Effects of rhythm regularization and rate control in improving left ventricular function in atrial fibrillation patients undergoing atrioventricular nodal ablation

OBJECTIVES

To assess the relative contributions of rate control and rhythm regularization to left ventricular function in atrial fibrillation (AF) patients undergoing atrioventricular nodal ablation. This was performed by assessing the effect of ventricular rhythm regularization on left ventricular function during AF, and the effect of varying heart rate on left ventricular function after ablation.

PATIENTS AND METHODS

Eleven patients with continuous AF and V/VI-R pacemakers undergoing therapeutic atrioventricular nodal ablation were studied. Preablation patients underwent two 30 min observation periods in a randomized, blinded fashion during which they were either in baseline AF (pacer set to default V/VI 50/min) or being paced using a rhythm stabilizing algorithm (RSA) designed to regularize rhythm without changing baseline ventricular rate. Six weeks after ablation, patients were again observed during the two following 30 min periods: pacing at a low clinically indicated rate (69+/-9 beats/min), and pacing at the rapid, mean preablation rate. During all observation periods, left ventricular function was measured continuously using a nuclear vest that provided validated measures of heart rate, ejection fraction, and normalized end-systolic volume (ESV) and end-diastolic (EDV) volume.

RESULTS

Before ablation, RSA successfully regularized rhythm, decreasing the coefficient of variation of interbeat intervals 20+/-5% to 10+/-4% (P<0.001). The heart rate with RSA (105+/-19 beats/min) was not significantly different from the baseline AF rate (102+/-21 beats/min). Increased rhythm regularity achieved by RSA significantly improved left ventricular function, decreasing ESV from 62+/-12 units to 57+/-11 units (P=0.03), and increasing the ejection fraction from 31+/-11% to 36+/-11% (P=0.03). After ablation, at the clinically indicated low pacing rate of 69+/-9 beats/min, a much greater improvement in ejection fraction was observed, increasing to 44+/-13% (P=0.005 compared with preablation). However, rapid regular pacing at the mean preablation rate of 110+/-18 beats/min eradicated this improvement, decreasing the ejection fraction to 31+/-8% (P=0.003), and increasing ESV from 53+/-13 units to 62+/-8 units (P=0.006).

CONCLUSIONS

Rhythm regularity achieved by a regularizing pacing algorithm can significantly, albeit modestly, improve left ventricular function in AF. However, more marked improvements in left ventricular function seen after ablation are primarily due to rate reduction alone.

Reliability and validity of serum sex hormone measurements

The laboratory reliability and validity of sex hormone measurements were examined at multiple levels, including lower levels characteristic of children and postmenopausal women. Serum was drawn from four adult male and four adult female healthy volunteers. From each individual's serum pool, a medium- and a low-dilution pool were created. Biochemical analyses for total and non-sex hormone-binding globulin (SHBG)-bound estradiol, estrone, estrone sulfate, progesterone, and SHBG were performed on female samples. Male samples were analyzed for total and non-SHBG-bound testosterone, dihydrotestosterone, androstenedione, and dehydroepiandrosterone sulfate. Two aliquots from each pool were assayed twice in each of two labs. All assays except SHBG in one lab used RIA procedures. Reliability was assessed by variance components analyses and estimated coefficients of variation (CVs). Validity was assessed by comparing observed measurements versus expected values based on known dilution ratios. For the testosterone and dihydrotestosterone assays, CVs were usually less than 10%. For estradiol and progesterone, CVs were usually less than 15%. Assays with larger estimated CVs included androstenedione, dehydroepiandrosterone sulfate, estrone, and estrone sulfate. Absolute levels differed markedly between labs for most assays. Observed measurements generally agreed with values expected from the dilution ratios. A notable exception was the estrone assay at the lowest dilution level, where observed measurements were 2-4 times those expected. A similar but less pronounced overestimation bias for the low levels of estradiol was also suggested. This intra- and interlaboratory variability and apparent low dilution overestimation should be accounted for in studies relating hormones to cancer risk, especially those involving children and postmenopausal women.