Surgical division of Wolff-Parkinson-White pathways utilizing the closed-heart technique: a 2-year experience in 47 patients

Kent bundle interruption for ventricular preexcitation has been successfully accomplished utilizing several different surgical techniques. The external closed-heart technique of Guiraudon combining surgical dissection and cryoablation has been used to interrupt 52 accessory pathways in 47 consecutive patients since May, 1985. The 35 male and 12 female patients ranged in age from 10 to 67 years (mean, 30 years). There were 25 left free wall, 13 right free wall, 13 posterior septal, and 1 anterior septal accessory pathways. Preoperative and intraoperative electrophysiological studies were performed in all patients to induce the arrhythmia and localize all accessory pathways. The operation consisted of dissection of the atrioventricular fat pad. Following this, the delta wave and retrograde accessory pathway conduction disappeared, thereby indicating successful pathway ablation. In 4 patients with right-sided accessory pathways, interruption of the pathway required cryoablation. Cryolesions (made with cryoprobe at -60 degrees C for two minutes) were created in the region of the accessory pathway insertion. All accessory pathways were successfully ablated without any deaths or heart block. Concomitant surgical procedures were performed in 4 patients. Two patients required a second operation the next day for an accessory pathway not found at the initial operation. Three patients had postpericardiotomy syndrome, and 4 had recurrent atrial fibrillation requiring therapy. The remaining patients have had no arrhythmia recurrence and have remained drug free after a follow-up of 1 month to 22 months (mean, 12.5 months). We conclude that the closed-heart technique of accessory pathway ablation is safe and reproducible, obviates the necessity for aortic cross-clamping and cardioplegic arrest, and allows instantaneous monitoring of conduction over the pathway.     

Organisation of common inputs to motoneuron pools of human masticatory muscles.

OBJECTIVE: To determine the pattern of organization of common inputs to the motoneuron pools of individual muscles in the masticatory system. METHODS: Six subjects bit on a rubber-coated wooden splint placed between the upper and lower incisor teeth. We recorded the surface electromyogram (EMG) of co-contracting masseter, temporalis and digastric muscles bilaterally during isometric jaw closing at 5%, 10%, 20% and 40% of maximal voluntary masseter EMG. RESULTS: The cross-correlograms of the EMGs of homologous muscle pairs indicate that there are common synaptic inputs to the motoneuron pools of the left and right masseter, and left and right digastric muscles, but not to left and right temporalis. The amplitude of the central peak in masseter and digastric correlograms increased with bite force. When the activity of ipsilateral muscle pairs was cross-correlated, central peaks were prominent for masseter-digastric and masseter-temporalis muscle pairs, and the peak amplitudes increased significantly with bite force. In contrast, no significant central peak was observed for temporalis-digastric muscle pairs at any level of voluntary biting. CONCLUSIONS: We conclude that there is synchronous modulation of input bilaterally to the masseter muscles and to the digastric muscles but not to the temporalis muscles. There is synchronous modulation of input to ipsilateral masseter-digastric and masseter-temporalis muscle pairs but not to temporalis and digastric muscles. SIGNIFICANCE: The extent of common input to motoneuron pools of muscles acting around a common joint varies for different muscle pairs, and is not simply a function of whether the muscles of the pair are synergists or antagonists.     

Emergence of disinhibition-induced synchrony in the CA3 region of the guinea pig hippocampus in vitro

Suppressing inhibition mediated by GABA_A receptors induces rhythmic bursts of synchronous firing in the CA3 region of the hippocampus. Extracellular and intracellular records were made from guinea pig hippocampal slices to examine the emergence of this synchrony. We found that application of GABA_A receptor antagonists initiated a sequence of changes in the activity of the CA3 neuronal population. First, the frequency of firing detected in multiunit records increased. Then, firing began to oscillate with increases followed by decreases in firing that occurred at intervals of 0.5–2 s. The coherence of the rhythmic activity at a single site increased with time, and discharges at distant sites in the CA3 region became correlated. Fluctuations in firing were associated with extracellular field potentials. Finally, epileptiform events associated with large field potentials began to recur at intervals of 5–10 s. The onset of fully synchronous events was sudden and correlated with a large increase in the amplitude of the field potential. Thus the CA3 population can express states of partial population synchrony preceding the onset of epileptiform discharges. A similar activity was induced and maintained by applying low doses of GABA_A receptor antagonists. Intracellular records suggest that inhibitory signalling mediated by GABA_B receptors contributes to the emergence of this activity. States of partial synchrony in the CA3 region exposed to GABA_A receptor antagonists therefore depend on alternating periods of firing, presumably dependent on excitatory synaptic mechanisms, and silence, mediated in part by the activation of GABA_B receptors.     

The use of regional, low dose streptokinase in recently thrombosed arterial grafts

Between August 1983 and January 1985, 20 patients aged 33-77 years, with occluded lower limb bypass grafts, were on 23 occasions treated with streptokinase via intra-arterial infusion. Streptokinase (5000 units/h) was effective in clearing occluded grafts in 15 patients on 16 occasions. The median duration of occlusion in these patients was 5 days and the median duration of streptokinase infusions was 24 h. Completion angiography following streptokinase thrombolysis revealed five graft stenoses and 12 outflow stenoses or occlusions. In two grafts no cause for graft failure could be identified. These results permitted the surgeon to make an accurate pre-operative assessment of the definitive therapy required to ensure graft patency.     

The combined effects of hypoxemia and mechanical ventilation on renal function

The combined effects of hypoxemia and mechanical ventilation on renal function were investigated in anesthetized dogs. Spontaneously breathing dogs (S) and dogs mechanically ventilated with a volume-ventilator (V) were made hypoxemic by breathing hypoxic gas to achieve PaO2 values of 35 and 22 mm Hg. At a PaO2 of 35 mm Hg, urine output and sodium excretion were increased in both groups. These responses closely followed the blood pressure response, which was greater in the V group. Renal blood flow (RBF), glomerular filtration rate (GFR), and fractional sodium excretion (FNA) were unchanged. At a PaO2 of 22 mm Hg, both groups demonstrated a reduction in urine flow, sodium excretion, FNA, RBF, and GFR. However, the mechanism involved was different and ventilator-dependent. At this low PaO2, arterial blood pressure was reduced in the S group with no change in renal resistance, while blood pressure increased in the V group with a marked increase in renal resistance as a result of the modification of the cardiovascular effects of lung inflation reflexes by mechanical ventilation. These results indicate that renal function is well-maintained at low PaO2 values (35 mm Hg) and reduced at more severe hypoxemia, mainly in response to systemic hemodynamics.     

Accelerated polymerization of acrylic bone cement using preheated implants

This article is an account of a procedure to accelerate polymerization of polymethylmethacrylate during total hip arthroplasty by preheating the stem of the femoral prosthesis. The increased temperature is shown to have a definite beneficial effect with regard to accelerated polymerization. Experimental investigations are presented to verify this supposition.