Comprehensive Study Guide on Restrictive Cardiomyopathy

Overview and Definition of Restrictive Cardiomyopathy

• Definition of RCM: Restrictive Cardiomyopathy (RCM) is defined as a rare form of heart muscle disease characterized by restrictive filling of the ventricles.
• Characteristics of Filling: The relaxation or filling phase of the heart in this condition is considered highly abnormal.
• Physiological Cause: The heart muscle becomes stiff and poorly compliant, which prevents the ventricular chambers from filling with blood normally.
• Systolic Function: In the early stages, the Left Ventricular (LV) systolic function remains essentially normal.
• Prevalence: RCM is the least common form among all cardiomyopathies. It is rare but can occur in young individuals.

Etiology and Classification

• Most Frequent Causes:
  • Infiltrative Diseases: Amyloidosis (the most common cause), Hemochromatosis, and Sarcoidosis.
  • Metabolic Storage Diseases: Glycogen storage disease and Fabry Disease.
  • Idiopathic: Cases where the primary cause is unknown.
• Less Common Forms:
  • Endomyocardial fibrosis associated with hypereosinophilic syndrome.
  • Carcinoid syndrome.
  • Metastatic malignancy.
  • Post-radiation or drug-induced cardiomyopathy.

Pathophysiology and Morphological Features

• Morphological Motto: "Normal Size, Stiff Muscle."
• Ventricular Dimensions:
  • LV size remains normal.
  • LV volume is generally preserved.
• Systolic vs. Diastolic Function:
  • LV Systolic Function (Ejection Fraction): Usually normal.
  • LV Diastolic Function: Severely impaired due to stiffness.
• Atrial Status: The atria (Left Atrium and Right Atrium) are typically enlarged (biatrial enlargement).
• Progression of Pathophysiology:
  • Heart Failure with Preserved Ejection Fraction (HFpEF): Also known as Diastolic Heart Failure.
  • Primary Dysfunction: Abnormal ventricular filling leads to increased Left Ventricular End-Diastolic Pressure ($LVEDP$), which subsequently causes dilated atria.
  • Later Stages: Eventually, the disease may progress to impaired LV systolic function and reduced Ejection Fraction ($EF$).

2D Echocardiographic Features

• Biatrial Enlargement: Significant expansion of both the left and right atria.
• Ventricular Volumes: LV volumes are preserved.
• Systolic Function: LV systolic function is preserved during the early stage.
• Inferior Vena Cava (IVC): The IVC appears dilated.
• Valvular Findings: Homogenous Atrioventricular (AV) valve thickening.
• Pericardial Findings: A small Pericardial Effusion (PE) may be present.

M-Mode Echocardiography Procedure and Findings

• Procedural Steps (Normal Values Assessment):
  • Step 1: Obtain a clear Parasternal Long Axis (PLAX) view.
  • Step 2: Select M-Mode button.
  • Step 3: Place the cursor to pass through the Interventricular Septum ($IVS$), LV cavity, and Posterior Wall ($PW$).
  • Step 4: Keep the cursor at the chordal level, just below the mitral valve leaflets.
  • Step 5: Record the M-mode tracing and freeze the image.
  • Step 6: Measure $IVSd$, $LVIDd$, $LVIDs$, and $PWd$.
  • Step 7: Assess LV function (Machine calculates Fractional Shortening ($FS\%$) and Ejection Fraction ($EF$)).
• Normal Adult Values for M-Mode:
  • $LVIDd$ (LV Internal Diameter in Diastole): $3.9 - 5.9\,cm$
  • $LVIDs$ (LV Internal Diameter in Systole): $2.0 - 4.0\,cm$
  • $IVSd$ (Interventricular Septum in Diastole): $0.6 - 1.0\,cm$
  • $PWd$ (Posterior Wall Thickness in Diastole): $0.6 - 1.0\,cm$
  • $FS\%$ (Fractional Shortening): $25 - 45\,\%$
  • $LVEF$ (Left Ventricular Ejection Fraction): $55 - 70\,\%$
• RCM-Specific M-Mode Findings:
  • Lack of septal bounce.
  • Myocardial hypertrophy (increased wall thickness).

Doppler Assessment: MR and TR

• Mitral Regurgitation (MR):
  • Assessed using Continuous Wave (CW) Doppler.
  • Used to calculate LV $dp/dt$.
  • MR can occur due to leaflet or papillary muscle involvement.
  • Diastolic MR: May occur due to significantly increased LV end-diastolic pressure.
• Tricuspid Regurgitation (TR):
  • Assessed using CW Doppler to determine Pulmonary Artery Systolic Pressure ($PASP$).
  • Formula: $PASP = 4 \times (\text{TR velocity})^2$
  • TR can be secondary to pulmonary hypertension.

Diastolic Function Assessment (PW Doppler)

• Pulse Wave (PW) Doppler Measurement:
  • Obtain Apical 4-Chamber ($A4C$) view.
  • Place sample volume ($2 - 5\,mm$) at the tips of the mitral valve leaflets.
  • Record E wave (early filling) and A wave (atrial filling).
• Normal Diastolic Parameters:
  • $E/A$ Ratio: $1.0 - 2.0$
  • Deceleration Time ($DT$): $160 - 240\,ms$
• RCM-Specific Diastolic Findings (Grade III Restrictive):
  • $E/A$ Ratio: $> 2.0$
  • Deceleration Time ($DT$): $< 160\,ms$ (specifically less than $140\,ms$ in early stages transition to restrictive).
  • Characteristics: Large E wave and small A wave.
• Tricuspid Inflow (PW Doppler):
  • Shows restrictive filling pattern.
  • Increased $E/A$ ratio ($> 2.1$).
  • Short $DT$ ($< 120\,ms$).

Tissue Doppler Imaging (TDI) for Diastolic Function

• Measurement:
  • Sample volume ($2 - 5\,mm$) placed at the medial mitral annulus (septal side) in $A4C$ view.
  • Recording includes $S'$ (systolic), $E'$ (early diastole), and $A'$ (late diastole) waves.
• RCM-Specific TDI Findings:
  • $E' < 8\,cm/s$.
  • Markedly diminished diastolic motion.
  • $E/E'$ ratio serves to assess filling pressures; it increases progressively as the disease stages advance.
  • $E/E' > 14 - 15$ indicates elevated LV filling pressure (Grade II/III).

Venous Flow Analysis

• Pulmonary Venous Flow:
  • Waves: $S$ wave (systolic forward flow), $D$ wave (diastolic forward flow), and $Ar$ wave (atrial reversal).
  • RCM Findings: Dilated pulmonary veins and a "Blunted $S$ wave" resulting from increased LA and LV pressures.
• Hepatic Vein Flow:
  • Reflects changes in pressure, volume, and compliance of the right atrium.
  • RCM Findings: Dilated Hepatic veins and a dilated Inferior Vena Cava ($IVC$).
  • Waveform identifies $S$, $D$, and $A$ waves similar to pulmonary veins, reflecting RA status.

Cardiac Amyloidosis

• Pathology: The most common cause of RCM, resulting from the deposition of amyloid fibrils in organs.
• Involvement: Can involve the myocardium, valves, interatrial septum, and pericardium.
• Echocardiographic Features of Amyloidosis:
  • Increased thickness of both LV and RV walls.
  • Normal or small LV cavity size.
  • Thickened atrial septum.
  • Pericardial effusion (in advanced disease).
  • Spectrum of diastolic dysfunction.
  • Thickening of valves and presence of multivalvular regurgitation.

Differential Diagnosis: RCM vs. Constrictive Pericarditis