Fig. 4.1
A comparison of typical pressure-volume loops for a single cardiac cycle of the left ventricle (a) and right ventricle (b). In the left ventricle, pressure continues to increase slightly throughout the entire duration of ventricular ejection. In the right ventricle, intracardiac pressure falls prior to closure of the pulmonic valve (red arrow), resulting in less myocardial work. End-diastole is indicated by the black arrows (Adapted with permission from Redington [2], with permission from Elsevier)
Ventricular interdependence occurs in both systole and diastole. Systolic interdependence is mediated by the shared musculature between the LV and the RV, which means that the contractile state of one ventricle can influence the performance of the other ventricle. Diastolic interdependence is a result of the common pericardial sac. The pericardium is unable to stretch acutely in response to ventricular dilatation, and is limited in its ability to accommodate chronic ventricular dilatation. Therefore, a volume load in either chamber will cause displacement of the septum into the other chamber, resulting in a decreased diastolic volume and an impairment of ventricular output (Fig. 4.2) [3]. As the RV is the more compliant chamber, this diastolic interaction most commonly occurs in volume overload states of the RV, such as an atrial septal defect.
Fig. 4.2
Ventricular interdependence. During normal loading conditions (left side of diagram), the intraventricular septum bulges into the right ventricle (RV). In the context of right ventricular volume overload, the septum becomes flattened, with an increase in RV volume and a decrease in left ventricular (LV) volume (Reprinted with permission from Greyson [3], © 2008, with permission from Lippincott Williams & Wilkins/Wolters Kluwer/Society of Critical Care Medicine)
Right Ventricular Adaptations to Disease States
RV pathophysiology can be broadly categorized by the mechanism of the insult and its rapidity of onset. Acute events, such as a pulmonary embolism, lead to maladaptive compensatory responses, and quickly progress to RV failure. Chronic disease processes, such as congenital heart defects, often present a gradual stress on the RV, allowing it to develop adaptive mechanisms to preserve cardiac output for a prolonged period of time prior to decompensation. Conditions characterized by volume overload are generally well tolerated by the RV due to its compliant nature. On the other hand, the RV has difficulty adapting to pressure overload due to its afterload-sensitivity (Fig. 4.3) [4]. Interestingly, the timing of onset of pressure overload is a crucial determinant of the RV response. In Eisenmenger syndrome, the RV is able to remain compensated much longer than in adult patients with acquired pulmonary hypertension (PH). This finding has been attributed to the preservation of the fetal phenotype, which is accustomed to systemic levels of vascular resistance [5]. Intrinsic myocardial diseases, such as various forms of nonischemic cardiomyopathies, may impair RV contractility, but rarely affect the RV in isolation. However, RV involvement in a cardiomyopathy can play a significant role in morbidity and mortality, particularly in the setting of pulmonary hypertension (PH). A list of diseases that cause RV dysfunction and RV failure can be found in Table 4.1.
Fig. 4.3
Response of canine right ventricular and left ventricular stroke volume to acute changes in afterload. The steep slope in the right ventricle indicates enhanced sensitivity to afterload (Reprinted with permission from Abel and Waldhausen [4], © 1967, with permission from Elsevier)
Table 4.1
Causes of right ventricular failure
Acute causes | Intrinsic myocardial disease |
Pulmonary Embolism | Cardiomyopathy |
Right Ventricular Infarction | Idiopathic |
Sepsis | Viral |
Acute lung injury | Familial |
ARDS | Ischemic |
TRALI | Infiltrative |
Acute Chest Syndrome | Restrictive |
Post-cardiotomy | Arrhythmogenic RV dysplasia |
Pulmonary hypertensive crisis | |
Cardiac tamponade | Pericardial disease |
Constrictive pericarditis | |
Chronic volume overload | Chronic pressure overload |
Tricuspid valve regurgitation | Pulmonary arterial hypertension |
Infective endocarditis | Pulmonary venous hypertension |
Rheumatic disease | Left heart failure |
Carcinoid | Pulmonary veno-occlusive disease |
Traumatic | Hypoxia-associated PH |
Pulmonic valve regurgitation | Chronic thromboembolic PH |
Congenital heart disease | Congenital heart disease |
Atrial septal defect | Tetralogy of Fallot |
Ebstein’s anomaly | Pulmonic stenosis |
Coronary artery fistula | L-transposition of the great arteries |
Anomalous pulmonary venous return | Pulmonary artery stenosis |
Eisenmenger’s syndrome |
Acute Pressure Overload
Following a submassive or massive pulmonary embolism (PE), there is a rapid rise in pulmonary vascular resistance (PVR) due to both obstructed blood flow and the release of vasoconstrictors [6]. Vasoconstriction may be further exacerbated by hypoxemia. The rapid rise in afterload increases RV wall tension, which quickly leads to RV dilatation and RV systolic dysfunction. As the RV pressure rises acutely, the interventricular septum shifts into the LV, reducing LV preload and further compromising cardiac output. Finally, coronary perfusion is impaired by both the compression of the right coronary artery by elevated RV wall stress and the reduction in cardiac output. In the setting of the increased myocardial oxygen demand in the failing RV, the reduction in coronary blood flow leads to a significant supply-demand imbalance. The final consequence of this sequence of events is worsening cardiac output, systemic hypotension and cardiac arrest.
Ischemia
Right ventricular infarction (RVI) occurs after occlusion of the right coronary artery in a sufficiently proximal portion to prevent perfusion of the RV branches. The immediate result of an RVI is RV free wall dyskinesis due to ischemia, although this alone may not be sufficient to produce clinical RV failure. Secondary effects include stiffening of the myocardium and dilation of the RV. Similar to the consequences of an acute PE, the acute pressure changes within the RV, in this case provoked by diastolic dysfunction, cause septal shifting and impaired LV-RV interaction. In addition septal ischemia further compromises LV performance, and diminishes the LV’s ability to compensate for RV dysfunction [7].
Chronic Pressure Overload
PH is the end-product of many cardiovascular and pulmonary diseases and is the most common cause of a chronic pressure overload on the RV. As the pulmonary artery (PA) pressure gradually increases over time, the RV adapts to the increase in afterload through multiple compensatory mechanisms. Myocyte hypertrophy and the expansion of the extracellular matrix result in increased chamber thickness. At the same time, the RV remodels into a more spherical shape with a smaller radius [8]. Through the application of LaPlace’s law, which states that wall stress is proportional to chamber radius and inversely proportional to chamber thickness, it is evident that the primary result of these initial adaptations is to reduce wall stress, countering the effect of the rise in afterload. In addition, central venous pressure (CVP) is allowed to rise, taking advantage of the Frank-Starling mechanism to maintain a normal stroke volume.
Several mechanisms have counterproductive effects, including reversion to a fetal gene pattern and upregulation of neurohormonal systems [8]. The result is a decrement in contractility, followed by progressive ventricular dilatation. As with acute RV pressure overload, dilatation increases myocardial oxygen demand while simultaneously reducing coronary perfusion and oxygen delivery. This supply-demand mismatch further compromises RV performance and ultimately leads to RV failure if the PH remains untreated. Both cardiac output and PA pressure fall when RV contractile reserve is no longer sufficient to maintain an adequate stroke volume (Fig. 4.4) [9].
Fig. 4.4
The natural history of persistent pulmonary hypertension. As pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) climb, cardiac output (CO) is initially maintained, but eventually begins to fall. When CO falls sufficiently to cause advanced RV failure, PAP fells as well due to insufficient pressure generation by the weak RV. PVR continues to rise despite falling PAP due to the concomitant fall in CO. MPAP mean pulmonary artery pressure, PCWP pulmonary capillary wedge pressure (Reprinted, with permission, from Haddad et al. [9], © 2008, with permission from Lippincott Williams & Wilkins/American Heart Association/Wolters Kluwer)
Chronic Volume Overload
The thin, distensible wall of the RV permits it to accommodate large changes in preload without incurring significant changes in pressure. States of chronic volume overload, such as an atrial septal defect, can persist for decades prior to the development of RV dysfunction. Two consequences of persistent RV dilatation are distortion of the tricuspid annulus and septal shift. The dilated tricuspid annulus permits tricuspid regurgitation, which can further exacerbate the volume load on the RV. Septal shift occurs when the pericardium is unable to distend any further to accommodate the dilation of the RV. As noted above, septal shift can subsequently impair LV filling and adversely affect LV performance. Finally, prolonged volume overload may cause PA pressures to rise due to increased flow through the pulmonary circuit. The development of PH is often the trigger for decompensation of the chronic volume overloaded state, as the dilated RV lacks the compensatory mechanisms to augment its contractility in the setting of increased afterload [10].
Intrinsic Myocardial Disease
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a cardiomyopathy characterized by fibro-fatty replacement of myocardium, with a predilection for RV involvement. It may present with focal RV dysfunction at the sites of involvement, and may ultimately progress to RV dilatation and global RV dysfunction. The typical clinical presentation is ventricular arrhythmias, with symptoms of RV failure affecting less than 10 % of ARVC patients [11]. In most patients, RV dysfunction can be present for decades without significant symptomatology. A similar observation has been made in animal experiments, in which an isolated reduction in RV contractility does not impair cardiac output in the setting of a normal PVR. In these animals, central filling pressures rise to permit sufficient flow through the pulmonary circuit. However, when PVR is raised, there is rapid cardiac decompensation, suggesting that the progression of RV dysfunction to RV failure may require the presence of an additional stressor, such as PH [12]. The Fontan operation, in which a passive conduit is created between systemic venous return and the pulmonary arteries, takes advantage of this physiology to maintain adequate flow to the LV despite the absence of RV contractility.
Diagnosis and Assessment of Right Ventricular Dysfunction and Failure
A thorough history and physical examination can provide important clues to the presence of RV failure, including the presence of a right-sided third heart sound, elevated jugular venous pressure, ascites and peripheral edema. A prominent pulmonic component of the second heart sound (P2) indicates the presence of PH. Patients may report early satiety, abdominal fullness and fatigue. Hepatic function and renal function are often compromised, and should be followed regularly in a patient with RV failure. Imaging studies play a crucial role in the initial assessment and serial monitoring of RV function. Echocardiography is the most frequently used imaging modality for RV assessment due to its ease of use, low cost and accessibility. However, CMRI has become the gold standard for evaluation of the RV because of its ability to overcome some of the anatomic limitations of two-dimensional (2D) echocardiography. While both echocardiography and CMRI can provide some assessment of RV hemodynamics, invasive measurement of intracardiac pressures by right heart catheterization is often required to diagnose the etiology of RV failure and determine the appropriate therapeutic approach.
Non-invasive Imaging Studies
RV size and function can be assessed with radionuclide ventriculography, using either first-pass or gated equilibrium techniques. While accurate measurements of volume and RV ejection fraction (RVEF) can be derived, this modality does not provide additional anatomic information, and exposes patients to radioisotopes. With the widespread availability of echocardiography, radionuclide ventriculography is rarely indicated as the primary method for RV functional assessment in the current era.
2D echocardiography has excellent spatial and temporal resolution, enabling precise evaluation of RV anatomy and valvular function. RV dimensions can be obtained through multiple views, providing an estimate of RV size. However, due to the RV’s anatomic configuration, the calculation of accurate RV volumes with 2D echocardiography is not possible. Qualitatively comparing RV size to LV size in the apical view can provide a reasonable assessment of RV dilatation. Additional anatomic information that can be easily obtained is the appearance of the tricuspid and pulmonary valves, and the presence of valvular stenosis or regurgitation. Doppler evaluation of the tricuspid regurgitant jet allows the estimation of the systolic pulmonary artery pressure through the use of the modified Bernoulli equation. Important information is also provided by the appearance of the interventricular septum in the short-axis views. Pressure overload states cause flattening of the septum, particularly during systole, which volume overload states cause flattening during diastole (Fig. 4.5). With increasing pressure or volume overload, the septum is further shifted into the LV, leading to the hemodynamic effects of ventricular interdependence discussed previously.
Fig. 4.5
A 2-dimensional echocardiogram image showing dilation of the right ventricle (RV) and flattening of the intraventricular septum (*) due to right ventricular pressure and volume overload. LV left ventricle
RV function is challenging to determine with 2D echocardiography due to the lack of accurate ventricular volumes and the sensitivity of the RVEF to loading conditions. Visual assessment is the most commonly used technique but may be limited due to the complex shape of the RV. Multiple techniques are available for quantitative measurement of RV function. RV fractional area change (RVFAC) measures the change in area of the RV between diastole and systole from the apical 4-chamber view. The tricuspid annular plane systolic excursion (TAPSE) measures the vertical motion of the tricuspid valve annulus, with a value of less than 1.6 cm indicating RV dysfunction. RVFAC and TAPSE are both load-independent, and may provide varying information under different hemodynamic conditions. The RV index of myocardial performance (RIMP), also known as the Tei index, is less influenced by loading conditions, and may be a more accurate measure of underlying RV contractility [13]. This index is measured with Doppler of flow through the RV outflow tract, and is calculated as the sum of RV isovolumic contraction time and RV isovolumic relaxation time divided by ventricular ejection time.
Recent advances in CMRI have established it as the best modality for obtaining accurate information about RV size and function. CMRI is not affected by the anatomic limitations that prevent 2D echocardiography from obtaining a complete picture of the RV. CMRI has excellent spatial and temporal resolution, permitting accurate assessment of RV volumes throughout the cardiac cycle. Additionally, CMRI provides information on ventricular hypertrophy, the presence of infiltrative diseases and the presence of fibrosis. For complex congenital heart disease, CMRI offers substantial advantages over 2D echocardiography for assessment of RV anatomy and function prior to and following surgical interventions. Barriers to more widespread application of CMRI in evaluation of the RV include the time required for testing, the cost of CMRI technology, and the need for technical expertise. Most importantly, CMRI is not compatible with most implantable cardiac devices, such as pacemakers, although the ongoing development of devices compatible with the magnetic field will allow for a broader application of CMRI in the assessment of RV failure [14].
Invasive Hemodynamic Assessment
Right heart catheterization (RHC) is a critical component of RV assessment, particularly in patients with PH. Measurement of the right atrial pressure (RAP), PA pressure and pulmonary capillary wedge pressure (PCWP) can distinguish the etiology of RV failure and help determine the therapeutic approach (Table 4.2). The most important information provided by RHC is about PH, which has been classified into groups by the World Health Organization:
Group I incorporates PAH, which may be idiopathic, familial or associated with specific entities such as congenital heart disease, collagen vascular disease, HIV infection or toxins
Group II includes PH that is found in conjunction with left heart disease and is the most common form of PH
Group III includes PH associated with lung disease or hypoxemia
Group IV is PH due to chronic thromboembolic disease
Group V is a miscellaneous category
Table 4.2
Hemodynamic profiles of different mechanisms of right ventricular failure
Cause of RV failure | RAP | PAP | PCWP | TPG | PVR | Clinical examples |
|---|---|---|---|---|---|---|
Volume overload without PH | ↑ | ↓ | ↓ | ↓ | ↓ | ASD Isolated TV disease |
Precapillary PH | ↑ | ↑ | ↓ | ↓ | ↓ | Idiopathic PAH CTEPH Hypoxia-associated PH Congenital Heart Disease |
Postcapillary PH | ||||||
Passive | ↑ | ↑ | ↑ | ↓ | ↓ | Left-sided Heart Failure MV Disease |
Mixed | ↑ | ↑ | ↑ | ↑ | ↑ | |
Reactive (after vasodilator challenge) | ↑ | ↑ | ↓ | ↓ | ↓ | |
Nonreactive (after vasodilator challenge) | ↑ | ↑ | ↓ | ↑ | ↑ | |
A RHC can assist in the diagnosis of PAH, by identifying PH in the presence of normal left-sided filling pressures. While left heart disease is often manifested on imaging studies by a reduced LV ejection fraction or mitral valve disease, RHC can identify elevated PCWP in the absence of valvular disease or LV dysfunction (heart failure with preserved ejection fraction). Distinguishing the underlying etiology of PH will direct the choice of therapy, as therapies that have proven benefit in some forms of PH have been shown to be harmful in PH related to left heart disease [15]. Beyond anatomy, RHC provides information about the severity of RV failure. For example, the RAP is typically about 50 % of the PCWP [16]. As RV failure progresses, the RAP will approach or exceed the PCWP. Another sign of worsening RV failure is a decrease in the PA pressure despite a rising RAP due to insufficient power generation by the RV.
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