Congestive heart failure

American Journal of Pharmaceutical Education, Summer 2002 by Zdanowicz, Martin M

PROLOGUE

The following paper presents the pathophysiology lecture content for congestive heart failure at the Massachusetts College of Pharmacy & Health Sciences. At the College, pathophysiology is a three credit course required for students in the PharmD, PA and BS in Pharmaceutical Sciences programs. The goal of this course is to give students a detailed understanding of the mechanisms involved in disease processes that affect the various organ systems. Knowledge of the pathophysioloic basis of disease is essential for success in the pharmacology and therapeutic courses the students face in the coming semesters, as well as for the clinical knowledge base that will be developed in future practice. Congestive heart failure (CHF) is a challenging but interesting topic to teach. It is a topic in which a detailed understanding of cardiovascular physiology is essential for grasping the effects of CHF on the body as well as the accompanying symptoms and therapeutic interventions that are employed. Students in pathophysiology are concurrently taking a two-semester course in human physiology and the topics between these two courses are closely integrated so that a detailed study of cardiovascular physiology occurs just before the presentation of CHF in pathophysiology.

Lecture material for CHF begins with a comparison between high output and low output types of failure with possible causes of each. A brief review of pulmonary and systemic circulatory pathways is then given to ensure that students are clear on the relationship of these two pathways to the left and right side of the heart. Students seem better able to grasp the consequences of CHF if the heart is split into the right and left side and then discussed independently of one another at first. A detailed discussion of the manifestations of left and right-sided heart failure then ensues with emphasis on the pathophysiologic basis for the various manifestations that are observed with left and right heart failure. Numerous diagrams are incorporated into the lecture to reinforce and clarify important concepts. The material continues with a discussion of the physiologic compensatory mechanisms that are active in a patient with CHF. It is stressed that early in the disease process, these compensatory mechanisms are useful in maintaining normal cardiac output function but that after a period of time, these renal and cardiovascular compensatory changes worsen heart failure and are often targets of therapeutic intervention. The clinical symptoms of CHF are presented along with various means of diagnosing the condition. After a detailed discussion of CHF from a pathophysiologic standpoint, students are asked to provide a rationale of how they might treat the symptoms of CHF based on their understanding of physiologic derangements that are present. The students are then given a brief overview of the various drug classes that are used in the treatment of CHF. The presentation of therapeutic agents is general and focuses mainly on the mechanisms) by which a certain drug or class of drugs is useful in CHF. Detailed discussion of the individual agents will take place in subsequent Pharmacology courses. A case study is also given at the end of the lecture material as a means of bringing all the information together and giving it some tangible clinical significance.

REVIEW OF PULMONARY AND SYSTEMIC

CIRCULATION

The left atrium receives oxygenated blood from the lungs via the pulmonary vein and transfers it through the mitral valve into the left ventricle. The left ventricle of the heart is the most heavily muscled chamber and is responsible for pumping oxygenated blood out into the aorta for delivery to the body. Deoxygenated blood returns from the body by the vena cava and enters the right atrium where it is then transferred into the right ventricle and pumped to the lungs for oxygenation via the pulmonary artery (Figure 1).

ETIOLOGY OF CHF

Heart failure is a condition in which the heart no longer functions effectively as a pump. Depending upon the cause, heart failure may be classified as low output failure or high output failure(l). Low output failure is said to occur when the pumping efficiency of the heart becomes reduced by factors that impair cardiac function. High output failure occurs when the cardiac output of the heart remains significantly elevated for a long period. With high output failure, the metabolic and oxygen demands of the heart exceeds what can be supplied by the coronary circulation and the function of the myocardium eventually fails. Some common causes of heart failure are listed in Table I.

Left Side Heart Failure

The left heart pumps oxygenated blood out to the systemic circulation. Common causes of left heart failure include myocardial infarction, cardiomyopathy and aortic valve stenosis (at this point it may be helpful to the students to review how heart valve defects lead to heart failure). Failure of the left heart effects blood flow out to the body (forward failure) as well as blood return to the heart from the pulmonary circulation (backward failure) (Figure 2). The manifestations of left heart failure include: