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The aim of this study was to determine the wound healing outcomes of patients with a plantar diabetic foot ulcer (DFU) treated with an interdisciplinary team approach, and to identify associated variables. A retrospective observational cohort study of 140 adult patients, with a plantar DFU, treated between 2012 and 2018 at a wound care clinic of a University affiliated hospital was conducted. Predictive and explicative analyses were conducted with logistic multivariate methods and with a Receiver Operating Characteristics curve. The best predictor of wound healing at 3 months was a 41.8% wound size reduction at 4 weeks (AUC: 0.86; sensitivity: 83.1%; specificity: 67.2%, positive predictive value: 72.8%; negative predictive value: 78.9%; positive and negative likelihood ratios: 2.53 and 0.25, respectively). Main baseline variables independently associated with this predictor were: a monophasic Doppler waveform (OR 7.52, 95% CI [2.64–21.39]), cigarette smoking (OR 4.7, 95% CI [1.44–15.29]), and male gender (OR 3.58, 95% CI [1.30–9.87]). The health care provider should be cautious and intensify its management of DFUs particularly with patients of male gender; smoking, having a monophasic waveform with a hand‐held Doppler, and not achieving a minimal 41.8% wound area reduction at 4 weeks of treatment.

Aim Early biphasic defibrillation is effective in out-of-hospital cardiac arrest (OHCA) cases. In the resuscitation of patients with OHCA, it is not clear how the defibrillation waveform interacts with the time to defibrillation to influence patient survival. The second, and any subsequent, shocks need to be administered by an on-line physician in Japan. Thus, we investigated the interaction between the defibrillation waveform and time to or the number of defibrillation on resuscitation outcomes. Methods This prospective observational study used data for all OHCAs that occurred between 2005 and 2014 in Japan. To investigate the interaction effect between the defibrillation waveform and the time to defibrillation or the number of defibrillations on the return to spontaneous circulation (ROSC), 1-month survival, and cerebral performance category (CPC) (1, 2), we assessed the modifying effects of the defibrillation waveform and the time to or the number of defibrillation on additive scale (i.e., the relative excessive risk due to interaction, RERI) and multiplicative scale (i.e., ratio of odds ratios (ORs)). Results In total, 71,566 cases met the inclusion criteria. For the measure of interaction between the defibrillation waveform and the time to defibrillation, ratio of ORs for ROSC was 0.84 (0.75–0.94), implying that the effect of time to first defibrillation on ROSC was negatively modified by defibrillation waveform. For the interaction between the defibrillation waveform and the number of defibrillations, RERI and ratio of ORs for CPC (1, 2) was −0.25 (−0.47 to −0.06) and 0.79 (0.67–0.93), respectively. It is implied that the effect of number of defibrillation on CPC (1, 2) was negatively modified by defibrillation waveform. Conclusions An increased number of defibrillations was associated with a decreased ROSC in the case of biphasic and monophasic defibrillation, while an increased number of defibrillations was related to an increased 1-month survival rate and CPC (1, 2) only in the case of biphasic defibrillation. When two or more defibrillations were performed, a biphasic waveform was more effective in terms of long-term survival than a monophasic waveform.

Background: Peripheral arterial disease is defined as a clinical disorder in which there is a stenosis or occlusion of the arteries of the limbs. The most common etiology is ischemia due to occlusive disease. The objective of this study is to assess the severity of lower-limb peripheral arterial diseases based on various Doppler parameters. Methods: This descriptive cross-sectional study comprised 55 patients with clinical signs and symptoms of lower-limb peripheral arterial disease. Both inpatients and outpatients attending the authors' institute were taken up for the study. In this study, Doppler sonography was performed using 3–12 MHz linear array and 1–7 MHz curvilinear array transducers (SAMSUNG RS80A Ultrasound System). Results: Out of 55 patients, Doppler sonography demonstrated echogenic plaques in 32 patients and corkscrew collaterals in 15 patients. Monophasic waveform with peak systolic velocity ratio of >2:1 was found in 42 patients, which is consistent with significant stenoses. Conclusion: Our study shows that Duplex Doppler sonography aided by color Doppler sonography can accurately locate the site and severity of stenosis/occlusion. It is safe, cost-effective, repeatable, and noninvasive.

The pulse waveform and current direction of transcranial magnetic stimulation (TMS) influence its interactions with the neural substrate; however, their role in the efficacy and reliability of single- and paired-pulse TMS measures is not fully understood. We investigated how pulse waveform and current direction affect the efficacy and test-retest reliability of navigated, single- and paired-pulse TMS measures. 23 healthy adults (aged 18–35 years) completed two identical TMS sessions, assessing resting motor threshold (RMT), motor evoked potentials (MEPs), cortical silent period (cSP), short- and long-interval intra-cortical inhibition (SICI and LICI), and intracortical facilitation (ICF) using either monophasic posterior-anterior (mono(PA); n=9), monophasic anterior-posterior (mono(AP); n=7), or biphasic (bi(AP-PA); n=7) pulses. Averages of each TMS measure were compared across the three groups and intraclass correlation coefficients were calculated to assess test-retest reliability. RMT was the lowest and cSP was the longest with bi(AP-PA) pulses, whereas MEP latency was the shortest with mono(PA) pulses. SICI and LICI had the largest effect with mono(PA) pulses, whereas only mono(AP) and bi(AP-PA) pulses resulted in significant ICF. MEP amplitude was more reliable with either mono(PA) or mono(AP) than with bi(AP-PA) pulses. LICI was the most reliable with mono(AP) pulses, whereas ICF was the most reliable with bi(AP-PA) pulses. Waveform/current direction influenced RMT, MEP latency, cSP, SICI, LICI, and ICF, as well as the reliability of MEP amplitude, LICI, and ICF. These results show the importance of considering TMS pulse parameters for optimizing the efficacy and reliability of TMS neurophysiologic measures.

Biphasic defibrillation waveforms are now accepted as being more effective at terminating ventricular fibrillation (VF) than monophasic waveforms. If two phases are better than one, this naturally leads to the hypothesis that additional phases improve efficacy. This study tests the hypothesis by adding one additional phase. We examined the efficacy of 18 different triphasic waveforms simultaneously. We tested the rate of recovery, i.e., successful defibrillation, of 21 guinea pigs (820-1,050 g) using triphasic, monophasic and biphasic defibrillation waveforms. The biphasic and monophasic were control waveforms. VF was electrically induced twenty times per animal and a single defibrillation attempt was made using a test waveform VF episode. Every waveform was adjusted to the energy required to defibrillate that animal 50% of the time, using a biphasic waveform as a control. The success rate of each triphasic waveform was pair-wise compared to the biphasic and monophasic control using the adjusted McNemar statistical test. Of the 18 triphasic waveforms tested, two were significantly poorer than the monophasic control (p

The efficacy of biphasic waveform cardioversion of atrial flutter in pediatric patients has not previously been demonstrated. Cardioversion outcomes were compared in two sequential groups of patients with atrial flutter undergoing transthoracic cardioversion using monophasic and biphasic waveforms at a single pediatric institution. The mean energy required for procedural success was 1.7 +/- 1.2 J/kg in the monophasic group compared to 0.9 +/- 0.6 J/kg in the biphasic group (p = 0.002). The mean number of attempts before achieving procedural success was 1.9 +/- 1.2 for the monophasic group and 1.3 +/- 1.0 for the biphasic group (p = 0.019). Procedure success rate was 89.5% (33/38) in the monophasic group compared to 100% (27/27) in the biphasic group (p = 0.13). Success rate for biphasic waveform cardioversion was 83% (5/6) when using energy less than 0.5 J/kg. These findings provide the impetus for lower starting energies and more widespread use of devices utilizing biphasic waveforms in pediatric patients.

Background— The passive implantable atrial defibrillator (PIAD) (with no battery or discharging capacitor and powered transcutaneously by radio-frequency energy) delivering a novel monophasic low-tilt waveform is more efficacious than the standard monophasic waveform at atrial defibrillation. Standard biphasic (STB) waveforms, however, are more efficacious and safer than monophasic waveforms. This study compared the efficacy and safety of the PIAD waveform with biphasic waveforms. Methods and Results— Sustained atrial fibrillation (AF) was induced by rapid atrial pacing. Cardioversion was attempted via 2 atrial defibrillation leads. The efficacy of the PIAD was compared with 3 biphasic waveforms (standard, single rounded, and double rounded) at varying voltage settings in 10 pigs. After a synchronized shock, hemodynamic changes between the PIAD, standard biphasic, and monophasic waveforms were compared at 1.5 and 3.0 J in 12 pigs. Myocardial injury (biochemical and histological) after ten 5-J PIAD shocks was compared with a no-shock group in 14 pigs. The PIAD 100-V setting was significantly more efficacious than the STB (100/−50 V: 100% [1.88±0.02 J] versus 90% [0.89±0.0 J]; P =0.025). No arrhythmic, hemodynamic, or myocardial injury was observed with the PIAD waveform. Conclusions— Defibrillation with the PIAD is more efficacious than with the STB waveform and appears safe. This device could provide a more effective option for cardioversion.

Objectie: To study whether two different types of monophasic waveform shocks (i.e. monophasic damped sinusoidal [MDS] and monophasic truncated exponential [MTE] waveform shocks) are of equivalent efficacy. Methods: Retrospective review of defibrillation efficacy and outcome in ventricular fibrillation/ventricular tachycardia (VF/VT) patients treated in the same EMS system with AEDs delivering either MDS waveform shocks (n= 40) or MTE waveform shocks (n= 40). Results: Defibrillation efficacy of the first shock was 82.5% in the MDS group and 70% in the MTE group (P= 0.19). Termination of VF by at least one of the first three shocks was found in 95 and 85% of the patients treated with MDS and MTE waveform shocks, respectively (P=0.22). Restoration of spontaneous circulation occurred in 75% of the MDS group and 30% of the MTE group (P=0.0001). Hospital admission rates were 52.5% in the MDS group and 17.5% in the MTE group (P= 0.001). Hospital discharge rates were 17.5% in the MDS group and 7.5% in the MTE group (P= 0.18). Conclusions: Our data suggest disparity in efficacy between MDS waveform shocks and MTE waveform shocks. Furthermore, our findings should be taken into consideration when the issue of the control group(s) in future clinical trials on new waveforms is discussed. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

The lower-limb venous return, assessed by the peak systolic venous velocities (PSVV) of the left common femoral vein, was recorded at different stages of operation for five patients undergoing major gynecologic operative laparoscopy. The average baseline PSVV was 23.1 cm/s. After positioning the patient in the Trendelenburg position, the PSVV increased to an average of 31.5 cm/s; this was a statistically significant increase. Creation of the pneumoperitoneum changed the waveform from a normal phasic pattern to a dampened, continuous, monophasic waveform. The average PSVV was reduced to 15.9 cm/s; this dampening was statistically significant. Further dampening was evident 1 hour intraoperatively, and the flow became intermittent, with cycles of dampened flow followed by periods of absent flow; these changes in PSVV were not statistically significant. Calf compressors did not increase the femoral PSVV at the beginning of operation, nor at I hour intraoperatively; the decrease was not statistically significant. After release of the pneumoperitoneum, the baseline waveform pattern and velocity returned. The Trendelenburg position used for gynecologic operative laparoscopy was associated with a statistically significant increase in the lower-limb PSVV. This increase did not fully counteract the dampening effect of a pneumoperitoneum on lower-limb PSVV. The authors' study did not support the benefit previously reported on the use of pneumatic calf compressors. The authors therefore recommend continuing the practice of antithrombotic measures for patients undergoing gynecologic operative laparoscopy.

Background —Clinical studies have shown that biphasic shocks are more effective than monophasic shocks for ventricular defibrillation. The purpose of this study was to compare the efficacy of a rectilinear biphasic waveform with a standard damped sine wave monophasic waveform for the transthoracic cardioversion of atrial fibrillation. Methods and Results —In this prospective, randomized, multicenter trial, patients undergoing transthoracic cardioversion of atrial fibrillation were randomized to receive either damped sine wave monophasic or rectilinear biphasic shocks. Patients randomized to the monophasic protocol (n=77) received sequential shocks of 100, 200, 300, and 360 J. Patients randomized to the biphasic protocol (n=88) received sequential shocks of 70, 120, 150, and 170 J. First-shock efficacy with the 70-J biphasic waveform (60 of 88 patients, 68%) was significantly greater than that with the 100-J monophasic waveform (16 of 77 patients, 21%, P P P =0.005). The following 3 variables were independently associated with successful cardioversion: use of a biphasic waveform (relative risk, 4.2; 95% confidence intervals, 1.3 to 13.9; P =0.02), transthoracic impedance (relative risk, 0.64 per 10-Ω increase in impedance; 95% confidence intervals, 0.46 to 0.90; P =0.005), and duration of atrial fibrillation (relative risk, 0.97 per 30 days of atrial fibrillation; 95% confidence intervals, 0.96 to 0.99; P =0.02). Conclusions —For transthoracic cardioversion of atrial fibrillation, rectilinear biphasic shocks have greater efficacy (and require less energy) than damped sine wave monophasic shocks.

OBJECTIVES We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation. BACKGROUND Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown. METHODS In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock. RESULTS First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 ± 1 vs. 33 ± 7 A, p CONCLUSIONS This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.

The upper limit of vulnerability (ULV) has been used in clinical studies to predict the DFT in patients with ICDs. Despite the ULV-DFT correlation, uncertainties about the optimal timing of the ULV determination remain. Previous studies using monophasic or biphasic shock waveforms reported differences in the ULV timing with respect to the electrocardiographic T wave. The purpose of this study was to directly compare the ULV timing for mono- versus biphasic T wave shocks. In ten isolated rabbit hearts, mono- and biphasic shocks were delivered randomly during the vulnerable window and at varying shock strengths to determine the ULV. The ULV timing was expressed as the coupling interval at the ULV, the myocardial repolarization state at the ULV measured by monophasic action potential recordings, and the relation between the ULV and the peak of the simultaneously recorded volume conducted T wave. The ULV for biphasic shocks occurred at longer coupling intervals than for monophasic shocks (188.0 +/- 9.5 ms vs 173.5 +/- 8.8 ms, P < 0.001). This resulted in a more repolarized myocardial state at the ULV for biphasic than for monophasic shocks (81.1% +/- 7.5% vs 66.9% +/- 9.0%, P = 0.002). The ULV for monophasic shocks occurred predominantly during the upslope of the T wave (8.0 +/- 9.7 ms before the peak of the T wave) whereas the ULV for biphasic shocks occurred at or after the peak of the T wave (5.9 +/- 9.3 ms after the peak of the T wave) (P < 0.001). Biphasic shocks delay the timing of the ULV as compared to monophasic shocks. This is important for the prediction of the DFT by ULV measurements.

Background The most important factor for improving out-of-hospital ventricular fibrillation survival rates is early defibrillation. This can be achieved if small, lightweight, inexpensive automatic external defibrillators are widely disseminated. Because automatic external defibrillator size and cost are directly affected by defibrillation waveform shape and because of the favorable experience with truncated biphasic waveforms in implantable cardioverter-defibrillators, we compared the efficacy of a truncated biphasic waveform with that of a standard damped sine monophasic waveform for transthoracic defibrillation. Methods and Results The principal goal of this multicenter, prospective, randomized, blinded study was to compare the first-shock transthoracic defibrillation efficacy of a 130-J truncated biphasic waveform with that of a standard 200-J monophasic damped sine wave pulse using anterior thoracic pads in the course of implantable cardioverter-defibrillator testing. Pad-pad ECGs were also examined after transthoracic defibrillation. After the elimination of data for 24 patients who did not meet all protocol criteria, the results from 294 patients were analyzed. The 130-J truncated biphasic pulse and the 200-J damped sine wave monophasic pulse resulted in first-shock efficacy rates of 86% and 86%, respectively ( P =.97). ST-segment levels measured 10 seconds after the shock in 151 patients in sinus rhythm were −0.26±1.58 and −1.86±1.93 mm for the 130- and 200-J shocks, respectively ( P Conclusions We found that 130-J biphasic truncated transthoracic shocks defibrillate as well as the 200-J monophasic damped sine wave shocks that are traditionally used in standard transthoracic defibrillators and result in fewer ECG abnormalities after the shock.

Strong energy stimulation is most effective method for the treatment of heart paralyzation (also called fibrillation), which is the main cause of sudden cardiac death. Automatic implantable defibrillator is available for the treatment of this arrhythmia. However, since the mechanism of termination of fibrillation by the electrical stimulation is not well understood, currently available automatic implantable defibrillator has many problems such as large size, heavy weight, short battery life and so on. The development of low energy defibrillation method is ideal for the improvement of current system. The purpose of this study is the development of multifunctional strong energy heart electric stimulator which is of help investigating the improvement of low energy defibrillation method. In this stimulator, number of stimulus, waveform shape such as monophasic and biphasic waveform, each subpart waveform duration, interphasic duration and output energy can be controlled. In the animal experiment using this stimulator, defibrillation energy requirement using biphasic waveform stimulation was less than50%of that using monophasic waveform stimulation.

Biphasic waveforms reduce defibrillation threshold compared with corresponding monophasic waveforms. However, effects of fibrillation duration on relative efficacy of monophasic and biphasic waveforms are unknown. This study used a newly developed defibrillation model, the isolated right- and left-sided working rabbit heart, with epicardial defibrillation electrodes, to compare threshold for a monophasic waveform (5 msec rectangular) and an asymmetrical biphasic waveform (5 msec each pulse, V2 = 50% V1). Mean voltage defibrillation threshold (V50) was determined from sigmoidal probability of successful defibrillation versus shock intensity curves after 5, 15, and 30 seconds of fibrillation in a paired study with 10 hearts. Results showed that biphasic waveforms had significantly lower voltage and energy thresholds at all fibrillation durations and that their relative efficacy improved with increasing fibrillation duration. Biphasic voltage threshold was 38.2 +/- 2.2, 44.7 +/- 4.8, and 46.6 +/- 3.2 V after 5, 15, and 30 seconds of fibrillation compared with monophasic thresholds of 51.7 +/- 4.4 (p less than 0.002), 63.0 +/- 7.6 (p less than 0.05), and 72.1 +/- 3.9 V (p less than 0.005). Biphasic waveform energy threshold was 0.67 that for the monophasic waveform after 5 seconds of fibrillation (0.12 +/- 0.01 versus 0.18 +/- 0.03 J, p less than 0.05). The ratio between biphasic waveform threshold and monophasic waveform threshold (B/M) decreased to 0.62 at 15 seconds. At 30 seconds, B/M was 0.52 (0.17 +/- 0.02 versus 0.33 +/- 0.04 J, p less than 0.02). This study also showed that biphasic waveform threshold was a nonlinear function of monophasic waveform threshold so that improved biphasic defibrillator waveform efficacy was greatest for hearts having higher monophasic thresholds.(ABSTRACT TRUNCATED AT 250 WORDS)

ObjectivesThe purpose of this study was to test the hypothesis that superiority of biphasic waveform (BW) over monophasic waveform (MW) defibrillation shocks is attributable to less intracellular calcium (Cai) transient heterogeneity.BackgroundThe mechanism by which BW shocks have a higher defibrillation efficacy than MW shocks remains unclear.MethodsWe simultaneously mapped epicardial membrane potential (Vm) and Cai during 6-ms MW and 3-ms/3-ms BW shocks in 19 Langendorff-perfused rabbit ventricles. After shock, the percentage of depolarized area was plotted over time. The maximum (peak) post-shock values (VmP and CaiP, respectively) were used to measure heterogeneity. Higher VmP and CaiP imply less heterogeneity.ResultsThe defibrillation thresholds for BW and MW shocks were 288 ± 99 V and 399 ± 155 V, respectively (p = 0.0005). Successful BW shocks had higher VmP (88 ± 9%) and CaiP (70 ± 13%) than unsuccessful MW shocks (VmP 76 ± 10%, p < 0.001; CaiP 57 ± 8%, p < 0.001) of the same shock strength. In contrast, for unsuccessful BW and MW shocks of the same shock strengths, the VmP and CaiP were not significantly different. The MW shocks more frequently created regions of low Cai surrounded by regions of high Cai (post-shock Cai sinkholes). The defibrillation threshold for MW and BW shocks became similar after disabling the sarcoplasmic reticulum (SR) with thapsigargin and ryanodine.ConclusionsThe greater efficacy of BW shocks is directly related to their less heterogeneous effects on shock-induced SR Ca release and Cai transients. Less heterogeneous Cai transients reduces the probability of Cai sinkhole formation, thereby preventing the post-shock reinitiation of ventricular fibrillation.

Objective: To compare the efficacy of cardioversion in patients with atrial fibrillation between monophasic damped sine waveform and rectilinear biphasic waveform shocks at a high initial energy level and with a conventional paddle position. Design: Prospective randomised study. Patients and setting: 227 patients admitted for cardioversion of atrial fibrillation to a tertiary referral centre. Results: 70% of 109 patients treated with an initial 200 J monophasic shock were cardioverted to sinus rhythm, compared with 80% of 118 patients treated with an initial 120 J biphasic shock (NS). After the second shock (360 J monophasic or 200 J biphasic), 90% of the patients were in sinus rhythm in both groups. The mean cumulative energy used for successful cardioversion was 306 J for monophasic shocks and 159 J for biphasic shocks (p < 0.001). Conclusions: A protocol using monophasic waveform shocks in a 200–360 J sequence has the same efficacy (90%) as a protocol using rectilinear biphasic waveform shocks in a 120–200 J sequence. This equal efficacy is achieved with a significantly lower mean delivered energy level using the rectilinear biphasic shock waveform. The potential advantage of lower energy delivery for cardioversion of atrial fibrillation needs further study.

Cardioversion of atrial fibrillation (AF) using traditional monophasic shock waveform is unsuccessful in up to 20% of cases, and often requires several shocks of up to 360 J. Based on the success with biphasic shock waveform in converting ventricular fibrillation, it was postulated that biphasic shocks would allow cardioversion with lower energy. In a international multicenter, double-blind, randomized trial of 203 patients, damped sine wave monophasic shocks were compared with impedance-compensated truncated exponential biphasic waveform shocks. Patients received up to five shocks: 100 J, 150 J, 200 J, a fourth shock at maximum output for the initial waveform (200 J biphasic, 360 J monophasic) and a final cross-over shock at maximum output of the alternate waveform. For each energy level, the biphasic waveform compared favorably to the monophasic waveform in successful cardioversion (100 J: 60% versus 22%, P < 0.0001; 150 J: 77% versus 44%, p < 0.0001; 200 J: 90% versus 53%, p < 0.0001). Success with 200 J biphasic was equivalent to 360 J monophasic shock (91% versus 85%, p = 0.29). Patients randomized to biphasic waveform required fewer shocks and lower total energy delivered; in addition, this waveform was associated with less dermal injury and no blistering. Biphasic shocks converted AF present for less than 48 hours with 80% efficacy, but conversion of AF present for more than 48 hours and more than 1 year the success rate was only 63 and 20%, respectively. The results of this study is similar to other investigations comparing biphasic and monophasic shock waveforms for conversion of atrial fibrillation. We recommend starting with biphasic energy of 100 J for atrial fibrillation of less than 48 hours duration, but using higher energies (150 J, 200 J or greater) when AF has been present for longer periods.

Newly developed biphasic waveforms improve defibrillation efficacy both by reduction of defibrillation threshold and by amelioration of shock-induced dysfunction depending on the relative shape of the first and second pulses. Each of these independent effects improves the waveform's safety factor, the ratio between the shock intensity that produces a specific degree of postshock dysfunction and the shock intensity that produces defibrillation (or cellular excitation). Symmetrical waveforms reduce defibrillation threshold to about 60% that of the corresponding monophasic waveform, probably by reduction of excitation threshold for ischemic cells, but increase postshock arrhythmias. Biphasic waveforms with 10% "tails" reduce postshock arrhythmias. This study tests the hypothesis that these independent mechanisms for improvement of defibrillation efficacy can be combined into a single triphasic waveform that will have a higher safety factor than either of the two biphasic waveforms of which it is composed. Cultured myocardial cells were subjected to high-intensity electric-field stimulation with a control monophasic rectangular waveform, a symmetrical biphasic waveform, and a triphasic waveform consisting of the biphasic waveform with an added 10% "tail." Each waveform portion was 5 msec in duration. Photocell mechanograms monitored contractile activity. We found that the duration of postshock arrest of spontaneous contractile activity increased with stimulus intensity for all waveforms. The voltage gradient producing a 4-second arrest after the biphasic waveform shock was 80.6 +/- 1.3% that of the control waveform (100%), while the voltage gradient for the triphasic waveforms was 87.1 +/- 0.73% of control. The difference between biphasic and triphasic waveforms was significant (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

High voltage pulsed galvanic stimulation (HVPGS) and low voltage neuromuscular stimulation (LVNMS) techniques were compared for peak torque of an induced isometric contraction, perceived discomfort, and subjective preference of treatment. The high voltage current used a 40-microseconds monophasic waveform, and the low voltage current used a 300-microseconds biphasic waveform. Both currents used a pulse rate of 50 pps. Both HVPGS and LVNMS were administered to one muscle group, either knee extensors or plantar flexors, of 24 healthy subjects. An isokinetic dynamometer was used to assess peak torque. The perceived discomfort experienced with each type of electrical stimulation was quantified by the use of a visual analog scale. For all dependent measures, data first were analyzed for the whole treatment group and then analyzed for each subgroup. Correlated t tests for the whole group and the plantar flexor muscle subgroup demonstrated that HVPGS produced a significantly greater average peak force of muscle contraction than LVNMS and HVPGS was perceived to be significantly less uncomfortable than LVNMS. No significant differences were found between treatments in the knee extensor muscle subgroup for these dependent variables. Chi-square analysis revealed a subject preference for HVPGS in the whole group and in both subgroups. This study indicates that HVPGS can produce a stronger, less uncomfortable, induced isometric muscle contraction than LVNMS.

Biphasic waveforms have been suggested as a superior waveform for ventricular defibrillation. To test this premise, a prospective randomized intraoperative evaluation of defibrillation efficacy of monophasic and biphasic waveform pulses was performed in 22 survivors of out of hospital ventricular fibrillation who were undergoing cardiac surgery for implantation of an automatic defibrillator.The initial waveform used in a patient for defibrillation testing, either monophasic or biphasic, was randomly selected. Subsequently, each patient served as his or her own control for defibrillation testing of the other waveform. The defibrillation threshold was defined as the lowest pulse amplitude that would effectively terminate ventricular fibrillation with a single discharge delivered 10 s after initiation of an episode of ventricular fibrillation induced with alternating current. Each defibrillation pulse was recorded oscilloscopically, and defibrillation pulse voltage, current, resistance and stored energy were measured.Fifteen (68%) of the 22 patients had a lower defibrillation threshold with the biphasic pulse, 3 (14%) had a lower threshold with the monophasic pulse and 4 (18%) had equal defibrillation thresholds (within 1.0 J) regardless of waveform. The mean leading edge defibrillation threshold voltage was 317 ± 105 V when the monophasic pulse was used and 267 ± 102 V (16% less) when the biphasic pulse was used (p = 0.008). Mean leading edge defibrillation threshold current was 7.9 ± 3.7 A when the monophasic pulse was used and 6.8 ± 3.8 A (14% less) when the biphasic pulse was used (p = 0.051). There were no differences in system resistance with the two waveforms: the leading edge resistance for the monophasic pulse was 45.3 ± 17.5 and 44.1 ± 14.4 ω for the biphasic pulse (p = 0.183). The stored energy defibrillation threshold was 8.5 ± 6.1 J when the monophasic pulse was used and 6.3 ± 5.2 J (26% less) when the biphasic pulse was used (p = 0.028). These findings show that in the majority of patients, biphasic pulse defibrillation is more efficient than monophasic pulse defibrillation.

Implantable cardiac defibrillators are now an accepted form of therapy for patients with life-threatening ventricular arrhythmias that cannot be controlled by antiarrhythmic drugs. These devices could be made even more acceptable if they were smaller, had increased longevity and the surgical procedure for implantation was less invasive. Reducing the energy requirements for internal defibrillation with use of a nonthoracotomy lead system would make all of these goals achievable. Monophasic and double and single capacitor biphasic waveforms were compared in 14 anesthetized dogs (25.5 ± 2.2 kg) with use of a nonthoracotomy lead system that has previously been shown to distribute the delivered voltage throughout the heart more equally. Cathodal catheter electrodes were placed in the right ventricular apex and outflow tract. The anodal electrode was a large cutaneous R2 patch placed over the left side of the chest. The mean energy requirement for defibrillation when a single capacitor biphasic waveform was used was significantly less (6.4 ± 2.6 J) than that for either the double capacitor biphasic or the monophasic waveform (18.0 ± 8.0 and 17.4 ± 8.0 J, respectively) of the same duration. Unexpectedly, the leading edge voltage for the phase I of the single capacitor biphasic waveform was significantly less (266 ± 51 V) than that for either the double capacitor biphasic or the monophasic waveform (336 ± 76 and 427 ± 117 V, respectively). In conclusion, in large dogs, defibrillation is possible at low energy levels with a single capacitor biphasic waveform.