Dynamic Left Ventricular Outflow Tract Obstruction as a Rare Mechanical Complication of Acute Myocardial Infarction

Description of Clinical Presentation: 74-year-old female patient with history of mitral valve prolapse (MVP), admitted due to anteroseptal acute myocardial infarction (AMI).

Diagnostic Techniques and Their Most Important Findings: Coronary angiography showed epicardial coronary arteries without stenosis (Figure 1). The initial echocardiogram showed akinesis of the apex and the remaining apical segments with left ventricular ejection fraction: 53% and prolapse of the P2 segment of the mitral valve with two flows of moderate mitral regurgitation (MR), without mechanical complications of AMI (Figure 2). Cardiac magnetic resonance (CMR) showed late gadolinium enhancement with transmural distribution in anteroseptal and apical walls confirming the diagnosis of myocardial infarction with non-obstructive coronary arteries (MINOCA), and in addition to confirm P2 prolapse, it showed hyperkinesis of basal segments with systolic anterior motion (SAM) of the anterior mitral leaflet which led to severe MR extending to the roof of the left atrium (Figure 2). She was initially managed in the intensive care unit with medical treatment, after which she presented hypotension (80/40 mmHg) after starting amlodipine and oral nitrates, managed with norepinephrine; due to suspected mechanical complications of the AMI, a second echocardiogram was performed, which showed the same initial abnormalities in segmental thickening, hyperkinesis of the basal segments, and SAM of the anterior mitral leaflet, leading to dynamic left ventricular outflow tract (LVOT) obstruction with a maximum gradient of 87.3 mmHg and severe MR (Figure 3). We concluded mechanical complication of AMI: LVOT obstruction, exacerbated by reduced preload (nitrates), afterload (amlodipine), and increased contractility (norepinephrine); the patient was managed with intravenous fluid therapy, progressive reduction of norepinephrine, and ivabradine to reduce heart rate and contractility. The outcome was satisfactory, with successful weaning from norepinephrine, echocardiographic improvement of the MR to mild, and resolution of the LVOT obstruction (maximum gradient: 14.9 mmHg) (Figure 3).

Learning Points from this Case: Dynamic LVOT obstruction has traditionally been associated with obstructive hypertrophic cardiomyopathy. However, it has also been described as a rare complication of AMI; it is usually associated with anteroapical AMI with basal segment hyperkinesis, as in this case. Despite the history of MVP, dynamic changes in the LVOT gradient and in the severity of MR compared with the initial echocardiogram allowed us to establish the diagnosis of this mechanical complication of AMI. In this case, it was a MINOCA; this complication has been described in the literature both in MINOCA and in AMI with significant coronary artery stenosis.

Figure 1. a: Electrocardiogram. b, c and d: Cardiac catheterization, right coronary artery (RCA), left main coronary artery (LMCA), circumflex artery (Cx), and left anterior descending artery (LAD).
Figure 2. a: Initial transthoracic echocardiogram (TTE), left ventricle (LV) apical 5-chamber view, P2 prolapse (arrow). b: TTE, LV apical 4-chamber view, color Doppler mode, mitral regurgitation (MR) flows (asterisks). c and d: cardiac magnetic resonance (CMR), cine sequences in 3-chamber views in diastole (c) and systole (d); in systole, the anterior mitral leaflet SAM (arrow) and MR flow (asterisks) can be seen. e: CMR, inversion recovery sequence, 4-chamber view with anteroseptal and apical transmural late gadolinium enhancement (asterisks).
Figure 3. a, b, c, and d: Second TTE. a: LV parasternal long-axis view (PLAX) with SAM of the anterior mitral leaflet (asterisk). b: M-mode LV PLAX, SAM of the anterior mitral leaflet (arrows). c: LV apical 5-chamber view, continuous-wave Doppler, obstructive LV outflow tract (LVOT) gradient with scimitar morphology and maximum gradient of 87.3 mmHg (arrow). d: LV apical 4-chamber view, color Doppler, increasing MR severity to severe compared with the initial TTE (asterisks). e, f, and g: Predischarge TTE. e: LV PLAX, without evidence of SAM (asterisk). f: LV apical 5-chamber view, continuous-wave Doppler, with resolution of the obstructive gradient (arrow). g: LV apical 4-chamber view, color Doppler mode, with decreased severity of MR to mild (asterisk).