Wedensky Modulation™
Wedensky™

Harbinger’s system evaluates cardiac electrical vulnerability by analyzing the changes in a patient’s myocardial tissue caused by sub-threshold stimulation during both depolarization (R-wave) and repolarization (T-wave) of the cardiac cycle. Like an electrocardiogram, the Harbinger system can be used regardless of a patient’s physical health and concurrent medical treatments. The Harbinger system provides the Wedensky Modulation Index (WMI) score, which is a number between 0 and 1 that provides clinicians with the ability to interpret a patient’s risk and determine an appropriate course of action.

The science behind the Harbinger tests, Wedensky modulation, is based on the fact that sub-threshold stimulation does not cause muscle contraction, but does impact the electrical conduction of the muscle. The Harbinger system measures this electrical conduction change, or modulation. Clinical studies like the HIP study have demonstrated that limited modulation is associated with potentially lethal arrhythmic risk.

To identify this electrical conduction change, the Harbinger system delivers sub-threshold electrical pulses to every other cardiac cycle (heart beat) via a patented orthogonal lead system. The three dimensional heart wave morphology changes are captured in high resolution ECG recording as a result of this stimulation. It is believed these changes are less apparent in patients with elevated risk for ventricular arrhythmias because their myocardial tissue is compromised, as shown by its limited response to sub-threshold stimulation. The Harbinger system reports these differences as a weighted index between 0 and 1 called the Wedensky Modulation Index (WMI), which provides a measure of risk stratification for a life-threatening arrhythmia.

The WMI index is computed by comparing QRS complexes from 400 consecutive heart beats: 200 sub-threshold stimulated heart beats and 200 non-stimulated heart beats that are used as reference. The ECG signals from the stimulated QRS complexes and the non-stimulated QRS complexes are separated into two groups, and each group is broken down into its time/frequency components, which are each represented by a wavelet surface (see the figure below). The WMI is based on the differences between these wavelet surfaces. The figure below shows two case studies where the reference and stimulated wavelet surfaces are displayed.

The Harbinger WMI score is assessed by subtracting the QRS complexes from stimulated heart beats from the QRS complexes of non-stimulated heart beats. This is illustrated in the figure below showing the results after subtraction of the two cases shown above. On the left side, a patient with a history of ventricular arrhythmia is shown. Almost no signal is left after the subtraction due to the fact that the Wedensky effect is attenuated in the patient’s myocardial cells. The healthy control subject to the right experienced the Wedensky effect upon stimulation and a strong signal is seen after the subtraction. In the case below, the WMI score for the patient with the ventricular arrhythmia history was .74, while the WMI score for the healthy control patient was .18.

Harbinger clinical studies have shown a statistical relationship between an index greater than 0.5 and future arrhythmic risk. This suggests that such patients receive aggressive preventive treatment. Harbinger has the ability to analyze the heart’s electrical conduction during depolarization (R-wave), during repolarization (T-wave), as well as for both depolarization and repolarization (R- and T-wave). Harbinger believes the WMI score will become the gold standard for SCD risk stratification in the near future.