Mitochondrial Structural Abnormalities and Cardiac Reverse Remodeling in Patients With Systolic Dysfunction

Abstract

Background: Mitochondrial dysfunction in the heart is associated with the development of heart failure (HF). However, the clinical consequences of mitochondrial structural abnormalities in patients with HF remain unexplored.

Methods and Results: Ninety-one patients with left ventricular (LV) systolic dysfunction who underwent endomyocardial biopsy (EMB) were enrolled in the study. Myocardial specimens were obtained from the right ventricular septum. Specimens were characterized using electron microscopy to assess mitochondrial size, outer membrane disruption, and cristae disorganization. The primary endpoint was a composite of cardiovascular death and unplanned hospitalization for HF. Patients were classified into LV reverse remodeling (LVRR)-positive (n=52; 57.1%) and LVRR-negative (n=39; 42.9%) groups. Cristae disorganization was observed in 21 (23.1%) patients: 6 (11.5%) in the LVRR-positive group and 15 (38.5%) in the LVRR-negative group (P=0.005). During the 1-year post-EMB observation period, 16 patients (17.6%) met the primary endpoint, with 2 (2.2%) cardiovascular deaths and 14 (15.4%) HF hospitalizations. Cristae disorganization (P=0.002) was significantly associated with the endpoints, independent of age (P=0.115), systolic blood pressure (P=0.004), B-type natriuretic peptide level (P=0.042), and mitral regurgitation (P=0.003).

Conclusions: We classified mitochondrial structural abnormalities and showed that cristae disorganization was associated with LVRR and worse prognosis. These findings may affect the management of patients with HF and systolic dysfunction who undergo EMB.

Heart failure (HF) is a major global health problem that contributes significantly to hospital admission, healthcare costs, and mortality rates.¹ The occurrence and progression of HF are associated with left ventricular (LV) remodeling, which is a process of ventricular enlargement and dysfunction. In recent years, several studies have revealed that approximately 40% of patients with HF with reduced ejection fraction (HFrEF) experience significant LV reverse remodeling (LVRR) after evidence-based medical treatment.^2,3 Although some patients achieve LVRR and improved clinical outcomes, others do not respond to treatment and remain vulnerable to sudden cardiac death and refractory HF requiring heart transplantation or mechanical circulatory support.⁴

Mitochondria are dynamic, double-membraned intracellular organelles that serve as the powerhouses of eukaryotic cells by mediating the supply of ATP available to fuel a myriad of enzyme-catalyzed chemical reactions. The heart has the highest abundance of mitochondria of any organ tissue. Mitochondria are estimated to occupy approximately one-third of the total cardiac cell volume.⁵ The primary function of mitochondria is to synthesize ATP through oxidative phosphorylation. Mitochondrial dysfunction has been widely observed in failing hearts, regardless of etiology.⁶ Previous studies in animal models have suggested that mitochondrial structure, complexes, and oxidative capacity are enhanced by pressure loading but diminish with the onset of HF and reduced LV ejection fraction (LVEF).^7,8 Meanwhile, a previous study in humans found altered mitochondrial morphology and oxidative capacity in end-stage patients with HFrEF.⁸ Although mitochondrial dysfunction is recognized as a maladaptive response, the specific mechanisms linking mitochondrial dysfunction to the development and progression of HF are complex and not fully understood.

In patients with HFrEF, endomyocardial biopsy (EMB) is appropriate in cases where there is a high probability of making a specific diagnosis that can only be confirmed by myocardial samples.^9–12 Recent studies have reported that myocardial tissue analysis could be useful for predicting the efficacy of medical treatments and prognosis in patients with HFrEF.^13,14 Similarly, morphological analysis of mitochondria in myocardial tissue may be useful for predicting prognosis in patients with HFrEF.

Electron microscopy (EM) reveals microstructural details and allows the observation mitochondrial degeneration. However, the significance of ultrastructural changes in mitochondria in patients with HF has not yet been thoroughly investigated. Accordingly, the aim of the present study was to evaluate whether mitochondrial morphology, as assessed using EM, could predict LVRR and cardiovascular prognosis in patients with LV systolic dysfunction.

Methods

Study Population

Patients with suspected non-ischemic cardiomyopathy who underwent biopsy between August 2019 and November 2021 at Tsukuba University Hospital were enrolled in the study. The indications for EMB were determined based on a consensus statement on endomyocardial biopsy from the Association for European Cardiovascular Pathology and Society for Cardiovascular Pathology.¹⁵ Patients were included in the study if they had LV systolic dysfunction with an LVEF <45%. We excluded patients who had received a heart transplant and those with unsuccessful sample collection for EM evaluation. Patients with fulminant or acute myocarditis were also excluded from the study.

Cardiomyopathies were defined and classified according to the Japanese Circulation Society/Japanese Heart Failure Society guidelines for the diagnosis and treatment of cardiomyopathies.¹⁶ In particular, familial or idiopathic dilated cardiomyopathy (DCM) was diagnosed in patients who presented with enlarged LVs and reduced LVEF without evidence of coronary artery disease and other known causes.^17,18

The primary endpoint was a composite of death from cardiovascular disease or unplanned hospitalization for HF. Cardiovascular death was defined as death due to HF, fatal myocardial infarction, sudden death, or stroke. HF death was defined as death associated with unstable and progressive deterioration in pumping function despite active therapy. All events for each component of the primary endpoint were reviewed and adjudicated by 2 physicians (M.Y. and T.I.). Clinical outcomes were evaluated for a maximum of 12 months after EMB.

The study conformed to the principles outlined in the Declaration of Helsinki. The study protocol was approved by the Ethics Committee of the Tsukuba Clinical Research & Development Organization (Approval no. R03-221), and information was provided online for patients to opt out of the study (http://www.md.tsukuba.ac.jp/clinicalmed/cardiology/researchgroup/research_group07.html).

Echocardiographic Study and Evaluation of LVRR

Standard 2-dimensional transthoracic echocardiographic examinations were performed prior to EMB according to the American Society of Echocardiography guidelines.¹⁸ LV end-diastolic volume (LVEDV) and LV end-systolic volume (LVESV) were calculated using the Simpson biplane disk method. LVEF was calculated and is expressed as percentage. The LV mass index was calculated by a 2-dimensional parasternal view using linear measurements of interventricular septum thickness, LV internal dimensions, and LV posterior wall thickness at end-diastole. The maximum left atrial volume was measured using Simpson’s biplane method and indexed to body surface area (left atrial volume index). Follow-up echocardiography was performed more than 6–12 months after EBM. LVRR was defined as an absolute increase in LVEF ≥10% to a final value of >35% as assessed with transthoracic echocardiography,^19,20 and a decrease in indexed LV end-diastolic diameter of at least 10% or an indexed LV end-diastolic diameter ≤33 mm/m².²

EMB Procedure and Histologic Evaluation

Myocardial specimens were collected from the right ventricular septum via the internal jugular venous approach using a 7-Fr bioptome (Cordis; Johnson & Johnson Co., New Brunswick, NJ, USA). At least 3 specimens were collected, with 1 specimen subjected to EM evaluation and another to light microscopic examination.

Mitochondrial structural abnormality was assessed by sequentially performed EM. EMB samples were fixed in 2.5% glutaraldehyde and post-fixed in 1% osmium tetroxide. Samples were dehydrated in ethanol and embedded in Epok 812 (Ernest F. Fullam, Inc., Latham, NY, USA). Ultrathin sections were cut using an ultramicrotome, stained with lead citrate and uranyl acetate, and examined under an electron microscope (HT7800; Hitachi Ltd., Ibaraki, Japan).

The measurement process involved observing a minimum of 100 mitochondria at a magnification of ×5,000 in a random field of view within each specimen. Adobe Photoshop (Ver. 25.2; ADOBE, San Jose, CA, USA) was used to measure the length, width, area, and perimeter of each mitochondrion. Outer membrane disruption and cristae disorganization were visually judged to be present. Cristae disorganization included cristae loss, detachment of the inner membrane, and vacuoles (Figure 1).²¹ The evaluation was conducted by an investigator (K.N.) who was blinded to the patient’s clinical background. In each case, 100 mitochondria were selected to calculate the proportion of mitochondria with morphological abnormalities. A receiver operating characteristic (ROC) curve of mitochondrial structural abnormalities for LVRR was created to determine the cut-off value with the highest area under the curve (AUC). The size of normal mitochondria in human cardiomyocytes has been reported be in the range 1–2 μm in length and 0.5–1 μm in width, with an area <2 µm².²² Large mitochondria have been reported to be approximately 5 μm in length and 1 μm in width.²² In the present study, in reference to that previous report, we defined large mitochondria as those larger than 5 μm² (1 μm×5 μm).

Figure 1.

Ultrastructural findings in mitochondria (high magnification). (A) Mitochondria without cristae disorganization. (B) Mitochondria showing the loss of cristae. (C) Mitochondria showing inner membrane detachment. (D) Mitochondria with vacuoles.

Statistical Analysis

The clinical characteristics of LVRR-positive and LVRR-negative patients are described as the median and interquartile range or as numbers and percentages. Blood test data and clinical characteristics obtained immediately before EMB were analyzed. Univariate and multivariable logistic regression analyses were performed to determine predictors of LVRR. Kaplan-Meier analysis was performed to determine the influence of cristae disorganization on the primary endpoint. The primary comparison between groups was performed using a log-rank test. The risk of reaching the clinical endpoint was determined using the Cox proportional hazards model. For all tests, two-tailed P<0.05 were considered statistically significant. Univariate factors with P<0.05 were fitted into the multivariable model to assess the effects of the parameters on endpoints. All statistical analyses were performed using GraphPad Prism version 8.4.3 (GraphPad Software Inc., San Diego, CA, USA) and SPSS version 29.0.2.0 (IBM, Armonk, NY, USA).

Results

Baseline Characteristics According to LVRR

We screened 276 patients who underwent EMB at Tsukuba University Hospital during the registration period. The following patients were excluded: 178 with LVEF ≥45%, 2 with failed biopsy specimen collection, and 5 who were lost to follow-up within 1 year. Finally, 91 patients with LV systolic dysfunction were included in the study. These patients were classified into LVRR-positive (n=52, 57.1%) and LVRR-negative (n=39, 42.9%) groups after follow-up echocardiography.

The median age of the patients was 59 years; 76.9% (n=70) of the patients were men. Regarding the final diagnosis of cardiomyopathy, 79 patients were diagnosed with idiopathic DCM, 5 were diagnosed with cardiac sarcoidosis, 4 were diagnosed with myocarditis, and 1 was diagnosed with muscular dystrophy. Systolic/diastolic blood pressure, heart rate, and body mass index were lower in the LVRR-negative than LVRR-positive group. There were no significant differences between the 2 groups in the history of HF or family history of cardiomyopathy. Biochemical markers, such as plasma B-type natriuretic peptide (BNP), high-sensitivity troponin T, and estimated glomerular filtration rate, also did not differ between the 2 groups. Baseline LVEDV, LVESV, LVEF, interventricular septal wall thickness, left ventricular posterior wall thickness, and LV mass index were lower in the LVRR-negative than LVRR-positive group. Implantable cardioverter defibrillator or cardiac resynchronization therapy-defibrillator implantation was less common in the LVRR-negative group (Table 1). There were no differences between the 2 groups with regard to treatment.

Table 1.

Baseline Characteristics of All Patients and for Those With and Without LVRR Separately

	Total (n=91)	LVRR positive (n=52)	LVRR negative (n=39)	P value
Sociodemographic characteristics
Age (years)	59 [45–69]	58 [44–68]	61 [47–71]	0.535
Male sex	70 (76.9)	42 (80.8)	28 (71.8)	0.320
SBP (mmHg)	122 [104–136]	124 [112–139]	112 [99–133]	0.045
DBP (mmHg)	76 [61–85]	79 [65–89]	65 [56–80]	0.001
Heart rate (beats/min)	80 [65–90]	85 [71–93]	70 [62–89]	0.032
Body mass index (kg/m2)	23.7 [20.9–27.1]	24.8 [22.5–28.7]	22.3 [20.1–25.3]	0.002
History of HF	73 (80.2)	44 (84.6)	29 (74.4)	0.229
Family history of cardiomyopathy	10 (11.0)	5 (9.6)	5 (12.8)	0.633
Comorbidities
Hypertension	29 (31.9)	20 (38.5)	9 (23.1)	0.122
Diabetes	19 (20.9)	11 (21.2)	8 (20.5)	0.942
Atrial fibrillation	22 (24.2)	10 (19.2)	12 (30.8)	0.208
Renal failure (HD)	3 (3.3)	3 (5.8)	0 (0)	0.130
Pacemaker	2 (2.2)	1 (1.9)	1 (2.6)	0.839
ICD or CRT-D	10 (11.0)	2 (3.8)	8 (20.5)	0.012
Biochemical data
Plasma BNP (pg/mL)	305 [90–822]	463 [141–928]	188 [77–510]	0.260
High-sensitivity troponin T (ng/mL)	0.02 [0.01–0.04]	0.02 [0.01–0.04]	0.02 [0.01–0.04]	0.633
eGFR (mL/min/1.73 m2)	63.1 [47–72.0]	63.2 [51–69.3]	62.4 [42.1–75.3]	0.983
Echocardiography
LVDd (mm)	61 [58–68]	60 [58–68]	63 [58–68]	0.540
LVEDV (mL)	186 [146–235]	193 [161–253]	177 [129–207]	0.017
LVESV (mL)	134 [90–178]	147 [101–190]	113 [80–154]	0.022
LVEF (%)	29 [22–38]	27 [20–34]	34 [26–41]	0.023
IVST (mm)	8.4 [7.5–9.7]	9.1 [7.6–10.4]	8.0 [7.0–8.9]	<0.001
LVPWT (mm)	9.1 [8.1–10.4]	9.7 [8.7–10.8]	8.3 [7.3–9.2]	<0.001
LV mass index	131 [112–156]	144 [122–161]	123 [108–138]	0.017
LAVI (mL/m2)	50 [36–67]	53 [39–65]	47 [35–75]	0.102
Moderate MR	22 (24.2)	9 (17.3)	13 (33.3)	0.079
Medications
β-blockers	88 (96.7)	50 (96.2)	38 (97.4)	0.738
ACEi/ARB	54 (58.7)	31 (59.6)	23 (59.0)	0.952
ARNI	21 (23.1)	14 (26.9)	7 (17.9)	0.320
SGLT2i	43 (47.3)	24 (46.2)	19 (48.7)	0.811
MRA	63 (69.2)	36 (69.2)	27 (69.2)	>0.999
Diuretic	49 (53.8)	24 (46.2)	25 (64.1)	0.091
Mitochondria size
Area (μm2)	0.42 [0.35–0.50]	0.41 [0.34–0.49]	0.42 [0.39–0.51]	0.817
Perimeter (μm)	2.58 [2.40–2.86]	2.57 [2.35–2.85]	2.59 [2.45–2.89]	0.399
Standard deviation of area	0.17	0.16	0.18	0.443
Length (μm)	0.78 [0.73–0.87]	0.77 [0.72–0.86]	0.79 [0.75–0.89]	0.218
Width (μm)	0.74 [0.67–0.80]	0.74 [0.66–0.82]	0.74 [0.69–0.78]	0.753
Mitochondrial structural abnormalities
Outer membrane disruption	9 (9.9)	3 (5.8)	6 (15.4)	0.165
Cristae disorganization	29 (31.9)	7 (13.5)	22 (56.4)	<0.001
Large mitochondria (>5 μm2)	2 (2.19)	2 (3.84)	0 (0)	0.505

Unless indicated otherwise, values are presented as the median [interquartile range] or as n (%). ACEi, angiotensin-converting enzyme inhibitor; ARB, angiotensin receptor blocker; ARNI, angiotensin receptor-neprilysin inhibitor; BNP, B-type natriuretic peptide; CRT-D, cardiac resynchronization therapy-defibrillator; DBP, diastolic blood pressure; eGFR, estimated glomerular filtration rate; HD, hemodialysis; HF, heart failure; ICD, implantable cardioverter defibrillator; IVST, interventricular septal wall thickness; LAVI, left atrial volume index; LV, left ventricular; LVDd, left ventricular internal dimension in diastole; LVEDV, left ventricular end-diastolic volume; LVEF, left ventricular ejection fraction; LVESV, left ventricular end-systolic volume; LVPWT, left ventricular posterior wall thickness; LVRR, left ventricular reverse remodeling; MR, mitral regurgitation; MRA, mineralocorticoid receptor antagonist; SBP, systolic blood pressure; SGLT2i, sodium-glucose cotransporter 2 inhibitor.

Relationship Between Mitochondrial Cristae Disorganization and LVRR

Mitochondrial area, perimeter, length, width, and standard deviation were measured (Table 1). The median area of the mitochondria was 0.42 μm²; perimeter, width, and length were 2.58, 0.78, and 0.74 μm, respectively. There were no significant differences in mitochondrial size according to the presence of LVRR.

The ROC curve for LVRR using cristae disorganization revealed an optimal cut-off value of 9% (AUC 0.69; 95% confidence interval [CI] 0.60–0.78; Figure 2). Therefore, cristae disorganization was considered present if observed in >9% of mitochondria in each field of view. Few mitochondria with outer membrane disruption were observed; hence, outer membrane disruption was considered present if observed in even 1 mitochondrion. Regarding abnormalities of mitochondrial structures, outer membrane disruption was observed in 9 (9.9%) patients in the entire cohort, 3 (5.8%) in the LVRR-positive group and 6 (15.4%) in the LVRR-negative group (P=0.165). Cristae disorganization was observed in 21 patients (23.1%) in the entire cohort (Figure 3), 6 (11.5%) and 15 (38.5%) in the LVRR-positive and -negative groups, respectively (P=0.005; Figure 3). Large mitochondria (> 5 μm²) were observed in only 2 (2.19%) patients, both in the LVRR-positive group (Figure 4).

Figure 2.

Receiver operating characteristic curve for the primary endpoint (a composite of cardiovascular death and unplanned hospitalization for heart failure) and cristae disorganization. AUC, area under the curve.

Figure 3.

Ultrastructural findings in mitochondria (low magnification). (A) Minimally damaged mitochondria. (B) Mitochondria with outer membrane disruption and cristae disorganization.

Figure 4.

Representative images of large mitochondria. (A) Large mitochondria with minimal damage. (B) Large mitochondria with cristae disorganization.

The results of logistic regression analysis of LVRR achievement are summarized in the Supplementary Table. Univariate analysis revealed that systolic blood pressure, heart rate, body mass index, LVEDV, LVESV, LVEF, LV mass index, and cristae disorganization were associated with LVRR. In multivariable analysis, cristae disorganization and high heart rate were identified as predictors of LVRR. Specifically, cristae disorganization was a significant predictor of LVRR in each model adjusted for age and sex (Model 1), vital signs and body mass index (Model 2), and baseline LV function (Model 3). High systolic blood pressure and body mass index also showed a tendency to be associated with LVRR.

Clinical Outcomes

Kaplan-Meier estimates of the time to endpoints in the presence of cristae disorganization are shown in Figure 5. During the 1-year post-EMB observation period, 16 patients (17.6%) met the primary endpoint, with 2 (2.2%) cardiovascular deaths and 14 (15.4%) HF hospitalizations. Of the patients with cristae disorganization, 10 (35.7%) met the primary endpoint, compared with 6 (10.5%) without cristae disorganization (hazard ratio 4.154; 95% CI 1.508–11.441; P=0.006).

Figure 5.

Kaplan-Meier curves according to the presence of cristae disorganization.

The results of the univariate and multivariable Cox proportional hazards model analyses are summarized in Table 2. Systolic blood pressure, log plasma BNP concentration, significant mitral regurgitation, and cristae disorganization were associated with the endpoints. In the multivariable Cox proportional hazards model, cristae disorganization (P=0.002) was significantly associated with endpoints independent of age (P=0.115), systolic blood pressure (P=0.004), BNP level (P=0.042), and significant mitral regurgitation (P=0.003).

Table 2.

Death From Cardiac Causes or Unplanned Hospitalization for HF by the Cox Proportional Hazard Model

Variable	Univariate		Multivariable Model 1		Multivariable Model 2
	HR (95% CI)	P value	HR (95% CI)	P value	HR (95% CI)	P value
Age	1.024 (0.989–1.061)	0.186	1.025 (0.994–1.058)	0.115
Male sex	0.748 (0.213–2.626)	0.651
SBP	0.970 (0.948–0.993)	0.010	0.965 (0.943–0.989)	0.004
Heart rate	1.006 (0.977–1.036)	0.680
Body mass index	0.921 (0.820–1.033)	0.159
Hypertension	0.445 (0.127–1.561)	0.206
Diabetes	2.421 (0.879–6.666)	0.087
Atrial fibrillation	1.467 (0.509–4.222)	0.478
Log[BNP]	1.801 (1.173–2.763)	0.007			1.603 (1.018–2.524)	0.042
eGFR	0.979 (0.957–1.002)	0.075
LVDd	1.031 (0.961–1.107)	0.392
LVEDV	0.999 (0.992–1.006)	0.766
LVESV	1.001 (0.993–1.008)	0.862
LVEF	0.958 (0.909–1.010)	0.110
LV mass index	0.990 (0.973–1.007)	0.245
LAVI	1.003 (0.993–1.014)	0.572
Moderate MR	7.729 (2.680–22.291)	<0.001			5.872 (1.790–19.255)	0.003
Cristae disorganization	4.154 (1.508–11.441)	0.006	4.905 (1.752–13.729)	0.002	3.671 (1.218–11.069)	0.021

Multivariable Model 1; age, SBP, cristae disorganization. Multivariable Model 2; log[BNP], MR, cristae disorganization. CI, confidence interval; HR, hazard ratio. Other abbreviations as in Table 1.

Discussion

To the best of our knowledge, this is the first study to reveal an association between mitochondrial structural abnormalities in cardiomyocytes and LVRR in patients with systolic dysfunction. We classified the mitochondrial structural abnormalities and showed that cristae disorganization was associated with LVRR and worse prognosis, along with mitral regurgitation, systolic blood pressure, and plasma BNP concentrations. To date, EMB has mainly been used for the differential diagnosis of cardiomyopathy. However, this study showed that myocardial biopsy could have additional value in predicting subsequent LVRR and prognosis.

Regarding the prognostic value of myocardial biopsy, a recent study reported that myocardial autophagy assessed using immunostaining was associated with LVRR.¹³ That study demonstrated the importance of autophagy in the failing hearts in patients with DCM, and that the number of autophagic vacuoles and cathepsin D expression levels may be independent predictors of LVRR.¹³ Another study reported an association between LVRR and abnormalities in myocardial DNA.¹⁴ That study suggested that DNA damage determines the outcome in patients with HF and that quantification of DNA damage is useful for predicting the response to medical treatment and long-term prognosis in patients with HFrEF, regardless of the underlying disease.¹⁴ Our proposed method for evaluating cristae disorganization in mitochondria is a semiquantitative but simple method that does not require immunostaining or additional procedures. Thus, our method is applicable to most patients undergoing EBM in clinical practice.

In patients with HF, mitochondrial fragmentation, vacuolar degeneration with reduced mitochondrial size, and cristae disorganization are detected using transmission EM, along with increased expression levels of dynamin-related protein 1 (DRP1) and Bcl-2 interacting protein 3 (BNIP3).^23–25 The degree of mitochondrial injury is correlated with an increase in plasma norepinephrine levels, suggesting that sympathoadrenal hyperactivity is involved in mitochondrial dysfunction in patients with HF.²⁶ However, the relationship between mitochondrial morphology and prognosis in patients with HF has not yet been established. In this study, we evaluated the size and prevalence of large mitochondria, outer membrane disruption, and cristae disorganization as structural abnormalities. Of these, only cristae disorganization was associated with LVRR and cardiovascular prognosis. Levels of mitofilin, a structural protein of the inner mitochondrial membrane, have also been reported to be significantly reduced in LV tissues from explanted failed human hearts compared with normal donor hearts, and downregulation of mitofilin in HeLa cells resulted in mitochondria with abnormal morphology characterized by disorganized inner membranes.^27,28 When cristae disorganization occurs, mitochondrial DNA is released and the type 1 interferon response is activated.²¹ The inflammatory response induced by elevated interferon levels may be one of the mechanisms contributing to LV remodeling and poor prognosis.

It has been hypothesized that the formation of large mitochondria in cardiomyocytes is a result of swelling, fusion, mitotic inhibition, and incomplete autophagy.²² Such alterations in mitochondrial structure and function have been implicated in important aspects of the pathogenesis of cardiovascular diseases beyond ATP synthesis, including vascular smooth muscle pathology, myofibril destruction, and altered cell differentiation.²⁹ The outer membrane plays a crucial role in retaining proteins that are fundamental for the physiological function of the organelle.³⁰ Therefore, outer membrane disruption is thought to be associated with decreased mitochondrial function or mitochondrial loss due to apoptosis. In the present study, only a few patients had large mitochondria or outer membrane disruption; consequently, the significance of these features could not be fully investigated. Alternatively, a study that indirectly reflects outer membrane disruption, such as one analyzing the presence of mitochondrial apoptosis, would be valuable. Further studies are required to clarify the significance of findings other than cristae disorganization.

Study Limitations

Our study has some limitations. First, it was a single-center study and the sample size was relatively small; thus, the statistical power may not be sufficient. Second, this was a retrospective study conducted in daily practice and included patients with cardiomyopathies of different etiologies. In particular, cases of mild myocarditis could not be strictly distinguished from those of inflammatory DCM and were included in the study. The mechanism of reverse remodeling in patients with myocarditis is different from that in patients with DCM, which may have potentially affected the results. Furthermore, we were unable to test for mitochondrial gene expression or respiratory enzyme activity in all patients. Therefore, we cannot entirely rule out the possibility that some patients with mitochondrial cardiomyopathy may have been included. Third, we obtained specimens only from the right ventricular septum; the results of this study may not be applicable to facilities where myocardial biopsies are performed on the LV. Finally, robust methods for evaluating mitochondrial structure have not been previously established, and some include qualitative evaluation. Further research is needed to standardize the evaluation of mitochondrial structure for clinical application of the study results.

Conclusions

We classified mitochondrial structural abnormalities and showed that cristae disorganization was associated with LVRR and worse prognosis. The results of this study may affect the management of patients with HF and systolic dysfunction who undergo EMB.

Acknowledgments / Sources of Funding / Disclosures

None.

IRB Information

The study protocol was approved by the Ethics Committee of the Tsukuba Clinical Research & Development Organization (Approval no. R03-221). Information was provided online for patients to opt out of the study (https://www.md.tsukuba.ac.jp/clinical-med/cardiology/research_group/research_group07.html).

Data Availability

The deidentified participant data will not be shared.

Supplementary Files

Please find supplementary file(s);

https://doi.org/10.1253/circj.CJ-24-0451

References

• 1.   Becher PM, Lund LH, Coats AJS, Savarese G. An update on global epidemiology in heart failure. Eur Heart J 2022; 43: 3005–3007, doi:10.1093/eurheartj/ehac248.
• 2.   Merlo M, Pyxaras SA, Pinamonti B, Barbati G, Di Lenarda A, Sinagra G. Prevalence and prognostic significance of left ventricular reverse remodeling in dilated cardiomyopathy receiving tailored medical treatment. J Am Coll Cardiol 2011; 57: 1468–1476, doi:10.1016/j.jacc.2010.11.030.
• 3.   Merlo M, Cannata A, Gobbo M, Stolfo D, Elliott PM, Sinagra G. Evolving concepts in dilated cardiomyopathy. Eur J Heart Fail 2018; 20: 228–239, doi:10.1002/ejhf.1103.
• 4.   Zecchin M, Merlo M, Pivetta A, Barbati G, Lutman C, Gregori D, et al. How can optimization of medical treatment avoid unnecessary implantable cardioverter-defibrillator implantations in patients with idiopathic dilated cardiomyopathy presenting with “SCD-HeFT criteria?” Am J Cardiol 2012; 109: 729–735, doi:10.1016/j.amjcard.2011.10.033.
• 5.   Piquereau J, Caffin F, Novotova M, Lemaire C, Veksler V, Garnier A, et al. Mitochondrial dynamics in the adult cardiomyocytes: Which roles for a highly specialized cell? Front Physiol 2013; 4: 102, doi:10.3389/fphys.2013.00102.
• 6.   Zhou B, Tian R. Mitochondrial dysfunction in pathophysiology of heart failure. J Clin Invest 2018; 128: 3716–3726, doi:10.1172/JCI120849.
• 7.   Chaanine AH, Sreekumaran Nair K, Bergen RH 3rd, Klaus K, Guenzel AJ, Hajjar RJ, et al. Mitochondrial integrity and function in the progression of early pressure overload-induced left ventricular remodeling. J Am Heart Assoc 2017; 6: e005869, doi:10.1161/JAHA.117.005869.
• 8.   Rosca MG, Tandler B, Hoppel CL. Mitochondria in cardiac hypertrophy and heart failure. J Mol Cell Cardiol 2013; 55: 31–41, doi:10.1016/j.yjmcc.2012.09.002.
• 9.   Ponikowski P, Voors AA, Anker SD, Bueno H, Cleland JGF, Coats AJS, et al. 2016 ESC guidelines for the diagnosis and treatment of acute and chronic heart failure: The Task Force for the diagnosis and treatment of acute and chronic heart failure of the European Society of Cardiology (ESC) developed with the special contribution of the Heart Failure Association (HFA) of the ESC. Eur Heart J 2016; 37: 2129–2200, doi:10.1093/eurheartj/ehw128.
• 10.   Chimenti C, Verardo R, Scopelliti F, Grande C, Petrosillo N, Piselli P, et al. Myocardial expression of Toll-like receptor 4 predicts the response to immunosuppressive therapy in patients with virus-negative chronic inflammatory cardiomyopathy. Eur J Heart Fail 2017; 19: 915–925, doi:10.1002/ejhf.796.
• 11.   Besler C, Urban D, Watzka S, Lang D, Rommel KP, Kandolf R, et al. Endomyocardial miR-133a levels correlate with myocardial inflammation, improved left ventricular function, and clinical outcome in patients with inflammatory cardiomyopathy. Eur J Heart Fail 2016; 18: 1442–1451, doi:10.1002/ejhf.579.
• 12.   Seferović PM, Tsutsui H, McNamara DM, Ristić AD, Basso C, Bozkurt B, et al. Heart Failure Association, Heart Failure Society of America, and Japanese Heart Failure Society position statement on endomyocardial biopsy. J Card Fail 2021; 27: 727–743, doi:10.1016/j.cardfail.2021.04.010.
• 13.   Kanamori H, Yoshida A, Naruse G, Endo S, Minatoguchi S, Watanabe T, et al. Impact of autophagy on prognosis of patients with dilated cardiomyopathy. J Am Coll Cardiol 2022; 79: 789–801, doi:10.1016/j.jacc.2021.11.059.
• 14.   Dai Z, Ko T, Fujita K, Nomura S, Uemura Y, Onoue K, et al. Myocardial DNA damage predicts heart failure outcome in various underlying diseases. JACC Heart Fail 2024; 12: 648–661, doi:10.1016/j.jchf.2023.09.027.
• 15.   Leone O, Veinot JP, Angelini A, Baandrup UT, Basso C, Berry G, et al. 2011 consensus statement on endomyocardial biopsy from the Association for European Cardiovascular Pathology and the Society for Cardiovascular Pathology. Cardiovasc Pathol 2012; 21: 245–274, doi:10.1016/j.carpath.2011.10.001.
• 16.   Kitaoka H, Tsutsui H, Kubo T, Ide T, Chikamori T, Fukuda K, et al. JCS/JHFS 2018 guideline on the diagnosis and treatment of cardiomyopathies. Circ J 2021; 85: 1590–1689, doi:10.1253/circj.CJ-20-0910.
• 17.   Bozkurt B, Colvin M, Cook J, Cooper LT, Deswal A, Fonarow GC, et al. Current diagnostic and treatment strategies for specific dilated cardiomyopathies: A scientific statement from the American Heart Association. Circulation 2016; 134: e579–e646, doi:10.1161/CIR.0000000000000455.
• 18.   Japp AG, Gulati A, Cook SA, Cowie MR, Prasad SK. The diagnosis and evaluation of dilated cardiomyopathy. J Am Coll Cardiol 2016; 67: 2996–3010, doi:10.1016/j.jacc.2016.03.590.
• 19.   Kubanek M, Sramko M, Maluskova J, Kautznerova D, Weichet J, Lupinek P, et al. Novel predictors of left ventricular reverse remodeling in individuals with recent-onset dilated cardiomyopathy. J Am Coll Cardiol 2013; 61: 54–63, doi:10.1016/j.jacc.2012.07.072.
• 20.   Escobar-Lopez L, Ochoa JP, Mirelis JG, Espinosa MA, Navarro M, Gallego-Delgado M, et al. Association of genetic variants with outcomes in patients with nonischemic dilated cardiomyopathy. J Am Coll Cardiol 2021; 78: 1682–1699, doi:10.1016/j.jacc.2021.08.039.
• 21.   He B, Yu H, Liu S, Wan H, Fu S, Liu S, et al. Mitochondrial cristae architecture protects against mtDNA release and inflammation. Cell Rep 2022; 41: 111774, doi:10.1016/j.celrep.2022.111774.
• 22.   Li A, Shami GJ, Griffiths L, Lal S, Irving H, Braet F. Giant mitochondria in cardiomyocytes: Cellular architecture in health and disease. Basic Res Cardiol 2023; 118: 39, doi:10.1007/s00395-023-01011-3.
• 23.   Ikeda Y, Shirakabe A, Maejima Y, Zhai P, Sciarretta S, Toli J, et al. Endogenous Drp1 mediates mitochondrial autophagy and protects the heart against energy stress. Circ Res 2015; 116: 264–278, doi:10.1161/CIRCRESAHA.116.303356.
• 24.   Chaanine AH, Joyce LD, Stulak JM, Maltais S, Joyce DL, Dearani JA, et al. Mitochondrial morphology, dynamics, and function in human pressure overload or ischemic heart disease with preserved or reduced ejection fraction. Circ Heart Fail 2019; 12: e005131, doi:10.1161/CIRCHEARTFAILURE.118.005131.
• 25.   Xu S, Wang P, Zhang H, Gong G, Gutierrez Cortes N, Zhu W, et al. CaMKII induces permeability transition through Drp1 phosphorylation during chronic beta-AR stimulation. Nat Commun 2016; 7: 13189, doi:10.1038/ncomms13189.
• 26.   Sabbah HN, Sharov V, Riddle JM, Kono T, Lesch M, Goldstein S. Mitochondrial abnormalities in myocardium of dogs with chronic heart failure. J Mol Cell Cardiol 1992; 24: 1333–1347, doi:10.1016/0022-2828(92)93098-5.
• 27.   John GB, Shang Y, Li L, Renken C, Mannella CA, Selker JM, et al. The mitochondrial inner membrane protein mitofilin controls cristae morphology. Mol Biol Cell 2005; 16: 1543–1554, doi:10.1091/mbc.e04-08-0697.
• 28.   Sabbah HN, Gupta RC, Singh-Gupta V, Zhang K, Lanfear DE. Abnormalities of mitochondrial dynamics in the failing heart: normalization following long-term therapy with elamipretide. Cardiovasc Drugs Ther 2018; 32: 319–328, doi:10.1007/s10557-018-6805-y.
• 29.   Brown DA, Perry JB, /\Allen ME, Sabbah HN, Stauffer BL, Shaikh SR, et al. Expert consensus document: Mitochondrial function as a therapeutic target in heart failure. Nat Rev Cardiol 2017; 14: 238–250, doi:10.1038/nrcardio.2016.203.
• 30.   Giacomello M, Pyakurel A, Glytsou C, Scorrano L. The cell biology of mitochondrial membrane dynamics. Nat Rev Mol Cell Biol 2020; 21: 204–224, doi:10.1038/s41580-020-0210-7.