New findings promise to have an impact on a range of areas in medicine, including sudden cardiac death (SCD) risk stratification. In this article we learn about PD2i technology, which uses a special algorithm to analyze 15 minutes of ECG data to predict SCD.

Tell us about the PD2i technology (including the differences between the PD2i Analyzer, PD2i VS, and PD2i CA).

PD2i is a measure of the degrees of freedom of one’s heart rate variability. This analysis can be used for different applications: measuring autonomic activity (PD2i Analyzer), assessing the need for an immediate life-saving intervention in trauma (PD2i Vital Sign, or PD2i VS), and predicting one’s risk of cardiac arrest/sudden cardiac death (PD2i CA).

Describe some of the research that has been done so far.

Intuitively it is known that the brain influences the heart rate. After all, we know our hearts can begin to race in concert with emotional highs and lows, and there are well known data regarding increased patient mortality in depressed or emotionally stressed patients. However, scientists have taken this understanding a step further.

First, in the swine model, Vicor’s director of research and development James Skinner, PhD traced the cardiac innervation back to the brain in normal animals and found that if he stimulated along that tract, even as high up as its origin in the mesial frontal cortex, he could induce ventricular arrhythmias and ventricular fibrillation (VF) in animals with normal hearts. Conversely, if he severed all nerve connections, he could even tie off the left anterior descending artery and cause an acute myocardial infarction — a maneuver that causes VF frequently in pigs — and would never get VF. This suggested to him that while, clearly, VF occurs in the heart, it is initiated by the brain. In fact, recent human clinical data seems to confirm this. The National ICD Registry data has shown that >75% of patients who receive prophylactic ICDs based upon the combined MADIT II/SCD-HeFT criteria, which are in turn based upon having a cardiomyopathy, have never needed the ICD to fire for VT/VF. Conversely, it has been known for some time that almost 80% of people who have had SCD would not have met those implant criteria (i.e., they did not have a cardiomyopathy). All these data point to the fact that having a “bad heart” is neither necessary nor sufficient to produce VF. It is no wonder the situation of SCD risk stratification has recently been described as being in “disarray” by a growing number of cardiologists and electrophysiologists. Existing risk stratification technologies have been hampered by inadequate sensitivity and specificity, difficulty in performing tests, or both.

Give us some background information about the creation of the PD2i technology. How did the PD2i come about?