Intraventricular conduction delay laboratory findings

Electrophysiological testing help localize the site of conduction delay or block within the conduction system of the ventricles.

• Electrophysiological testing help localize the site of conduction delay or block within the bundle of His by recording distal, middle, and proximal HB potentials using multipolar catheters to.
• His-ventricular HV interval longer than 70 milliseconds predicts a higher risk of AV block, especially in symptomatic patients.
• An HV interval exceeding 100 milliseconds identifies a group of patients at a very high risk of AV block.
• In the presence of RBBB with or without additional fascicular block, the HV interval should be normal as long as conduction is unimpaired in the remaining fascicle.

The administration of procainamide known to impair the HPS can unmask extraordinary sensitivity to the usual therapeutic doses of the drug, which can itself indicate poor HPS reserve. In normal procainamide typically produces a 10% to 20% increase in the HV interval. Abnormal HV interval responses to procainamide representing evidence of a higher risk for infra-Hisian AV block include any of the following:

• doubling of the HV interval
• prolongation of the HV interval to more than 100 milliseconds
• second- or third-degree infra-Hisian block

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