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).(ABSTRACT TRUNCATED AT 250 WORDS)

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SUMMARY As echocardiography is being used more often, its value and accuracy are becoming more fully appreciated. Coincident with wider application of this imaging technique is the potential for identifying normal anatomic variants and their possible erroneous interpretation as pathologic states. In this report we describe the M-mode and two-dimensional echocardiographic features of a congenital remnant known as the Chiari network. This structure can present as a highly mobile, highly reflectant echo target that can be seen in several locations in the right atrium. We report here an index case that could be well examined echocardiographically and that was a cause of considerable concern due to the presence of congestive heart failure and a history of staphylococcal endocarditis. The presence of the Chiari network was confirmed pathologically. Subsequently, we found similar echocardiographic findings in 19 of 1248 patients (1.5%) studied in our laboratory. This congenital remnant, which is found pathologically in 2-3% of normal hearts, could be confused with valve disruption, vegetation or other mass lesion, particularly when associated with a suggestive clinical situation.M-MODE and two-dimensional echocardiography have gained wide acceptance for providing safe, repeatable and accurate diagnostic information in a variety of complicated clinical situations. Suspicion of valvular heart disease, particularly infection of the valves, represents an important indication for echocardiographic examination.1 2 Increasing experience with these techniques has allowed a better, and in some cases new, appreciation of normal and abnormal cardiac anatomy, motion and structural relationships.3 These include structures often described at cardiac surgery or at postmortem examination, but not previously demonstrable in ambulatory patients. We describe the echocardiographic appearance of the Chiari network, a not uncommon anatomic finding that might be considered a "normal variant."4 This structure, particularly in the setting of fever, congestive heart failure, pulmonary infiltrates and a history of i.v. drug abuse, could be mistaken for evidence of active infection or disruption of normal right-sided structures, possibly requiring urgent cardiac surgery. Materials

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Background-The first Björk-Shiley convexoconcave (BSCC) prosthetic heart valves were implanted in 1978. The 25th anniversary provided a stimulus to summarize the research data relevant to BSCC valve fracture, patient management, and current clinical options.

Factors affecting bubble formation during delivery of defibrillator pulses to arrhythmogenic cardiac tissue via a catheter are unknown. We investigated the role of energy, electrode surface area, interelectrode distance, and electrode polarity on bubble formation and on current and voltage waveforms during delivery of damped sinusoidal discharges from a standard defibrillator to anticoagulated bovine blood. Gas composition was studied with mass spectrometry. Defibrillator energy settings were varied between 5 and 360 J. The principal catheter used for study was a Medtronic 6992A lead. Additional electrodes tested included 2, 5, and 10 mm long No. 6F, 7F, and 8F copper electrodes.Interelectrode distances used to assess the effect of anode-cathode spacing were 1, 5, 10, and 20 cm. Bubble volume increased linearly from 0.043 to 0.134 ml per cathodal pulse and from 0.030 to 3.50 ml per anodal pulse as energy settings were increased from 5 to 360 J (r = .99). Typical smooth waveforms for both current and voltage were seen only in the absence of bubbles. The voltage waveform was distorted for each cathodal pulse of 100 J or more and for each anodal pulse of 10 J or more only if bubbles were present. The effect of electrode surface area on bubble formation was tested at a 200 J energy setting and at a 10 cm interelectrode distance with the use of cathodal pulses. Bubble formation varied inversely with electrode surface area (r = .876). Bubble formation, however, varied minimally as interelectrode spacing was changed from 1 to 20 cm. The effect of polarity on bubble formation when the Medtronic 6992A distal electrode and an 8.5 cm disk electrode separated by 10 cm were used was highly significant. For a 200 J pulse, bubble formation with the catheter as anode was 3.30 + 0.10 ml and with the catheter as cathode it was 0.070 + 0.002 ml (p < .001). Mass spectrometry of both anodal and cathodal gas samples demonstrated the constituents of the gas bubble to include a variety of gases, which is inconsistent with simple electrolytic production of the bubbles observed. The predominance of nitrogen in either polarity sample suggested that the principal source of the bubble was dissolved air. In summary, bubble formation at an electrode receiving damped sinusoidal outputs from a standard defibrillator does not vary significantly with varying interelectrode distance. However, it is directly proportional to energy and inversely proportional to electrode surface area. Anodal catheter discharges produce considerably more bubbles than do cathodal discharges. Distortions in the voltage waveform correlate with physical factors leading to high-pressure shockwave generation and to subsequent extrusion of dissolved gases from solution. Circulation 73, No. 3, 525-538, 1986.

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These preliminary results of continuous infusion of cefuroxime 3 g/d for prophylaxis of sternal wound infections in CABG patients indicate that serum concentrations are highly variable, but reliably above the minimum inhibitory concentration for the common anticipated pathogens in this setting. Further comparative trials in a larger number of patients are necessary before this mode of administration can be routinely advocated for prophylaxis.