Dataset Information

Squat-to-stand provocation of dynamic left ventricular outflow tract obstruction in hypertrophic cardiomyopathy: a case report.

ABSTRACT:

Background

Left ventricular outflow tract (LVOT) obstruction is an important determinant of the management of hypertrophic cardiomyopathy (HCM). With a nationwide shortage of amyl nitrite in 2019, we implemented a 'repetitive squat-to-stand' manoeuvre to provoke LVOT obstruction during echocardiography.

Case summary

A 64-year-old female was referred with symptomatic HCM refractory to pharmacologic therapy. Transthoracic echocardiography showed minor LVOT obstruction with conventional imaging at rest and during Valsalva manoeuvre, but severe obstruction was confirmed with the repetitive squat-to-stand manoeuvre. Alcohol septal ablation via the first septal perforator was performed with subsequent resolution of symptoms.

Discussion

Due to the dynamic nature of LVOT obstruction, a series of provocative manoeuvres including Valsalva manoeuvre, inhalation of amyl nitrite, and exercise are often necessary to maximally augment ventricular obstruction. The recent unavailability of amyl nitrite during a nationwide shortage prompted the implementation of a protocol of repetitive squat-to-stand manoeuvre in our echocardiography laboratory. Rising from the squatting position decreases preload and afterload, both of which augment dynamic LVOT obstruction. Repetition of squatting and standing appears to enhance the sensitivity of the manoeuvre, particularly when exertional symptoms are reproduced. In this case, repetitive squat-to-stand manoeuvre led to the identification of severe LVOT obstruction which may not have been diagnosed otherwise, alteration of treatment to septal reduction therapy, and subsequent resolution of symptoms.

SUBMITTER: Peng LT

PROVIDER: S-EPMC7898584 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle characterized by otherwise unexplained thickening of the left ventricle. Left ventricular outflow tract (LVOT) obstruction is present in approximately two-thirds of patients and substantially increases the risk of disease complications. Invasive treatment with septal myectomy or alcohol septal ablation can improve symptoms and functional status, but currently available drugs for reducing obstruction have pleiotropic effects and variable therapeutic responses. New medical treatments with more targeted pharmacology are needed, but the lack of preclinical animal models for HCM with LVOT obstruction has limited their development. HCM is a common cause of heart failure in cats, and a subset exhibit systolic anterior motion of the mitral valve leading to LVOT obstruction. MYK-461 is a recently-described, mechanistically novel small molecule that acts at the sarcomere to specifically inhibit contractility that has been proposed as a treatment for HCM. Here, we use MYK-461 to test whether direct reduction in contractility is sufficient to relieve LVOT obstruction in feline HCM. We evaluated mixed-breed cats in a research colony derived from a Maine Coon/mixed-breed founder with naturally-occurring HCM. By echocardiography, we identified five cats that developed systolic anterior motion of the mitral valve and LVOT obstruction both at rest and under anesthesia when provoked with an adrenergic agonist. An IV MYK-461 infusion and echocardiography protocol was developed to serially assess contractility and LVOT gradient at multiple MYK-461 concentrations. Treatment with MYK-461 reduced contractility, eliminated systolic anterior motion of the mitral valve and relieved LVOT pressure gradients in an exposure-dependent manner. Our findings provide proof of principle that acute reduction in contractility with MYK-461 is sufficient to relieve LVOT obstruction. Further, these studies suggest that feline HCM will be a valuable translational model for the study of disease pathology, particularly LVOT obstruction.

Project description:BACKGROUND:Cardiovascular magnetic resonance (CMR) imaging in patients with hypertrophic cardiomyopathy (HCM) enables the assessment of not only left ventricular (LV) hypertrophy and scarring but also the severity of mitral regurgitation. CMR assessment of mitral regurgitation is primarily based on the difference between LV stroke volume (LVSV) and aortic forward flow (Ao) measured using the phase-contrast (PC) technique. However, LV outflow tract (LVOT) obstruction causing turbulent, non-laminar flow in the ascending aorta may impact the accuracy of aortic flow quantification, leading to false conclusions regarding mitral regurgitation severity. Thus, we decided to quantify mitral regurgitation in patients with HCM using Ao or, alternatively, main pulmonary artery forward flow (MPA) for mitral regurgitation volume (MRvol) calculations. METHODS:The analysis included 143 prospectively recruited subjects with HCM and 15 controls. MRvol was calculated as the difference between LVSV computed with either the inclusion (LVSVincl) or exclusion (LVSVexcl) of papillary muscles and trabeculations from the blood pool and either Ao (MRvolAoi or MRvolAoe) or MPA (MRvolMPAi or MRvolMPAe). The presence or absence of LVOT obstruction was determined based on Doppler echocardiography findings. RESULTS:MRvolAoi was higher than MRvolMPAi in HCM patients with LVOT obstruction [47.0 ml, interquartile range (IQR)?=?31.5-60.0 vs. 35.5 ml, IQR?=?26.0-51.0; p <?0.0001] but not in non-obstructive HCM patients (23.0 ml, IQR?=?16.0-32.0 vs. 24.0 ml, IQR?=?15.3-32.0; p?=?0.26) or controls (18.0 ml, IQR?=?14.3-21.8 vs. 20.0 ml, IQR?=?14.3-22.0; p?=?0.89). In contrast to controls and HCM patients without LVOT obstruction, in HCM patients with LVOT obstruction, aortic flow-based MRvol (MRvolAoi) was higher than pulmonary-based findings (MRvolMPAi) (bias?=?9.5 ml; limits of agreement: -11.7-30.7 with a difference of 47 ml in the extreme case). The differences between aortic-based and pulmonary-based MRvol values calculated using LVSVexcl mirrored those derived using LVSVincl. However, MRvol values calculated using LVSVexcl were lower in all the groups analyzed (HCM with LVOT obstruction, HCM without LVOT obstruction, and controls) and with all methods of MRvol quantification used (p???0.0001 for all comparisons). CONCLUSIONS:In HCM patients, LVOT obstruction significantly affects the estimation of aortic flow, leading to its underestimation and, consequently, to higher MRvol values than those obtained with MPA-based MRvol calculations.