Comparison of Early Surgery Versus Conventional Treatment in Asymptomatic Severe Mitral Regurgitation

Relation of N-terminal pro-B-type natriuretic peptide to symptoms, severity, and left ventricular remodeling in patients with organic mitral regurgitation

Natriuretic peptides reflect cardiac stress and may therefore be useful in the management of patients with valvular heart disease. Data regarding these biomarkers in organic mitral regurgitation (MR) are sparse. In this study, 144 patients with moderate or severe organic MR were prospectively enrolled in an observational, multicenter study to analyze the relation of N-terminal-pro-B-type natriuretic peptide (NT-pro-BNP) to symptoms, severity of MR, and echocardiographic parameters. NT-pro-BNP levels (median 373 pg/ml, interquartile range 150 to 997) were associated with age, gender, creatinine, New York Heart Association (NYHA) functional class, atrial fibrillation, left ventricular (LV) end-systolic dimension, and the LV ejection fraction. Independent predictors of increased NT-pro-BNP levels were NYHA functional class (p = 0.003), atrial fibrillation (p = 0.005) and LV end-systolic dimension (p = 0.029). MR severity and left atrial dimension were not independently associated with NT-pro-BNP levels. NT-pro-BNP levels increased significantly with NYHA class (p <0.001) but not with MR severity (p = 0.144). NT-pro-BNP levels were significantly higher in symptomatic patients than in asymptomatic patients (582 pg/ml [interquartile range 246-1,360] vs 157 pg/ml [interquartile range 64 to 256], p <0.0001). The area under the receiver-operating characteristic curve to predict symptoms for NT-pro-BNP was 0.80 (95% confidence interval 0.71 to 0.88), which was significantly higher than for all echocardiographic variables (p <0.001 for all). In conclusion, NYHA functional class, atrial fibrillation, and LV end-systolic dimension are independent predictors of increased NT-pro-BNP levels in patients with moderate or severe organic MR. Therefore, NT-pro-BNP may be helpful in the clinical evaluation and management of patients with MR, especially when it is doubtful whether symptoms are related to MR or not.

Releasable annuloplasty ring insertion--a novel experimental implantation model

OBJECTIVE

Experimental testing of annuloplasty ring (AR) effects requires a control group if the AR is implanted conventionally. Our goal was to develop a reversible AR insertion method that allows for beating heart assessment with and without an AR, providing the ability to evaluate the effects of an AR in the same animal (internal control). We tested the feasibility of this technique in an in vivo ovine model using four-dimensional (4-D) radiopaque marker tracking.

METHODS

Before the operation, a rigid AR (Edwards Geoform, Edwards Lifesciences, Irvine, CA, USA) was prepared by stitching the middle parts of eight double-armed sutures evenly spaced through the ring fabric using a Spring Eye needle. The resulting loops were 'locked' with polypropylene sutures. In addition, two drawstring sutures were attached to the AR. Using cardiopulmonary bypass and cardioplegic arrest, 12 adult sheep had 16 radiopaque markers sewn to the mitral annulus. The AR was implanted by stitching the eight sutures equidistantly in a perpendicular direction through the mitral annulus. The sheep were transferred to the catheterisation laboratory and 4-D marker coordinates were obtained using biplane videofluoroscopy (60 Hz) with the AR inserted (Geo-AR). The locking sutures were then released, the AR was pulled up to the atrial roof using the drawstring sutures and another dataset was acquired (control). Maximum and minimum mitral annular areas (MAA(max), MAA(min)) during the cardiac cycle were derived from implanted markers. Data are provided from one representative animal.

RESULTS

AR insertion and release were uneventful in all animals. Whereas the mitral annulus was dynamic in the control state (MAA(max): 9.0 cm(2), MAA(min): 7.8 cm(2)), mitral annular dynamics were abolished in the Geo-AR case (MAA(max): 6.2 cm(2), MAA(min): 6.0 cm(2)).

CONCLUSIONS

This novel releasable AR implantation method is feasible and permits in vivo assessment of AR effects in the same heart. The new technique should facilitate experimental AR testing and promote the development of ARs based on physical criteria.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.