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Restriction Versus Constriction
Acknowledgment
The authors thank Dr. Karen Modesto for her contribution to the previous edition of this chapter.
Constrictive pericarditis (CP) and restrictive cardiomyopathy (RCM) are both characterized by impairment of ventricular filling and manifest predominantly as so-called diastolic heart failure. However, the underlying pathophysiology in these two conditions is vastly different, which allows us to distinguish between these two conditions even though their clinical presentation may be quite similar. The distinction between CP and RCM is crucial because whereas CP is surgically curable, there are currently no curative therapies for most forms of RCM, with cardiac transplantation remaining the only potential option.
Cause
CP is usually a consequence of long-standing pericardial inflammation that ultimately leads to pericardial scarring, fibrosis, and calcification. Myocardial involvement may also occur but usually in the late stages. There are two main forms of CP: (1) the fibroelastic form (acute or subacute) in which the patients present with subtle signs and symptoms and (2) the rigid shell form (chronic) in which the pericardium is usually calcified and the patients present with advanced heart failure, hepatic dysfunction, and so on. In developed countries, CP is mostly idiopathic in origin or secondary to viral pericarditis, cardiac surgery, or radiotherapy. In contrast, tuberculosis remains the leading cause of CP in developing nations ( Table 73.1 ).
TABLE 73.1
Common Underlying Causes of Constrictive Pericarditis and Restrictive Cardiomyopathy
| Constrictive Pericarditis | Restrictive Cardiomyopathy |
|---|---|
|
|
Unlike CP, RCM is primarily a myocardial or endomyocardial disorder characterized by a nondilated stiff ventricle(s) with severe diastolic dysfunction. There may be predominant involvement of the left ventricle, right ventricle, or both. A number of primary cardiac or systemic disorders can give rise to RCM. In the United States, the most common cause of RCM is amyloidosis (primary, familial, and senile amyloidosis), whereas in the tropics (especially in Africa), endomyocardial fibrosis is quite common (see Table 73.1 ).
Hemodynamics In Constriction And Restriction
The primary pathology in CP is the loss of pericardial elasticity with its replacement with a rigid fibrocalcific shell that prevents ventricular filling ( Fig. 73.1 ). Characteristically, there is no impediment to ventricular filling during early diastole, but as soon as the total cardiac volume reaches the limit set by the rigid pericardium, further ventricular filling is suddenly halted. Second, because the total cardiac volume is now constrained by the pericardium, any filling of one ventricle occurs at the expense of the other ventricle. This is known as ventricular interdependence. Although, to some extent, it is present in normal ventricles as well, it is greatly exaggerated in CP. Third, thickened, calcific pericardium shields the cardiac chambers from changes in intrathoracic pressures, a phenomenon known as dissociation of intracardiac and intrathoracic pressures. As a consequence of this, the reduction in intrathoracic pressure and subsequent pulmonary venous pressure during inspiration is not accompanied by an equivalent reduction in left ventricular (LV) diastolic pressure, and consequently, the pressure gradient between the pulmonary veins and LV diastolic pressure is markedly reduced. This results in reduced transmitral filling during inspiration and vice versa during expiration (see Fig. 73.1 ). Finally, the inflamed pericardium leads to tethering of the underlying myocardium, resulting in impairment of its contractile function. This tethering effect affects mainly the free walls of the atria and ventricles; the interatrial and interventricular septae are relatively spared. These hemodynamic and functional abnormalities result in several characteristics findings ( Tables 73.2 and 73.3 ) that are helpful in distinguishing between these two conditions, as discussed later.
TABLE 73.2
Differentiating Features of Constrictive Pericarditis and Restrictive Cardiomyopathy
| Feature | Constrictive Pericarditis | Restrictive Cardiomyopathy |
|---|---|---|
| Jugular venous waveform | Prominent X and Y descents (Y decent is of brief duration); Kussmaul sign often present | Prominent Y descent but not X descent; Kussmaul sign less common |
| Cardiac auscultation | S3 with high-pitched pericardial knock; no S4; mitral and tricuspid regurgitation usually absent | Increased S2 and S3 with low-pitched triple rhythm; S4 often present; mitral and tricuspid regurgitation common |
| Chest radiograph | Pericardial calcification (20%–30% prevalence); mild cardiomegaly and pulmonary venous congestion; bilateral pleural effusion less common | Pericardial calcification rare; mild cardiomegaly with biatrial enlargement, pulmonary venous congestion; bilateral pleural effusion more common |
| Electrocardiogram | Low amplitude (<50%); atrial fibrillation; P wave usually wide and notched | High or low amplitude (amyloidosis), atrial fibrillation, depolarization abnormalities (BBB), pathologic Q waves, and impaired atrioventricular conduction; P wave may be wide and increased in amplitude |
| Echocardiogram: gray-scale imaging | Increased pericardial thickness; normal wall thickness; septal bounce and respirophasic septal deviation | Increased wall thickness; thickened cardiac valves (amyloid); granular sparkling texture (amyloid); biatrial enlargement; apical obliteration (endomyocardial fibrosis) |
| Doppler studies | Significant respiratory variation in mitral and tricuspid inflow velocities; exaggerated medial mitral annular early diastolic velocity; expiratory augmentation of hepatic vein diastolic flow reversal | No significant respiratory variation in mitral and tricuspid inflow velocities; inspiratory augmentation of hepatic vein diastolic flow reversal; mitral and tricuspid regurgitation common |
| Cardiac catheterization | RVEDP and LVEDP usually equal; ventricular filling pressure waveforms show “square-root” sign; RV systolic pressure <50 mm Hg; RVEDP more than one-third of RV systolic pressure | LVEDP often >5 mm Hg greater than RVEDP; “square-root” sign is variable; RV systolic pressure usually >50 mm Hg; RVEDP less than one-third of RV systolic pressure |
| CT or cardiac MRI | Demonstrate a thickened pericardium in most cases; pericardial hyperenhancement after gadolinium contrast injection denotes inflammation | Pericardium usually of normal thickness; myocardial LGE seen in various inflammatory or infiltrative forms of RCM |
| Endomyocardial biopsy | May be normal or may demonstrate nonspecific hypertrophy or myocardial fibrosis | May reveal specific cause of RCM, especially in infiltrative conditions |
| BNP | Normal or minimally elevated BNP | Significantly elevated BNP |
BBB, Bundle branch block; BNP, brain natriuretic peptide; CT, computed tomography; LGE, late gadolinium enhancement; LVEDP, left ventricular end-diastolic pressure; MRI, magnetic resonance imaging; RCM, restrictive cardiomyopathy; RV, right ventricular; RVEDP, right ventricular end-diastolic pressure; S, heart sound.
TABLE 73.3
Distinctive Echocardiographic Findings in Constrictive Pericarditis and Restrictive Cardiomyopathy
| Parameter | Constrictive Pericarditis | Restrictive Cardiomyopathy |
|---|---|---|
| Septal bounce | Yes | No |
| Respirophasic septal deviation | Yes | No |
| Mitral inflow respiratory variation | ≥25% | None (<10%) |
| Tricuspid inflow respiratory variation | >40% | None |
| LV isovolumic relaxation time | Decreases during expiration, increases during inspiration | No change |
| Mitral annular e′ | Relatively preserved or even exaggerated, medial e′ ≥ lateral e′ | Markedly attenuated, medial e′ < lateral e′ |
| Mitral E/e′ | <8–10 | >15 |
| Hepatic vein flow reversal | Diastolic reversal with expiration | Significant reversal during both inspiration and expiration but more pronounced during inspiration |
| Myocardial mechanics |
|
|
| Other findings | Thickened pericardium with or without calcification; tethering of RV free wall; distortion of LV and/or RV contours | Increased LV and/or RV wall thickness; thickened cardiac valves (amyloid); granular sparkling texture (amyloid); biatrial enlargement; apical obliteration (endomyocardial fibrosis) |
E, Peak transmitral early diastolic flow velocity; e′, peak early diastolic mitral annular velocity; LV, left ventricular; RV, right ventricular
In RCM, on the other hand, impairment to ventricular filling occurs throughout diastole. Additionally, because the stiffness is intrinsic to the myocardium and there is no external constraint, ventricular interdependence is not exaggerated, and there is no dissociation of intracardiac and intrathoracic pressures. Furthermore, because RCM is a myocardial disease, myocardial dysfunction is invariably present and is generally global, with no specific predilection for free walls or septae.
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