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Arrhythmia Mechanisms - Focal Tachycardias

Focal Tachycardia

          "Automaticity is the property of cardiac cells to undergo spontaneous diastolic depolarization and initiate an electrical impulse in the absence of external electrical stimulation". - quote from Cardiac Electrophysiology - From Cell to Bedside, 3rd edition Zipes / Jalife


Identifying Characteristics

          One of the indications that a tachycardia may be focal in nature may be found in the consistency of the cycle length. As focal tachycardias are generated due to an abnormlity of automaticity, they often display changes in rate that are not found in reentry arrhythmias. This phenomenon is referred to as "ramping up" or "ramping down", depending upon whether or not the arrhythmia is accelerating at the onset or decelerating to termination.

          While the effect is not always visualized, if you do see ramping up or ramping down, this is an excellent indication that you are dealing with a focal tachycardia.

          This RVOT tachycardia demonstrates ramping down. The interval between the first two depolarizations measures at 380ms. This decreases to 400, then to 420, 450 and then 550ms where the run terminates.

          In sustained runs, both ramping up and ramping down may be noted during a single tachycardia. Ramping up will occur at the onset and ramping down at the termination of the arrhythmia. Keep in mind that you can have an arrhythmia without rate changes of this nature, it may still be a focal tach. If, however, you do see this phenomenon, it indicates that you are almost certainly dealing with a focal tach.

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