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are also other indicators of PH in dogs with MMVD. A study suggested that a tricuspid pressure gradient was associated with a combination of either an increased or decreased left ventricular diastolic dimension, decreased pulmonary arterial acceleration/deceleration time, increased right ventricular diastolic diameter and left atrial to aortic root (LA/Ao) ratio.
Treatment of PH
Because most cases of PH are secondary to an underlying disease process, treatment aimed at eliminating or improving the underlying disease status is the basis for therapy. If the PH is not controlled by primary disease therapy or if the etiology of the PH appears to be idiopathic, then direct pulmonary arterial pressure modulation through the use of pulmonary vasodilators should be implemented. For example, it is
An Urban Experience
not uncommon that MMVD dogs with a recent onset
of signs of CHF present with mild PH that may reverse once effective CHF therapy has started. Dogs with PH despite having their signs of CHF controlled by medical therapy probably benefit from medical therapy aimed
at reducing pulmonary arterial pressure, but there are few veterinary studies available supporting this. Dogs with more pronounced PH are more likely to benefit from this type of therapy. In human medicine, there
are several different medical treatments available,
such as endothelin-receptor blockers, prostacyclin analogues, and L-arginine, but these are not available
in veterinary patients because of costs and lack of efficacy in this specie. The current most commonly used drug for controlling PH in dogs is, therefore, Sildenafil. Pimobendan is another drug that lowers the pulmonary arterial pressure (as well as systemic arterial resistance).
   Pulmonary arterial hypertension
     Secondary to other disease
  Collagen vascular disease
   Congenital left-to-right shunt
   Portal hypertension
     HIV infection
     Drugs and toxins
   Other conditions
  Associated with substantial venous or capillary involvement
 Pulmonary veno-occlusive disease
     Pulmonary capillary hemangiomatosis
   Persistent pulmonary hypertension of newborn
   Pulmonary hypertension with left heart disease
 Left-sided atrial or ventricular disease
    Left-sided valvular heart disease
     Pulmonaty hypertension associated with lung disease
Chronic obstructive pulmonary disease
    Interstitial lung disease
   Upper airway obstruction
   Alveolar hypoventilation disorders
    Exposure to high altitude
      Developmental abnormalities
      Pulmonary hypertension due to chronic thrombotic or embolic disease or both
Thromboembolic obstruction of proximal pulmonary arteries
     Thromboembolic obstruction of distal pulmonary arteries
     Nonthrombotic pulmonary embolism (tumuor, parasites, foreign body)
     Pulmonary Langerhans’ cell histiocytosis
   Compression of pulmonary vessels
       Fibrosing mediastinitis
 Table 1. Pulmonary Hypertension World Health Organisation (WHO) clinical classification system based on etiology

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