Page 13 - VetCPD Jnl Volume 7, Issue 4

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Figure 1: 6-lead ECG (10mm/mV; 50 mm/s) showing atrial fibrillation with intermittent aberrant conduction. The wide and bizarre complex (9th complex) is preceded by a short R-R interval that follows a long R-R interval. This is likely a supraventricular complex conducted through the ventricles with aberrancy, rather than a ventricular premature complex. This is called “Ashman phenomenon” and occurs because the myocardial refractory period is proportional to the R-R of the preceding cycle (i.e. a long R-R interval prolongs the refractory period; if a short R-R interval follows, the right bundle branch - which has longer refractory periods than the left bundle branch - will likely still be recovering when reached by the impulse; this will therefore be conducted slower than normal, originating a QRS complex with a right bundle branch
block morpholo
gy). Alternative
ly, this ectopic
complex may be
a ventricul
ar premature
complex.
Only
Figure 2: 6-lead ECG (10mm/mV;50 mm/s) showing fast atrial fibrillation with a ventricular rate of approximately 220 bpm. Please note the irregular R-R intervals, lack of P waves, tall and narrow QRS and f waves (mainly seen during the longer R-R intervals).