Decompensated cor pulmonale is referred to here by the more descriptive term "isolated right ventricle overload" or iRVO. It is "isolated" because it is distinct from right ventricle (RV) overload due to left heart dysfunction. "Overload" refers to sufficient dilation and wall tension to impair LV filling. This definition does not refer to milder RV dysfunction, which may occur before developing iRVO.
Systemic circulation requires a pressure gradient with low pressure in the right atrium (RA), known as central venous pressure (CVP), and high pressure in the large arteries, known as mean arterial pressure (MAP). The RV functions to keep CVP low. Its relatively large size (when unfolded), thin wall, and location in the negative pressure thorax allow it to easily fill to various volumes without increasing diastolic pressure.1 These characteristics are independent of coronary perfusion, and the RV can often function despite significant coronary ischemia.2 As pulmonary artery pressure (RV afterload) increases, the thin-walled RV can easily dilate and be forced to generate significantly more wall tension to maintain forward flow. In this setting, oxygen demand increases, and maintaining enough coronary perfusion pressure (MAP - CVP) becomes essential.2
Image 3.1 The heart and vasculature are like a battery and circuit. The heart functions to maintain high pressure on one side (MAP) and low pressure on the other (CVP). This gradient, the perfusion pressure, maintains blood flow throughout the vasculature.
Progressive RV dilation eventually tensions the pericardium, which transmits RV pressure to the left ventricle (LV). This pericardial tension obstructs LV filling and increases hydrostatic pressure in the pulmonary vasculature. Poor LV filling due to RV dilation is the defining characteristic of iRVO and causes tachycardia, increased LV contractility, peripheral vasoconstriction, pulmonary edema, and volume retention. Hypotension develops when compensatory measures are inadequate. In this setting, more blood flow to the heart (venous return) can paradoxically decrease cardiac output as it dilates the RV and tensions the pericardium further. Greater venous return can improve RV forward flow and impair LV filling simultaneously, leading to increased pulmonary edema and orthopnea.
Image 3.2 Pathophysiology of iRVO where positive feedback loops can cause acute cardiovascular collapse.
The vicious positive feedback loop diagrammed above can quickly accelerate iRVO into cardiac arrest and is the proposed mechanism for how pulmonary emboli cause sudden death.1 Conditions that significantly increase RV wall tension can cause iRVO. This condition may be more common than often realized in settings where tuberculosis is endemic and home oxygen therapy is typically unavailable. Etiologies may be acute, chronic, solitary, or multifactorial.
Patients with iRVO develop multiple nonspecific signs and symptoms and can decompensate when high cardiac output is required, such as with anemia, sepsis, and physical exertion. They may complain of fatigue, early satiety, dyspnea on exertion, orthopnea, PND, palpitations, weight gain, and swelling. Physical exam often reveals tachycardia, a narrow pulse pressure, peripheral edema (unless acute or with excellent lymphatic function), jugular venous distention, and extra heart sounds such as S2 splitting and a tricuspid regurgitation murmur. There may be a prominent cardiac impulse in the low parasternal area or epigastrium, especially if the lungs are hyperinflated. Tachyarrhythmias can occur and are often poorly tolerated. Venous congestion from high RA pressures can lead to pericardial effusion, ascites, as well as hepatic, intestinal, and renal dysfunction. Patients may have significant hypoxia if there is underlying lung disease or atrial shunting across a patent foramen ovale. Other findings and complications may occur related to the underlying cause.
Assessing for iRVO requires a good apical four-chamber (A4C) view and is confirmed with a good short-axis view at the level of the mid-papillary muscles from either the parasternal or subcostal windows.3 Take care to get an A4C view where the RV appears widest, as transducer rotation can cause the image to cut through a narrower section of the RV. In a normal A4C view, 1) the RV cavity has a characteristic triangular shape, and 2) the RV width is consistently less than the corresponding LV width. In contrast, in an A4C view of iRVO, 1) the RV loses its triangular shape, 2) the RV dilates, and 3) the LV shrinks. The goal is to compare the LV and RV chamber sizes in end-diastole (when ventricles are fullest). In the A4C view, an RV to LV ratio greater than one is specific for iRVO, where, by definition, RV dilation impairs LV filling.4,5 In some cases, the RV wall may appear hypertrophied from chronic overload. However, PoCUS cannot differentiate acute vs. chronic RV overload, as other data are necessary to make this distinction.
Image 3.3 Comparing a normal apical 4-chamber view (A) with a patient with isolated RV overload (B) where the RV is dilated and impairs LV filling such that the ratio of the width of the RV to that of the LV is >1. Avoid mistaking iRVO with a normal A4C view obtained with the transducer orientation flipped 180 degrees in error (C). To identify this error after an exam, notice that the LV wall is usually thicker than the RV wall and that the tricuspid valve inserts into the septum more apically than the mitral valve (A, B).
Use a good mid-papillary muscle short-axis view to confirm the A4C findings of iRVO. Consider using a subcostal short-axis view as an alternative or in addition to the parasternal short-axis view, especially when the parasternal window is suboptimal. Normal short-axis views show the thin-walled RV loosely wrapping around the right-anterior side of the LV, and the thicker-walled LV appears round throughout the cardiac cycle. In iRVO, RV pressures are higher, especially in early diastole, such that the pressurized RV flattens the intraventricular septum. This changes the LV's appearance from a round shape to a D-shape due to septal flattening. This finding helps confirm iRVO after finding a large RV-to-LV ratio. Septal flattening is not specific for iRVO by itself as paradoxical septal wall motion can occur in other settings.6
Image 3.4 Comparing a normal parasternal short-axis view (A) with a patient with isolated RV overload (B) where the RV is dilated and impairs LV filling such that the intraventricular septum flattens as the RV paradoxically compresses the LV during diastole (C).
The subcostal four-chamber (SC4C) view and parasternal long axis (PLAX) view can reveal apparent RV enlargement, but these views alone should not be used to rule iRVO in or out. You may see that the RV outflow tract on the PLAX view is enlarged (wider than the aorta and left atrium) and you may notice paradoxical interventricular septal movement.
Image 3.5 Comparing a normal subcostal 4-chamber view (A) with a patient with isolated RV overload (B). Avoid using this SC4C view alone to determine if iRVO is present.
Image 3.6 Comparing a normal parasternal long-axis view (A) to one in a patient with isolated RV overload (B). Avoid using this PLAX view alone to determine if iRVO is present.
Because right-heart pressures and CVP are high in iRVO, the IVC view will typically show a full IVC that does not collapse significantly with changes in thoracic pressure. However, this finding is not specific to iRVO since the IVC is similarly distended in other conditions.
Image 3.7 An IVC view of a patient with isolated RV overload where the IVC is distended and collapses minimally with inspiratory efforts.
There are quantitative measurements that can assess RV function, such as TAPSE or peak tricuspid regurgitation velocity. However, these measures do not distinguish iRVO from RV dysfunction associated with left heart disease, which should be diagnosed and treated concerning the underlying left heart disease.
Image 3.8 A4C views comparing iRVO (A) and biventricular heart failure with reduced LVEF (B). Both patients have RV dilation and systolic dysfunction, but only the first has iRVO (RV-to-LV ratio >1). Distinguishing these conditions is critical for determining a safe and effective treatment strategy. Images with different depths are scaled for comparison.
The PoCUS findings for iRVO are specific but will not identify milder forms of RV dysfunction. Milder cases of pulmonary embolism and other causes of RV dysfunction may not present with iRVO as defined here, so the absence of these PoCUS findings should not be used to rule out PE or milder forms of pulmonary hypertension.
Besides addressing triggers like sepsis or anemia and complications such as arrhythmias or cardiorenal syndrome, treatment for iRVO should aim to 1) minimize RV afterload, 2) lower an elevated CVP, and 3) maintain a minimum MAP. Due to a lack of available human trial data, these strategies are primarily based on expert opinion and animal studies.7,8
Image 3.9 Pathophysiology and treatments of iRVO.
One or multiple factors may contribute to RV afterload and together trigger iRVO. The underlying etiology(s) may be challenging to identify and treat quickly. However, most patients should receive supplemental oxygen and bronchodilators, especially if chronic lung disease is suspected. Also, consider starting therapy for acute pulmonary embolism.
Avoiding positive-pressure ventilation (PPV) in patients with iRVO is particularly important. If PPV is necessary, RV function should be monitored, large tidal volumes should be avoided, and plateau pressures should be minimized by avoiding high PEEP and allowing enough time for exhalation (lower I:E ratio). Prone positioning should also be considered, given it is associated with increased gas exchange and lower thoracic pressure compared to supine positioning in ventilated patients.9 Some treatments directly reduce RV afterload by selectively vasodilating the pulmonary arterioles. The indications for and how to safely administer these pulmonary vasodilators, including inhaled nitric oxide and phosphodiesterase-5 inhibitors, are beyond the scope of this chapter.
Optimal RV wall stretch, as described by the Frank-Starling mechanism, does not improve cardiac output in iRVO because RV dilation-induced pericardial tension obstructs LV filling. For the same reason, lowering RV preload in iRVO may even increase cardiac output. Besides improving LV stroke volume, reducing CVP can directly improve coronary perfusion pressure, which is the primary limiter of RV contractility in this overloaded state.2 Therefore, the counterintuitive strategy for iRVO is to decrease excess RV filling to increase LV filling and increase RV perfusion.
Jardin et al. demonstrated that progressive volume loading past a threshold in 10 COPD patients caused RV enlargement and decreased LV end-diastolic size and cardiac output.10 Belenkie et al. found the same result when giving volume to dogs suffering from acute pulmonary embolism.11 It seems counterintuitive to treat hemodynamically unstable patients with volume reduction. However, cohort studies demonstrate the benefit and safety of IV furosemide instead of volume expansion in patients with acute pulmonary embolism.12,13
Significant volume reduction may be necessary before RV diastolic pressure drops enough so that the pericardium no longer obstructs LV filling. However, additional volume removal is less beneficial after signs and symptoms improve. Critical care experts in China refer to this as what translates to "reversed fluid resuscitation" and specifically say that RV dysfunction is not a reason to routinely maintain a higher CVP.14 Acute volume reduction in iRVO is often well-tolerated. Hypotension from volume reduction occurs more readily if venous return or diastolic function are impaired, e.g. with high intra-thoracic or pericardial pressure or significant right ventricle hypertrophy. Monitor for signs of over-diuresis, such as orthostatic hypotension and hyponatremia that improve when you stop diuretics or administer IV fluids.
To address ongoing volume retention, patients with persistent iRVO often need chronic diuretic treatment as well as a modified diet, weight monitoring, and regular follow-up encounters. They should also avoid non-steroidal anti-inflammatory drugs, which impair diuresis. European pulmonary hypertension experts also recommend that these patients wear a medical bracelet or carry a medical passport that clearly states that no one should give them IV fluids without consulting a specialist.15
The overloaded RV's function is limited by demand ischemia, and RV perfusion is directly proportional to the difference between the CPP (MAP - CVP) and RV afterload.2 Therefore, if RV afterload increases and CPP drops, RV perfusion and function will deteriorate further, which will further impact LV filling and decrease the MAP even further in a vicious cycle. Therefore, keeping MAP above a threshold that maintains adequate CPP and RV perfusion is essential. This minimum MAP can be similar to MAP goals for other shock states, such as 65mmHg. Still, a higher goal may be beneficial if CVP or RV wall tension can't be reduced with the strategies discussed above.16 Experts recommend using IV infusions of titrated norepinephrine with or without fixed low-dose vasopressin. Other vasopressors or inotropes such as phenylephrine, epinephrine, dopamine, dobutamine, or milrinone can also be effective as alternative or adjunctive agents.17 The following list summarizes strategies to maintain a normal MAP.
The term iRVO describes hemodynamically significant cor pulmonale where RV overload is not due to left heart disease and impairs LV filling. PoCUS in iRVO reveals an RV-to-LV ratio >1 on 4-chamber views and interventricular septal flattening on short-axis views. Assessing for iRVO cannot rule out pulmonary embolism or milder forms of pulmonary hypertension. Besides treating triggers and complications, management for iRVO should focus on lowering RV afterload, lowering an elevated CVP, and maintaining a normal MAP.