It is not generally believed that there is a relation between atrial flutter, thought to be due to a single reentrant circuit, and atrial fibrillation, thought to be due to simultaneously circulating multiple-reentrant wave fronts. However, there are many reasons to suggest that these rhythms are more closely related than previously thought. To test the hypothesis that the length of an area of functional block in the right atrial free wall is critical to the conversion of atrial flutter to atrial fibrillation and of atrial fibrillation to atrial flutter, we studied spontaneous and ATP-induced conversion of stable atrial flutter to sustained atrial fibrillation and spontaneous conversion of sustained atrial fibrillation to stable atrial flutter. We studied 13 episodes of the conversion of stable atrial flutter to sustained atrial fibrillation and sustained atrial fibrillation to stable atrial flutter in seven dogs with sterile pericarditis. Six episodes were spontaneous and seven were ATP related. All episodes were studied by using a multisite mapping system to record 190 unipolar electrograms (converted in the software to 95 bipolar electrograms) from the right atrial free wall along with ECG lead II. Atrial flutter induction was attempted by atrial stimulation (S1S2 or S1S2S3) or by rapid atrial pacing for > or = 20 beats from selected sites at selected rates. For both the spontaneous and the ATP-related episodes, stable atrial flutter was defined as any episode of > or = 5 minutes, and sustained atrial fibrillation was any episode of > or = 1 minute. During all the episodes of stable atrial flutter, a line of functional block with a mean length of 24 +/- 4 mm was localized on the right atrial free wall. When the previously stable line of functional block decreased to a mean of 16 +/- 3 mm (P < .05), either spontaneously or after ATP administration (40 mg i.v.), the new line of functional block was not long enough to maintain stable atrial flutter, and conversion to atrial fibrillation resulted. This shortened line of functional block continued to change and migrate over the right atrial free wall throughout sustained atrial fibrillation. These observations were similar for both spontaneous and ATP-induced conversions. When sustained atrial fibrillation evolved to stable atrial flutter, there was reformation of a long line of functional block, long enough (> or = prior length) to create a stable reentrant circuit, which then captured the right atrial free wall and subsequently both atria.(ABSTRACT TRUNCATED AT 400 WORDS)

Objective: To determine accuracy of the 7-8-9 Rule in a cohort of neonates.Study Design: This study was cross-sectional in design. Seventy-five consecutive neonates who required oral intubation from June 2004 to November 2004 for cardiopulmonary failure, respiratory distress, or surfactant administration were the subjects of this study. The initial endotracheal tube (ETT) depth of insertion was determined using either an estimated birth weight or actual weight in the 7-8-9 Rule calculation followed by auscultation and subsequent adjustment if necessary. Midtracheal position was identified as the point halfway between the inferior clavicle and carina on a chest radiograph. The initial depth was compared to the midtracheal depth to determine clinical accuracy of the 7-8-9 Rule. The depth predicted by the 7-8-9 Rule was also calculated using only actual weights. This predicted depth was compared to the midtracheal depth to determine true accuracy of the 7-8-9 Rule. Accuracy was determined using mean paired differences with 95% confidence intervals (CI) between initial or predicted depth and ideal, midtracheal ETT depth. Linear regression was used to adjust for confounding variables.Results: Mean (range) gestational age was 32 weeks (23 to 44 weeks) and weight was 2001 g (490 to 4400 g). Eighteen (24%) infants weighed 1000 g or less, 20 (27%) weighed between 1001 and 2000 g, 21 (28%) weighed between 2001 and 3000 g, 15 (20%) weighed between 3001 and 4000 g, and one (1%) weighed more than 4000 g. Thirteen of the 18 extremely low birth weight infants weighed <750 g. The initial depth of insertion was 0.004 cm above midtracheal position (95% CI À0.13 to 0.14, P ¼ 0.96). After controlling for head position, the initial depth did not significantly differ from the midtracheal position among weight groups. Predicted depth using the 7-8-9 Rule placed the ETT 0.12 cm above midtracheal position (95% CI À0.30 to 0.06, P ¼ 0.20). However, after controlling for head position, the 7-8-9 Rule positioned the ETT significantly below midtracheal position in infants weighing <750 g (mean 0.62 cm; 95% CI 0.30 to 0.93, P ¼ 0.002). Conclusions:The 7-8-9 Rule appears to be an accurate clinical method for endotracheal tube placement in neonates weighing more than 750 g. When the 7-8-9 Rule is applied to infants weighing <750 g, caution is warranted. The current rule may lead to an overestimated depth of insertion and potentially result in clinically significant consequences.

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