Four-dimensional Flow Cardiac MRI for Hemodynamic Assessment of Alcohol Septal Ablation for Hypertrophic Obstructive Cardiomyopathy with Multiple Obstructions

Abstract

Four-dimensional (4D) flow cardiac MRI can be used to assess hemodynamics in patients with hypertrophic obstructive cardiomyopathy (HOCM) undergoing alcohol septal ablation (ASA). However, to the best of the authors’ knowledge, no study has reported on insufficient or successful ASA evaluated with 4D flow cardiac MRI in HOCM with multiple obstructions. This case report presents a 74-year-old female patient who was diagnosed with HOCM with left ventricular (LV) outflow tract obstruction and midventricular obstruction. Repeat ASA targeting the LV outflow tract the first time and the midventricle the second time was conducted. Four-dimensional flow cardiac MRI performed before ASA, after the first ASA, and after the second ASA showed serial changes in the flow pathway and acceleration at the midventricle.

Supplemental material is available for this article.

© RSNA, 2023

Key Points

• ■ A new use of four-dimensional (4D) flow cardiac MRI was assessed in a 74-year-old female patient diagnosed with hypertrophic obstructive cardiomyopathy with left ventricular outflow obstruction and midventricular obstruction.

• ■ Four-dimensional flow cardiac MRI performed before, after the first, and after the second alcohol septal ablation (ASA) showed serial changes in the flow pathway and flow acceleration at the midventricle, demonstrating insufficient and successful ASA.

Introduction

Four-dimensional (4D) flow cardiac MRI is a technique to measure all three-directional components of blood flow velocities in the three spatial dimensions during the cardiac cycle. Three-dimensional velocity encoding has enabled the evolution of 4D flow cardiac MRI from the conventional two-dimensional phase-contrast cardiac MRI (1,2). The main advantage of this technique is three-dimensional flow assessment at any part of the chest anatomy even after the scanning (3). Alcohol septal ablation (ASA), a catheter-based septal reduction therapy for drug-refractory hypertrophic obstructive cardiomyopathy (HOCM), affects the hemodynamics of the ascending aorta and left ventricle (LV), including LV outflow (4,5).

We present a case of a patient with HOCM who underwent repeat ASA targeting the LV outflow tract the first time and the midventricle the second time. The purpose of the case report is to introduce how 4D flow cardiac MRI can be used to assess whether ASA has achieved sufficient septal wall reduction in a case with multiple obstructions.

Case Report

A 74-year-old female patient presented to our outpatient clinic with a complaint of dyspnea on exertion and was diagnosed with HOCM. She had used bisoprolol and cibenzoline but still experienced New York Heart Association (NYHA) class III dyspnea. Transthoracic echocardiography (TTE) showed marked interventricular septal wall thickness, systolic anterior motion of the mitral valve, and LV outflow tract obstruction (LVOTO) with a peak pressure gradient (PG) of 36 mm Hg combined with midventricular obstruction (MVO) with an estimated peak PG of 73 mm Hg (Fig 1A–1C). Cardiac MRI performed before ASA revealed the absence of late gadolinium enhancement (LGE) in the LV (Fig 2A, 2B). Since the patient had drug-refractory HOCM with a combination of LVOTO and MVO, surgical myectomy was initially suggested. However, given the patient's refusal and frailty, ASA was eventually conducted. Selective ablation was performed on the first branch of the identified target vessels, ablating the septal wall of the LV outflow tract. Cardiac MRI performed after the first ASA showed dense LGE limited at the most basal anteroseptal wall (Fig 2C, 2D). The patient's symptoms improved immediately after the first ASA but worsened 3 months later. TTE revealed improved LVOTO with a peak PG of 32 mm Hg but considerably deteriorated MVO with an estimated peak PG of 107 mm Hg (Fig 1D–1F). Since LV obstruction seemed most predominant at the midventricle, a second ASA targeting the septal wall at the midventricle was conducted. After ablation via three septal arteries, the peak-to-peak PG between the LV and ascending aorta decreased from 43 mm Hg to 11 mm Hg (Fig 3A, 3B). The peak PGs of the LV outflow tract and midventricle (Fig 1G–1I) decreased to 16 mm Hg and 12 mm Hg at TTE, respectively. The patient's heart failure symptoms improved to NYHA class II. Cardiac MRI performed after the second ASA revealed transmural LGE in the basal and midventricular septum (Fig 2E, 2F).

Figure 1:

Transthoracic echocardiography images in a 74-year-old female patient with hypertrophic obstructive cardiomyopathy with a combination of left ventricular outflow tract obstruction and midventricular obstruction. (A–I) Images with systolic color Doppler in the three-chamber view (left) and pulse-wave or continuous-wave Doppler measurements at the left ventricular outflow tract (center) and midventricle (right). The images before alcohol septal ablation (ASA) (A–C), after the first ASA (D–F), and after the second ASA (G–I) are in the top, middle, and bottom rows. Pulse-wave Doppler imaging was primarily used (B, E, H, I); however, in the case of accelerated velocity, continuous-wave Doppler imaging was used as a substitute (C, F). PG = pressure gradient.

Figure 2:

Late gadolinium–enhanced cardiac MR images. Images (A, B) before alcohol septal ablation (ASA), (C, D) after the first ASA, and (E, F) after the second ASA. Broken lines in the four-chamber view (left column) correspond to the short-axis view (right column). Arrows indicate distinct late gadolinium enhancement at the most basal anteroseptum (C, D) and at the midventricular septum (E, F).

Figure 3:

Left ventricular (LV) and aortic (Ao) pressures (A) before and (B) after the second alcohol septal ablation (ASA). Peak-to-peak pressure gradient between apical LV and aorta was 43 mm Hg before the second ASA (A). After the ASA targeting the septal wall at the midventricle, the peak-to-peak pressure gradient decreased to 11 mm Hg (B).

The accompanying 4D flow cardiac MR images, including streamline (Fig 4A, Movie 1) and vector (Fig 4D) images before ASA, showed the flow pathway to be close to the central LV and flow acceleration at the midventricle, sandwiched between the hypertrophic ventricular wall. This suggested the presence of MVO. Four-dimensional flow cardiac MR images showed no changes after the first ASA (Fig 4B, 4E; Movie 2). However, after the second ASA, the flow pathway shifted close to the septal wall on a straighter course (Fig 4C, Movie 3) and revealed slower flow at the midventricle (Fig 4F), suggesting the relief of MVO. Four-dimensional flow cardiac MRI enabled the comparison of hemodynamic changes before and after the first and second ASA, allowing for flow visualization of LVOTO combined with MVO.

Figure 4:

Four-dimensional flow cardiac MR images. (A–C) Streamline and (D–F) vector images visualize changes in the blood flow pathway (broken arrows in A–C) and flow velocity at the midventricle (arrowheads in D–F) after repeat alcohol septal ablations (ASA). White bars in D–F indicate the same length between the atrioventricular sulcus and midventricle. Streamline images before and after the first ASA (A, B) show the flow pathway to be close to the central left ventricle, suggesting that the midventricular septum was protruding and the flow pathway was being pushed to the lateral wall. After the second ASA (C), the flow pathway shifted close to the septal wall on a straighter course, which indicates a reduced protrusion of the midventricular septum and relief of the midventricular obstruction. The reduction in flow velocity at the midventricle after the second ASA (F) also suggested the relief of midventricular obstruction. Ao = aorta, LV = left ventricle.

Movie 1:

Download video file ^{(3.3MB, mp4)}

Streamline movie of four-dimensional flow cardiac MR images obtained before alcohol septal ablation.

Movie 2:

Download video file ^{(3.1MB, mp4)}

Streamline movie of four-dimensional flow cardiac MR images obtained after the first alcohol septal ablation.

Movie 3:

Download video file ^{(3.2MB, mp4)}

Streamline movie of four-dimensional flow cardiac MR images obtained after the second alcohol septal ablation.

Discussion

ASA is an invasive treatment for drug-refractory HOCM and is recommended in the guidelines of the European Society of Cardiology, the American Heart Association, and the Japanese Circulation Society (6–8). However, the selection criteria for patients suitable for ASA need to be discussed (9,10). In this case with a combination of LVOTO and MVO, the first ASA ablated only the basal myocardium of the septum, which was thought to contribute to LVOTO. However, the intervention improved neither the PG between the LV and ascending aorta nor the NYHA class. Preoperative TTE evaluation of HOCM with a combination of LVOTO and MVO is challenging. Specifically, the presence of multiple obstructions in the LV prevents the accurate determination of their exact location using continuous-wave Doppler imaging and the evaluation of the PG exceeding the limited value at each obstructive point using pulse-wave Doppler imaging, necessitating invasive pressure assessment using a catheter. In this regard, 4D flow cardiac MRI has the advantage of evaluating complex three-dimensional hemodynamics with accelerated blood flow velocity and identifying anatomic locations by both flow visualization and quantification. In this case, 4D flow cardiac MRI performed before ASA, after the first ASA, and after the second ASA was performed to clarify the following three points: first, whether this patient had a combination of LVOTO and MVO; second, why the first ASA was insufficient; and third, why the second ASA succeeded and reduced the PG between the LV and the ascending aorta.

Previous studies have visualized blood flow patterns of the LV and ascending aorta using 4D flow cardiac MRI before and after ASA (4,5,11). The previously reported hemodynamic changes before and after ASA were not observed in this case. One of the speculations is that, in this case, intraventricular obstruction was most predominant at the midventricle rather than the outflow tract. The substantial pressure drop at the midventricle might weaken the PG at the outflow tract, resulting in absence of the reported blood flow characteristics in the simple LVOTO. However, in this case, the 4D flow cardiac MRI–derived hemodynamic changes across the repeat ASAs not only visualized the blood flow pattern but also clarified the reason why the first ASA was insufficient. In this regard, we demonstrated the novelty of using 4D flow cardiac MRI for the management of HOCM in patients requiring repeat ASAs. Among the limitations of 4D flow cardiac MRI are that it cannot be performed at all hospitals and requires expertise in image analysis and evaluation. Therefore, there is room for improvement in terms of its versatility.

In conclusion, we demonstrated improvements in LV hemodynamics by performing sequential 4D flow cardiac MRI in a patient with drug-refractory HOCM, with a combination of LVOTO and MVO, after repeat ASAs.