Clinical Cases - Heart

A 63 year old woman presented to the emergency room with pain in her left shoulder that radiated to the breastbone and to the pit of her stomach. With ITTP guidance, the medical student took a very thorough history. The following was discovered. The woman has had many attacks of pain for ten years, with lengthy intervals between them. However, the attacks have occurred everyday for the past two weeks, forcing her to stop working. Exertion in the form of gardening or exercising precipitates the attacks. The pain is not severe, and it is always relieved by rest.

Exam revealed:

• shoulder joint within normal limits, range of motion free
  
• heart slightly enlarged, otherwise within normal limits
  
• no elevation of cardiac enzymes
  

Administration of sublingual nitroglycerin resulted in pain relief. She was diagnosed with angina pectoris and discharged until further tests could be performed.

Questions to consider:

1. What causes angina pectoris?

   Angina pectoris, "chest pain," is due to myocardial ischemia. The pain is frequently precipitated by exercise, stress, or eating. During periods of increased oxygen demand, narrowed arteries may not be able to deliver adequate blood supply. By definition, angina is coupled with exertion, and relieved by 1-2 minutes of rest.

2. Describe the blood supply to the heart, listing the major arteries and branches.

   The ascending aorta gives off the right and left coronary arteries. The right coronary artery arises from the right aortic sinus and travels through the coronary groove; its major branches are the sinuatrial nodal artery, the right marginal branch, the posterior interventricular branch, and the atrioventricular nodal artery. The right coronary artery supplies the right atrium, right ventricle, interventricular septum, SA and AV nodes, AV bundles, and parts of the left atrium and ventricle.
   
   The left coronary artery divides into the anterior interventricular (left anterior descending or LAD) branch and a circumflex branch. The former supplies both ventricles as well as most of the interventricular septum. The circumflex branch supplies the left atrium, left heart surface, and the inferior base of the left ventricle, and it gives off a marginal branch.

3. Why is pain related to myocardial ischemia often "referred"?

   Cardiac pain is often referred to areas of the body surface which send sensory impulses to the same levels of the spinal cord that receive cardiac sensation. This is true especially on the left side. The sensory nerve fibers from the heart connective tissue and blood vessel walls travel through the cardiac plexus, sympathetic chain, and up to the dorsal roots and ganglia of spinal nerves T1-T4. Make sure you look up the dermatomes of T1-T4 to see the cutaneous distribution of this part of the spinal cord, as this is the common site of referred pain. The common sites of referred pain include the neck, jaws, shoulders, arms, and stomach.

4. Why did nitroglycerin work?

   Nitrites, like nitroglycerin, rapidly enter the vascular bed underneath the tongue when given sublingually. The drug dilates the coronary arteries, thus increasing the blood supply to the heart.

The woman showed up at the emergency room again, one week later. Her pain was more severe, lasted more than an hour, and was unrelieved by rest or nitroglycerin. She is diagnosed with myocardial infarction, and admitted immediately.

5. What is myocardial infarction?

   A myocardial infarct is an area of necrosis resulting from a sudden insufficiency of arterial or venous blood supply to the heart's muscular wall.

6. What arteries of the heart are most commonly occluded? Why do occlusions rapidly lead to infarct in the heart?

   The anterior interventricular branch of the left coronary artery, the right coronary artery, and the circumflex branch of the left coronary artery. The arteries are functionally end arteries. Each major artery leads to a specific region of cardiac muscle with little to no overlap. In the heart, major collateral blood supply is lacking. Thus, occlusion of a coronary artery will have major and devastating effects on the tissue it normally supplies.

7. The patient decides to undergo elective CABG (pronounced "cabbage," stands for coronary artery bypass graft) surgery. What is a bypass, and why is it done?

   A bypass is a shunt. The internal thoracic artery or vein grafts are used to shunt blood from the aorta to branches of the coronary arteries beyond the occlusion, "bypassing" the obstructed area to reestablish blood flow.

A fifty-three year old female lawyer presents to your Emergency Room after being found in her office slumped over her desk. Paramedics on the scene find her unresponsive with no pulse or respiration. The paramedics performed CPR and defibrillated her on the scene, resulting in the return of a pulse, with a systolic blood pressure of 90 mm Hg. On arrival at the Emergency Room the patient has developed spontaneous respiration and is regaining consciousness. You, therefore, are able to obtain a limited history from her which includes a positive history for smoking, an inactive lifestyle, hypertension, and a professional practice as a litigator (a job/lifestyle with high amounts of stress). The patient denies any previous history of chest pain, nausea/vomiting or referred pain. She reports that with this incident she was nauseated and felt pain in her back, left shoulder and arm. You order an ECG, cardiac enzymes levels, oxygen, and make arrangements for an immediate cardiac angiography. In addition, you order an aspirin to be given by mouth, as well as intravenous nitroglycerin and heparin drips. On physical examination you hear a slight murmur over the 5th left intercostal space. Her ECG reading and cardiac enzyme levels were both abnormal and helped you make the diagnosis of acute myocardial infarction.

Questions to consider:

1. What is coronary artery disease (CAD), and how does it present?

   Coronary artery disease is the narrowing of coronary arteries secondary to plaque formations from atherosclerosis. The three ways that CAD presents are: angina, infarction, and sudden death.

2. What modifiable risk factors for CAD does this patient have?

   Tobacco use, hypertension, and inactivity complicated by possible dietary habits.

3. What is an Acute Myocardial Infarction (AMI)?

   Interruption of the blood flow to a portion of the heart that causes myonecrosis (necrosis of cardiac tissue).

4. How is the diagnosis of AMI made?

   Identifying symptoms, abnormal ECG changes and increased serum levels of cardiac isoenzymes.

5. What is the significance of the pain in the patient's back, left shoulder and arm, as well as the nausea?

   Heart muscle itself is insensitive to stimuli that in somatic tissue would result in the perception of pain (e.g. cutting). But ischemic events, by diminishing blood flow in coronary vessels and possibly leading to tissue necrosis, produce metabolic byproducts (such as lactic acid). These byproducts are thought to be an important source of painful stimulation of the myocardial nerve endings. The visceral afferent fibers travel within the sympathetic cardiac nerves to the sympathetic trunk on their way to the spinal cord, which they enter through dorsal roots at levels T1-T5. These visceral afferents are thus in the same dorsal roots as the somatic afferents returning from the medial border of the left upper limb and left side of the chest wall (look at any standard dermatome chart). For reasons not well-understood, the visceral pain (originating in the heart) is referred to the cutaneous region innervated by nerve fibers that enter the spinal cord at the same levels.

6. What is the significance of the heart murmur?

   The patient may have developed mitral valve regurgitation. If this were a new onset of a murmur it may indicate papillary muscle rupture.

7. Which artery supplies the papillary muscles?

   Right coronary artery posteriorly, and the left coronary artery anteriorly.

8. What does the left anterior descending (LAD or anterior interventricular) coronary artery supply?

   Anterior wall, septum and the anterolateral wall.

9. What branches come off the LAD?

   Diagonals and septal perforators.

References:

Moore's Clinical Anatomy 4th Edition pp. 120-142.
Medicine Recall pp 24-29, 55-58.