Biphasic Waveform Research Articles

Abstract 310: Body Mass Index and Initial Defibrillation for In-Hospital Cardiac Arrest

Background: Higher transthoracic impedance may influence the success of defibrillation. We evaluated the relationship between body mass index (BMI) and post-defibrillation outcomes for in-hospital ventricular fibrillation or pulseless ventricular tachycardia (VF/VT). Methods: Within the Get With The Guidelines - Resuscitation multicenter observational registry, we identified adult patients who received biphasic waveform defibrillation for in-hospital VT/VF cardiac arrest between 2008 and2012. We evaluated the relationship between BMI and defibrillation outcomes using a generalized linear mixed regression to adjust for patient arrest characteristics and comorbidities while accounting for within hospital clustering. The primary outcome was successful termination of VF/VT. Secondary outcomes included termination of VF/VT to an organized rhythm with pulse, return of spontaneous circulation ≥ 20 minutes (ROSC), survival at 24 hours, and survival to discharge. Results: A total of 10,561 adult subjects with VF/VT from 268 hospitals were analyzed. BMI was not associated with termination of VT/VF following defibrillation. However, compared to normal BMI patients, underweight and morbidly obese patients were less likely to have termination of VT/VF with restoration of a pulse. Further, underweight patients were less likely to survive to 24 hours and discharge. In contrast, overweight and obese patients were more likely to survive to 24 hours and discharge (see Table). Summary: Successful termination of VF/VT was not associated with BMI. However, a non-linear relationship exists between BMI and termination of VF/VT to an organized rhythm with pulse, ROSC, survival at 24 h and survival at discharge.

Wireless simultaneous stimulation-and-recording device to train cortical circuits in somatosensory cortex.

We describe for the first time the design, implementation, and testing of a telemetry controlled simultaneous stimulation and recording device (SRD) to deliver chronic intercortical microstimulation (ICMS) to physiologically identified sites in rat somatosensory cortex (SI) and test hypotheses that chronic ICMS strengthens interhemispheric pathways and leads to functional reorganization in the enhanced cortex. The SRD is a custom embedded device that uses the Cypress Semiconductor's programmable system on a chip (PSoC) that is remotely controlled via Bluetooth. The SRC can record single or multiunit responses from any two of 12 available inputs at 1-15 ksps per channel and simultaneously deliver stimulus pulses (0-255 μA; 10 V compliance) to two user selectable electrodes using monophasic, biphasic, or pseudophasic stimulation waveforms (duration: 0-5 ms, inter-phase interval: 0-5 ms, frequency: 0.1-5 s, delay: 0-10 ms). The SRD was bench tested and validated in vivo in a rat animal model.

Average current is better than peak current as therapeutic dosage for biphasic waveforms in a ventricular fibrillation pig model of cardiac arrest

ObjectiveDefibrillation current has been shown to be a clinically more relevant dosing unit than energy. However, the effects of average and peak current in determining shock outcome are still undetermined. The aim of this study was to investigate the relationship between average current, peak current and defibrillation success when different biphasic waveforms were employed. MethodsVentricular fibrillation (VF) was electrically induced in 22 domestic male pigs. Animals were then randomized to receive defibrillation using one of two different biphasic waveforms. A grouped up-and-down defibrillation threshold-testing protocol was used to maintain the average success rate of 50% in the neighborhood. In 14 animals (Study A), defibrillations were accomplished with either biphasic truncated exponential (BTE) or rectilinear biphasic waveforms. In eight animals (Study B), shocks were delivered using two BTE waveforms that had identical peak current but different waveform durations. ResultsBoth average and peak currents were associated with defibrillation success when BTE and rectilinear waveforms were investigated. However, when pathway impedance was less than 90Ω for the BTE waveform, bivariate correlation coefficient was 0.36 (p=0.001) for the average current, but only 0.21 (p=0.06) for the peak current in Study A. In Study B, a high defibrillation success (67.9% vs. 38.8%, p<0.001) was observed when the waveform delivered more average current (14.9±2.1A vs. 13.5±1.7A, p<0.001) while keeping the peak current unchanged. ConclusionIn this porcine model of VF, average current was better than peak current to be an adequate parameter to describe the therapeutic dosage when biphasic defibrillation waveforms were used.The institutional protocol number: P0805.

Transient flow response after femoral artery catheterization for diagnostic neuroangiography in infants and children: Doppler US assessment of the ipsilateral femoral artery.

Hemodynamic changes in the distal arteries during transfemoral catheterization in children have not been documented. To evaluate arterial flow changes of the lower extremities ipsilateral to the puncture site using Doppler US during transfemoral cerebral angiography in children. Twenty-seven children who underwent transfemoral cerebral angiography at our institution between April 2013 and August 2013 compose our study population. Doppler US was performed to evaluate diameters and peak systolic velocities of the common femoral artery and superficial femoral artery before and after femoral sheath insertion. Children were classified into three groups based on the spectral waveform changes of the superficial femoral artery after femoral sheath insertion. Thereafter, one-way ANOVA followed by the Bonferroni post-hoc comparisons test were performed to compare values among the groups. Mean common femoral artery and superficial femoral artery baseline diameters were 4.10 mm and 3.32 mm, and mean baseline peak systolic velocities were 218.26 and 166.51 cm/s, respectively. Fourteen of 27 children showed persistent triphasic flow in the superficial femoral artery (group 1); 7 children showed altered flow of biphasic (n = 3) or monophasic (n = 4) waveforms (group 2); and 6 children showed pulsus tardus et parvus pattern (group 3) after femoral sheath insertion. Mean baseline diameter of the common femoral artery and mean subtracted value between common femoral artery and femoral sheath size were significantly smaller in group 3 than the other groups. Size discrepancy between common femoral artery and femoral sheath was <1 mm in all cases of group 3. Superficial femoral artery diameter and peak systolic velocity significantly decreased after femoral sheath insertion in group 3 compared to groups 1 and 2. A significant skin temperature drop after sheath insertion in the ipsilateral lower extremity was noted in group 3 (-1.83°C), compared to groups 1 and 2 (+0.42 and -0.86°C, respectively). Changes in the spectral waveforms of superficial femoral arteries frequently occur in children during transfemoral cerebral angiography (13/27, 48%). Significant arterial flow disturbance was noted on Doppler US in children with a common femoral artery <1 mm larger than the femoral sheath diameter.

Abstract 181: Patterns of Waveform and Energy Use in Defibrillation for Cardiac Arrest: Insights from the Get With The Guidelines-Resuscitation Registry

Background: Early defibrillation for termination of life-threatening arrhythmias is key to survival of cardiac arrest. Biphasic waveform defibrillation has been suggested as superior to monophasic waveform defibrillation, but little is known about trends in defibrillation waveform and energy used for in-hospital cardiac arrest. Methods: Within Get With The Guidelines-Resuscitation, a national registry of in-hospital cardiac arrest, we identified subjects over age 18 with an in-hospital cardiac arrest due to ventricular fibrillation or pulseless ventricular tachycardia between 2005 and 2012. We restricted the study cohort to this time period, as defibrillation waveform and energy were not captured prior to 2005. We examined calendar year trends in defibrillation waveform and energy of first defibrillation attempt using the chi-square test. Results: A total of 22,108 patients from 504 facilities were identified. In 2005, in which there were 2898 in-hospital cardiac arrest cases, 1911 (66%) events were treated with biphasic defibrillation and 987 (34%) with monophasic defibrillation. By 2012, nearly all (97% [1460/1502]) events were treated with biphasic defibrillation; p for trend &lt; 0.0001 (see Figure). For biphasic defibrillation, the predominant energy used for first defibrillation attempt was 200 J (55.91% of events) with 150 J being the next most common (18.21% of events) with a trend toward more frequent use of 200 J (p &lt; 0.0001). Conclusion: Biphasic defibrillation at 200 J is now the predominant waveform and energy used for initial defibrillation during in-hospital cardiac arrest. Additional work is needed to determine if a rise in use of biphasic defibrillation is improving outcomes.

Simulation of fiber conduction block using high frequency alternative current with asymmetric biphasic waveform and its mechanism of action

Introduction : High Frequency Alternating Currents is a safe, reversible and selective method for nerve conduction block that has been under study during the last decade as a treatment for the diseases involving abnormal neural impulses. However, reducing the stimulus amplitude, and the undesired onset response, as well as optimizing the stimulus parameters for more effective block is still under study. In this article, simulation of the electrical stimulation of neural fibers is used to study the efficiency of the asymmetric biphasic waveforms in inducing the block condition, and to investigate its mechanism of action. Materials and Methods : Computer simulations were carried out based on a detailed model of mammalian peripheral nerve fibers. Electrical stimulation of a 51-node axon with two point-source electrodes was simulated, one for inducing conduction block, and the other for applying a test stimulus. Asymmetric biphasic waveform was applied and the neural responses including the block phenomena and its mechanism were studied. Results: High frequency stimulation induces three different responses in the fiber, based on its amplitude and position related to the electrode: no excitation, repetitive excitation and block. The proposed waveform provides lower block thresholds and by increasing the asymmetry of the waveform, the net charge required to induce conduction block was significantly reduced in comparison with the sine and symmetric rectangular waveforms. The stimulation increases the average membrane voltage and this is higher when asymmetric waveform is used which can explain the higher efficiency of this waveform for inducing conduction block. Conclusion: Lower thresholds for the proposed waveform is very important in clinical use of the high frequency alternating currents due to higher efficiency of the stimulation, lower power consumption of the stimulator, and lower side effects of the stimulation, and can be considered as a step towards the clinical use of high frequency stimulations. Keywords : High Frequency Alternating Current, Asymmetric Rectangular Waveform, Nerve Conduction Block, Computer Simulation

Transintercostal-Evoked Spinal Cord Potential in Thoracic Aortic Surgery

We have developed a novel method of measuring spinal cord-evoked potentials with stimulation and recording at the intercostal nerves (transintercostal-evoked spinal cord potential: Tic-ESCP). The purpose of this study was to examine the feasibility and accuracy of Tic-ESCP during thoracic aortic surgery. In addition to the conventional electrodes (cranial and intrathecal), stimulating and recording electrodes were placed on the intercostal nerves that were located at a cephalad and caudal level relative to the aneurysm after the pleura on the intercostal nerves was opened. Specially designed hook-type electrodes were anchored to the nerves and surroundings atraumatically and fixed on the pleura. The conventional transcranial motor-evoked potential (Tc-MEP) and Tic-ESCP were recorded simultaneously. Eight patients were examined in this study. In all patients, Tic-ESCP could be clearly recorded with biphasic waveforms consisting of first a positive wave and a subsequent negative wave. In all 8 patients, the waveform of Tc-MEP and Tic-ESCP changed during aortic reconstruction. In 2 cases, the waveform of Tc-MEP and Tic-ESCP decreased below 50% of baseline during aortic clamping and the intercostal arteries were reconstructed with no resultant spinal cord injury. In 1 case with a shaggy aorta, Tc-MEP and Tic-ESCP had different values and each evoked potential could have reflected that regional spinal cord infarction and paraplegia had occurred. Tic-ESCP was clinically feasible and changes were compatible with the conventional Tc-MEP. The Tic-ESCP waveforms were simple and appeared to be specific to the spinal cord within the target range, in contrast to the other evoked potentials which are multimorphic and reflect the amplitudes at the brain and multiple levels of the spinal cord.

Use of Pupil Size to Determine the Effect of Electromagnetic Acupuncture on Activation Level of the Autonomic Nervous System

Magnetic fields are widely considered as a method of treatment to increase the therapeutic effect when applied to acupoints. Hence, this study proposes a new method which creates significant stimulation of acupoints by using weak magnetic fields. We conducted this experiment in order to confirm the effect on the activation level of the autonomic nervous system by measuring pupil sizes in cases of stimulation by using manual acupuncture and electromagnetic acupuncture (EMA) at BL15. We selected 30 Hz of biphasic wave form with 570.1 Gauss. To confirm the biopotential by the magnetic flux density occurring in EMA that affected the activation of the autonomic nervous system, we observed the biopotential induced at the upper and the mid left and right trapezius. We observed a significant decrease in pupil size only in the EMA group (p < 0.05), thus confirming that EMA decreased the pupil size through activation of the parasympathetic nerve in the autonomic nervous system. Moreover, we confirmed that the amplitude of the biopotential which was caused by 570.1 Gauss was higher than ±20 μA. Thus, we can conclude that EMA treatment successfully activates the parasympathetic nerve in the autonomic nervous system by inducing a biotransformation by the induced biopotential.

Is Defibrillation Testing Necessary for Implantable Transvenous Defibrillators?

Because the implantable cardioverter defibrillator (ICD) was introduced into clinical practice, insertion of these devices has typically involved defibrillation testing (DT). However, DT has never been shown to independently improve patient outcomes. The rationale for DT has always been that the induction of ventricular fibrillation (VF) immediately after ICD insertion allows the implanting team to verify that the ICD can appropriately sense VF and deliver a high-energy shock that can effectively terminate this arrhythmia.1 The first ICD systems were complex, using epicardial patches and monophasic shock waveforms, thus accurate sensing and termination of VF were frequently in question. However, the ICD evolved over time, with the introduction of transvenous systems, biphasic waveforms, and active cans, which made failure to sense and treat VF much less common.2,3 Modern ICDs are also capable of delivering energies >40 J, thus many have started to question the rationale for DT in the modern era.4–7 Response by Russo et al on p 351 During the past 10 years, there has been a dramatic shift in practice, such that DT is performed in <50% of ICD implants in some jurisdictions. This change was not driven by the results of randomized trials, but by changing opinions of clinicians,4 based on the following insights from observational studies: (1) intraoperative DT is usually successful and clinicians do not always act on unfavorable results; (2) intraoperative DT is an unproven surrogate for clinical shock efficacy; (3) the likelihood of a failed appropriate clinical shock is low and does not appear lower among patients who have DT; and (4) DT is associated with uncommon, but serious complications and adds cost and complexity to the ICD implant procedure. A large randomized evaluation of DT will soon be completed8; however, the observational data …

Is defibrillation testing necessary for implantable transvenous defibrillators?: defibrillation testing is necessary at the time of implantable cardioverter defibrillator implantation.

Clinical trials have documented the efficacy of implantable cardioverter-defibrillators (ICDs) for the primary and secondary prevention of sudden cardiac death.1–7 These trials have typically involved induction of ventricular fibrillation (VF) at the time of implantation to demonstrate effective arrhythmia termination. In fact, defibrillation testing (DT) was also performed at the time of implantation of ICDs in those patients whose data were used to seek approval of the US Federal Drug Administration for general use, and instructions for usage include labeling with DT. This is also the case for the recently approved subcutaneous ICD. Response by Healey et al on p 346 Higher defibrillation thresholds (DFTs) were seen with older ICDs implanted using an epicardial approach, abdominal pulse generators, or monophasic waveforms. In contrast, modern technology now includes devices with biphasic waveform shocks and pectoral active can systems that result in more effective defibrillation.8–11 In addition, devices now have higher output, routinely delivering ≥35 J and also increasing the chance of effective defibrillation. Therefore, it has been suggested that these new defibrillation technologies may eliminate the need for DT. Although the risk of failing defibrillation is now much lower, patients receiving ICDs today may have more comorbidities, more severe heart failure, and a higher risk of failing shocks. If a high defibrillation energy requirement is identified at the time of initial implantation, system revision is typically performed with the intent of increasing the likelihood that the ICD will effectively terminate ventricular tachycardia (VT) or VF when it occurs spontaneously. So, we need to ask ourselves, why would a physician implant this potentially life-saving device without testing? The term DFT refers to the minimum shock strength that defibrillates.12 Historically, a threshold below a specific value has been used as an acceptable criterion for device implantation. …

Defibrillators

Defibrillators

ERPs reveal individual differences in morphosyntactic processing

We investigated individual differences in the neural substrates of morphosyntactic processing among monolingual English speakers using event-related potentials (ERPs). Although grand-mean analysis showed a biphasic LAN-P600 pattern to grammatical violations, analysis of individuals׳ ERP responses showed that brain responses varied systematically along a continuum between negativity- and positivity-dominant ERP responses across individuals. Moreover, the left hemisphere topography of the negativity resulted from component overlap between a centro-parietal N400 in some individuals and a right hemisphere-dominant P600 in others. Our results show that biphasic ERP waveforms do not always reflect separable processing stages within individuals, and moreover, that the LAN can be a variant of the N400. These results show that there are multiple neurocognitive routes to successful grammatical comprehension in language users across the proficiency spectrum. Our results underscore that understanding and quantifying individual differences can provide an important source of evidence about language processing in the general population.

Light responses of primate and other mammalian cones

Retinal cones are photoreceptors for daylight vision. For lower vertebrates, cones are known to give monophasic, hyperpolarizing responses to light flashes. For primate cones, however, they have been reported to give strongly biphasic flash responses, with an initial hyperpolarization followed by a depolarization beyond the dark level, now a textbook dogma. We have reexamined this primate-cone observation and, surprisingly, found predominantly monophasic cone responses. Correspondingly, we found that primate cones began to adapt to steady light at much lower intensities than previously reported, explainable by a larger steady response to background light for a monophasic than for a biphasic response. Similarly, we have found a monophasic cone response for several other mammalian species. Thus, a monophasic flash response may in fact be the norm for primate and other mammalian cones as for lower-vertebrate cones. This revised information is important for ultimately understanding human retinal signal processing and correlating with psychophysical data.

Abstract T P124: Effect of Neuromuscular Magnetic Stimulation on the Hemiplegic Upper Extremity in Subacute Stroke Patients

Objects: To investigate effects of neuromuscular magnetic stimulation (NMMS) on the wrist and hand muscle comparing with neuromuscular electric stimulation (NMES) in subacute stroke patients. Subject and Method: 20 Patients with subacute hemiplegic stroke were randomized into 2 groups; NMMS group (N=10) and a NMES group (N=10). Stimulation delivered 10-minute session, twice a day, 5 days a week for 3 weeks in both group to the affected forearm in alternating extensor/flexor muscle. The stimulation parameters required to produce slow movement through the full range at maximum patient comfort: NMMS (10 Hz, 10 s stimulation, 20 s rest, 10 min treatment time and 2,000 total pulse) and NMES (a symmetrical biphasic waveform, 30 us pulse width, 40 Hz).The hand function (Box and blocks test, Jebson-Taylor hand function test), hand performance (Wrist and hand muscle strength, grip power) and spasticity were done at baseline, after 1 week, and at the end of the treatment period (after 3 weeks). Repeated measurement ANOVA was used for statistical analysis. Results: There were statistically significant improvements in measures of wrist flexor and hand flexor/extensor strength over the treatment period (p&lt;0.05), but not significantly different between the groups. Although box and block test improved at 3 weeks in both groups, this was not statistically significant. Other measured outcome were not significantly improved. Conclusions: The both NMMS and NMES improves wrist and hand muscle strength in subacute hemiplegic stroke patients, with no significant difference between the stimulation. Therefore magnetic stimulation of peripheral muscle could be useful as much as a electrical stimulation. However, long term period follow-up was needed.

Low and high-frequency somatosensory evoked potentials recorded from the human pedunculopontine nucleus

ObjectiveTo investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg). MethodsTwenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation. ResultsSEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05±0.61ms) shifted of 0.18±0.07ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4±0.2ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials. ConclusionWhile the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level. SignificanceOur results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area.

The optimal distance between two electrode tips during recording of compound nerve action potentials in the rat median nerve.

The distance between the two electrode tips can greatly influence the parameters used for recording compound nerve action potentials. To investigate the optimal parameters for these recordings in the rat median nerve, we dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spacings. Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part. When the distance between two stimulating electrode tips was increased, the threshold and supramaximal stimulating intensity of compound nerve action potentials were gradually decreased, but the amplitude was not changed significantly. When the distance between two recording electrode tips was increased, the amplitude was gradually increased, but the threshold and supramaximal stimulating intensity exhibited no significant change. Different distances between recording and stimulating sites did not produce significant effects on the aforementioned parameters. A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve. In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference (however also required a higher threshold and higher supramaximal stimulus), was found to be superior to the antidromic compound action potential.

Effects of Nonalcoholic Fatty Liver Disease on the Hepatic Vein and Artery

Objective: To evaluate the effect of the different stages of non-alcoholic fatty liver disease on hepatic vein waveform pattern and hepatic artery resistance index. Methods: 32 patients diagnosed with non-alcoholic fatty liver disease and 14 healthy volunteers as a control group were included in the study. In both groups, liver size was measured and the degree of fatty infiltration was graded by gray-scale ultrasonographic examination. Hepatic vein waveform pattern was assessed and hepatic artery resistance index was measured by duplex Doppler ultrasonography examination. The degree of fatty infiltration was compared with hepatic vein waveform pattern and hepatic artery resistance index values in the patient group. Results: Liver echogenicity was grade 1 in 15 patients, grade 2 in 12 patients, and grade 3 in 5 patients. In the control group, liver echogenicity was not increased. Liver size was increased with the degree of fatty infiltration (p<0.001). The presence of biphasic or monophasic hepatic vein waveform pattern in non-alcoholic fatty liver disease patients was statistically significant (p=0.04). However, mean hepatic artery resistance index was not significantly different (p=0.38). Both hepatic vein waveform pattern and hepatic artery resistance index were not related to the degree of fatty infiltration (p=0.99 and p=0.81, respectively). Conclusion: Vascular compliance of the liver can vary with the fatty infiltration of hepatocytes. This effect can be displayed as abnormal hepatic vein waveform pattern rather than alterations in hepatic artery resistance index values by duplex Doppler ultrasonography.

A prototypical interface for deep brain stimulation

This paper presents a prototypical interface circuit for deep brain stimulation surgery. It provides four channel outputs with a stimulating current. This stimulating circuit adjusts its output current by utilizing the switched-capacitor DAC and voltage-to-current transconductance amplifiers with the power-down mode to achieve a higher resolution and to save the power dissipation. The biphasic stimulating waveform is generated using a bridge switching technique and the programmable pulse signals are adjustable for width and frequency. By fabricating with a standard 0.35-μm CMOS technology at a 3.3V supply voltage, the reduced output stimulating current has 8-bit resolutions for amplitudes between 5μA and 155μA, 4-bit resolutions for frequencies between 126Hz and 244Hz, and 4-bit resolutions for time intervals between 0μs and 120μs.

Morphological and electrophysiological field observations on electric freshwater fish of the genus Mormyrops Müller 1843 (Teleostei: Mormyridae) from West and southern Africa

Different specimens of Mormyrops anguilloides (Linnaeus 1758) were reported to display electric organ discharge (EOD) pulses of either initially head-positive or initially negative polarity, a hypothetical sex difference that has not been substantiated to date. The morphology and EODs of M. anguilloides of both sexes and a sexually mature size from the Comoé and Bandama rivers, Côte d'Ivoire, and the Lower and Middle Zambezi, Mozambique, displayed initially positive EODs. The morphologically similar M. breviceps Steindachner 1895 of both sexes and a sexually mature size from the Bandama River displayed initially head-negative EODs of biphasic waveform and long duration (0.93–1.15 ms) in the very-low-frequency spectral range. Mormyrops anguilloides from the Comoé and Bandama rivers were differentiated in caudal peduncle depth and in EOD waveform, pulse duration and spectral energy content. The former samples displayed a biphasic, lower-frequency EOD pulse of up to 0.42 ms duration, the latter a tetraphasic, high-frequency EOD of up to 0.33 ms. It is suggested that reports of EODs of both polarities in M. anguilloides indicate the presence of an unrecognised species.

Low‐Tilt Monophasic and Biphasic Waveforms Compared with Standard Biphasic Waveforms in the Transvenous Defibrillation of Ventricular Fibrillation

Commercially available implantable defibrillators utilize a high-tilt waveform. Studies in atrial fibrillation and transthoracic defibrillation of ventricular fibrillation (VF) have shown improved defibrillation efficacy using low-tilt (LT) waveforms. We investigated the feasibility, efficacy, and safety of a LT waveform in the transvenous defibrillation of VF and hypothesized that it would be more efficacious than standard tilted biphasic (STB) waveforms. The investigation was performed in four phases in a porcine model: an efficacy study of LT monophasic waveforms (n= 9), an efficacy study of LT biphasic waveforms (n= 9), a comparison study between the most successful LT waveforms and clinically available STB waveforms (n= 15), and a safety study (n= 9). A total of 1,056 shocks were delivered (phase 1: 288, phase 2: 288, phase 3: 480). The LT biphasic 8/4-ms waveform was significantly more likely to successfully defibrillate than the LT monophasic and STB waveforms with an odds ratio of 122.3 (95% confidence interval: 32.5, 460.2, P< 0.001). The calculated defibrillation threshold (E50) for the LT 8/4-ms waveform was 12.7 J compared to 43.5 J and 45.5 J for STB waveforms 6/6 ms and 8/4 ms, respectively, and 47.7 J for LT 12-ms waveform. The LT 8/4-ms waveform had no lasting detrimental effect on cardiac function, and any transient hemodynamical or biochemical changes observed were comparable to those observed with STB waveforms. LT waveforms are effective and appear safe in transvenous defibrillation in a porcine model of VF. The LT biphasic 8/4-ms waveform is more efficacious than conventional waveforms.