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15. Heart Failure, Cardiopulmonary Arrest, and Cardiogenic Shock
15.1 Heart Failure
Sometimes the terms heart failure, heart attack, and heart disease are loosely used. In fact heart attack and heart failure are due to heart diseases, while all heart diseases may not have heart failure or heart attack. Heart attack, most common in humans, is an acute condition when heart functioning is stopped suddenly. It is due to severe arrhythmias or blockage of the coronary arteries. On the other hand, heart failure is a gradual process which is an outcome of severe heart disease and is characterized by inability of the heart to pump blood efficiently to different parts of the body. It is commonly due to mitral valve insufficiency and dilated cardiomyopathy. Chronic mitral valve insufficiency is seen primarily in small breeds of dog, while dilated cardiomyopathy is seen most commonly in adults of large and medium breeds such as Doberman, Great Dane, Labrador, Irish wolfhound, German Shepherd, Scottish Dearhound, etc. Timely diagnosis is of great importance in the management of the cases with heart failure as delay may be catastrophic. Compromised heart in heart failure leads to systolic (forward failure) and/or diastolic (backward failure) dysfunctions causing inadequate perfusion of tissues and/or edema of dependent parts with varying clinical manifestations. Various cardiac and systemic compensatory responses are also triggered in the body in response to failing heart.
Right-sided heart backward failure—The backward failure of the right heart during diastole leads to hepatic congestion, ascites, and hydrothorax.
Left-sided heart backward failure—The backward failure of the left heart during diastole leads to pulmonary congestion and edema.
Right-sided heart forward failure—The forward failure of the right heart during systole leads to inadequate systemic blood flow.
Left-sided heart forward failure—The forward failure of the left heart during systole leads to inadequate tissue perfusion.
15.1.1 Common Causes of Heart Failure
Poor contraction of myocardium.
15.1.2 Diagnostic Approach in Heart Failure
Diagnosis of heart failure in dogs in early stage is sometimes very illusive where characteristic features are absent. Therefore a systematic approach right from history, detailed clinical examination, use of noninvasive modern diagnostic technology (electrocardiography, echocardiography, and radiography), to the use of cardiac biomarkers is to be taken in each suspected case of heart failure.
History in cases of heart failure is quite variable except marked weakness.
Some owners report disruption of sleep due to intense, persistent nocturnal coughing and dyspnea.
Dogs show marked weakness and easy exertion.
Dogs show panting on exercise.
Dogs are uncomfortable with exercise and show no interest physical activities.
Dogs are reluctant to lie down. Panting increases in recumbency (orthopnea).
Distension of abdomen and/or edema of hind limbs is also reported.
The history of persistent cough may indicate left-sided heart involvement. But solely it may not be diagnostic as it is also seen in cases with tracheal collapse, pulmonary edema, dirofilariasis, compression of the left main stem bronchus, and chronic pulmonary disease. Development of dyspnea in dogs with heart failure is a late sign, while in humans it is an early sign of failing heart. All these complaints are nonspecific but definitely create suspicion of heart failure and suggest further investigations to exclude or include other causes.
220.127.116.11 Clinical Manifestations
Heart and lung abnormalities.
Arrhythmia on auscultation of the heart.
Gallop sounds (in severe left ventricular volume overload).
Rales and crackling sound on thorax auscultation in dorso-caudal area of the lung.
Signs related to low output/forward failure.
Dehydration/prolonged capillary refill time.
Weak femoral pulse and pulse deficit.
Signs related to backward failure.
Persistent unproductive coughing.
Reluctance to lie down.
Jugular vein distension (hepatojugular reflux).
Abdominal distension (ascites).
Muddy or cyanotic mucus membrane.
Classical cases of congestive heart failure are clinically characterized by signs of both forward and backward failure. Respiratory diseases also exhibit dyspnea and rales; therefore their origin needs to be ascertained. Clinical manifestations depend on the side of the heart involved. Nevertheless, decreased stamina, difficult breathing, sleepiness, decreased appetite, fainting, and coughing are commonly associated with heart failure due to either mitral valve insufficiency or dilated cardiomyopathy. Right-sided heart failure is associated with poor venous return causing leakage of some blood into the right atrium through the tricuspid valve backing the blood into circulation and consequently causing congestion. The fluid is build up in the abdomen (ascites) and/or in limbs (peripheral edema).
In case of left heart failure, due to poor contractility, whole blood is not pushed into circulation, and some blood is leaked into the left atrium through mitral valve and then back into the lungs causing lung edema leading to coughing and dyspnea.
Classification of Functional Heart Failure
Class I. There are no symptoms in class I heart failure. Clinical signs do not develop even on exercise.
Class II. Clinical signs such as fatigue, dyspnea, or coughing develop on exercise in class II heart lure.
Class III. Clinical signs such as fatigue, dyspnea, or coughing develop with minimum activity.
Class IV. Clinical signs such as dyspnea and coughing are seen even at rest. These signs are exaggerated with minimum physical activity making the dog highly uncomfortable.
18.104.22.168 Cardiac Biomarkers and Biochemical Indices
CBC, liver and kidney profile, thyroid profile, and sodium and potassium estimations are generally done to create basic profile to exclude or include liver, kidney, ions, or thyroid involvement. But none of these is specific for heart failure. Recently cardiac biomarkers such as cTn-I and NT pro-BNP are being estimated to detect myocardial damage even in early stage when signs of heart failure are not apparent. These biomarkers indicate myocardial damage. Lowered vitamin D3 level (4.2–28.9 ng/mL, mean 13.55 ± 1.67 ng/mL) and increased cTn-I level (mean 5.19 ± 1.78 ng/mL, range 0.1–28.97 ng/mL) have recently been observed in dogs with left heart failure at this hospital (Varshney et al. 2019). Some reports indicate that lower level of vitamin D3 predisposes to heart failure. Oxygen tension (PvO2) is also lowered in dogs with heart failure.
22.214.171.124 Radiographic Findings in Heart Failure
Pulmonary venous and capillary congestion.
Change in cardiac silhouette (Fig. 15.2a).
Interstitial and/or alveolar edema (Fig. 15.2b).
Hepatomegaly/splenomegaly (Fig. 15.3).
Ground glass appearance of the abdomen suggesting ascites (Fig. 15.4).
Compression of main stem bronchi (Fig. 15.5).
Pulmonary edema in dorso-caudal hilar region gives strong indication of left heart failure. Cases showing these radiographic changes should invariably be subjected to electrocardiography.
126.96.36.199 Electrocardiographic Findings in Heart Failure
Atrial premature complexes.
“P” mitrale (broad P wave)
Ta wave (right atrial enlargement).
Tall “R” (increased amplitude of R wave).
Ventricular escape complex.
Ventricular premature complex.
S-T segment changes.
Prolonged Q-T interval.
Change in polarity of “T” wave.
Bundle branch blocks.
Alternans of “R”.
188.8.131.52 Echocardiographic Findings in Heart Failure
Echocardiography is another important noninvasive diagnostic modality for imaging the heart and its surrounding structures. It is one step ahead of electrocardiography and provides important information about size of the heart chambers, thickness of the wall, wall motion, valve configuration and motion, the proximal great vessels, and detection of the pericardial and pleural effusions which is not possible by electrocardiography. Identification of mass lesion within and adjacent to the heart is also possible by echocardiographic examination. Like other diagnostic modalities, its interpretation should be viewed within the context of a thorough history, clinical picture, complete cardiovascular examination, and other tests.
15.1.3 Treatment of Heart Failure
Since congestive heart failure is a progressive condition with physical changes in the valves and weakened ventricular wall, the primary aim of the treatment is to relieve distressing symptoms and make the life of the dog comfortable. Specific treatment of congestive heart failure depends on the underlying heart disease and its severity. Nevertheless, the main goal of the treatment is to reduce fluid buildup and to increase contractibility of the heart to improve the quality and length of pet’s life. Nowadays a variety of medications and specific diets are available to help in achieving this target. Cough suppressant (butorphanol or hydrocodone), restricting sodium in the diet (to reduce water holding), cardiac diet, providing rest, oxygen therapy, and medications such as diuretics, ACE inhibitors, vasodilators, and positive inotropes are the integral part of the management of congestive heart failure to relieve fluid accumulation, to maintain or increase cardiac output, to minimize myocardial oxygen demand, and to control rhythm disturbances.
Low-sodium diets. Dogs with heart failure should be given diets low in sodium. Potassium chloride may be added to improve the flavor of the diet.
Supplementation of l-carnitine (50 mg/kg orally twice or thrice daily) may have an added advantage.
Use of diuretics—Diuretics are the main part of therapy in the management of heart failure.
Furosemide is used @ 2–4 mg/kg BID-TID PO or 2–8 mg/kg IV up to every hour. If furosemide alone is not working satisfactorily, triamterene (2–4 mg/kg PO daily) can be considered. Spironolactone (2–4 mg/kg per day PO), hydrochlorothiazide (2–4 mg/kg BID PO), and chlorothiazide (20–40 mg/kg BID-TID PO) are the other diuretics of choice.