ABSTRACT
Length-dependent activation of calcium-dependent myocardial force generation provides the basis for the Frank-Starling mechanism. To directly compare the effects of mutations associated with hypertrophic cardiomyopathy and dilated cardiomyopathy, the native troponin complex in skinned trabecular fibers of guinea pigs was exchanged with recombinant heterotrimeric, human, cardiac troponin complexes containing different human cardiac troponin T subunits (hcTnT): hypertrophic cardiomyopathy-associated hcTnTR130C, dilated cardiomyopathy-associated hcTnTΔK210 or the wild type hcTnT (hcTnTWT) serving as control. Force-calcium relations of exchanged fibers were explored at short fiber length defined as 110% of slack length (L 0) and long fiber length defined as 125% of L 0 (1.25 L 0). At short fiber length (1.1 L 0), calcium sensitivity of force generation expressed by -log [Ca2+] required for half-maximum force generation (pCa50) was highest for the hypertrophic cardiomyopathy-associated mutation R130C (5.657 ± 0.019), intermediate for the wild type control (5.580 ± 0.028) and lowest for the dilated cardiomyopathy-associated mutation ΔK210 (5.325 ± 0.038). Lengthening fibers from 1.1 L 0 to 1.25 L 0 increased calcium sensitivity in fibers containing hcTnTR130C (delta-pCa50 = +0.030 ± 0.010), did not alter calcium sensitivity in the wild type control (delta-pCa50 = -0.001 ± 0.010), and decreased calcium sensitivity in fibers containing hcTnTΔK210 (delta-pCa50 = -0.034 ± 0.013). Length-dependent activation indicated by the delta-pCa50 was highly significantly (P < 0.001) different between the two mutations. We hypothesize that primary effects of mutations on length-dependent activation contribute to the development of the diverging phenotypes in hypertrophic and dilated cardiomyopathy.
ABSTRACT
Importance: The benefit of mechanical thrombectomy (MT) in patients with stroke presenting with mild deficits (National Institutes of Health Stroke Scale [NIHSS] score <6) owing to emergency large-vessel occlusion (ELVO) remains uncertain. Objective: To assess the outcomes of patients with mild-deficits ELVO (mELVO) treated with MT vs best medical management (bMM). Data Sources: We retrospectively pooled patients with mELVO during a 5-year period from 16 centers. A meta-analysis of studies reporting efficacy and safety outcomes with MT or bMM among patients with mELVO was also conducted. Data were analyzed between 2013 and 2017. Study Selection: We identified studies that enrolled patients with stroke (within 24 hours of symptom onset) with mELVO treated with MT or bMM. Main Outcomes and Measures: Efficacy outcomes included 3-month favorable functional outcome and 3-month functional independence that were defined as modified Rankin Scale scores of 0 to 1 and 0 to 2, respectively. Safety outcomes included 3-month mortality and symptomatic and asymptomatic intracranial hemorrhage (ICH). Results: We evaluated a total of 251 patients with mELVO who were treated with MT (n = 138; 65 women; mean age, 65.2 years; median NIHSS score, 4; interquartile range [IQR], 3-5) or bMM (n = 113; 51 women; mean age, 64.8; median NIHSS score, 3; interquartile range [IQR], 2-4). The rate of asymptomatic ICH was lower in bMM (4.6% vs 17.5%; P = .002), while the rate of 3-month FI (after imputation of missing follow-up evaluations) was lower in MT (77.4% vs 88.5%; P = .02). The 2 groups did not differ in any other efficacy or safety outcomes. In multivariable analyses, MT was associated with higher odds of asymptomatic ICH (odds ratio [OR], 11.07; 95% CI, 1.31-93.53; P = .03). In the meta-analysis of 4 studies (843 patients), MT was associated with higher odds of symptomatic ICH in unadjusted analyses (OR, 5.52; 95% CI, 1.91-15.49; P = .002; I2 = 0%). This association did not retain its significance in adjusted analyses including 2 studies (OR, 2.06; 95% CI, 0.49-8.63; P = .32; I2 = 0%). The meta-analysis did not document any other independent associations between treatment groups and safety or efficacy outcomes. Conclusions and Relevance: Our multicenter study coupled with the meta-analysis suggests similar outcomes of MT and bMM in patients with stroke with mELVO, but no conclusions about treatment effect can be made. The clinical equipoise can further be resolved by a randomized clinical trial.
