Heart Failure With Mildly Reduced Ejection Fraction

Let's dive into heart failure with mildly reduced ejection fraction (HFmrEF), a complex cardiac condition that requires a nuanced understanding. Often overshadowed by its more prominently recognized counterparts, heart failure with preserved ejection fraction (HFpEF) and heart failure with reduced ejection fraction (HFrEF), HFmrEF represents a unique subset of heart failure patients. This article aims to provide a comprehensive overview of HFmrEF, covering its definition, pathophysiology, diagnosis, management, and future directions.

Understanding Heart Failure with Mildly Reduced Ejection Fraction (HFmrEF)

Heart failure (HF) is a clinical syndrome characterized by the heart's inability to pump sufficient blood to meet the body's needs. Which means hFmrEF, also known as heart failure with mid-range ejection fraction, is defined as heart failure with an EF between 41% and 49%. Think about it: ejection fraction (EF), a measure of the percentage of blood the left ventricle pumps out with each contraction, is a key metric used to classify heart failure. This category sits between HFrEF (EF ≤ 40%) and HFpEF (EF ≥ 50%).

The recognition of HFmrEF as a distinct entity has evolved over time. Initially, patients with EF in this range were often grouped with either HFrEF or HFpEF. That said, accumulating evidence suggests that HFmrEF patients exhibit unique clinical characteristics, responses to therapies, and underlying pathophysiology, warranting its classification as a separate category.

Pathophysiology: A Complex Interplay of Factors

The pathophysiology of HFmrEF is believed to be a complex combination of factors that are seen in both HFrEF and HFpEF. It's neither purely a systolic dysfunction (as in HFrEF) nor purely a diastolic dysfunction (as in HFpEF), but rather a blend of both.

Here's a breakdown of the key pathophysiological mechanisms:

Systolic Dysfunction: In HFmrEF, the heart muscle may have a slightly impaired ability to contract forcefully. This can be due to factors such as myocardial ischemia, prior myocardial infarction, or subtle forms of cardiomyopathy. The reduced contractility leads to a decrease in the amount of blood ejected with each beat, contributing to the overall heart failure syndrome.
Diastolic Dysfunction: Impaired relaxation and filling of the left ventricle during diastole is another important feature of HFmrEF. This can be caused by factors such as left ventricular hypertrophy, fibrosis, or increased stiffness of the heart muscle. Diastolic dysfunction leads to elevated filling pressures, which can result in pulmonary congestion and shortness of breath, common symptoms of heart failure.
Cardiac Remodeling: Over time, the heart may undergo structural changes in response to the underlying stressors. This process, known as cardiac remodeling, can involve changes in the size, shape, and composition of the heart. In HFmrEF, remodeling can contribute to both systolic and diastolic dysfunction, further exacerbating the heart failure syndrome.
Neurohormonal Activation: The body's neurohormonal systems, such as the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS), are often activated in heart failure. This activation is initially compensatory, helping to maintain blood pressure and cardiac output. That said, chronic activation of these systems can lead to adverse effects, such as increased sodium and water retention, vasoconstriction, and further cardiac remodeling.
Inflammation and Endothelial Dysfunction: Emerging evidence suggests that inflammation and endothelial dysfunction play a role in the pathophysiology of HFmrEF. Inflammation can contribute to myocardial damage and fibrosis, while endothelial dysfunction can impair blood vessel function and contribute to ischemia.

Diagnosing HFmrEF: A Multifaceted Approach

Diagnosing HFmrEF involves a comprehensive assessment of the patient's clinical history, physical examination findings, and diagnostic test results. Since the symptoms of HFmrEF can overlap with other conditions, a systematic approach is essential to arrive at an accurate diagnosis.

Here's an outline of the diagnostic process:

Clinical History and Physical Examination:
- Symptoms: Common symptoms of HFmrEF include shortness of breath (dyspnea), fatigue, swelling in the ankles and legs (edema), and exercise intolerance. Patients may also experience orthopnea (shortness of breath when lying down) and paroxysmal nocturnal dyspnea (sudden shortness of breath at night).
- Risk Factors: Identifying risk factors for heart failure is crucial. These include hypertension, coronary artery disease, diabetes, obesity, valvular heart disease, and a history of myocardial infarction.
- Physical Examination: The physical examination may reveal signs of fluid overload, such as jugular venous distension, pulmonary crackles (rales), and peripheral edema. A heart murmur may be present if there is underlying valvular heart disease.
Echocardiography:
- Echocardiography is the cornerstone of HFmrEF diagnosis. It provides detailed information about the structure and function of the heart.
- Ejection Fraction (EF): As mentioned earlier, an EF between 41% and 49% is a key diagnostic criterion for HFmrEF.
- Left Ventricular Size and Function: Echocardiography can assess the size and function of the left ventricle, including measurements of left ventricular volumes and wall thickness.
- Diastolic Function Assessment: Doppler echocardiography can be used to assess diastolic function, including parameters such as E/A ratio, E/e' ratio, and deceleration time. Evidence of diastolic dysfunction is often present in HFmrEF.
- Valvular Abnormalities: Echocardiography can identify any valvular abnormalities that may be contributing to heart failure.
Electrocardiogram (ECG):
- An ECG can help identify underlying cardiac abnormalities, such as arrhythmias (e.g., atrial fibrillation), left ventricular hypertrophy, or evidence of prior myocardial infarction.
Blood Tests:
- B-type Natriuretic Peptide (BNP) or N-terminal pro-BNP (NT-proBNP): These are biomarkers that are elevated in heart failure. They can help support the diagnosis and assess the severity of heart failure.
- Complete Blood Count (CBC): A CBC can help identify anemia or other blood disorders that may be contributing to symptoms.
- Renal Function Tests: Assessing kidney function is important, as kidney disease is common in heart failure patients and can affect treatment decisions.
- Liver Function Tests: Liver function tests can help identify liver disease, which can also contribute to symptoms.
- Thyroid Function Tests: Thyroid disorders can affect heart function, so it is important to rule them out.
Other Diagnostic Tests:
- Cardiac Magnetic Resonance Imaging (MRI): Cardiac MRI can provide more detailed information about the structure and function of the heart, including assessment of myocardial fibrosis and scar tissue.
- Coronary Angiography: If coronary artery disease is suspected, coronary angiography may be performed to assess the presence and severity of blockages in the coronary arteries.
- Cardiopulmonary Exercise Testing (CPET): CPET can help assess exercise capacity and identify the underlying mechanisms of exercise intolerance.

Management Strategies for HFmrEF

The management of HFmrEF is aimed at alleviating symptoms, improving quality of life, and preventing disease progression. Given the overlap in pathophysiology with both HFrEF and HFpEF, treatment strategies often involve a combination of approaches used in both conditions. On the flip side, it's crucial to recognize that evidence supporting specific therapies in HFmrEF is still evolving.

Here's a comprehensive overview of the management strategies:

Lifestyle Modifications:
- Dietary Changes:
  - Sodium Restriction: Limiting sodium intake to less than 2 grams per day can help reduce fluid retention and alleviate symptoms.
  - Fluid Restriction: In some cases, fluid restriction may be necessary to manage fluid overload.
  - Weight Management: Maintaining a healthy weight can reduce the workload on the heart.
- Exercise:
  - Regular Aerobic Exercise: Supervised exercise programs can improve exercise capacity and quality of life.
  - Cardiac Rehabilitation: Cardiac rehabilitation programs provide structured exercise training, education, and support.
- Smoking Cessation: Smoking is a major risk factor for heart disease and should be avoided.
- Alcohol Consumption: Limiting alcohol consumption is important, as excessive alcohol intake can worsen heart failure.
Pharmacological Therapies:
- Diuretics:
  - Diuretics, such as furosemide and torsemide, are used to reduce fluid overload and alleviate symptoms such as shortness of breath and edema.
  - make sure to monitor electrolytes and kidney function when using diuretics.
- Angiotensin-Converting Enzyme (ACE) Inhibitors or Angiotensin Receptor Blockers (ARBs):
  - ACE inhibitors and ARBs are commonly used in HFrEF to block the RAAS system. While evidence in HFmrEF is less strong, these medications are often considered, particularly in patients with hypertension or other indications.
- Beta-Blockers:
  - Beta-blockers are also commonly used in HFrEF to reduce heart rate and improve cardiac function. Their role in HFmrEF is less clear, but they may be beneficial in some patients, especially those with arrhythmias or hypertension.
- Mineralocorticoid Receptor Antagonists (MRAs):
  - MRAs, such as spironolactone and eplerenone, block the effects of aldosterone and can help reduce fluid retention and improve outcomes in HFrEF. Their use in HFmrEF is being investigated, and some studies suggest potential benefits.
- Angiotensin Receptor-Neprilysin Inhibitor (ARNI):
  - ARNI, such as sacubitril/valsartan, combines an ARB with a neprilysin inhibitor. This medication has been shown to improve outcomes in HFrEF and is being studied in HFmrEF. Some evidence suggests potential benefits in reducing hospitalizations and improving quality of life.
- Sodium-Glucose Cotransporter 2 (SGLT2) Inhibitors:
  - SGLT2 inhibitors, such as empagliflozin and dapagliflozin, have been shown to improve outcomes in both HFrEF and HFpEF. Recent studies suggest that SGLT2 inhibitors may also be beneficial in HFmrEF, reducing the risk of hospitalization for heart failure and cardiovascular death.
- Digoxin:
  - Digoxin can help control heart rate and improve symptoms in some patients with HFmrEF, particularly those with atrial fibrillation. That said, it does not improve survival.
- Ivabradine:
  - Ivabradine reduces heart rate by selectively inhibiting the If current in the sinoatrial node. It may be considered in patients with HFmrEF who have a resting heart rate of 70 bpm or higher despite being on guideline-directed medical therapy.
Device Therapies:

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- Implantable Cardioverter-Defibrillator (ICD):
  - An ICD may be considered in patients with HFmrEF who are at high risk of sudden cardiac death due to ventricular arrhythmias.
- Cardiac Resynchronization Therapy (CRT):
  - CRT may be considered in patients with HFmrEF who have a wide QRS complex on their ECG and evidence of left ventricular dyssynchrony. CRT can help improve cardiac function and reduce symptoms.
Management of Comorbidities:
- Hypertension: Controlling blood pressure is essential in HFmrEF.
- Coronary Artery Disease: Managing coronary artery disease with medications, angioplasty, or bypass surgery can improve heart function.
- Diabetes: Controlling blood sugar levels is important in patients with diabetes and HFmrEF.
- Atrial Fibrillation: Managing atrial fibrillation with medications or ablation can help improve heart function and reduce the risk of stroke.
- Obesity: Weight loss can improve heart function and reduce symptoms.
- Sleep Apnea: Treating sleep apnea can improve heart function and reduce symptoms.
- Anemia: Addressing anemia can improve oxygen delivery to the heart and reduce symptoms.
- Chronic Kidney Disease: Managing chronic kidney disease is important, as kidney disease can worsen heart failure.
Monitoring and Follow-Up:
- Regular follow-up appointments with a cardiologist are essential to monitor symptoms, adjust medications, and assess the effectiveness of treatment.
- Patients should be educated about their condition, medications, and lifestyle modifications.
- Monitoring weight, blood pressure, and heart rate at home can help detect changes early.
- Regular blood tests and echocardiograms may be needed to assess heart function and monitor for complications.

The Scientific Basis for Treatment Choices

Treatment choices in HFmrEF are often guided by evidence from studies on HFrEF and HFpEF, as well as smaller studies specifically focused on HFmrEF. Here's a look at the evidence supporting some key treatments:

ACE Inhibitors/ARBs: These medications have a strong evidence base in HFrEF, showing benefits in reducing mortality and hospitalizations. Their use in HFmrEF is often extrapolated from this data, with the understanding that RAAS activation plays a role in this condition as well.
Beta-Blockers: Similar to ACE inhibitors/ARBs, beta-blockers have proven benefits in HFrEF. In HFmrEF, their use is often designed for individual patient characteristics, such as the presence of hypertension or arrhythmias.
MRAs: Studies in HFrEF have demonstrated the benefits of MRAs in reducing mortality and hospitalizations. Their role in HFmrEF is still being investigated, but some studies suggest potential benefits, particularly in patients with persistent symptoms despite other therapies.
ARNI (Sacubitril/Valsartan): The PARADIGM-HF trial, which primarily included patients with HFrEF, showed significant benefits with sacubitril/valsartan compared to enalapril. Subsequent analyses have suggested that sacubitril/valsartan may also be beneficial in patients with HFmrEF, leading to its consideration in this population.
SGLT2 Inhibitors: Recent trials, such as EMPEROR-Reduced (in HFrEF) and EMPEROR-Preserved (in HFpEF), have demonstrated the benefits of SGLT2 inhibitors in reducing heart failure hospitalizations and cardiovascular death. These findings have led to the investigation of SGLT2 inhibitors in HFmrEF, with promising results suggesting similar benefits.

Future Directions and Research

Research into HFmrEF is ongoing, with the goal of better understanding the underlying pathophysiology and identifying more effective treatment strategies.

Here are some key areas of future research:

Phenotyping HFmrEF: Identifying distinct subgroups or phenotypes within HFmrEF based on clinical characteristics, biomarkers, and imaging findings could help tailor treatment strategies to individual patients.
Targeted Therapies: Developing therapies that specifically target the underlying pathophysiological mechanisms in HFmrEF could lead to more effective treatments. This could include therapies that address myocardial fibrosis, inflammation, or endothelial dysfunction.
Clinical Trials: Conducting large-scale clinical trials specifically focused on HFmrEF is essential to evaluate the efficacy and safety of different treatment strategies.
Biomarker Research: Identifying novel biomarkers that can help diagnose HFmrEF, assess its severity, and predict prognosis could improve patient care.
Imaging Techniques: Advancing imaging techniques, such as cardiac MRI and PET scans, could provide more detailed information about the structure and function of the heart in HFmrEF, leading to better diagnosis and treatment.

HFmrEF: Frequently Asked Questions

Is HFmrEF a stable condition, or does it tend to progress to HFrEF or HFpEF? The natural history of HFmrEF is variable. Some patients may remain stable for many years, while others may progress to either HFrEF or HFpEF. Regular monitoring and appropriate management are essential to prevent disease progression.
Are there any specific lifestyle recommendations that are particularly important for HFmrEF patients? In addition to general heart-healthy lifestyle recommendations, such as a low-sodium diet and regular exercise, it's important for HFmrEF patients to closely monitor their weight and fluid intake and to report any changes in symptoms to their healthcare provider promptly.
How often should HFmrEF patients have their ejection fraction checked? The frequency of EF checks depends on the individual patient's clinical stability and treatment plan. In general, EF should be checked at baseline and periodically thereafter, especially if there are changes in symptoms or treatment.
What is the role of exercise in HFmrEF? Supervised exercise programs can improve exercise capacity, quality of life, and symptoms in HFmrEF patients. That said, you'll want to start slowly and gradually increase the intensity and duration of exercise under the guidance of a healthcare professional.
Are there any specific medications that should be avoided in HFmrEF? Certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and some antiarrhythmic drugs, can worsen heart failure and should be used with caution or avoided in HFmrEF patients. it helps to discuss all medications with a healthcare provider.

Conclusion

Heart failure with mildly reduced ejection fraction represents a distinct and important category of heart failure. Here's the thing — its pathophysiology is complex, involving elements of both systolic and diastolic dysfunction. Practically speaking, diagnosis requires a comprehensive assessment, including clinical history, physical examination, echocardiography, and blood tests. Management strategies involve lifestyle modifications, pharmacological therapies, device therapies, and management of comorbidities.

While treatment decisions are often guided by evidence from studies on HFrEF and HFpEF, ongoing research is crucial to better understand HFmrEF and identify more effective therapies. Future research directions include phenotyping HFmrEF, developing targeted therapies, and conducting large-scale clinical trials. By improving our understanding and management of HFmrEF, we can improve the lives of patients living with this challenging condition.