Failing Heart Overview

Failing Heart 1

• This presentation covers the failing heart
• The presenter is Prof Kamalan Jeevaratnam, DAHP, DVM, MMedSc (Mal), PhD (Cambridge), FRCVS (UK) from the School of Veterinary Medicine, University of Surrey.

Learning Outcomes

• Review normal anatomy and physiology of the cardiovascular system (CVS).
• Understand the pathophysiology and causes of heart failure.
• Describe common clinical signs/presentations associated with failing heart.
• Describe the pathophysiological process leading to observed clinical signs/presentations in failing hearts.
• Understand and describe the use of classification schemes for heart failure.

What are the roles of the cardiovascular system?

• Delivery of substances: oxygen, glucose, water, amino acids, fatty acids, and other nutrients
• Removal of substances: carbon dioxide, hydrogen ions, and other waste products
• Distribution: heat, hormones, cells, and bioactive agents
• Two fundamental mechanical functions of the heart:
  • Eject enough blood into the aorta and pulmonary arteries to meet tissue perfusion requirements.
  • Receive blood from pulmonary and systemic veins to provide adequate drainage of capillary beds.

Normal anatomy of the heart

• 75% of circulating blood is in the systemic circulation, 25% in pulmonary circulation.
• Encased in pericardium
• 4 chambers: left atrium, right atrium; left ventricle, right ventricle.
  • Left atrium and right atrium are separated by the interatrial septum.
  • Left ventricle and right ventricle are separated by the interventricular septum.
• 4 valves: tricuspid, mitral, aortic, and pulmonary. (Tricuspid and mitral are atrioventricular valves).
• Major vessels: coronary arteries, pulmonary trunk, and aorta.

Normal conduction system of the heart

• SA node (sinoatrial node) is the normal pacemaker.
• Spreads throughout the right and left atria via intermodal pathways to the AV node.
• AV node then to bundle of His, then left and right bundle branches, and Purkinje fibres to ventricular myocardium.

The heart as a pump

• The heart consists of two pumps that work in series
  • Left heart pumps oxygenated blood from lungs to the body (high pressure system)
  • Right heart pumps blood from the veins to the lungs (low pressure system)
• The pressure in the different heart chambers is shown as numerical examples (120/80, 25/10, 8-10, 0-4, 120/10, 25/4).

Cardiac Physiology

• Preload: volume of blood returning to the ventricle (ventricular end-diastolic volume). Affected by venous blood pressure and return rate.
• Afterload: tension, force, or stress acting on ventricular wall myocytes after shortening, affected by arterial and arteriolar vascular smooth muscle constriction/dilation.
• Heart Rate: determined by the rate of spontaneous sinoatrial nodal discharge and under autonomic control.
• Cardiac output = stroke volume x heart rate

Frank Starling Law

• Greater amount of blood in ventricles results in greater contractile strength, increasing stroke volume.
• More cross-bridges cycling, and greater availability of Ca++ to initiate cycling.

Heart Failure - Pathophysiology

• Heart failure is a pathophysiological state where the heart is unable to function to meet the animals' requirements.
• Progression of heart failure involves neuroendocrine dysfunction and biomechanical dysfunction.
• Dysfunction can lead to systolic or diastolic dysfunction.

What are the principle causes of cardiac injury?

• Myocardial failure: impaired contractility can be primary (dilated cardiomyopathy) or secondary (e.g., nutritional deficiencies, metabolic cardiomyopathies, toxicities, infiltrative cardiomyopathy, atrial fibrillation).

Volume Overload

• Valvular insufficiency: incompetence of atrioventricular valves commonly caused by endocardiosis, endocarditis, or congenital issues.
• Shunts: septal defects or persistent foramen, similar to valvular leaks in pathophysiology.

Excessive afterload/pressure overload

• Short increases in afterload help with contractility but chronic afterload will depress contractility.
• Reduced ejection rate if afterload is always high.
• Pulmonary or systemic hypertension, obstruction of ventricular outflow tracts, stenosis (narrowing) cause increased afterload.

Inadequate preload & diastolic dysfunction

• Reduces ability to adequately fill the chambers and causes diastolic dysfunction.
• This is related to issues like pericarditis, pericardial effusion, myocardial fibrosis, and restrictive cardiomyopathy; failure of ventricular relaxation.
• It increases ventricular end-diastolic pressure, exerting stress on the heart and leading to remodeling.

Algorithm of functional categories and etiologies of congestive heart failure in cats

• Details the functional categories (Diastolic heart failure, Primary myocardial failure, Ventricular volume overload, Pressure overload) and their etiologies(e.g. Hypertrophic Cardiomyopathy, Dilated Cardiomyopathy, Taurine Deficiency).

Clinical signs and presentation

• Coughing: common in dogs with significant cardiac disease, less common in cats. May indicate concurrent respiratory issues. Horses may cough due to pulmonary oedema.
• Dyspnoea: difficulty breathing, present in various heart conditions (acute pulmonary oedema, chronic disease, exertional, resting etc).
• Oedema/Ascites: fluid accumulation in the abdomen, commonly in dogs (less so in cats).
• Cyanosis: bluish discoloration of mucus membranes, usually from reduced oxygenation, commonly a late-stage finding in heart failure.
• Syncope: loss of consciousness due to reduced cerebral blood flow, typically brief and recurrent. Common in conditions like heart failure. Could be related to cardiac arrhythmia in some cases.
• Abnormal heart sounds and cardiac murmurs: S1 and S2 are normal heart sounds. S3 and S4 can indicate issues; murmurs indicate turbulent blood flow and may be physiologic or pathologic.

Weakness, exercise intolerance, and weight loss

• Weakness and exercise intolerance are nonspecific, often associated with changes in activity level, particularly as early signs of heart failure as the heart can't keep up with demand.
• Weight loss is more commonly seen in dogs with chronic severe right-sided heart failure (RHF) and is due to conditions like congestion of the pancreas, altered digestion, or protein-losing enteropathy.

Venous distension

• Jugular vein distension is examined while the animal is standing to assess venous pressure.
• Distension, pulse extending above lower third of neck, could indicate right heart failure or tricuspid regurgitation.
• Generalized jugular distension might indicate systemic hypertension.

Classification of heart failure

• Different classes (Class I-IV) classify patients according to severity of clinical signs in the context of heart disease, reflecting how the disease affects activity levels (e.g., Class I = asymptomatic; Class IV = severe clinical signs at rest).

Stages of Heart Disease

• Stage A: High-risk animals without present heart disease
• Stage B: Animals with structural heart disease (e.g., murmur) but no signs of heart failure.
• Stage C: Individuals experiencing heart failure symptoms related to structural heart disease.
• Stage D: Animal with advanced heart failure that is refractory to standard treatment.

Causes of the failing heart

• Acquired valvular disease, including degenerative mitral valve disease, endocarditis, endocardiosis, and equine valvular regurgitation
• Pericardial disease (pericarditis, traumatic reticulo-pericarditis)
• Hypertension (pulmonary and systemic)
• Cardiomyopathies (e.g., dilated, arrhythmogenic right ventricular, hypertrophic, feline cardiomyopathy)
• Heartworm disease
• Cardiac arrhythmias (e.g., atrial fibrillation)

References

• List of veterinary textbooks.