Cor pulmonale is the traditional term for changes in the cardiovascular system resulting from the chronic hypoxia (and usually hypercapnia) of chronic lung disease, mainly PHT and fluid retention. It does not include similar changes seen in some left-sided disorders such as mitral incompetence.
Cor pulmonale can occur in most situations where there is chronic hypoxia (see Box 23.1):
• Most often in the setting of hypoxic and hypercapnic COPD
• Hypoventilation syndromes (scoliosis, neuromuscular diseases, obesity)
• Much less common when there is no associated rise in PaCO2 (e.g. with ILDs, altitude, right-to-left shunts).
Cor pulmonale is often also referred to as ‘right heart failure’, which is misleading as the cardiac output in cor pulmonale is usually normal or high with increased peripheral perfusion (hence, the ‘bounding pulse’ and warm peripheries of type II ventilatory failure). If allowed time to adapt, the right ventricle (RV) can generate much higher pressures (e.g. in idiopathic pulmonary arterial hypertension (IPAH)) than are usually seen in cor pulmonale in response to the hypoxia. In true right heart failure, the RV acutely fails to develop an adequate cardiac output, e.g. following right-sided MI or PEs that occlude a large proportion of the pulmonary vascular bed. This also produces a raised JVP, as occurs in the fluid overload of cor pulmonale, but, in contrast, there will of course be a low cardiac output and poor peripheral perfusion.
Patients often present with their first episode of ankle swelling during an exacerbation of their COPD when, for the first time, the PaCO2 rises and the PaO2 falls, far enough to provoke the above events. Body weight may not actually rise very much with the onset of ankle oedema; however, the extra salt and water, retained in the capacitance vessels leading up to the exacerbation, move into the subcutaneous tissues, probably due to the CO2-induced vasodilatation, raising mean capillary hydrostatic pressure.
Loss of pulmonary vascular bed from emphysema also contributes to the raised PAP, and the ECG often shows RV hypertrophy. During an exacerbation, extra hypoxia will produce further rises in PAP, with which the hypertrophied RV usually copes, helped by the raised JVP providing a larger pre-load to increase RV filling. Excessive diuresis can lead to a true fall in right-sided output due to inadequate filling of the RV.
• The underlying disease causing the hypoxia, e.g. COPD/bronchiectasis
• Easily visible veins and a raised JVP
• Cyanosis and a suffused conjunctiva (polycythaemia and vessel dilatation from the raised CO2)
• Sometimes marked polycythaemia, very rare consequences due to hyperviscosity
• Peripheral vasodilatation, with a ‘bounding’ pulse and warm peripheries
• Ankle swelling and pitting oedema
• RV hypertrophy (sternal heave uncommon, masked by hyperinflated lung between heart and chest wall; more often seen with the higher pressures of IPAH
• Tricuspid incompetence (not usually severe)
• CXR—enlarged pulmonary arteries/underlying lung disease
• FBC—may have associated polycythaemia
• Oximetry—cor pulmonale is unlikely if awake SaO2 >92%
• Blood gases—cor pulmonale progressively more likely as PaO2 drops below 8kPa (equivalent SaO2 ≈ 91%) and PaCO2 rises above 6kPa
• ECG—may indicate right axis deviation (RAD), p pulmonale (right atrial hypertrophy), and right bundle branch block (RBBB)
• Echo—dilated or hypertrophied RV, tricuspid regurgitation (TR), providing estimate of PAP, and exclude other diagnoses such as a patent atrial septal defect (ASD)
• Overnight oximetry—to reveal unexpected degrees of hypoxia, e.g. from OSA, obesity, neuromuscular disease.
Minimal ankle oedema needs no treatment. ‘Trimming’ the ankles to normal is unnecessary and may reduce RV output by reducing RV filling. If the oedema is more substantial, then the following may help:
• Treat underlying condition to raise PaO2 and lower PaCO2
• Raise PaO2 through added O2; provide long-term O2 at home
• In hypoventilation syndromes, home overnight NIV likely to be the correct management
• Promote a limited diuresis with judicious use of diuretics
• Always elevate legs when sitting
• Some will venesect if haematocrit exceeds 0.6, but no RCT evidence of physiological benefit or a reduction in hyperviscosity complications.
In general, ‘cor pulmonale’ is overtreated. It is often a relatively harmless by-product of hypoxia, rather than a problem in its own right. Treating the blood gas disturbance and making it easier for the patient to get his shoes on are the main therapeutic aims. The long-term O2 trials showed that improving the PaO2 was useful, not that lowering the PAP was important.