VANCOUVER, B.C. – Patients with baseline PR intervals less than 200 ms have a better response to biventricular cardiac resynchronization therapy than do those with longer baseline intervals, a finding that may help predict who will respond to pacing, judging from recent data.
Investigators compared biventricular CRT [cardiac resynchronization therapy] outcomes in 66 patients with baseline PR intervals less than 200 ms to outcomes in 37 patients with intervals of 200 ms or greater.
Ms. Preya Simlote
Overall, left ventricular ejection fractions improved from 23.7% to 32.2%, but patients with baseline intervals below 200 ms had greater improvement (+11.8% vs. +4.9%) and had greater reductions in left ventricular end-systolic diameters (–0.37 mm vs. –0.06 mm) and mitral regurgitation grade (–0.16 vs. –0.03). Left ventricular end-diastolic diameters deteriorated in both groups, but less so among patients with shorter baseline PR intervals (+0.05 mm vs. +0.1 mm), according to the lead investigator Preya Simlote, a medical student at Thomas Jefferson University Hospital in Philadelphia.
Men accounted for two-thirds of the patients, and the average age in the study was 68 years. Patients had either coronary artery disease or nonischemic cardiomyopathy and were followed for a mean of about 282 days.
At baseline, patients in the longer–PR interval group had slower heart rates (68.7 bpm vs. 75.3 bpm), shorter QRS intervals (144.4 ms vs. 154.8 ms), worse mitral regurgitation (grade 2.29 vs. 1.95), and larger left atriums.
The findings suggest that the severity of "preexisting conduction system disease ... may be a more powerful marker of poor outcomes [than] the effects of short [atrioventricular] delay and truncated transmitral flow," the investigators concluded.
"We were kind of expecting that maybe people who had the longer PR interval would show more improvement. What we actually found was the opposite," Ms. Simlote said.
"Patients are given CRT based on their QRS interval and their symptoms, and their left ventricular ejection fraction. This suggests perhaps we should also be checking patients’ PR interval to predict how they will respond to CRT," she said at the 18th World Congress on Heart Disease.
Ms. Simlote had no disclosures.