Differences measured by the ECG
After successful transplantation, the electrical conduction system of the transplanted pig heart was monitored using a 12-lead ECG. The researchers studied the ECG data recorded after one day of the xenotransplant operation (organ transplantation in which the donor and recipient are of different species). They examined factors such as the QT interval, the PR interval, and the QRS complex.
The former indicates the time electric current takes to travel from the heart’s lower chamber to perform a complete cycle. Whereas PR and QRS denote the time, electricity goes from the top chamber to the lower chamber of the heart. Both these parameters are associated with the movement of electric current through the heart during a heartbeat.
The researchers started out expecting that the xenotransplant may behave the same way that pig hearts usually behave. Electricity travels quickly from the top to the bottom chamber (due to some well-described anatomic differences between the pig heart and the human heart). This allows the pig heart to go through a full heartbeat cycle faster than the human heart.
“We expected to see that in the xenotransplant as well: that the timing intervals on the 12-lead ECG would be faster than what we typically see in human hearts. However, the timing intervals were longer, not only as long as typically in humans but even longer than that,” one of the authors and cardiologist at the University of Maryland Medical Center (UMMC), Dr. Timm Dickfeld told IE.
The PR, QRS, and QT time intervals for the heart of a normal pig inside a pig’s body range between 50-120 milliseconds (ms), 70-90 ms, and 260-380 ms, respectively. Whereas for the genetically modified pig heart inside the human patient, the PR, QRS, and QT times were 190 ms, 138 ms, and 538 ms, respectively. The researchers also noticed prolonged PR and QRS intervals for some time in the ECG readings taken later.