was ≤ that obtained with the 2.5-ms waveform in 78.5% of the cases. The mean difference in DFT voltage using the 3.5-ms waveform and the 4.5-ms waveform was not significant (P = 0.4). However, the 3.5-ms waveform gave a lower DFT than the 4.5-ms waveform in 19 patients although the reverse was true in only nine (P = 0.02 not significant for multiple comparisons). CONCLUSIONS: The use of a 3.5- or 4.5-ms time constant-based waveforms had lower DFTs when compared to the 2.5-ms waveform. This study suggests that the first defibrillation attempt at implantation should be with 3.5- or 4.5-ms time constant-based waveforms. The 3.5-ms-based waveform trended toward the best choice.

Does defibrillation threshold increase as left ventricular ejection fraction decreases?

AIMS: Advanced cardiac disease, entailing more hypertrophy, fibrosis, scarring, dilatation and conduction delays, poses the question of whether defibrillation thresholds (DFTs) increase as left ventricular ejection fraction (LVEF) decreases. This question has been approached indirectly or insufficiently in previous studies. In this study we add and expand on our previous work, stratifying DFT for various LVEF ranges. METHODS AND RESULTS: This retrospective analysis included DFT data from three acute, multicentre, randomized studies that included 230 ICD/CRT-D patients. All DFTs were obtained with the SVC coil turned ON and with pulse-width optimized waveforms based on a 3.5 ms membrane time constant. As the LVEF decreased, DFT estimates increased from 395.2 +/- 115 V for LVEF > or = 46% to 425.8 +/- 117.6 V for LVEF < or = 25%. However, these changes in DFT estimates were very minor and not statistically significant. Only 3% of the patients in this population had an elevated DFT of >20 J. CONCLUSION: This analysis shows that over a very broad range of LVEF, DFT changes minimally (approximately 1 J), if at all. Our results are consistent with previous studies that demonstrated no difference in the DFT estimates: (a) between patient groups receiving ICD (typically higher LVEF) vs. CRT-D (typically lower LVEF) and (b) between patient groups receiving a device for primary prevention indications (typically lower LVEF) vs. secondary prevention indications (typically higher LVEF).

Long-term changes in high-voltage impedance of defibrillating leads.

BACKGROUND: The maturation of the high-voltage impedance (HVLI) of defibrillating leads has not been explored thoroughly. Since impedance influences the charge, current, and energy delivered to the heart in both fixed pulse-width and fixed tilt implantable cardioverter-defibrillator (ICD) waveforms, changes in HVLI might have an effect on the defibrillation threshold. This analysis examined the maturation of defibrillation lead HVLI. METHODS: The data were collected in 515 recipients of ICDs capable of storing high-voltage shock diagnostics, including HVLI. Data with constant superior vena cava (SVC) coil configuration (coil ON or OFF) were collected for up to 24 months. HVLI values were recorded, plotted, and normalized by the value at implant; the percentage of patients in whom HVLI increased or decreased by > or =6 Omega was calculated, and the maturation of leads with SVC ON versus OFF was compared. RESULTS: A > or =6 Omega increase or decrease in HVLI was observed in 41% of patients more than 3 months after ICD implant, with the magnitudes as follows: 6-7.5 Omega change = 16%, 8-9.5 Omega= 11%, 10-11.5 Omega= 6%, and > or =12 Omega= 8%. In this subgroup, 67% of patients showed an increase in impedance, and the remaining 33% of patients showed a decrease. For ICD-programmed SVC OFF, the right ventricular (RV) Coil-to-Can HVLI increased by 8 Omega after 6 weeks and did not significantly change thereafter. CONCLUSIONS: HVLI changed significantly in 41% of leads after 3 months. The HVLI trend of the RV Coil-to-Can configuration appeared to be similar to the SVC Coil/Can-to-RV and Coil-to-Can configurations. Changes in HVLI of 6-12 Omega will alter the characteristics of the shock waveform and could require retuning of the waveforms to maintain adequate DFT safety margin. If re-tuning the shock waveforms is not performed, these HVLI changes have the potential to result in elevated DFT. These HVLI changes may partially account for the 15% increase in DFT over time reported in the literature.

Performance of dedicated versus integrated bipolar defibrillator leads with CRT-defibrillators: results from a Prospective Multicenter Study.

INTRODUCTION: Right ventricular (RV) anodal stimulation may occur in cardiac resynchronization therapy defibrillators (CRT-D) when left ventricular (LV) pacing is configured between the LV lead and an electrode on the RV defibrillator lead. RV defibrillator leads can have a dedicated proximal pacing ring electrode (dedicated bipolar) or utilize the distal shocking coil as the proximal pacing electrode (integrated bipolar). This study compares the performance of integrated versus dedicated leads with respect to anodal stimulation incidence, sensing, and inappropriate ventricular tachyarrhythmia detection in patients implanted with CRT-D. METHODS: Two hundred ninety-two patients were randomly assigned to receive dedicated or integrated bipolar RV leads at the time of CRT-D implantation. Patients were followed for 6 months. RESULTS: Patients with dedicated bipolar RV leads exhibited markedly higher rates of anodal stimulation than did patients with integrated leads. The incidence of anodal stimulation was 64% at implant for dedicated bipolar RV leads compared to 1% for integrated bipolar RV leads. The likelihood of anodal stimulation in patients with dedicated leads fell progressively during the 6-month follow-up (51.5%), but always exceeded the incidence of anodal stimulation in patients with integrated leads (5%). Clinically detectable undersensing and oversensing were very unusual and did not differ significantly between lead designs. There were no inappropriate ventricular tachyarrhythmia detections for either lead type. CONCLUSION: Integrated bipolar RV defibrillator leads had a significantly lower incidence of RV anodal stimulation when compared to dedicated bipolar RV defibrillation leads, with no clinically detectable oversensing or undersensing, and with no inappropriate ventricular tachyarrhythmia detections for either lead type.

Optimization of superior vena cava coil position and usage for transvenous defibrillation.

BACKGROUND: Prior studies of active pectoral implantable defibrillator (ICD) lead systems demonstrated a lowering of defibrillation thresholds (DFTs) with the addition of a superior vena cava (SVC) coil. These studies were done on fixed-tilt waveforms where a large reduction in impedance leads to large phase duration changes. OBJECTIVE: The present study was designed to evaluate the SVC coil benefit and intercoil spacing on DFTs with a "tuned" waveform. METHODS: This prospective, multicenter study included 113 patients randomized at implant to a 17-cm and a 21-cm intercoil spacing ICD lead. DFTs were measured with SVC coil turned ON versus OFF in a random order, using an optimized binary search method. RESULTS: DFT voltage (423 +/- 120 vs. 438 +/- 118 V; P = .042) and stored energy (9.8 +/- 5.6 vs. 10.2 +/- 5.8 J; P = .043) were significantly reduced with the SVC coil ON. However, intercoil distance had no significant effect on DFT voltage (437.3 +/- 115.1 vs. 407.7 +/- 123.8 V; P = .19) or stored energy (10.3 +/- 5.4 vs. 9.2 +/- 5.8 J; P = .31). Subgroup analyses showed that the dual-coil leads were most effective when placed in the high position (innominate vein-SVC junction) or when the single-coil shock impedance was > or =58 Omega, regardless of intercoil spacing. CONCLUSION: With a tuned waveform, the addition of an SVC coil to the shocking pathway reduces DFTs, although this difference was smaller than reported previously. Intercoil distance had no significant effect on the defibrillation parameters.

Atrial overdrive pacing and incidence of heart failure-related adverse events in permanently paced patients.

BACKGROUND: Atrial overdrive pacing algorithms may be effective in preventing or suppressing atrial fibrillation (AF). However, the maintenance of a heart rate incessantly faster than spontaneous could induce left ventricular (LV) dysfunction and promote heart failure (HF) on the long term. OBJECTIVE: This post hoc analysis examined the effects of a new overdrive algorithm on the incidence of HF-related adverse events in 411 patients enrolled in the ADOPT-A trial. MATERIALS AND METHODS: The AF Suppression algorithm was randomly programmed ON in 209 patients (treatment group) versus OFF in 202 patients (control group). The incidence of HF-related adverse events and HF-related deaths over a 6-month follow-up was compared between the two groups. Patients with versus without HF-related clinical events were also compared to each other within each group. RESULTS: There were eight HF-related adverse clinical events (3.8%) in the treatment group and 11 (5.4%) in the control group, including four HF-related deaths (1.9 vs. 2.0%) in each group during follow-up. Baseline NYHA functional class in patients with versus without HF-related adverse events was 1.4 +/- 0.5 versus 1.5 +/- 0.7 in the control, and 1.5 +/- 0.8 versus 1.5 +/- 0.6 in the treatment group. LV ejection fraction (EF) was 49 +/- 7% in patients with, versus 57 +/- 12% in patients without HF-related adverse events, in the control group, and 43 +/- 14% in patients with, versus 56 +/- 13% in patients without HF-related adverse events, in the treatment group. LVEF was lowest and similar in both groups among patients who died from HF (35 +/- 10% in the control and 38 +/- 27% in the treatment group). CONCLUSIONS: In ADOPT-A, HF-related clinical events and deaths were related to LV dysfunction and not to atrial pacing overdriven by the AF suppression algorithm.

Real-time percutaneous optical imaging of anatomical structures in the heart through blood using a catheter-based infrared imaging system.

The ability to optically image structures and instrumentation within the heart during procedures is limited by the presence of blood in the field. The goal of our research was to design, develop, and evaluate technology for a catheter-based optical imaging system that enables intracardiac and intravascular visualization in real time through blood. Based on Mie optical scattering theory, imaging through blood using infrared light was theoretically feasible, but scattering in the near-infrared wavelengths (1100 to 1300 nm) generated substantial noise in the image despite relatively low absorption. Using illumination between 1550 and 1650 nm provided better images, as the effect of scattering is less while the effect of absorption is greater. Absorption losses can be overcome by increasing light intensity. Infrared (IR) transmitting endoscopes were constructed using novel flexible illumination and imaging bundles. Endoscope designs, all 7.5 Fr. in outer diameter, were used to obtain images of the coronary sinus, tricuspid valve, and great vessels in 25 pigs, 16 dogs, 1 calf, and 1 sheep. Imaging was successful in all 43 animals, but the coronary sinus was not always visualizable. After obtaining FDA 510(k) approval, the device was used to acquire images in 50 patients during placement of electrophysiologic leads via right heart catheterization. Clinical experience demonstrates successful visualization in the heart in 45 patients, although coronary sinus images were obtained only in 39 patients. High heart rates, large dilated hearts, and problems with catheter design prevented visualization in all patients. On occasion, it was possible to visualize the tricuspid valve. Infrared endoscopy allows for visualization of intimal surfaces of blood vessels, cardiac chambers, and valves through flowing blood. While technical challenges remain, the feasibility of the approach has been demonstrated.

Successful catheter ablation of electrical storm after myocardial infarction.

BACKGROUND: We report on 4 patients (aged 57 to 77 years; 3 men) who developed drug-refractory, repetitive ventricular tachyarrhythmias after acute myocardial infarction (MI). All episodes of ventricular arrhythmias were triggered by monomorphic ventricular premature beats (VPBs) with a right bundle-branch block morphology (RBBB). METHODS AND RESULTS: Left ventricular (LV) mapping was performed to attempt radiofrequency (RF) ablation of the triggering VPBs. Activation mapping of the clinical VPBs demonstrated the earliest activation in the anteromedial LV in 1 patient and in the inferomedial LV in 2 patients. Short, high-frequency, low-amplitude potentials were recorded that preceded the onset of each extrasystole by a maximum of 126 to 160 ms. At the same site, a Purkinje potential was documented that preceded the onset of the QRS complex by 23 to 26 ms during sinus rhythm. In 1 patient, only pace mapping was attempted to identify areas of interest in the LV. Six to 30 RF applications abolished all local Purkinje potentials at the site of earliest activation and/or perfect pace mapping and suppressed VPBs in all patients. No episode of ventricular tachycardia or fibrillation has recurred for 33, 14, 6, and 5 months in patients 1, 2, 3, and 4, respectively. CONCLUSIONS: Incessant ventricular tachyarrhythmias after MI may be triggered by VPBs. RF ablation of the triggering VPBs is feasible and can prevent drug-resistant electrical storm, even after acute MI. Catheter ablation of the triggering VPBs may be used as a bailout therapy in these patients.

A new pacemaker algorithm for the treatment of atrial fibrillation: results of the Atrial Dynamic Overdrive Pacing Trial (ADOPT).

OBJECTIVES: The Atrial Dynamic Overdrive Pacing Trial (ADOPT) was a single blind, randomized, controlled study to evaluate the efficacy and safety of the atrial fibrillation (AF) Suppression Algorithm (St. Jude Medical Cardiac Rhythm Management Division, Sylmar, California) in patients with sick sinus syndrome and AF. BACKGROUND: This algorithm increases the pacing rate when the native rhythm emerges and periodically reduces the rate to search for intrinsic atrial activity. METHODS: Symptomatic AF burden (percentage of days during which symptomatic AF occurred) was the primary end point. Patients underwent pacemaker implantation, were randomized to DDDR with the algorithm on (treatment) or off (control), and were followed for six months. RESULTS: Baseline characteristics and antiarrhythmic drugs used were similar in both groups. The percentage of atrial pacing was higher in the treatment group (92.9% vs. 67.9%, p < 0.0001). The AF Suppression Algorithm reduced symptomatic AF burden by 25% (2.50% control vs. 1.87% treatment). Atrial fibrillation burden decreased progressively in both groups but was lower in the treatment group at each follow-up visit (one, three, and six months) (p = 0.005). Quality of life scores improved in both groups. The mean number of AF episodes (4.3 +/- 11.5 control vs. 3.2 +/- 8.6 treatment); total hospitalizations (17 control vs. 15 treatment); and incidence of complications, adverse events, and deaths were not statistically different between groups. CONCLUSIONS: The ADOPT demonstrated that overdrive atrial pacing with the AF Suppression Algorithm decreased symptomatic AF burden significantly in patients with sick sinus syndrome and AF. The decrease in relative AF burden was substantial (25%), although the absolute difference was small (2.50% control vs. 1.87% treatment).