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Patient Summary

A 78-year-old woman with atrial fibrillation and heart failure with preserved ejection fraction presented with recurrent dyspnea and volume overload. A transthoracic echocardiogram demonstrated severe right ventricular enlargement and dysfunction. A CT pulmonary angiogram demonstrated partial anomalous pulmonary venous return and a transesophageal echocardiogram revealed a sinus venosus defect with left to right shunting. A right heart catheterization with oximetry saturation (“shunt run”) demonstrated pulmonary hypertension and a large left to right shunt (Qp/Qs ~ 3). She was referred for cardiac surgery and underwent repair of the sinus venosus defect and baffling of the anomalous pulmonary venous flow to the left atrium.

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Case Media

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Episode Schematics & Teaching

Pearls

1. It is critical to determine whether there is more to a diagnosis of heart failure with a preserved ejection fraction. Utilize all available clinical data and risk calculators to determine if there are more appropriate diagnoses causing the patients symptoms, especially when certain aspects of the presentation does not add up.
   
2. Right ventricular failure may be related to pressure overload (i.e., pulmonary hypertension, PV stenosis), volume overload (i.e., tricuspid regurgitation, left to right shunt lesions), or primary myocardial process (i.e., ischemia, infiltration, ARVC). In cases of severe right ventricular enlargement and dysfunction without apparent cause, look for a left to right shunt lesion (i.e., VSD, ASD, PAPVR). Sometimes further imaging (TEE, cardiac CT, cardiac MRI) is necessary to detect these lesions if not visualized on TTE.
   
3. Left to right shunts can be quantified in the cardiac catheterization laboratory by measuring oxygen saturation in each chamber and detecting an O2 “step up” (increase in oxygen saturation from one chamber to the next). Large left to right shunts are quantified using the Fick principle and comparing the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs).
   
4. Large left-to-right shunts can cause right ventricular volume overload and pulmonary hypertension. Patients often present with signs and symptoms of right ventricular failure including shortness of breath, exercise intolerance, volume overload, atrial arrhythmias, and recurrent heart failure. Some may develop right-to-left shunting and possible paradoxical embolism.
   
5. ACC/AHA guidelines recommend closure of a sinus venosus defect if the PA systolic pressure is < 50% systemic pressures AND PVR is <1/3 of SVR. It is a Class III recommendation (potentially harmful) to close a defect if PA systolic pressure is >2/3 of systemic systolic pressure and/or PVR >2/3 SVR.

Quotable:

About ACHD – “As we go through this physiology, I just want to remind all of the listeners out there that you have the opportunity to apply the knowledge you have from medical school about physiology to the adult human heart. You can’t make assumptions as we sometimes do in the setting of normal cardiac anatomy. We really need to think about the compliances of the downstream structures and where is the blood flow.” – Keri Shafer, MD

Notes

1. What are features and causes of RV failure?

• The clinical symptoms of right ventricular failure include fatigue, dyspnea, lower extremity edema, elevated JVP, early satiety, and abdominal swelling. Although there is overlap between the symptoms of right ventricular failure and left ventricular failure, in isolated right ventricular failure orthopnea, paroxysmal nocturnal dyspnea, and pulmonary edema are typically absent.
• It is convenient to break down the etiologies of right heart failure into “buckets”. Specifically, volume overload, pressure overload, and primary cardiomyopathic processes. Causes of right ventricular volume overload include valvular disease (tricuspid regurgitation, pulmonic insufficiency) and left-to-right shunts (ASD, VSD, sinus venosus defect, coronary sinus defect, PAPVR). Causes of right ventricular pressure overload, or excessive afterload, include pulmonary arterial hypertension, pulmonary embolism and chronic thromboembolic pulmonary hypertension, pulmonic stenosis, chronic hypoxemia, and longstanding elevated left atrial pressure causing group 2 PH (mitral regurgitation/stenosis, HFrEF, HFpEF). Cardiomyopathic processes include cardiac amyloidosis, right ventricular myocardial infarction, post-transplant right ventricular dysfunction, and arrhythmogenic right ventricular cardiomyopathy. Also, keep in mind that these disease processes often overlap.

2. What is partial anomalous pulmonary venous return (PAPVR)?

• Normally, the four pulmonary veins return oxygenated blood to the left atrium.
• Partial anomalous pulmonary venous return is a spectrum of congenital heart defects when one or more (but not all) of the pulmonary veins return oxygenated blood from the lungs to the systemic venous system (typically the SVC, IVC, or RA).
• The most common PAPVRs are LUPV (left upper pulmonary vein) à ascending vertical vein à innominate vein or RUPV à SVC. The latter is often associated with a concurrent sinus venosus defect connecting the RA and LA.
• Scimitar syndrome is a subtype of PAPVR in which part or all of the blood from the right lung is returned into the IVC. On chest X-ray, the outline of the anomalous drainage and associated congestion gives the appearance of a scimitar.

3. What is a sinus venosus defect? What is the sinus venosus?

• Early in development, the atria are one single chamber. The sinus venosus is the posterior entryway for blood returning to this primitive atrium.
• Eventually, the sinus venosus closes and moves rightward due to hemodynamic shifts during development.
• In adults, the sinus venous becomes the smooth posterior wall of the adult right atrium called the sinus venarum and is separated from the anterior wall of the RA by the cristae terminalis.
• If a persistent channel through the sinus venosus remains into adulthood, it can result in an intra-cardiac shunt. This is termed a sinus venosus defect and accounts for 10-15% of all inter-atrial shunts.
• Typically, this shunt is left-to-right and may lead to right ventricular volume overload, dysfunction and pulmonary hypertension. Some patients may develop right-to-left shunting or paradoxical embolism. Arrhythmias are an important complication.
• As above, sinus venosus defects are associated with PAPVR with RUPV à SVC.
• NOTE: a sinus venosus defect is NOT a defect in the atrial septum and so is not an “ASD”. Rather it is a defect connecting either the SVC-RA junction (more common) or the IVC-RA junction to the LA. The former is associated with a RUPV PAPVR and the latter is associated with a RLPV PAPVR.

4. What are the imaging modalities that are used to identify sinus venosus defects?

• Sinus venosus defects are poorly visualized on transthoracic echocardiography (TTE).
• If there is clinical suspicion for an inter-atrial shunt not visualized on TTE, then a transesophageal echocardiogram (TTE) should be performed. Additional imaging modalities include cross-sectional imaging with cardiac CT or cardiac MRI, which may also identify the presence of concomitant PAPVR.
• In cases of RV dilation and dysfunction without know etiology, evaluation for sinus venosus defect +/- PAPVR should be pursued.

5. What is the role for right heart catheterization in characterizing shunt defects?

• A right heart catheterization is useful for multiple reasons.
• Intracardiac pressure measurements serve as a surrogate for volume status.
• One can also obtain oxygen saturation in each cardiac chamber to identify the presence of a “step up”, or unexpected increase in oxygen saturation, which signifies a left-to-right shunt. To simplify, a left-to-right shunt is when oxygenated blood from the systemic circulation (left) inappropriately mixes with the pulmonary circulation (right), increasing the oxygen concentration. This can occur via anomalous pulmonary veins, defects at the atrial or ventricular level, or sometimes systemic arterio-venous fistulas.
• To obtain pressure measurements, a balloon-tipped catheter (Swann-Ganz catheter, PA catheter) is inserted through a vein and advanced through the heart and “wedged” in the pulmonary artery to estimate left atrial pressure. Normal pressure measurements are as follows (in mmHg): Right atrium < 8, right ventricle 25/5 (systolic/end diastolic pressure), pulmonary artery 25/15 (systolic/diastolic), and pulmonary capillary wedge pressure 8-12. Cardiac output can also be measured by thermodilution and via the Fick principle.
• In our case, the patient’s pressure measurements were: RA 20, RV 72/24, PA 68/36 (47), PCWP 26.
• As the catheter is passed through the great vessels and cardiac chambers and into the pulmonary artery, small amounts of blood can be sent for oximetry. Blood can be taken from the proximal and distal SVC, proximal and distal IVC, right atrium (low, mid, high), RV, PA and aorta. Taking multiple samples in each chamber are only necessary when the level of a suspected shunt is unknown. A left to right shunt is detected by an oximetry “step up” where oxygenated blood from the systemic circulation blood mixes with deoxygenated blood from the venous circulation.
• An oxygen saturation step up of >7% is considered significant at the level of the great veins and RA while a step up of >5% is considered significant at levels distal to the RA.
• For intra-cardiac shunts, the degree of left to right shunting can be quantified by calculating the ratio of pulmonary blood flow (Qp; oxygen consumption divided by the difference in AV oxygen content across the lungs) to systemic blood flow (Qs; oxygen consumption divided by the difference in the arteriovenous oxygen content across the systemic circulation). This ratio is calculated using the Fick principle for cardiac output, and by making a few assumptions.

• Because intra-cardiac shunts will affect the mixed venous (pulmonary artery oxygen saturation), a systemic mixed venous saturation needs to be calculated to estimate “pre-shunt” mixed venous O2. This is defined by Flamm’s formula: (3*SVC +IVC)/4
  • We also assume that oxygen consumption, hemoglobin concentration and atmospheric pressure are constant. This allows for many of the terms in the complex calculation to cancel out, leaving only the oximetry saturations.
  • Ultimately, the simplified equation for Qp/Qs becomes the difference in saturation across the systemic circulation (Ao – calculated mixed venous) divided by the difference across the pulmonic circulation (PV sat – PA sat).
  • Practically, the pulmonary venous saturation cannot be obtained without transeptal puncture or retrograde catheterization through the left sided valves. In the absence of a significant R to L shunt, we expect systemic arterial saturation and pulmonary venous saturation to be the same, and thus the pulmonary venous saturation is often replaced by systemic arterial saturation in this equation.
• Small shunts are defined by Qp/Qs <1.5. These are often asymptomatic and generally do not need to be treated. Large shunts are defined by Qp/Qs >2 and often require closure.
• Our patient’s saturations were as follows: SVC 50%, IVC 43%, RA 77%, PA 79%, Ao 94%.
  • The calculated mixed venous saturation is then 48.25% ((3*50% + 1*43%) / 4 = 48.25%).
  • Finally, her Qp/Qs = (94 – 48.25)/(94-79) = 3.1.
• When we walk through this equation with our patient’s data, her Qp/Qs is 3.1, meaning that for every 1 L of cardiac output through the systemic circulation, 3.1 L are going through the pulmonary circulation.

6. What are the indications and contraindications to correction of sinus venosus defects and PAPVR?

• According to the 2018 ACC/AHA guidelines, in adults with a primum ASD, sinus venous defect or coronary sinus defect causing impaired functional capacity, right atrial and/or right ventricular enlargement and net left to right shunt sufficiently large to cause physiological sequelae (Qp/Qs >1.5:1) – without cyanosis at rest or during exercise – should be referred for surgical repair unless precluded by comorbidities.
•  It is important to evaluate for pulmonary hypertension, as the recommendations differ based on the degree of concomitant pHTN.
• Surgical correction is:
  • Class I (B-NR) if the systolic PA pressure is less than 50% of the systemic pressure and the PVR is less than one third of the SVR.
  • Class III, or potentially harmful, (C-LD) if the PA systolic pressure is greater than 2/3 of the systemic systolic pressure or if the PVR is greater than 2/3 of the SVR and/or if there exists a right to left shunt.
• Those with PA systolic pressures between 50% and 2/3 systemic pressures and PVRs between 1/3 and 2/3 should be considered for repair on a case-by-case basis (Class IIb, our patient in this case).

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References

Stout KK, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019;139(14). doi:10.1161/cir.0000000000000603. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000603

De Faria Yeh D, Bhatt AB, Gaggin HK, Januzzi JL. Adult Congenital Heart Disease. In: MGH Cardiology Board Review. 2nd ed. Cham: Springer International Publishing; 2021:387-420. https://www.springer.com/gp/book/9783030457914

Askari AT, Messerli AW. In: Cardiovascular Hemodynamics An Introductory Guide. Cham: Springer International Publishing; 2019. https://www.springer.com/gp/book/9783030191306

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CardioNerds Case Report Production Team