Please click here to obtain permission to reproduce this image.
Click on image to view larger version.
Figure 1 Two distinct AV pathways are present in mutant transgenic mice. (A) Electrocardiographic leads I, II (LI and LII), and aVF are shown, as well as the His-bundle electrogram (HBE). Atrial pacing at 110 ms with conduction down the bypass tract for the first five beats and fusion of atrial (A) and ventricular (V) intracardiac electrograms on the HBE. The sixth beat (arrow) and subsequent beats conduct with a longer PR interval and narrower QRS complex, suggesting block in the bypass tract and conduction down the AV node. Note separation of the atrial and ventricular electrograms on the HBE and the presence of a His potential (HIS). (B) The left panel displays ECG leads I, II, and aVF, as well as the HBE, and shows a premature atrial extrastimuli (S2) delivered at a coupling interval of 105 ms and a drive train (S1) at 150 ms. All three beats conduct with a short PR interval and wide QRS complex, suggestive of manifest pre-excitation down an accessory AV pathway. The middle panel displays the same electrograms, with the premature atrial extrastimulus coupled at 100 ms. The first two beats conduct with a short PR interval and wide QRS complex, but the atrial extrastimulus conducts with a longer PR interval and narrow QRS complex, and the A and V electrograms are separated by a clear HIS. This indicates that the accessory pathway is refractory and conduction is via the AV node. The right panel displays the same electrograms in another mouse, with the atrial extrastimuli coupled at 75 ms to the drive train at 150 ms. The first two beats and atrial extrastimuli conduct with a short PR interval and wide QRS complex; on the HBE, there is fusion between the A and V electrograms, suggesting conduction down the accessory AV connection. The last beat is followed by retrograde atrial depolarization (Echo), with a long VA time, suggesting retrograde conduction up the AV node.
|
