1680 Left ventricular filling pressure assessment with exercise stress echocardiography in patients with non-valvular atrial fibrillation

Background

Noninvasive parameters of LV filling pressure (E/e’) and pulmonary pressures (RVSP) by Doppler echocardiography correlate with functional capacity and outcome in sinus rhythm (SR). Their role in AF is less clear. Elevated left ventricular filling pressures (E/e’) and pulmonary artery systolic pressures (PASP) by Doppler stress echocardiography correlate with impaired functional capacity in patients in sinus rhythm (SR). However, there is limited data in atrial fibrillation (AF).

Purpose

The aim of this study was to delineate the characteristics of patients with AF referred for exercise stress echocardiography and determine the prevalence and significance of E/e’ and PASP elevations in AF.

Methods

Subjects were patients referred for exercise treadmill stress echocardiography (n= 14,937) and underwent regional wall motion assessment, Doppler assessment of mitral inflow (E) and early tissue relaxation (e’) velocities and PASP at rest and immediately following maximum symptom limited exercise. Exclusion criteria included significant valvular heart disease (moderate or greater stenosis and/or regurgitation of any cardiac valve or previous valve repair or replacement) (1%), congenital heart disease (<1%) or refusal to participate in research (<1%).

Results

Patients with AF (n = 310, 2%) were older (71 ± 10 vs 59 ± 13 years, p < 0.001). While resting blood pressure was similar, resting heart rates were higher in AF (80 ± 17 bpm vs 73 ± 13 bpm, p < 0.0001). AF patients achieved lower workloads (6.4 ± 2.4 METS vs 9 ± 2.4 METS, p < 0.001) with lower peak double products (22336 ± 6677 vs 25148 ± 5438, p < 0.001). Rates of resting (27% vs 10%, p < 0.0001) and exercise-induced (37% vs 20%, p < 0.0001) regional wall motion abnormalities were higher in AF. Mean E/e’ was higher in AF at rest (12 ± 5 vs 9 ± 3, p < 0.001) and with exercise (12 ± 5 vs 10 ± 4, p < 0.001), with a higher percentage of patients in AF having E/e’ ≥15 at rest (20% vs 6% in SR, p= <0.001) and with exercise in (23% vs 8%, p < 0.001). PASP was higher in AF at rest (33 ± 8 mm Hg vs 28 ± 6 mm Hg, p < 0.001) and with exercise (48 ± 12 vs 42 ± 11, p < 0.001) compared to SR. E/e’ correlated with exercise capacity in AF and in SR, with an E/e’ cutoff of 11.7 that was best predictive of impaired functional capacity (< 5 METS in women and < 7 METS in men).

Conclusions

Abnormalities of E/e’ and PASP are more prevalent in patients with AF and correlate with impaired functional capacity. In patients with AF, a medial E/e’ ratio of ≥ 12 immediately following exercise is best associated with impaired functional capacity.

Analysis of the genes involved in the insulin transmembrane mitogenic signal in Chinese hamster ovary cells, CHO-K1, utilizing insulin-independent mutants

CHO-K1 cells, wild type (WT), grow in a defined medium with insulin as the only essential hormone. When starved for insulin, these cells accumulate in G0/G1 stage. Insulin binding to its receptor stimulates DNA synthesis and cell division and induces an increase in abundance of mRNA for c-fos, c-jun, Krox-20, Krox-24 (zif/268), fra-1, jun-B, c-myc, and JE. The kinetics of induction of these genes are similar to that shown with serum induction of 3T3. These genes show maximum stimulation at insulin concentrations of 20, 160, or 320 ng/ml and their expression is inhibited at higher concentrations. The addition of cycloheximide results in superinduction. The WT and insulin-independent mutants show no detectable signal for KC, fos-b, or nur77 and no increase over the basal level of pI-15, probably eliminating these genes as participants in the insulin mitogenic signal. These mutants synthesize DNA in the absence of insulin at rates that vary from 4 to 12 times that of the quiescent (insulin unstimulated) WT and are further inducible by insulin. The mutants have "constitutive" levels of Krox-24 (zif/268), fra-1, jun-B, c-myc, and JE (INS-type 2 genes) mRNAs that vary from mutant to mutant, reaching a maximum of an 8-fold increase for fra-1 and JE over the quiescent WT levels. There were no detectable levels of mRNA for genes c-fos and Krox-20 and no increase in level of mRNA for c-jun (INS-type 1 genes) as compared to the quiescent WT. Thus, although these INS-type 1 and type 2 genes may be involved in the full insulin mitogenic signal, the constitutive up-regulation of only genes in INS-type 2 is sufficient for insulin-independent DNA synthesis and cell division. Analysis of hybrids constructed between WT and mutant 27 indicate that the mutant phenotype is recessive, pointing to the existence of a regulatory gene producing a negative regulator.