Cardiogenic Shock
Cardiogenic shock arises from a variety of cardiac dysfunctions in dogs, including an enlarged or dilated heart muscle, compression of the heart lining, outflow obstructions, blood clots, severe heart disease, heartworm disease, or severe arrhythmias. Additionally, systemic diseases can indirectly affect the heart’s ability to function properly, such as blood poisoning. This leads to decreased blood pressure and compromised blood flow to tissues, resulting in reduced tissue oxygen delivery. Cardiogenic shock occurs when there is a significant impairment in cardiac function, resulting in decreased stroke volume and cardiac output, as well as congestion in the veins and narrowing of blood vessels.
While most causative conditions for cardiogenic shock involve markedly depressed left or right ventricle function, other factors like cardiac compression and inadequate filling of the ventricles can also contribute. Reduced cardiac outflow can lead to dangerously low blood pressure, which diminishes blood flow to tissues. Conditions such as leaking from the pericardium or severe inflow or outflow obstructions to the ventricles can exacerbate the situation. Consequently, diminished blood flow to tissues causes organ ischemia and energy depletion, leading to abnormal organ function. Organs particularly affected include the brain, heart, lungs, liver, and kidneys. As shock progresses, congestive heart failure may develop, characterized by abnormal rises in left atrial pressure and pulmonary venous pressure, which can result in fluid accumulation in the lungs. Cardiogenic shock can affect dogs of any breed, age, or gender.
Symptoms and Types
- Paleness of mucous membranes (due to reduced blood flow)
- Cold extremities
- Fluctuating heart rate and respiratory rate
- Harsh lung sounds and crackles
- Coughing
- Feeble pulse
- Muscle weakness
- Mental lethargy
- Decompensation of the heart may be linked to a history of previously managed heart disease and the use of cardiac medications.
- Suspicions of previously undiagnosed cardiac disease may arise from a history of coughing, intolerance to exercise, weakness, or episodes of loss of consciousness.
Causes
Primary Cardiac Disease:
- Dilated heart muscle: Often observed in large-breed dogs with taurine deficiency.
- Severe valve insufficiency or other end-stage diseases affecting heart valves.
- Disturbances in heart rhythm.
- Constriction of the pericardium, which tightens around the heart.
Secondary Cardiac Dysfunction:
- Sepsis (systemic infection) leading to decreased cardiac contractility.
- Elevated levels of phosphorus in the blood.
- Pulmonary blood clot.
- Presence of gas in the pleural (chest) cavity.
Risk Factors:
- Concurrent illnesses causing hypoxemia (low oxygen levels in arterial blood), acidosis (excessive hydrogen ions in arterial blood), and electrolyte imbalances.
Diagnosis
Given the numerous potential causes of this condition, your veterinarian is likely to employ a process called differential diagnosis. This method involves a thorough examination of outward symptoms, systematically ruling out each of the more common causes until the correct disorder is identified and can be treated effectively.
Blood pressure measurement will confirm low blood pressure, while electrocardiography can help detect arrhythmias. Pulse oximetry, which measures oxygen saturation by analyzing light absorption fluctuations in well-vascularized tissue during heart contraction and dilation, may indicate low blood pressure. Blood gas analysis can reveal metabolic acidosis, characterized by decreased pH and bicarbonate concentration in body fluids, typically caused by acid accumulation or abnormal losses of fixed base from the body (e.g., due to diarrhea or renal disease). A chest x-ray might show an enlarged heart or signs of pulmonary edema (congestive heart failure). Echocardiography can provide insights into conditions such as cardiomyopathy, heart valve disease, impaired heart muscle contractility, or pericardial compression.
Treatment
In cases where cardiac dysfunction has progressed to shock, intensive hospitalized treatment is imperative. Drainage of the pericardium is necessary for patients experiencing compression of the heart lining, and fluid therapy will be cautiously administered until cardiac function improves. Positive inotropes, which enhance muscular contractions, along with vasodilators to widen blood vessels and improve blood flow, may be used. Additionally, decompression of a leaking pericardial sac is crucial, as congestive heart failure can worsen.
Cardiovascular monitoring will involve electrocardiogram (ECG) readings to assess the heart’s electrical activity, while measurement of central venous pressure and blood pressure will help gauge the effectiveness of the treatment. Oxygen supplementation is essential since reduced blood flow leads to decreased oxygen reaching the tissues. Oxygen may be administered via an oxygen cage, mask, or nasal tube. Furthermore, your veterinarian will select appropriate drugs tailored to your dog’s specific condition.
Living and Management
Following the initial treatment, your veterinarian will schedule follow-up appointments to assess your dog’s progress. During these visits, they will monitor key indicators such as heart rate, pulse intensity, mucous membrane color, respiratory rate, lung sounds, urine output, mental activity, and rectal temperature. This ongoing monitoring is crucial to ensure that your dog’s recovery is progressing as expected and to address any emerging concerns promptly.