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Of 67 patients with reciprocal atrioventricular (A-V) nodal tachycardia consecutively studied by programmed electrical stimulation of the heart, nine patients showed second degree block toward the ventricle and one patient toward the atrium during tachycardia. In four patients the occurrence of block was critically related to the prematurity of the test stimulus initiating the tachycardia. In three patients block developed following increase in rate of tachycardia. In two patients block could be elicited by introducing premature ventricular stimuli during tachycardia. Our observations indicate that different mechanisms may be responsible for second degree block during reciprocal supraventricular tachycardia. The finding of second degree block during reciprocal supraventricular tachycardia excludes a tachycardia with A-V conduction over the A-V node - His pathway and V-A conduction over an accessory A-V pathway.

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Background-ENTIRE-TIMI 23 evaluated enoxaparin with full-dose tenecteplase (TNK) and half-dose TNK plus abciximab. Methods and Results-Patients (nϭ483) with ST-elevation MI presenting Ͻ6 hours from symptom onset were randomized to full-dose TNK and either unfractionated heparin (UFH) (bolus 60 U/kg; infusion 12 U/kg per hour) or enoxaparin (1.0 mg/kg subcutaneously every 12 hoursϮinitial 30 mg intravenous bolus), or half-dose TNK plus abciximab and either UFH (bolus 40 U/kg; infusion 7 U/kg per hour) or enoxaparin (0.3 to 0.75 mg/kg subcutaneously every 12 hoursϮinitial intravenous bolus of 30 mg). With full-dose TNK and UFH, the rate of TIMI 3 flow at 60 minutes was 52% and was 48% to 51% with enoxaparin. Using combination therapy, the rate of TIMI 3 flow was 48% with UFH and 47% to 58% with enoxaparin. The rate of TIMI 3 flow among all UFH patients was 50% and was 51% among enoxaparin patients. Through 30 days, death/recurrent MI occurred in the full-dose TNK group in 15.9% of patients with UFH and 4.4% with enoxaparin (Pϭ0.005). In the combination therapy group, the rates were 6.5% with UFH and 5.5% with enoxaparin. The rate of major hemorrhage with full-dose TNK was 2.4% with UFH and 1.9% with enoxaparin; with combination therapy, it was 5.2% using UFH and 8.5% with enoxaparin. Conclusions-Enoxaparin is associated with similar TIMI 3 flow rates as UFH at an early time point while exhibiting advantages over UFH with respect to ischemic events through 30 days. These findings with enoxaparin are achieved with a similar risk of major hemorrhage.