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Biomedical subjects

R Weiss

Publications and source records attributed to R Weiss.

At least 127 records · Page 7Linked to original sources
PubMed1998

Unilateral Blastomyces dermatitidis endophthalmitis and orbital cellulitis. A case report and literature review.

PURPOSE: The authors report the clinical, cytologic, and histopathologic findings of a unique presentation of concomitant unilateral endophthalmitis and orbital cellulitis secondary to Blastomyces dermatitidis. DESIGN: Case report. METHODS: A 29-year-old healthy woman with a history of pulmonary tuberculosis presented with a painful right eye and rapidly decreasing vision. Fundus examination showed a diffuse elevated choroidal lesion at the posterior pole. With an otherwise unremarkable systemic work-up, the patient was treated with systemic antibiotics and corticosteroids for a presumed diagnosis of choroidal tuberculous granuloma. After an initial response to the treatment, the patient's condition deteriorated rapidly with visual acuity decreasing from 20/25 to no light perception in 3 months. Ipsilateral proptosis developed with magnetic resonance imaging showing a poorly defined orbital mass. Surgical enucleation and an orbital biopsy were performed. RESULTS: Histopathologic examination of the orbital specimen and an intact enucleated globe showed a diffuse necrotizing granulomatous process with the presence of numerous yeasts consistent with B. dermatitidis. This subsequently was confirmed by positive culture of B. dermatitidis from the orbital specimen. CONCLUSIONS: This is a unique case of concurrent unilateral endophthalmitis and orbital cellulitis secondary to B. dermatitidis. Intraocular dissemination of blastomycosis should be suspected in the differential diagnosis of endophthalmitis in patients with previous or active pulmonary lesions of equivocal nature. Early diagnosis and prompt treatment with antifungal medications are essential.

Adult↗
PubMed1998

Autonomic nervous system activity and the spontaneous initiation of ventricular tachycardia. ESVEM Investigators. Electrophysiologic Study Versus Electrocardiographic Monitoring Trial.

OBJECTIVES: We hypothesized that neurohormonal activity contributes to the initiation of sustained ventricular tachycardia (VT) as reflected in indices of heart rate variability (HRV). BACKGROUND: Autonomic nervous system activity participates in experimental arrhythmias but clinical studies have been inconsistent. METHODS: Holter electrocardiograms from 53 patients with VT were analyzed. Heart rate variability indices were determined over 5 and 15 min and 24 h and examined for changes before the onset of VT. Heart rate variability indices in the frequency domain included ultra low frequency power (FP) (ULFP): 0-0.0033 Hz; very low FP (VLFP): 0.0033-0.04 Hz; low FP (LFP): 0.04-0.15 Hz; high FP (HFP): 0.15-0.4 Hz; total power (TP); normalized LFP (LFPn); normalized HFP (HFPn), and the ratio: LFP/HFP. RESULTS: Heart rate variability indices were severely diminished: TP: 12,009+/-11,076 ms2; ULFP: 10,087+/-9,565 ms2; VLFP: 1,416+/-1,571 ms2; LFP: 544+/-620 ms2; HFP: 161+/-176 ms2, and LFP/HFP: 3.68+/-2.83. Heart rate increased before VT (80.4+/-17.3 to 85.3+/-17.4 bpm, p < 0.001). Several HRV variables declined 30 min before VT compared to 24-h values (VLFP: -5.89+/-17.81%, p = 0.031; LFP: -5.23+/-14.3%, p = 0.003; HFP: -4.35+/-13.7%, p = 0.04). LFPn and the LFP/HFP ratio decreased significantly before the onset of VT (-17.7+/-46.9%, p = 0.035 and -8.24+/-38.8%, p = 0.037, respectively), whereas HFPn increased slightly (4.29+/-29.9%, p = 0.097). CONCLUSIONS: Heart rate rose, whereas LFP, LFPn and LFP/HFP fell before the onset of VT. This pattern of changes could be explained by a rise in sympathetic activity and saturation of the HRV signal resulting in dissociation of the average and rhythmical effects of sympathetic activity. These findings suggest that alterations in autonomic activity contributed to arrhythmogenesis in this group of patients.

Aged↗
PubMed1998

Detection of Borrelia burgdorferi in urine specimens from dogs by a nested polymerase chain reaction.

A nested PCR (nested flagellin PCR) carrying an internal E. coli DNA control was established and compared with an in-vitro culture method for the detection of Borrelia burgdorferi in urine specimens of dogs. The predicted specific amplicon of the flagellin gene fla was generated from all cultured strains of B. burgdorferi tested (comprising three European genospecies). In contrast, all 13 strains of seven other flagellated bacterial species were negative. The PCR detection limit yielded 20 cells of B. burgdorferi per ml of double-distilled water and approx. 250 bacteria per ml of dog urine. Using the bacterial culture method, urine specimens collected from 216 dogs in Germany were all diagnosed negative for spirochetes by in-vitro culture and dark-field microscopy. In contrast, DNA of B. burgdorferi was detected in 32 specimens (14.8%) by PCR. 31 urine specimens (14.4%) showed inhibitory activity in the PCR assay. However, 94 (44%) were inhibitory in the culture assay. The majority of the PCR-positive dogs exhibited major clinical symptoms which have not been reported in the course of B. burgdorferi infection previously, e.g. cystitis (14/32 dogs) or prostatitis (5/32 dogs). Our results indicate that the analysis of urine specimens by the nested flagellin PCR is a highly valuable procedure for the diagnosis of B. burgdorferi infections in dogs.

Animals↗
PubMed1998

Randomized comparison of a 90 uF capacitor three-electrode defibrillation system with a 125 uF two-electrode defibrillation system.

INTRODUCTION: A variety of factors, including the number of defibrillation electrodes and shocking capacitance, may influence the defibrillation efficacy of an implantable defibrillator system. Therefore, the purpose of this study was to compare the defibrillation energy requirement using a 125 uF two-electrode defibrillation system and a 90 uF three-electrode defibrillation system. METHODS AND RESULTS: The defibrillation energy requirements measured with both systems were compared in 26 consecutive patients. The two-electrode system used a single transvenous lead with two defibrillation coils in conjunction with a biphasic waveform from a 125 uF capacitor. The three-electrode system used the same transvenous lead, utilized a pectoral implantable defibrillator generator shell as a third electrode, and delivered the identical biphasic waveform from a 90 uF capacitor. The two-electrode system was associated with a higher defibrillation energy requirement (10.8 +/- 5.5 J) than was the three-electrode system (8.9 +/- 6.7 J, p < 0.05), however, the leading edge voltage was not significantly different between systems (361 +/- 103 V vs. 397 +/- 123 V, P = 0.07). The two-electrode system also had a higher shocking resistance (49.0 +/- 9.0 ohms vs. 41.4 +/- 7.3 ohms, p < 0.001) and a lower peak current (7.7 +/- 2.6 A vs. 10.1 +/- 3.7 A, p < 0.001) than the three-electrode system. CONCLUSIONS: A three-electrode defibrillation system that utilizes a dual coil transvenous lead and a subcutaneous pectoral electrode with lower capacitance is associated with a lower defibrillation energy requirement than is a dual coil defibrillation system with higher capacitance. This finding suggests that the utilization of a pectoral generator as a defibrillation electrode in conjunction with smaller capacitors is a more effective defibrillation system and may allow for additional miniaturization of implantable defibrillators.

Aged↗
PubMed1998

Low values on 50 gram glucose challenge test or oral 100 gram glucose tolerance test are associated with good perinatal outcome.

We set out to reevaluate the hypothesis that high normal (negative) results of 50 g oral glucose challenge test or high normal glucose level on 100 g oral glucose tolerance test are associated with complications of pregnancy and delivery. This was a prospective study involving 735 nondiabetic women. The first group (n=352) was made up of pregnant women with normal 50 g oral glucose challenge test without previous history of diabetes mellitus or gestational diabetes. The second group (n=383) was made up of pregnant women without previous history of diabetes mellitus or gestational diabetes with an abnormal 50 g oral glucose challenge test and with normal 100 g oral glucose tolerance test and not more than one previous delivery. In nondiabetic women, we demonstrated a positive correlation between high normal 50 g glucose challenge test values and the incidence of preeclampsia, caesarean section rate, macrosomia, neonatal hyperlipidaemia and minor congenital abnormalities. We failed to confirm any relationship to any pregnancy complication in pregnant women with 2-hour glucose levels in the range 6.7-9.1 mmol/l on the 100 g oral glucose tolerance test. We have demonstrated a positive relationship between the incidence of premature rupture of membranes and 1-hour glucose level, caesarean section rate and maternal 1-hour glucose level or 1-hour glucose level minus fasting glucose level of 4.2 mmol/l, instrumental delivery rate and maternal 3-hour glucose level, incidence of neonatal macrosomia and 1-hour glucose level, and incidence of neonatal hyperlipidaemia and at least one high but normal glucose level on the 100 g oral glucose tolerance test. With regard to pregnancy and delivery complications there were no significant difference if the high normal value is on the 50 g glucose challenge test or on the 100 g oral glucose tolerance test. It is concluded that one high normal 100 g oral glucose tolerance test or high normal 50 g glucose challenge test are associated with adverse pregnancy and delivery outcome. Nondiabetic women with 50 g glucose challenge test value of 6.1 mmol/l and/or 100 g oral glucose tolerance test values of 5 mmol/l have a favourable pregnancy and delivery outcome.

Journal Article↗
PubMed1998

Properties of serological group B streptococci of dog, cat and monkey origin.

This study was designed to identify and characterize further Streptococcus agalactiae isolated during routine diagnostics from three diseased dogs and a cat, as well as from the inner organs of a monkey which died on a sepsis with beta-haemolytic streptococci. The cultures could be identified as streptococci of serological group B by cultural, biochemical and serological properties and by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR)-amplified 16S ribosomal DNA. A further characterization of the isolates by serotyping and by determination of antibiotic resistances revealed a close relationship of these isolates to the human biotype of this species.

Animals↗
PubMed1998

Demonstration of Malassezia furfur and M. sympodialis together with M. pachydermatis in veterinary specimens.

In the present study, 47 wild-type isolates of the genus Malassezia were isolated from dog and cat specimens by means of a simple differentiating system recently published. The purpose was to determine whether any of the other seven Malassezia spp. apart from M. pachydermatis occur in carnivores. Of the 47 isolates, three had been obtained from cats (ear 2, skin 1) and 44 from dogs (ear 37, skin 3, faeces 2, claw and paw 2). After primary isolation, they were subcultured on mDixon agar and then purified and differentiated by means of assimilation of Cremophor EL, splitting of esculin, growth on lipid-free medium and formation of tryptophan-dependent pigments and fluorochromes. Thus, a total of 100 strains could be obtained from the 47 primary isolates. Referring to the source material, M. pachydermatis was found in 83%, M. furfur in 45% and M. sympodialis in 75%. More than 80% of cultures were mixed, comprising two or all three species; a single species was isolated in only nine cases. This shows that animals are not colonized by M. pachydermatis alone, as has been thought until now, but in nearly all cases by mixed cultures. Thus, (domestic) animals could well be a reservoir for other Malassezia species such as M. furfur and M. sympodialis. Surprisingly, Malassezia yeasts were also isolated from dog faeces, indicating that they apparently pass through the gastrointestinal tract in unchanged form after having been taken up by licking colonized areas. The survivability of Malassezia yeasts in highly acid milieu was also demonstrated in vitro. The study confirms the usefulness of the new test procedures and allows new statements concerning the epidemiology of Malassezia yeasts.

Animals↗
PubMed1998

A prospective evaluation of two defibrillation safety margin techniques in patients with low defibrillation energy requirements.

INTRODUCTION: In patients undergoing defibrillator implantation, an appropriate defibrillation safety margin has been considered to be either 10 J or an energy equal to the defibrillation energy requirement. However, a previous clinical report suggested that a larger safety margin may be required in patients with a low defibrillation energy requirement. Therefore, the purpose of this prospective study was to compare the defibrillation efficacy of the two safety margin techniques in patients with a low defibrillation energy requirement. METHODS AND RESULTS: Sixty patients who underwent implantation of a defibrillator and who had a low defibrillation energy requirement (< or = 6 J) underwent six separate inductions of ventricular fibrillation, at least 5 minutes apart. For each of the first three inductions of ventricular fibrillation, the first two shocks were equal to either the defibrillation energy requirement plus 10 J (14.6+/-1.0 J), or to twice the defibrillation energy requirement (9.9+/-2.3 J). The alternate technique was used for the subsequent three inductions of ventricular fibrillation. For each induction of ventricular fibrillation, the first shock success rate was 99.5%+/-4.3% for shocks using the defibrillation energy requirement plus 10 J, compared to 95.0%+/-17.2% for shocks at twice the defibrillation energy requirement (P = 0.02). The charge time (P < 0.0001) and the total duration of ventricular fibrillation (P < 0.0001) were each approximately 1 second longer with the defibrillation energy requirement plus 10 J technique. CONCLUSION: This study is the first to compare prospectively the defibrillation efficacy of two defibrillation safety margins. In patients with a defibrillation energy requirement < or = 6 J, a higher rate of successful defibrillation is achieved with a safety margin of 10 J than with a safety margin equal to the defibrillation energy requirement.

Aged↗
PubMed1998

Characterization of native and recombinant forms of an unusual cobalt-dependent proline dipeptidase (prolidase) from the hyperthermophilic archaeon Pyrococcus furiosus.

Proline dipeptidase (prolidase) was purified from cell extracts of the proteolytic, hyperthermophilic archaeon Pyrococcus furiosus by multistep chromatography. The enzyme is a homodimer (39.4 kDa per subunit) and as purified contains one cobalt atom per subunit. Its catalytic activity also required the addition of Co2+ ions (Kd, 0.24 mM), indicating that the enzyme has a second metal ion binding site. Co2+ could be replaced by Mn2+ (resulting in a 25% decrease in activity) but not by Mg2+, Ca2+, Fe2+, Zn2+, Cu2+, or Ni2+. The prolidase exhibited a narrow substrate specificity and hydrolyzed only dipeptides with proline at the C terminus and a nonpolar amino acid (Met, Leu, Val, Phe, or Ala) at the N terminus. Optimal prolidase activity with Met-Pro as the substrate occurred at a pH of 7.0 and a temperature of 100 degrees C. The N-terminal amino acid sequence of the purified prolidase was used to identify in the P. furiosus genome database a putative prolidase-encoding gene with a product corresponding to 349 amino acids. This gene was expressed in Escherichia coli and the recombinant protein was purified. Its properties, including molecular mass, metal ion dependence, pH and temperature optima, substrate specificity, and thermostability, were indistinguishable from those of the native prolidase from P. furiosus. Furthermore, the Km values for the substrate Met-Pro were comparable for the native and recombinant forms, although the recombinant enzyme exhibited a twofold greater Vmax value than the native protein. The amino acid sequence of P. furiosus prolidase has significant similarity with those of prolidases from mesophilic organisms, but the enzyme differs from them in its substrate specificity, thermostability, metal dependency, and response to inhibitors. The P. furiosus enzyme appears to be the second Co-containing member (after methionine aminopeptidase) of the binuclear N-terminal exopeptidase family.

Amino Acid Sequence↗
PubMed1998

HIV-related non-Hodgkin's lymphoma: CHOP induction therapy and interferon-alpha-2b/zidovudine maintenance therapy.

In a prospective multicenter study 68 out of 158 patients with HIV infection and malignant lymphoma were assigned to a risk-adapted induction therapy using the following algorithm: High-risk patients fulfilled 2 of 3 criteria: T4 lymphocytes <50/microL; WHO activity index 3 or 4; pre-existing AIDS-defining opportunistic infection. Normal-risk patients received 4 to 6 cycles of CHOP chemotherapy; those that achieved complete remission (CR) received zidovudine (500 mg/d) and interferon-alpha maintenance therapy (5 million units three times a week) for one year. High-risk patients received low-dose CHOP or vincristine/prednisone chemotherapy. Supportive care was performed with pentamidine inhalation and G-CSF. Intrathecal (it) methotrexate was given for CNS prophylaxis. The median survival was 634 days for 38 patients of the normal-risk group and 129 days for 30 patients of the high-risk group. 18 high-risk patients treated with low-dose CHOP had better survival (156 days) than 12 patients treated with vincristine/prednisone (72 days p=0.044). 68% of the patients in the normal-risk group achieved complete remission. 5 out of 18 high-risk patients treated with low-dose CHOP achieved complete remission. Three normal-risk patients developed fatal opportunistic infections during chemotherapy. Immune parameters deteriorated after CHOP induction and partially recovered with maintenance treatment. We conclude that the normal-risk patients survived longer than reported in most published studies. Toxicity was low. Low-dose CHOP seems to be superior to vincristine/prednisone therapy in high-risk patients.

Adult↗
PubMed1997

Long-term follow-up after radiofrequency ablation of paroxysmal supraventricular tachycardia in patients with tachycardia-induced atrial fibrillation.

Four of 12 patients (33%) with paroxysmal supraventricular tachycardia (PSVT) and tachycardia-induced atrial fibrillation (AF) had recurrences of paroxysmal AF after successful catheter ablation of the PSVT. This study demonstrates that AF often remains a problem after radiofrequency catheter ablation of PSVT in patients with tachycardia-induced AF, and it may not be possible to predict in which patients this will be the case.

Atrial Fibrillation↗
PubMed1997

Adenosine-induced atrial arrhythmia: a prospective analysis.

BACKGROUND: Adenosine is considered safe and effective for paroxysmal supraventricular tachycardia (PSVT), but anecdotal experience suggests that adenosine can precipitate atrial arrhythmias. OBJECTIVES: To determine the frequency and mechanisms of adenosine-induced atrial arrhythmias. SETTING: Clinical electrophysiology laboratory at a university medical center. DESIGN: Prospective observational study. PATIENTS: 200 consecutive patients with PSVT undergoing an electrophysiology procedure. INTERVENTION: During PSVT, 12 mg of adenosine was administered centrally through the femoral vein. MEASUREMENTS: Frequency of adenosine-induced atrial fibrillation. RESULTS: Paroxysmal supraventricular tachycardia terminated after adenosine administration in 198 patients (99% [95% CI, 96% to 100%]). Adenosine led to atrial fibrillation (n = 22) or atrial fibrillation and atrial flutter (n = 2) in 24 patients (12% [CI, 7.5% to 16.5%]). An atrial premature complex occurred in all 24 patients who developed atrial fibrillation, atrial flutter, or both and in 102 of the 176 patients (58%) who did not (P < 0.001). The mean (+/-SD) time from the preceding atrial complex to the atrial premature complex was shorter when an atrial arrhythmia occurred, and the mean ratio of this interval to the preceding atrial cycle length was also lower when atrial fibrillation developed (0.37 +/- 0.16 compared with 0.49 +/- 0.16; P = 0.002). CONCLUSIONS: The incidence of atrial fibrillation induced by 12 mg of adenosine administered through the femoral vein was 12%. Fibrillation seems to be associated with a "long-short" atrial sequence. If the mechanism of PSVT is unknown and the Wolff-Parkinson-White syndrome is possible, administration of adenosine should be limited to medical facilities that have emergency resuscitation equipment.

Adenosine↗
PubMed1997

A prospective evaluation of catheter ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an implantable cardioverter-defibrillator.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies. METHODS AND RESULTS: Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69+/-6 years, and 17 were men. The mean ejection fraction was 0.22+/-0.08, and all patients had coronary artery disease. During the 36+/-51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34+/-55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25+/-88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4+/-0.6 (range, 1 to 3) ablation procedures and required 12.5+/-9.2 applications of energy. During 11.8+/-10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60+/-80 before successful ablation to 0.1+/-0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9). CONCLUSIONS: Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.

Aged↗
PubMed1997

Cost comparison of radiofrequency modification and ablation of the atrioventricular junction in patients with chronic atrial fibrillation.

BACKGROUND: Because it is not clear which technique is less expensive, the purpose of this study was to compare the cost of radiofrequency modification and ablation of the atrioventricular (AV) node in drug-refractory patients with atrial fibrillation and an uncontrolled ventricular rate. METHODS AND RESULTS: The initial nominal charges for a successful procedure were compared in 10 patients with chronic atrial fibrillation who underwent modification of the AV node ($13 109+/-2002) and 14 similar patients who underwent ablation and pacemaker implantation ($28 302+/-2023, P<.001). On the basis of the long-term follow-up of patients who underwent each procedure, it was assumed that 31% of patients selected for the modification procedure would require a permanent pacemaker for inadvertent AV block or because of AV nodal ablation after a failed modification procedure and that the recurrence rate after AV node ablation would be 2%. The annual charges during follow-up were predicted and adjusted for recurrences and the need for additional procedures. The adjusted total charges at 1 year of follow-up were significantly lower for the modification procedure ($19 389+/-2002) than for the ablation procedure ($28 485+/-2023, P<.001). After 10 years of follow-up, the cumulative, adjusted charges for modification were $20 016 (42%) less than for ablation. CONCLUSIONS: The initial charges generated by AV node modification are significantly lower than for AV node ablation in patients with chronic atrial fibrillation. Even when adjusted for higher failure and recurrence rates, the modification procedure retains a major cost advantage over ablation during long-term follow-up.

Aged↗
PubMed1997

Effect of verapamil and procainamide on atrial fibrillation-induced electrical remodeling in humans.

BACKGROUND: Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling. METHODS AND RESULTS: In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil). CONCLUSIONS: Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

Adult↗
PubMed1997

Probability of successful defibrillation at multiples of the defibrillation energy requirement in patients with an implantable defibrillator.

BACKGROUND: The probability of successful defibrillation has been determined in normal animals but not in patients undergoing defibrillator implantation. Therefore, the purpose of this prospective study was to determine the probability of successful defibrillation in humans on the basis of a step-down defibrillation energy requirement. METHODS AND RESULTS: Fifty-three consecutive patients underwent five separate inductions of ventricular fibrillation after the defibrillation energy requirement was determined with the use of small decrements and a step-down protocol (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, and 0.8 J). The first shock energy for defibrillation was either 1.0, 1.3, 1.5, 1.7, or 2.0 times the defibrillation energy requirement, and the likelihoods of successful defibrillation were 70+/-27%, 84+/-12%, 86+/-25%, 80+/-29%, and 88+/-32%, respectively (P=.03). The frequencies of uniformly successful defibrillation (5 of 5 defibrillation attempts) were 30%, 27%, 60%, 64%, and 73%, respectively (P=.01). Seven patients in whom the defibrillation energy requirement was <4 J had an overall rate of successful defibrillation of 54+/-20% compared with 86+/-20% in the remaining 47 patients (P=.002). The likelihood of successful defibrillation at twice the defibrillation energy requirement was 98% in the 46 patients with a defibrillation energy requirement of >4 J and 67% in the 7 patients with a defibrillation energy requirement of <4 J (P=.17). An absolute safety margin of 7 J was associated with a 96% probability of successful defibrillation. CONCLUSIONS: The probability of successful defibrillation is 70% at the defibrillation energy requirement. The probability plateaus at 88%, at twice the defibrillation energy requirement. A 96% probability of successful defibrillation is achieved at an absolute safety margin of 7 J, and a 98% success rate is achieved at energies that are twice the defibrillation energy requirement if the defibrillation energy requirement is >4 J. If the defibrillation energy requirement is <4 J, larger multiples of the defibrillation energy requirement are needed to achieve a high probability of successful defibrillation.

Arrhythmias, Cardiac↗