The heart is a muscular organ composed of four chambers: two upper chambers called atria and two lower chambers called ventricles. These four chambers pump blood through the body in a rhythmic pattern with the help of the four valves in the heart. The movement of blood through the body can be felt at the wrist or neck and is known as the pulse.
Although the heart is full of blood, it cannot receive oxygen and nutrients from the blood inside the chambers. The heart muscle must rely on the arteries on the surface of the heart to nourish it and keep it working properly. These surface arteries are known as coronary arteries.
There are three main coronary arteries: the right coronary artery, the left anterior descending coronary artery and the circumflex coronary artery. These three arteries branch into thousands of small arteries like tree trunk branches into limbs, bringing oxygen and nutrients to the heart muscle cells.
Electrical System of the Heart
Under normal circumstances, heart rate is controlled by the sinus node (or SA node), a structure located on the outside of the right atrium, which responds appropriately to the body's needs. The electrical impulse travels through the atrium and reaches the atrioventricular node (AV node), which is the normal connection to the ventricles, the bottom chambers of the heart
that pump blood to the lungs and body. The electrical impulse travels through the AV node, to the bundle of His, then to the left and right bundle branches, and finally to the ventricular muscle. Abnormalities can occur anywhere on that route; patients can be born with additional connections between the atrium and ventricle called accessory pathways as well as additional pathways within the AV node. Either of those abnormalities can support electrical impulses traveling in a circle that cause rapid heartbeats and result in supraventricular tachycardia. Small abnormal areas in either the atrium or the ventricle can cause "atrial tachycardia," and "ventricular tachycardia." Blocks at various points can cause slow heart rates and episodes of passing out, or "syncope." Diffuse sickness of the atrium can cause very rapid and chaotic signals in the atrium resulting in atrial fibrillation or somewhat more organized rhythms called atrial flutter. Damage to the ventricle can cause ventricular tachycardia as well as ventricular fibrillation, which can be life-threatening and cause sudden cardiac arrest. All of these problems are amenable either to treatment with catheter-based ablation or to device therapy with pacemakers or defibrillators.
Cardiac Risk Stratification
As heart disease continues to be the most common single cause of death in the American population, increasing medical efforts are directed at identifying high-risk patients early in the course of their disease, hopefully before symptoms have had a chance to develop. A wide variety of tests can be employed toward this purpose, all starting with a visit with a physician to most appropriately guide testing depending on a patient's history, physical examination, family history, lifestyle and desire for aggressive risk factor control. Many patients find that a more precise identification of their individual risk can be extremely helpful to them in deciding how best to control their lifetime risk of a cardiovascular event.
Congestive Heart Failure
Heart failure is one of the most common and fastest-growing cardiac problems, especially as more people survive cardiac events that prior to modern therapies would have been fatal and as the population ages. It can be defined as an inability for the heart to supply the needs of the body, and can be present either with depressed contractile ("squeezing") function of the heart, known as systolic heart failure, or with apparently normal contraction of the heart muscle, known as diastolic heart failure. Common symptoms include fatigue, shortness of breath, coughing, swelling (particularly of the legs and feet), abdominal distention, and poor appetite; in around 50 percent of patients this is associated with coronary artery disease (i.e., blockages in the arteries of the heart) but can also be associated with valve problems, diseases of the heart muscle itself, or systemic medical illnesses. Evaluation will typically start with an echocardiogram (ultrasound of the heart) and in appropriate patients some kind of assessment of the presence or absence of coronary artery disease. If reversible causes of heart failure are found, they will be treated; almost all if not all patients can be significantly helped by a combination of medicines and minimally invasive procedures. An assessment of the risk of life-threatening arrhythmias will inform the decision about whether an implantable device called a defibrillator or ICD is necessary. Finally, in the extreme cases in which severe symptoms persist despite medical management, more advanced therapies such as stem cell transplantation, implantation of left ventricular assist devices, or cardiac transplantation are considered.