Comprehensive Study Guide: Pulmonary Hypertension and Echocardiographic Assessment

Pulmonary Hypertension and Left Heart Interconnectivity

• Context of Research and Clinic findings     * There is a significant link between tricuspid regurgitation (TR) peak velocity and pulmonary hypertension.     * While some clinics use TR peak velocity to assess diastolic dysfunction, scientific literature indicates it is primarily a marker of pulmonary hypertension.     * Pulmonary hypertension is often a secondary finding in patients with left heart failure. When other etiologies (like lung disease or shunts) are ruled out, the etiology is typically left heart failure, which implies potential diastolic dysfunction.     * Pulmonary hypertension can be caused by various factors beyond diastolic dysfunction, such as severe mitral regurgitation.     * Standard assessment for diastolic dysfunction still relies heavily on the "eight" parameters (though some guidelines mention seven); velocity propagation slope is used less frequently now but remains a valid measurement.

Color M-Mode Propagation Velocity ($V_p$)

• Technique and Procedure     * View Selection: Utilize the apical four-chamber view.     * Optimization: Decrease the depth to focus specifically on the left ventricle (LV) and mitral valve, similar to the view used for a Simpson’s trace. The left atrium (LA) is less critical for this specific measurement.     * Color Doppler Setup: Turn on color Doppler and adjust the color box to cover the entire left ventricle (the whole sector).     * M-Mode Cursor: Activate the M-mode cursor (not pulsed or continuous wave Doppler) and place it directly through the middle of the mitral valve.     * Display Interpretation: On the M-mode display, the horizontal component represents time. During systole, the leaflets are in the cursor path; during diastole, they move out of the path, and jets of color shoot toward the apex.
• Measuring the Slope     * The color jets have a "tilt" because it takes time for blood to move toward the apex.     * The slope of the angle of this color jet indicates the distal resistance in the apex and relates to the loss of ventricular compliance.     * Numerical Threshold: The critical value is $45\,\text{cm/s}$.     * Interpretative Result: A slope less than $45\,\text{cm/s}$ (a more gradual, non-steep slope) suggests a loss of compliance and restrictive filling.     * Historical Context: This measurement was considered highly sensitive and diagnostic when first invented (utilized at leading institutions like UCLA or the Mayo Clinic), though its current clinical prevalence varies.

Defining Pulmonary Hypertension (PH)

• Definition     * Pulmonary hypertension is defined as abnormally high blood pressure in the pulmonary arteries ($\text{HTN}$).     * It specifically refers to arterial pressures, though depending on the etiology, it may also affect capillaries, venules, and veins.     * Unlike systemic hypertension measured in the brachial artery, pulmonary hypertension focuses on the arterial pressure within the lungs.
• Anatomical Distinction     * The high pressure must be in the arteries within the lungs to be defined as pulmonary hypertension.     * If a stenosis exists in the pulmonary trunk (proximal to the lungs), the pressure proximal to the stenosis would be high, but the pressure within the lungs would actually be low. Therefore, PH originates from problems within the lung vasculature or backing up into it.

Etiology Groups of Pulmonary Hypertension

• Group 1: Pulmonary Artery Stenosis (Primary Pulmonary Hypertension)     * Mechanism: Abnormal narrowing of the small arteries within the lungs themselves (not the pulmonary trunk or the main left/right branches).     * Causes:         * Atherosclerosis: Plaque buildup, though this is less common in pulmonary arteries than in systemic ones.         * Idiopathic: Spontaneous constriction of the arteries/arterioles for unknown reasons.     * Hemodynamics: Pressure is high proximal to the narrowing in the small lung arteries. Once blood passes the stenosis, pressure drops. Consequently, pressure in the capillaries, venules, and veins may be normal or low.     * Symptoms: This type is often asymptomatic because the pulmonary venous side remains unaffected.

• Group 2: Volume Overload Due to Shunts     * Mechanism: An abnormal opening in the septum (interventricular or interatrial) causes blood to move from the high-pressure left side to the right side.     * Impact: The right side receives normal systemic return plus the shunted blood, creating a massive volume overload for the right ventricle (RV) and pulmonary arteries.     * Progression: The excess volume causes the vessels in the lungs to dilate, eventually building up pressure. This represents a case where a volume overload creates a secondary pressure overload.

• Group 3: Pulmonary Congestion     * Internal Lung Disease: Conditions like emphysema, lung cancer, pneumonia, bronchitis, or COPD. These cause inflammation and swelling, leading to fluid buildup and congestion.     * Left Heart Failure:         * If the left side of the heart fails to pump effectively, blood backs up into the left atrium (leading to dilation).         * This back-pressure travels into the pulmonary veins, then the capillaries, and finally the pulmonary arteries.         * Contributing Conditions: Mitral stenosis, mitral regurgitation, aortic valve disease, myocardial infarction (MI), and diastolic dysfunction.

Complications and Right Heart Failure

• Pressure Overload to the Right Ventricle     * Initially causes concentric Right Ventricular Hypertrophy ($\text{RVH}$), which is the abnormal thickening of the muscular walls.     * Because the RV is not as robust as the LV, it cannot sustain pressure overload indefinitely.
• Progression to Dilation     * The walls eventually stretch and dilate. This leads to Right Atrial ($\text{RA}$) dilation.     * Once dilated, the right heart achieves a state of failure (Right Heart Failure).
• Systemic Symptoms (Venous Congestion)     * Lower Extremity Edema: Pale, puffy water retention in the legs.     * Ascites: Fluid buildup in the abdominal cavity.     * Jugular Venous Distension ($\text{JVD}$): Dilation of the veins in the neck.     * Organomegaly: Fluid-induced enlargement of organs, specifically Hepatomegaly (liver) and Splenomegaly (spleen).     * Shortness of Breath: Highly common in Group 2 and 3; however, in Group 1 (Artery Stenosis), shortness of breath might not occur unless the heart failure is so severe it causes pulmonary hypotension (low pressure to the lungs).

Echocardiographic Assessment of Pressures

• Core Measurement Parameters     1. PASP (Pulmonary Artery Systolic Pressure): The peak pressure in the pulmonary artery during systole.     2. MPAP (Mean Pulmonary Artery Pressure): The average pressure throughout the cardiac cycle ($\text{Normal range: } 9 – 18\,\text{mmHg}$).     3. PAEDP (Pulmonary Artery End Diastolic Pressure): The pressure in the artery at the very end of diastole ($\text{Normal range: } 4 – 12\,\text{mmHg}$).

• PASP Severity Grading     * Normal: $< 30\,\text{mmHg}$ (average normal is often $25\,\text{mmHg}$).     * Borderline / High Normal: $30 – 35\,\text{mmHg}$.     * Mild PH: $35 – 45\,\text{mmHg}$.     * Moderate PH: $45 – 60\,\text{mmHg}$.     * Severe PH: $> 60\,\text{mmHg}$.     * Critical PH: $> 80\,\text{mmHg}$.

• The Bernoulli Equation     * The simplified formula used to convert velocity into a pressure gradient ($\triangle P$):     * $\triangle P = 4 \times v^2$     * Example: A TR velocity of $3\,\text{m/s}$ results in a gradient of $4 \times (3)^2 = 36\,\text{mmHg}$.

• Right Atrial Pressure ($\text{RAP}$) Estimation     * Estimated using the Inferior Vena Cava ($\text{IVC}$) diameter and its collapsibility during a sniff test.     * Normal ($3\,\text{mmHg}$): Diameter $< 2.1\,\text{cm}$ and $> 50\%$ collapse.     * Intermediate ($8\,\text{mmHg}$): One parameter is abnormal (either diameter $> 2.1\,\text{cm}$ OR collapse $< 50\%$).     * High ($15\,\text{mmHg}$): Both parameters are abnormal (diameter $> 2.1\,\text{cm}$ AND collapse $< 50\%$).     * Highest ($20\,\text{mmHg}$): Extremely dilated IVC with $0\%$ collapse.     * Note: If the IVC is not visible, some labs default to an estimate of $5\,\text{mmHg}$ or $10\,\text{mmHg}$.

Specific Pressure Calculations

• Calculating PASP     * Assumption: In the absence of pulmonic valve stenosis, Right Ventricular Systolic Pressure ($\text{RVSP}$) is equal to $\text{PASP}$.     * Measurement: Peak velocity of tricuspid regurgitation ($v_{\text{TR}}$).     * Formula: $\text{PASP} = (4 \times v_{\text{TR}}^2) + \text{RAP}$.

• Calculating MPAP     * Measurement: Early diastolic (peak) velocity of Pulmonic Insufficiency/Regurgitation ($v_{\text{PI early}}$).     * Formula: $\text{MPAP} = (4 \times v_{\text{PI early}}^2) + \text{RAP}$.

• Calculating PAEDP     * Measurement: End-diastolic velocity of Pulmonic Insufficiency ($v_{\text{PI end}}$). This occurs after the "A-dip" in the PI waveform.     * Formula: $\text{PAEDP} = (4 \times v_{\text{PI end}}^2) + \text{RAP}$.

Additional Diagnostic Signs

• RVOT Acceleration Time     * Measured in the Right Ventricular Outflow Tract.     * In the presence of pressure overload/PH, the acceleration time becomes shorter.     * A time $< 100\,\text{ms}$ is generally considered abnormally short.
• M-Mode of Pulmonic Valve     * Look for the "A-dip" (or A-bounce) which occurs right before systole due to atrial contraction.     * In severe PH (specifically high $\text{PAEDP}$), the A-dip disappears because the high pressure in the pulmonary artery prevents the valve from bouncing downward.

Questions & Discussion

• Q (Paul): How do you perform the color propagation speed velocity again?
• A: The speaker explained the process using apical four-chamber view, reduced depth for LV, full-sector color box, and M-mode through the mitral valve to find the slope of the color jet toward the apex ($45\,\text{cm/s}$ threshold).
• Q (Admin): Will the Zoom recording be available?
• A: The links will be sent by Joanna on Monday. Recorded links expire after about a month; permanent links on the school server take a few weeks for IT to process.
• Q (Diamond): At my hospital, if we can't see the IVC, we are told to use $5\,\text{mmHg}$ for the RAP. Have you heard of that?
• A: The speaker noted that while some use $10\,\text{mmHg}$, labs vary. The important factor is that a dilated, non-collapsing IVC indicates high RAP, even if the specific numerical assignment (15 vs 20) varies by institution. Digital machines like Samsung often use scales of 5, 10, 15 whereas others use 3, 8, 15.