Role of controlled septal infarct in hypertrophic obstructive cardiomyopathy

Gene Therapy to Inhibit the Calcium Channel β Subunit

Calcium cycling figures prominently in excitation-contraction coupling and in various signaling cascades involved in the development of left ventricular hypertrophy. We hypothesized that genetic suppression of the L-type calcium channel accessory beta-subunit would modulate calcium current and suppress cardiac hypertrophy. A short hairpin RNA template sequence capable of mediating the knockdown of the L-type calcium channel accessory beta-subunit gene was incorporated into a lentiviral vector (PPT.CG.H1.beta(2)). Transduction of ventricular myocytes in vivo with the active short hairpin RNA partially inhibited the L-type calcium current. In neonatal rat cardiomyocytes, L-type calcium channel accessory beta-subunit gene knockdown reduced calcium transient amplitude. Similarly, [(3)H]leucine incorporation was attenuated in PPT.CG.H1.beta(2)-transduced neonatal rat cardiomyocytes compared with nonsilencing controls in a phenylephrine-induced hypertrophy model. In vivo gene transfer attenuated the hypertrophic response in an aortic-banded rat model of left ventricular hypertrophy, with reduced left ventricular wall thickness and heart weight/body weight ratios in PPT.CG.H1.beta(2)-injected rats at four weeks post transduction. Fractional shortening was preserved in rats treated with PPT.CG.H1.beta(2). These findings indicate that knockdown of L-type calcium channel accessory beta-subunit is capable of attenuating the hypertrophic response both in vitro and in vivo without compromising systolic performance. Suppression of the calcium channel beta subunit may represent a novel and useful therapeutic strategy for left ventricular hypertrophy.

Comparison of percutaneous transluminal septal myocardial ablation versus septal myectomy for the treatment of patients with hypertrophic obstructive cardiomyopathy—A meta analysis

BACKGROUND

The effects of percutaneous transluminal septal myocardial ablation (PTSMA) with septal myectomy in patients with hypertrophic obstructive cardiomyopathy (HOCM) are not thoroughly compared.

METHODS

Three articles comparing the effects of PTSMA and septal myectomy treatment for HOCM were identified from a search in Pubmed, and a meta analysis was conducted.

RESULTS

177 patients (86 underwent PTSMA and 91 underwent septal myectomy) were included. Interventricular septum thickness was decreased from 22.1 to 15.1 mm (p<0.05) in PTSMA group and from 22.0 to 13.9 mm (p<0.05) in septal myectomy group; left ventricular end-diastolic dimension was increased from 41.8 to 45.2 mm (p<0.05) in PTSMA group and from 41.8 to 43.9 mm (p<0.05) in septal myectomy group; NYHA class was improved from 3.17 to 1.47 (p<0.05) in PTSMA group and from 2.97 to 1.36 (p<0.05) in septal myectomy group; there were no differences in the two groups. However, left ventricular outflow tract gradient was decreased from 76.0 to 15.7 mm Hg (p<0.05) in PTSMA group and from 74.7 to 9.4 mm Hg (p<0.05) in septal myectomy group and the effect of septal myectomy was better than PTSMA (p<0.05).

CONCLUSIONS

The effects of septal myectomy treatment for HOCM are better with regard to relief of LVOT gradient, and lower risk of pacemaker requirement, compared to PTSMA. Large randomized clinical trials further comparing the two treatments are suggested.

Contrast Material–enhanced Visualization of the Ablation Medium for Magnetic Resonance– monitored Ethanol Injection Therapy: Imaging and Safety Aspects

PURPOSE

This study was performed to test whether the dissociation rate of free Gd3+ ions from gadoterate meglumine is significantly increased when the contrast agent is dissolved in ethanol and whether the magnetic resonance (MR) signal of gadolinium/ethanol solutions is enhanced to a degree that promises reliable detection during MR imaging-guided intralesional administration, such as for the treatment of low-flow venous malformations.

MATERIALS AND METHODS

The apparent gadoterate meglumine-induced enhancement of the longitudinal proton relaxation rate of sterile ethanol/water solutions, stored at a temperature of 24 degrees C +/- 5 degrees C in the dark, was monitored for 2 weeks. The content of dissociated Gd3+ ions was determined after 6 and 8.5 months of storage. The signal difference between contrast agent/ethanol solutions and muscle tissue was assessed with imaging at 0.5 T and 1.5 T.

RESULTS

Commercialized gadoterate meglumine diluted with 94% ethanol was not shown to have released toxic Gd3+ during storage times that exceed its physiologic circulation and excretion times after intravenous injection by a factor of more than 100. A maximum dissociation rate of 0.05% per month was estimated from the detection limit of the analysis. The apparent molar relaxivity of the contrast agent in the mixtures varied by less than 0.1 L/mmol per second with no temporal trend. Gradient-echo ethanol/muscle contrast increased with Gd concentrations to maximums of 15 mmol/L (at 0.5 T) and 25 mmol/L (at 1.5 T).

CONCLUSIONS

Neither limited solubility nor release of Gd3+ ions could be identified as a general safety hazard associated with the application of gadoterate meglumine/ethanol solutions at Gd concentrations of 0.5-25 mmol/L, and such ablation mixtures could be efficiently and reliably visualized.

Creation of a genetic calcium channel blocker by targeted gem gene transfer in the heart

Calcium channel blockers are among the most commonly used therapeutic drugs. Nevertheless, the utility of calcium channel blockers for heart disease is limited because of the potent vasodilatory effect that causes hypotension, and other side effects attributable to blockade of noncardiac channels. Therefore, focal calcium channel blockade by gene transfer is highly desirable. With a view to creating a focally applicable genetic calcium channel blocker, we overexpressed the ras-related small G-protein Gem in the heart by somatic gene transfer. Adenovirus-mediated delivery of Gem markedly decreased L-type calcium current density in ventricular myocytes, resulting in the abbreviation of action potential duration. Furthermore, transduction of Gem resulted in a significant shortening of the electrocardiographic QTc interval and reduction of left ventricular systolic function. Focal delivery of Gem to the atrioventricular (AV) node significantly slowed AV nodal conduction (prolongation of PR and AH intervals), which was effective in the reduction of heart rate during atrial fibrillation. Thus, these results indicate that gene transfer of Gem functions as a genetic calcium channel blocker, the local application of which can effectively modulate cardiac electrical and contractile function.

Alcohol septal ablation for obstructive hypertrophic cardiomyopathy

Treatment of obstructive hypertrophic cardiomyopathy remains challenging. Medical therapy, surgical therapy, and pacemaker therapy have been shown to be beneficial in some patients over the years. Alcohol septal ablation is a catheter-based intervention that causes a controlled infarct in the septum leading to a decrease in the left ventricular outflow tract obstruction. Along with the impressive reductions in left ventricular outflow tract gradient, there is subjective and objective improvement in symptoms. Development of complete heart block requiring a permanent pacemaker after alcohol septal ablation remains a frequent complication, but has decreased in some recent studies. Alcohol septal ablation has been shown to improve diastolic function, decrease mitral regurgitation, decrease left ventricular hypertrophy and mass, as well as cause changes at the cellular and molecular level that improve myocardial function. Comparison of alcohol septal ablation to surgical myectomy has shown favorable results. Long-term follow-up of alcohol septal ablation has shown sustained results out to several years.