Editorial: Left ventricular outflow tract obstruction is seen in various clinical settings of diverse patients.

Left ventricular outflow tract (LVOT) obstruction can be frequently seen in patients with hypertrophic cardiomyopathy (HCM). Maron et al. reported that 37% of HCM patients had LVOT obstruction with peak systolic gradient at rest ≥50 mmHg [1]. Surprisingly, they also reported that an additional 33% of HCM patients had provocable LVOT obstruction with exercise, that is, a total of 70% of the patients had LVOT obstruction at rest or with exercise. Patients with obstructive HCM show mitral valve systolic anterior motion (SAM) that is determined largely by the interrelation of LVOT geometry, the size and mobility of the mitral leaflets, and the presence and distribution of fibrous thickening [2]. In addition, both Venturi and drag forces also play a role in inducing mitral valve SAM and the following LVOT obstruction [3], [4]. It should be noted that mitral regurgitation (MR) in varying degrees is found in obstructive HCM patients with or without association with structural deformities of the valve apparatus. LVOT obstruction can cause cardiovascular symptoms, such as chest pain and dyspnea, on exertion or at rest. Syncope or presyncope may be the consequence of arrhythmias or autonomic disorder, but would derive from LVOT obstruction when related to larger exertion or to swift standing [5]. Both the degree of LVOT obstruction and the severity of symptoms are associated with the prognosis in HCM patients [6], [7]. Thus, the diagnosis of LVOT obstruction and the treatment are important.

In this issue of the Journal of Cardiology Cases, Kim et al. present a case with reversible severe MR caused by mitral valve SAM and LVOT obstruction in the absence of left ventricular hypertrophy (LVH) [8]. As described above, the most common etiology of LVOT obstruction is HCM. However, LVOT obstruction is observed also in hypertensive patients with the diffuse type of LVH [9], [10]. In addition, LVOT obstruction is observed also in patients even without overt LVH [11], [12]. LVOT obstruction seen in patients without LVH is generally latent, and is observed by provocation with exercise, inotropic agents, vasodilators, or Valsalva maneuver. In contrast, the present case demonstrated by Kim et al. had no significant LVH but mitral valve SAM, following LVOT obstruction and severe MR at rest without any provocation when she was referred to their hospital. In addition, LVOT obstruction and severe MR were totally dynamic and disappeared after oral administration of a beta blocker. These are the unique points of the present case.

Three factors can be raised as causes of a series of rare abnormalities in the present case demonstrated by Kim et al. First, the hyperadrenergic state due to heart failure could induce the LV hyperkinetic motion that emphasized LVOT obstruction. Secondly, basal septal bulge due to sigmoid septum could also emphasize LVOT obstruction. It has been reported that sigmoid septum is an important determinant of dynamic LVOT obstruction [13]. Lastly, it can be guessed that the redundancy of mitral valve is the most characteristic finding and can be the most important cause of dynamic LVOT obstruction in this case. In supplementary echocardiographic movie files in this case report, the anterior mitral leaflet appears to be especially thick and redundant. Mechanisms of LVOT obstruction are diverse among patients. As also described in the Discussion section of this case report, not only LV size, LV systolic function, and basal septal bulge due to true septal hypertrophy or sigmoid septum but also papillary muscle displacement, increased mitral leaflet area, and both Venturi and drag forces were considered as contributing factors of SAM, the following LVOT obstruction, and MR [2], [3], [4], [11], [12], [14], [15]. Preload reduction, afterload reduction, and the hyperadrenergic state due to exercise, inotropic agents, or worsening heart failure can modify the LV size and contractility. It leads to dynamic deterioration of preexisting LVOT obstruction or unmasking of latent LVOT obstruction [1], [3], [10], [11], [12], [13], [15].

From this excellent case report by Kim et al., again, we should learn that not only HCM patients or hypertensive LVH patients but also those with sigmoid septum or mitral valve elongation can have SAM, LVOT obstruction, and significant MR even without overt LVH. Also, the LVOT obstruction can dynamically change in various clinical settings.