How Does Left Heart Failure Cause Pulmonary Hypertension?
Pulmonary hypertension (PH) due to left heart failure (PH-LHF) exemplifies the most common form of PH, which accounts for 65 to 80% of PH cases. The pathobiology of PH-LHF is highly heterogeneous and the mechanism completely is unknown. According to WHO classification of PH, the etiology of group II PH-LHF is described into three subgroups
- Left heart systolic dysfunction,
- Left heart diastolic dysfunction and,
- Left heart valvular disease.
In recent days, some new terms have been used by the clinical experts. They are heart failure with reduced LV ejection fraction (HFREF) and heart failure with preserved LV ejection fraction (HFPEF). Both HFREF and HFPEF are similar to systolic and diastolic heart failure. PH in HFREF is basically connected to ischemic and dilative cardiomyopathy. In HFPEF, many conditions can cause this heart failure. Example, mitral valve disease, hypertensive, and coronary artery disease incidence rate are more ~ 30 to 50% leading to PH-HFPEF. The condition in patients with PH due to HFPEF is pathetic and responsible for very poor prognosis. A huge proportion is affected with LHF as there is no specific treatment or any other therapy option. PH is marked as severe and pulmonary vascular disease becomes a key factor of heart failure syndrome.
How is Pulmonary Hypertension (PH) As A Result Of Left Heart Diseases Classified
Heart Failure associated with decreased Left Ventricular EF:
- Dilated cardiomyopathy
- Ischemic cardiomyopathy
Heart Failure With Preserved Left Ventricular EF:
- Diabetic cardiomyopathy
- Hypertensive heart disease
- Hypertrophic cardiomyopathy
- Coronary heart disease
- Aortic valve stenosis
- Aortic valve regurgitation
- Mitral valve stenosis
- Mitral valve regurgitation
Persistent pulmonary hypertension even after the correction of the above mentioned defects
- Cor triatriatum
- Myxoma or left atrial thrombus
Physiological Processes Associated With Disease
PH-LHF Patients have defects particularly they show increased LV or left atrial filling pressures. The abnormalities begin with the increase in pressures because of filling in the left side of the heart which results in passive increase in backward pressure on the pulmonary veins. These filling defects occur in either in the left atrium or left ventricle or sometimes both. The backward pressure firmly causes high pulmonary venous pressures which can outcomes in the disintegration of the alveolar-capillary. The process occurs very insignificantly and the wall of alveolar–capillary becomes a delicate structure. This often mentioned as alveolar capillary stress failure generally characterized by capillary leakage and acute alveolar edema condition.
However, alveolar capillary stress failure is a reversible phenomenon. If not treated, the increase in venous pressure continues, and may become irreversible as alveolar–capillary wall undergoes remodeling. Severe deposition of type IV collagen makes the disease complex and permanent; this may be the factor for various local injuries i.e. increase the impedance to gas transfer, resulting in a decrease in lung diffusion capacity.
Left ventricular or left atrium injury leading to structural remodeling and dysfunction is the root cause of the progression of heart failure. A prolonged form of increased pulmonary venous pressure can seriously cause several remodeling and pathological changes in the pulmonary veins and arteries, as well as vascularization of arterioles, medial hypertrophy, and formation of neointima in the distal pulmonary arteries.
All these factors trigger spike of pulmonary vascular resistance (PVR). In some cases, endothelial damage also occurs causing disproportion in the formation of vasoactive mediators. The best example for vasoactive mediators includes nitric oxide and endothelin, which can cause impairment in vascular smooth muscle relaxation in this condition. Pathological and functional variations in the distal pulmonary arteries and arterioles are accountable for the increase of PVR.
The elevated level of PVR, structural remodeling, and dysfunction of the left side of the heart, valvular heart disease results in pulmonary hypertension (PH). Based on this, PH can hemodynamically be put into three categories namely mild, moderate, and severe, classified depending on values of mean pulmonary artery pressure, trans-pulmonary pressure gradient, and calculated PVR. Left-sided heart failure is an important and common cause of pulmonary hypertension (PH).
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