Monophasic Waveforms Research Articles

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. …

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 …

Defibrillators

Defibrillators

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.

External defibrillation on an implantable defibrillator

To the Editor: Despite the best efforts of healthcare providers, guideline-conform treatment failure is expected to occur, particularly in real-world emergency situations [1]. In the case reported here, a 79-year-old man with a history of coronary artery disease and implantation of a cardioverter defibrillator (ICD) presented to the emergency room with recurrent ventricular tachycardia. The junior physician-incharge applied an external biphasic DC shock of 200 J to the patient, holding the paddle in one hand and placing it directly over the ICD (Electronic Supplementary Material Fig. 1)—but without success. Arrhythmic stability was finally achieved by multiple, appropriate ICD shocks and intravenous amiodarone. Subsequent device interrogation and defibrillation testing of the ICD showed no instance of device malfunction. Coronary angiography revealed arteries free of significant stenoses. Strong electromagnetic interference induced by transthoracic DC shocks may cause permanent damage or alter the operation of the implanted device [2]. When attempting external defibrillation, clinicians are advised to place the paddles/pads as far as possible from any pulse generator and to choose biphasic over monophasic shock waveforms. A less deleterious effect might be expected if the orientation of the applied electric field is perpendicular—and not parallel—to the device with its lead(s), whereas if the device is located in the left pectoral region, an anterior– apex paddle position may be also acceptable. With an anterior–posterior electrode orientation and a distance between device and hand-held shock electrode of [8 cm, Manegold et al. [3] did not observe any dysfunction in patients with rightor left-sided implanted pacemakers or ICDs treated with external cardioversion for atrial fibrillation.

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.

Biphasic versus monophasic defibrillation in out-of-hospital cardiac arrest: a systematic review and meta-analysis

ObjectiveBiphasic defibrillation is more effective than monophasic one in controlled in-hospital conditions. The present review evaluated the performance of both waveforms in the defibrillation of patients of out-of-hospital cardiac arrest (OHCA) with initial ventricular fibrillation (Vf) rhythm under the context of current recommendations for cardiopulmonary resuscitation. MethodsFrom inception to June 2012, Medline, Embase, and the Cochrane Central Register of Controlled Trials were searched systemically for randomized controlled trials (RCTs) and observational cohort studies that compared the effects of biphasic and monophasic shocks on Vf termination, return of spontaneous circulation (ROSC), and survival to hospital discharge in OHCA patients with initial Vf rhythm. No restrictions were applied regarding language, population, or publication year. ResultsFour RCTs including 572 patients were identified from 131 potentially relevant references for meta-analysis. The synthesis of these RCTs yielded fixed-effect pooled risk ratios (RRs) for biphasic and monophasic waveforms on Vf termination survival to hospital discharge (RR, 1.14; 95% CI, [0.84-1.54]). ConclusionBiphasic waveforms did not seem superior to monophasic ones with respect to Vf termination, ROSC, or survival to hospital discharge in OHCA patients with initial Vf rhythm under the context of current guidelines. However, most trials were conducted in accordance with previous guidelines for cardiopulmonary resuscitation. Therefore, further trials are needed to clarify this issue.

Aplasia of the left external iliac artery and persistant sciatic artery

An 82-year-old man complaning about paresthesia in both thighs had a pathologic Doppler ultrasound, with monophasic waveform and reduced velocity in the left common femoral artery. Downstream left segment and in the right lower limb the flow was triphasics. There was no evidence for atherosclerotic disease. He was referred to perform an angiography-CT scan. Arterial phase contrast-enhanced MDCT with multiplanar reformation (MPR) and 3-D surface-rendered image showed an absence of the left external iliac artery in front of the left external iliac vein (Fig. A). The left common femoral artery is corretly opacified, reconstituted from a persistant sciatic artery (Fig. B) (suggested by an abnormal artery running posterior to the pelvis), a left obturator artery (Fig. C, arrowhead), an ilio-lumbar artery (Fig. C, arrow).

P 232. Leaving the beaten track of TMS waveform restrictions: Concepts and prototype for a ‘convertible’ stimulator that can generate almost every type of existing and future waveform

Introduction Waveforms are an important issue in magnetic stimulation. They provide the key to an important characteristic of neurons: their distinctive nonlinear dynamics. Different waveforms seem to have different activation sites and may allow selective stimulation. This is reflected for example by their different corticospinal D-and I-wave patterns ( Di Lazzaro, 2004 ). However, available pulse types are very restricted. In essence, the only established waveforms are monophasic and biphasic pulses. In addition to selective stimulation and neuromodulation, higher efficiency ( Goetz, 2012 ) could enable highly focal small coils to overcome thermal issues and provide high repetition rates. Objectives Current devices can only provide very distinct pulses for technological reasons. Even in alternative, more flexible approaches, the underlying circuitry is limited to a certain class of stimuli. Among these stimuli, only a subclass does not change the device state of charge and can therefore be generated repetitively. Our objective was to conceive and design a technology that is able to generate almost any waveform. Accordingly, the selection of waveforms would no longer depend on device capabilities and technology, but merely follow the user’s needs. Methods For this aim, we had to abandon all traditional concepts and designs for pulse generation in magnetic stimulation as well as other fields of science and engineering. We developed novel topologies that can handle the special requirements of magnetic stimulation pulses, namely high voltage, high current and high speed. The winning approach uses a dynamical reconfiguration of small energy storages: Metaphorically speaking, it uses a high number of small-voltage batteries that can be combined in any parallel and series connection—dynamically changeable for every time step—so as to exactly control the coil voltage accurately to the curve outlined by the desired waveform. The key components of the technology are no longer expensive high-voltage semiconductors, but inexpensive mass-produced devices used in consumer electronics. We designed a control strategy for the distributed concept and implemented a prototype for characterization of the concept. Results The system can generate almost any waveform, both existing and potential future pulse shapes. All waveforms can be generated with a recovery of the pulse energy from the coil, which has been known from biphasic stimulators. We achieved this even for classical monophasic waveforms, which can—except for rare research devices ( Schmid et al., 1993 )—provide high pulse repetition rates, although being preferred. The high losses prevent that. Furthermore, the generation of waveforms is not done by any mechanical reconfiguration, but controlled dynamically. Therefore, the system can even fundamentally change the waveform from pulse to pulse in a theta-burst or double-pulse protocol. Conclusion The generation of arbitrary waveforms is possible and has several advantages also for classical waveforms. Among others, this includes the ability to use high repetition rates for almost every waveform and profit from cost-effective mass-produced components.

Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge

We describe two new, closely related species of toothed Brachyhypopomus (Hypopomidae: Gymnotiformes: Teleostei) from the central Amazon basin and create a new subgenus for them. Odontohypopomus, new subgenus of Brachyhypopomus, is diagnosed by (1) small teeth present on premaxillae; (2) medialmost two branchiostegal rays thin with blades oriented more vertically than remaining three rays; (3) background color in life (and to lesser extent in preservation) distinctly yellowish with head and sides peppered with small, widely spaced, very dark brown stellate chromatophores that greatly contrast with light background coloration; (4) a dark blotch or bar of subcutaneous pigment below the eye; (5) electric organ discharge waveform of very long duration (head-positive phase approx. 2 milliseconds or longer, head-negative phase shorter or absent) and slow pulse repetition rate (3–16 Hz). The type species of the new subgenus, Brachyhypopomus (Odontohypopomus) walteri sp. n., is diagnosed by the following additional character states: (1) subcutaneous dark pigment at base of orbit particularly prominent, (2) body semi-translucent and nearly bright yellow background coloration in life, (3) a biphasic electric organ discharge (EOD) waveform of very long duration (between 3.5 and 4 milliseconds at 25° C) with head-positive first phase significantly longer than second head-negative phase in both sexes. Brachyhypopomus (Odontohypopomus) bennetti sp. n. is diagnosed by two character states in addition to those used to diagnose the subgenus Odontohypopomus: (1) a deep electric organ, visible as large semi-transparent area, occupying approximately 14–17% body depth directly posterior to the abdominal cavity in combination with a short, but deep, caudal filament, and (2) a monophasic, head-positive EOD waveform, approximately 2.1 milliseconds in duration in both sexes. These are the only described rhamphichthyoid gymnotiforms with oral teeth, and Brachyhypopomus bennetti is the first Brachyhypopomus reported to have a monophasic (head-positive) EOD waveform. Unlike biphasic species, the waveform of its EOD is largely unaffected by tail damage from predators. Such injuries are common among specimens in our collections. This species’ preference for floating meadow habitat along the major channels of the Amazon River basin may put it at particularly high risk of predation and “tail grazing.”

Doppler Assessment of Hepatic Veins in Fatty Liver Disease

The goal of this study was to document the progressive effects of fatty infiltration of the liver on hepatic veins (HVs) by measuring Doppler waveforms in rats and dogs. It was used in two groups of animals: a) rats (10 healthy adult rats as controls, and a group of 10 rats had fatty infiltration of the liver) and b) dogs (a clinical group of 15 obese dogs and a control group of 10 healthy dogs). All of the groups underwent hepatic B-mode, duplex Doppler sonography and hepatic biopsy or cytology. B-mode fatty infiltration was classified into four degrees corresponding to increasing degrees of hepatic echogenicity for all groups: (0) absent, (1) mild, (2) moderate, and (3) severe fatty infiltration. The Doppler sonography spectra of HVs were classified into three groups: normal or triphasic waveforms, biphasic waveforms, and monophasic or flat waveforms. Obese dogs and rats with fatty infiltration of the liver presented abnormal right HV Doppler waveforms. There was a statistically significant difference in the waveforms of HV flow between the obese and control group of dogs. These findings are clinically relevant because changes in waveforms could be used as a tool to monitor fatty liver disease.

The value of Doppler waveform analysis in predicting major lower extremity amputation among dialysis patients treated for diabetic foot ulcers

AimsThis study examined the predictors for lower extremity amputation (LEA) in patients with diabetic foot ulcers according to kidney function and, in the case of dialysis patients, specifically evaluated the vasculature with the ankle–brachial index (ABI) and Doppler waveforms. MethodsAmong 658 diabetic patients admitted to the Diabetic Foot Care Center, 286 had an estimated glomerular filtration rate (eGFR)≥60ml/min per 1.73m2, 275 had an eGFR<60, and 97 patients were under maintenance dialysis. All clinical variables were analyzed. A specialist retrospectively reviewed Doppler images of 78 of the patients in dialysis to evaluate peripheral arterial disease. ResultsForty-two percent of patients with eGFR<60 presented with ABI≤0.90. For ABI values>1.40, the proportion of dialysis patients (31.3%) was greater than the proportion of patients with eGFR<60 (5.3%). Wagner wound classifications, reduced serum albumin levels, and low ABI values were the predictors for major LEA among patients in the non-dialysis groups. Nevertheless, these indicators were not predictive of the risk of amputation in diabetic patients on dialysis. The presence of poor monophasic waveforms in the dorsalis pedis artery or posterior tibial artery served as an independent predictor (odds ratio: 7.61; P=0.008) for major LEA among dialysis patients. The sensitivity and specificity were 88.0% and 59.6%, respectively. ConclusionsPoor monophasic Doppler waveforms of below-the-knee arteries, commonly found among dialysis patients in treatment for diabetic foot ulcers, can serve as an independent predictor for major LEA.

Do clinical examination gloves provide adequate electrical insulation for safe hands-on defibrillation? II: Material integrity following exposure to defibrillation waveforms

IntroductionMaintaining contact with the patient during defibrillator discharge has been proposed as a method for reducing no flow time but carries an associated risk of electrocution of the rescuer. This study describes an investigation to determine if typical clinical examination gloves possess the dielectric strength needed to prevent breakdown at defibrillation voltages; a factor essential to protect the rescuer. MethodsFour types of examination glove typically used in a clinical environment were tested with two types of defibrillation waveform commonly used. For each type of glove, 10 samples were tested initially using a monophasic defibrillation waveform and then, using a fresh sample of gloves, with a Biphasic waveform. For each glove the number of shocks required before electrical breakdown occurred was recorded. ResultsKimberly Clark KC300 (nitrile), Kimberly Clark KC500 purple (nitrile), PH Medisavers GN90 (nitrile) and Bodyguards GL6622 (Vinyl) were tested using a monophasic defibrillation waveform and broke down after a median of 1, 4.5, 1 and 1 shocks respectively. The equivalent values for Biphasic defibrillator were 2, >10, 2.5 and 1 shocks. DiscussionTypical clinical examination gloves do not possess the dielectric strength required to protect a rescuer from defibrillation voltages during hands-on chest compressions.

Ventricular pacing threshold after transthoracic external defibrillation with two different waveforms: an experimental study

Although an increase in the ventricular pacing threshold (VPT) has been observed after administration of transthoracic shock for ventricular defibrillation, few studies have evaluated the phenomenon with respect to the defibrillation waveform energy. Therefore, this study examined the VPT behaviour after transthoracic shock with a monophasic or biphasic energy waveform. Domestic Landrace male piglets implanted with a permanent pacemaker stimulation system were divided into three groups: no ventricular fibrillation (VF) induction and transthoracic shock with monophasic or biphasic energy (group I); VF induction, 1 min of observation without intervention, 2 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group II); and VF induction, 2 min of observation without intervention, 4 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group III). After external shock, the VPT was evaluated every minute for 10 min. A total of 143 experiments were performed. At the end of the observation period, groups I and II showed steady VPT values. Group III showed an increase in VPT with monophasic or biphasic external energy, with no difference between the external energy sources. The monophasic but not the biphasic waveform was associated with higher VPT values when the VF was longer. Defibrillation does not have a significant impact on pacing threshold, but a longer VF period is related to a higher VPT after defibrillation with monophasic waveform.

Comparison of Outcomes After Use of Biphasic or Monophasic Defibrillators Among Out-of-Hospital Cardiac Arrest Patients

The use and popularity of the biphasic waveform defibrillator as a replacement for the monophasic waveform defibrillator are increasing, but it is unclear whether this can improve the rate of survival among out-of-hospital cardiac arrest patients. This study aimed to verify the hypothesis that the outcome of out-of-hospital cardiac arrest patients who received defibrillation shock with the biphasic waveform defibrillator was better than that of patients who received defibrillation shock with the monophasic defibrillator. This prospective, nationwide, population-based, observational study included 21 172 out-of-hospital cardiac arrest patients with initial ventricular fibrillation or pulseless ventricular tachycardia from January 1, 2005, through December 31, 2007. Defibrillation shock was performed by monophasic defibrillator on 8224 (39%) patients and by biphasic defibrillator on 12 948 (61%) patients. The rate of survival at 1 month with minimal neurological impairment was 11.6% (951/8192) in the monophasic defibrillator group and 12.8% (1653/12 928) in the biphasic defibrillator group. Hierarchical logistic regression analysis using a generalized estimation equation showed no significant difference between the biphasic and monophasic groups in 1-month survival with minimal neurological impairment (adjusted odds ratio, 1.07; 95% confidence interval, 0.91-1.26; P=0.42). Confirmatory propensity score analyses showed similar results. Although monophasic defibrillators are being replaced by biphasic defibrillators, our nationwide population-based observational study failed to demonstrate a statistically significant association between defibrillation waveform and 1-month survival rate with minimal neurological impairment.

PS172. Accuracy of Sharp Monophasic Waveform in Predicting Distal Arterial Disease in Lower Extremity

The aim of this study is to establish the significance of sharp monophasic waveform (SMW) in predicting distal arterial disease. It also attempts to clarify several inconsistencies in literature regarding the classification of arterial waveforms. The waveform that is the main focus of this study has been classified as both ‘sharp monophasic' and ‘low resistive biphasic'.

Evaluation of disease activity in ankylosing spondylitis; diagnostic value of color Doppler ultrasonography

Spondyloarthropathies including ankylosing spondylitis (AS) require early diagnosis to prevent irreversible changes. Sacroiliitis is a common initial manifestation of AS and is frequently diagnosed by magnetic resonance imaging (MRI). The goal of our study was to assess color Doppler ultrasonography as a potential diagnostic tool in suspected sacroiliitis in comparison with MRI representing the gold standard. Fifty-one consecutive patients with AS and sacroiliitis and 30 control subjects underwent contrast-enhanced MRI and high resolution color Doppler and duplex ultrasonography of both sacroiliac joints (SIJ) for the detection of vascularization and blood flow spectral Doppler waveform analysis. MRI demonstrated active disease in 27 and inactive disease in 24 patients. CDUS detected pulsatile monophasic wave spectral waveform flow in 22 patients with the active disease, and triphasic in 7 patients with inactive disease and in 8 control patients. The sensitivity, specificity, positive predictive value and negative predictive value for active sacroiliitis detection with CDUS were 82 % (95 % CI, 68-91 %), 92 % (95 % CI, 85-96 %), 91 % (95 % CI, 84-96 %), and 84 % (95 % CI, 70-92 %), respectively, for pulsatile monophasic wave spectral waveform Doppler sonography. MRI of SIJ was negative in all 30 (60 SIJ) control participants. Our results show that CDUS is a practical and useful tool in the diagnosis of active sacroiliitis.

Simultaneous Comparison of Many Triphasic Defibrillation Waveforms

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<0.05). One was superior to the biphasic waveform (p<0.1), but not statistically so. We concluded that, while adding a phase to a monophasic waveform does improve efficacy, adding an additional phase to a biphasic waveform does not necessarily improve efficacy.

Regional Hemodynamic Changes After an Axillary Brachial Plexus Block

Brachial plexus block (BPB) causes vasodilatation and an increase in blood flow to the ipsilateral upper limb. However, no reports have comprehensively evaluated the regional hemodynamic changes after a BPB. Eight healthy adult patients who were scheduled for elective hand surgery had an ultrasound-guided axillary BPB for anesthesia. Regional hemodynamic parameters were measured in the ipsilateral brachial artery, using pulsed-wave Doppler (PWD) ultrasound before the block (0 minute) and at regular intervals for 30 minutes after the block. Skin temperature on the dorsum of the ipsilateral hand was also recorded at the same time intervals. Regional hemodynamic parameters that were measured in the brachial artery included peak systolic velocity (PSV, cm/s), end-diastolic velocity (EDV, cm/s), mean velocity (Vmean) and time-averaged mean velocity (TAVM, cm/s), ratio of PSV and EDV (S/D), diameter (d, cm), resistance index (RI), and pulsatility index (PI). Brachial artery blood flow (Q) was calculated as the product of TAVM and cross-sectional area. The ultrasound-guided axillary BPB was successful in all the patients studied. The earliest change after the BPB was a change in the morphology of the PWD spectral waveform from a triphasic to a monophasic waveform and an elevation in the diastolic blood flow velocity. Over time, there was also a significant increase in PSV, EDV, Vmean, TAVM, d, brachial artery blood flow, and skin temperature and a decrease in S/D ratio, RI, and PI. Most of these changes were seen as early as 5 minutes after the block. The increase in EDV (3.7-fold) was the most notable change, and it was greater (P < 0.05) than the increase in PSV (1.5-fold) and Vmean (2.8-fold). Regional hemodynamic changes that occur after an axillary BPB include a change in the morphology of the PWD spectral waveform, arterial vasodilatation, an increase in blood flow velocity, and an increase in blood flow through the ipsilateral brachial artery.

Atrial Burst Pacing with Biphasic and Monophasic Waveforms for Atrial Fibrillation

Biphasic pacing is a novel mode of pacing that was suggested to increase cardiac conduction velocity as compared with cathodal monophasic pacing. We aimed to evaluate the safety and efficacy of rapid atrial pacing to convert atrial fibrillation (AF) to normal sinus rhythm. Multiple biphasic (anodal/cathodal), reverse biphasic (cathodal/anodal), and monophasic (cathodal) atrial pacing therapies were performed among 12 patients undergoing left atrial catheter ablation for AF. The efficacy end point was successful conversion of AF to sinus rhythm, and safety end point no induction of ventricular arrhythmias. Patients were paced at three cycle lengths (100, 200, and 333 msec) for 60 seconds at three locations (right and left atrial appendages and coronary sinus). Among the 66 biphasic (anodal/cathodal) pacing procedures one procedure in a patient with chronic AF, which involved pacing at the left atrial appendage with a cycle length of 200 msec, led to conversion of AF to sinus rhythm. None of the 66 monophasic pacing procedures or the 66 reverse biphasic (cathodal/anodal) pacing procedures was associated with AF termination. None of the biphasic pacing procedures was associated with induction of ventricular arrhythmias. Rapid atrial pacing using a variety of waveforms at the cycle length and output used in the current study was found to be safe. There was a single success in converting a chronic AF to sinus rhythm.