Pulmonary hypertension is a pathological finding generally underdiagnosed in small animal clinics, consisting of increased systolic or diastolic blood pressure in the pulmonary circulation. Its appearance can be due to multiple causes, most of them related to cardiac or pulmonary alterations, which determines not only the diagnosis, but also the treatment of this alteration.
If you are interested in knowing more about pulmonary hypertension in dogs, we recommend that you consult the following article on our site, in the that we detail the most important aspects of this pathological finding, including its causes, symptoms, diagnosis and treatment.
What is pulmonary hypertension in dogs?
Before defining what pulmonary hypertension is, it is necessary to explain in broad terms how the cardiovascular system, formed by the circulatory (with arteries, veins and capillaries) and the heart. The cardiovascular system is divided into two circuits: the general or systemic circulation and the pulmonary circulation. The purpose of the general circulation is to transport oxygenated blood to the tissues, while the purpose of the pulmonary circulation is to transport deoxygenated blood to the lungs so that it can be reoxygenated again. Both circuits converge and cross at the level of the heart, made up of two left chambers (left atrium and left ventricle, which communicate with each other) and two right chambers (right atrium and right ventricle, which also communicate with each other). The left atrium receives oxygenated blood from the pulmonary circulation, which passes into the left ventricle, from where it is distributed to all tissues through the general circulation. The right atrium receives deoxygenated blood from the general circulation, which passes to the right ventricle from where it is distributed to the lungs, through the pulmonary circulation, to be oxygenated again.
Once we know the two types of circulation that exist, we can proceed to define pulmonary hypertension, which consists of aincreased blood pressure in the pulmonary circulation.
Types of pulmonary hypertension in dogs
Pulmonary hypertension can be of two types:
- Primary or idiopathic pulmonary hypertension: when the underlying cause is unknown
- Secondary pulmonary hypertension: when it appears as a complication of other diseases. It is the most frequent.
In turn, secondary pulmonary hypertension can be classified into three groups depending on its aetiology:
- Hyperkinetic pulmonary hypertension: is caused by increased blood flow to the lung, usually due to vascular malformations that allow the passage of blood from the left side to the right side of the heart.
- Passive pulmonary hypertension: occurs due to difficulty in pulmonary venous drainage, generally as a result of left heart failure.
- Angio-occlusive pulmonary hypertension: Occurs due to increased vascular resistance in the lung. It is the most common type of severe pulmonary hypertension.
Symptoms of pulmonary hypertension in dogs
The clinical picture associated with pulmonary hypertension can be variable. In dogs with mild pulmonary hypertension, often the only clinical signs seen are those associated with the primary pathology causing the hypertension.
In patients with moderate or severe pulmonary hypertension, the clinical manifestations that can be observed are:
- The characteristic of the primary pathology that is causing the hypertension.
- Cough.
- Exercise intolerance.
- Dyspnea (respiratory distress): Initially only dyspnea on exertion may occur, but in severe cases dyspnea at rest may be seen.
- Cyanosis: bluish discoloration of the mucous membranes.
- Syncope: these are episodes that occur with sudden loss of consciousness, followed by complete and usually sudden recovery. They are usually caused by situations of excitement or intense physical exercise, although in severe cases, a simple walk or climbing a few steps can trigger them.
- When associated with the presence of right congestive heart failure, it can be observed abdominal distention due to ascites, jugular distension, jugular pulse and pleural effusion.
Causes of pulmonary hypertension in dogs
The specific causes that can lead to high blood pressure in dogs are classified into the following disease groups:
- Diseases that cause increased pressure in the left atrium: in cases of left heart failure due to degenerative mitral valve disease or cardiomyopathy. They give rise to passive pulmonary hypertension.
- Diseases that produce volume overload at the pulmonary circulation level: due to vascular malformations such as atrial septal defect (persistent Botal foramen), ventricular septal defect, and patent ductus arteriosus (PDA). They lead to hyperkinetic pulmonary hypertension.
- Obstructive diseases of the pulmonary circulation: such as dirofilariosis, angiostrogillosis, neoplasia, septicemia, autoimmune hemolytic anemia, hyperadrenocorticism, nephrotic syndrome and coagulation disseminated intravascular disease (DIC). They give rise to angio-occlusive pulmonary hypertension.
- Chronic lung diseases: such as interstitial lung disease, chronic obstructive diseases or chronic stay at high altitudes. These situations produce a decrease in arterial oxygen pressure, which causes vasoconstriction of the pulmonary arterioles and causes angio-occlusive hypertension.
Diagnosis of Pulmonary Hypertension in Dogs
The presumptive diagnosis of pulmonary hypertension can be made by:
- Medical history and anamnesis: caregivers often describe a clinical picture characterized by exercise intolerance, dyspnea, cough, syncope, etc.
- Physical Examination-The general examination may detect signs such as abdominal distention due to ascites or dyspnea at rest. Murmurs may be detected on cardiopulmonary auscultation.
- Chest x-ray: dilation of the right chambers of the heart, the pulmonary trunk and the pulmonary arteries, as well as infiltrates can be detected pulmonary. In addition, manifestations of the primary pathology that causes hypertension may be observed.
- Laboratory analysis: especially important in cases of dirofilariosis and angiostrongylosis.
- Electrocardiogram: in most patients with pulmonary hypertension the electrocardiogram is normal, although in severe cases high P waves and peaky, deep S waves and right axis deviation.
- Two-dimensional echocardiography and M mode: in patients with moderate to severe hypertension, hypertrophy and dilatation of the right ventricle may be observed, as well as dilation of the pulmonary artery. However, there are patients with pulmonary hypertension who do not show echocardiographic abnormalities, so a negative result in this test should not rule out pulmonary hypertension.
All these steps help guide the diagnosis. However, to reach a definitive diagnosis of pulmonary hypertension in dogs, it is necessary to demonstrate the increase in pressure at the level of the pulmonary circulation. Systemic pressure, that is, the pressure that exists at the level of the general circulation, can be easily determined using both invasive and non-invasive techniques. However, determining pulmonary pressure is more complex. Invasive techniques are not useful since the pulmonary arterial system is not directly accessible, except by cardiac catheterization. For this reason, non-invasive techniques must be used, such as the Doppler echocardiographic study, which allows estimation of pulmonary artery pressures.
Specifically, Doppler echocardiography allows the diagnosis of pulmonary hypertension by detecting a high blood velocity value in tricuspid or pulmonary regurgitationPulmonary hypertension values will be considered those in which the tricuspid regurgitation velocity is greater than 2.4 m/s and those in which the pulmonary regurgitation velocity is greater than 2 m/s.
Treatment of pulmonary hypertension in dogs
To address the treatment of pulmonary hypertension in dogs, the following points must be taken into account:
- Support treatment: its objective is to control the primary pathology and its complications.
- Treatment with pulmonary arterial vasodilators: when supportive treatment manages to control the primary pathology but pulmonary hypertension persists and symptoms associated with her, pulmonary arterial vasodilators, such as sildenafil, should be administered.
- Treatment of right-sided congestive heart failure (when available).
Prevention of pulmonary hypertension in dogs
As we have explained in this article, pulmonary hypertension can be caused by multiple causes. Preventing its appearance is difficult or even impossible in some cases, since there are animals with a strong predisposition due to breed or age to develop diseases that originate secondarily pulmonary hypertension.
The fact that preventing the onset of pulmonary hypertension is difficult makes it especially important early diagnosis of pathologies that can cause hypertension, in order to establish adequate treatment as soon as possible and avoid complications. In this sense:
- In dogs of small breeds and older age, which have a special predisposition to suffer from degenerative disease of the mitral valve, they should be carry out regular check-ups to detect the disease as soon as possible and prevent the appearance of pulmonary hypertension.
- In puppies it is important to perform a good cardiopulmonary auscultation at an early age, in order to detect congenital abnormalities that may be the cause of hypertension pulmonary.
- The dogs that live in high- altitude areas with respect to sea level should be monitored periodically to prevent the effects of low blood pressure of oxygen.
