Its strength again is its negative predictive value being able to exclude sustained VT or VF from the etiology of the syncope. A normal study does not eliminate sustained VT as a cause of syncope if the arrhythmia is from an automatic focus and therefore does not preclude the indication for EP testing in patients with unexplained syncope. However these are of questionable success. Differing lead placement and filtration techniques can result in differing test results. VLPs can disappear if the same data is reprocessed at a higher filter frequency.
False negatives can also occur when the ventricular arrhythmia is due to triggered automaticity.
False positives may sometimes due to detection of delayed ventricular activation that is inadequate to complete a reentrant circuit or not an adequate trigger to set off the arrhythmia. All drugs that slow conduction and prolong QRS may also prolong VLPs. Even with EP guided effective antiarrhythmic therapy, VLPs may not be abolished. Detection of those prone to exercise induction of lethal arrhythmias is very important. The knowledge of their presence in patients without MI has not as yet been overwhelmingly helpful.