A Continuous Lead II Rhythm Strip (25 mm/S) Recorded from a Dog With Sick Sinus Syndrome Showing an Ectopic Atrial Rhythm Interrupted by Several Short Pauses. The Third Pause Initiates a Paroxysm of Supraventricular Tachycardia (250 beats/Min) Followed by Asystole (6.6 S) Terminated by a Junctional Escape Complex.