“Vicor has published clinical trial data using the PD2i® non-linear algorithm as a predictor of cardiac death, showing it to be highly accurate, with a sensitivity approaching 100 percent and a specificity of approximately 86 percent. All that is required to conduct the analysis is a recording of a thousand heartbeats in sinus rhythm — approximately 20 minutes of ECG at resting heart rates. The algorithm can use recordings made at rest and is relatively impervious to noise and non-stationarities in the data. This has helped set it apart from other nonlinear measures and seems to account for its unparalleled accuracy.”
Vicor’s PD2i® Nonlinear Algorithm — An Overview
Recently cleared by the U.S. Food and Drug Administration as a measure of heart rate variability (HRV), Vicor’s PD2i® nonlinear algorithm evaluates the neurological relationship between the heart and brain. It does this by measuring the degrees of freedom of the variability of a patient’s heart rate.
Since several sensory-motor loops such as temperature, pH, baroreceptor reflex and others have been found to control heart rate, Vicor Chief Scientist Dr. James Skinner determined that the degree of cooperation between those loops is reflected in the degrees of freedom of the heart rate’s variability — a phenomenon caused by the brain’s influence.
In healthy individuals, these loops tend to work in opposition and more or less independently. But when the loops begin to coordinate to a high degree, paradoxically, it’s a sign that the body is not doing well and that the brain is “marshaling the forces” to work together to keep the body alive. Yet this “hyper‑coordinated” condition is not sustainable and can lead to ventricular tachycardia, ventricular fibrillation, and cardiac death.
Knowing the degrees of freedom may permit far more accurate evaluation of near-term risk of cardiac death than previously possible. Dr. Skinner developed the PD2i® nonlinear algorithm and software to precisely calculate the degrees of freedom, even in the presence of data issues that confound other methods. And the PD2i® result is extremely easy to interpret.
Several applications are in the process of being commercialized. The PD2i Analyzer™ measures heart rate variability and is expected to identify patients with autonomic nervous system dysfunction. The PD2i CA™ is anticipated to risk-stratify probability of cardiac death from arrythmia or pump failure. And the PD2i VS™ is expected to help triage trauma victims. Vicor has already received FDA 510(k) marketing clearance for the PD2i Analyzer™. Current procedural terminology (CPT) codes for reimbursement for the measure of heart rate variability are already established. Vicor anticipates receiving FDA 510(k) marketing clearance in 2010 for the PD2i CA™ and PD2i VS™; additional applications are being studied.
The PD2i® traces in the top file were taken from a healthy subject. The PD2i® traces in the bottom file were taken from a patient who went on to suffer ventricular tachycardia/fibrillation. The bottom file shows repeated low-dimensional excursions below PD2i® ≤1.4. (When risk-stratifying cardiac death, PD2i® ≤1.4 appears to be the cut off between a normal and abnormal result.)
More Accurate than Conventional Diagnostics
Conventional diagnostics, which only evaluate the heart, are of limited use in risk-stratifying imminent cardiac death. Their inadequacy is demonstrated by the fact that under current implantation guidelines, more than 20 ICDs must be implanted to save a single life. Of greater concern, nearly 80 percent of those do die from cardiac death would not qualify for implantation under current criteria. Clearly, a superior diagnostic is long overdue.
The PD2i® test may be that diagnostic.
The following example is a case in point. Both patients below meet current implantation guidelines. But which will die without an ICD?
The ECG for Patient 032 (above left) is typical by current interpretations. Conversely, the ECG for Patient 160 (above right) is grossly abnormal by current interpretations. Relying on the above tracings, a physician might well recommend “watchful waiting” for Patient 032 and ICD implantation for Patient 160.
In contrast, PD2i® testing correctly indicated both Patient 032’s imminent cardiac death and Patient 160’s lack of risk:
Unlike the ECGs, the PD2i® nonlinear algorithm correctly predicted that Patient 032 was in need of an ICD, and that Patient 160 required no intervention.
In summary, the PD2i® nonlinear algorithm, as demonstrated by this example, should reduce both false positives and false negatives; indications for who does and who does not need an ICD.
A Valuable Addition to Medical Practices
The PD2i® test offers several advantages over competing diagnostics:
- more predictive than competing tests
- non-invasive
- performed by nurse or technician on resting patient
- uses inexpensive, non-proprietary EKG electrodes
- result available in less than twenty minutes
- easy to use
- yields a simple binary result
- compact; no treadmill required
- forgiving of data issues plaguing other diagnostics; not derailed by irregular or ectopic beats
- can be performed on patients taking beta-blockers
- low up-front cost, low cost per test
Research Inquiries Welcome
Vicor’s PD2i® nonlinear algorithm is potentially applicable to any stream of biological data and offers unprecedented real-time insight into autonomic activity, and the interaction between the heart and brain. Data collection is simple, quick, non-invasive, performed at rest, does not require data stationarity, and can be done in‑field.
Vicor is currently involved in collaborative research efforts with the U.S. Army Institute of Surgical Research (USAISR), the Catalan Institute of Cardiovascular Science, the University of Rochester, the renowned Dr. Alfred Buxton, and the University of Mississippi in both prospective and retrospective trials.
If you are a researcher interested in using the PD2i® nonlinear algorithm in a study or applying it to an existing dataset, please contact us.
