Welcome to the Basic Cardiology area of our Patient Education section. This section is designed for you to educate yourself on some basic cardiology terminology. All the topics listed in this section will have some information for you to read.
ANATOMY AND PHYSIOLOGY
The heart is a muscular pump about the size of your fist, and its primary function is to pump oxygenated blood to the rest of the body. It is made up of four chambers, the right and left atria on the top, and the right and left ventricles on the bottom. The septum is a thin muscular wall that separates the right and left sides of the heart. Each contraction of the heart occurs in response to an electrical impulse that starts in the upper portion of the heart. Blood is moved in a closed circuit through the body by the pumping of the heart. The heart contracts and pumps blood out to the body (systole) and relaxes to fill with more blood (diastole).
The heart muscle itself is like all other organs in the body and requires oxygen to function. The oxygen-rich blood is circulated to the heart muscle through the coronary arteries. There are two main arteries: the right coronary artery and the left main coronary artery, both starting at the aorta (the main blood vessel of the body). These vessels then branch off into smaller and smaller vessels along the surface of the heart.
In studying and testing the heart, it is essential to understand which system in the heart is having problems:
1. Electrophysiology – Is the conduction system (the wiring) in the heart following the normal pathway?
2. Coronary circulation – Is the heart muscle getting adequate blood supply and oxygen through the coronary arteries (the plumbing)?
Cardiac contractility, or pumping ability, is an integral part of heart function. The heart’s conduction and circulatory systems may be excellent, but if the heart muscle does not contract well, significant symptoms can result.
We can assess contractility through an echocardiogram which is an ultrasound test of the heart. Many things can affect how well the heart contracts. These include certain medications, heart attacks, overuse of alcohol, and cardiomyopathy (primary heart muscle disease). The causes of decreased contractility and alternatively “stiff” heart muscle, and their treatment options should be discussed with your cardiologist.
RIGHT CORONARY ARTERY (RCA)
The RCA supplies blood to the bottom (inferior) portion and part of the back (posterior) portion of the left ventricle. The posterior portion of the septum, separating the ventricles, is also supplied with blood from the RCA.
LEFT ANTERIOR DESCENDING BRANCH (LAD)
The LAD supplies blood to the front (anterior) portion of the left ventricle, including most of the anterior portion of the septum separating the ventricles.
LEFT CIRCUMFLEX BRANCH (LCX)
The LCX supplies blood to the left side (lateral) portion and the back (posterior) portion of the left ventricle.
In order to perform work, the heart, like all other organs in the body, needs oxygen and nutrients. The heart has its unique circulation, the coronary arteries, of which there are two: the right coronary artery (RCA) and the left coronary artery (LCA). The left coronary artery divides into the left anterior descending (LAD) branch and the left circumflex branch. The right coronary artery and the branches of the left coronary artery provide numerous smaller branches that penetrate the heart muscle, supplying it with blood. Both coronary arteries originate from the main blood vessel of the body, called the aorta, and run along the surface of the heart. In the majority of human hearts, coronary circulation follows a predictable pattern.
CARDIAC CATHETERIZATION +/- STENT
Diagnostic procedure performed in the hospital, whereby a catheter (usually is passed through an artery in the wrist or sometimes in the groin) which is advanced to the heart’s arterial vessels and contrast dye is injected to assess for “blockages” or plaque that may or may not obstruct blood flow. If the blockage requires opening, then a stent can be deployed within the blockage. On occasion, a right heart catheterization (catheter placed through a vein in the groin) may also be performed to assess the heart’s right-sided filling pressures.
If the coronary arteries and veins are considered the plumbing of the heart, then the conduction system (shown in black below) can be considered the electrical wiring of the heart. Through this wiring, each muscle fiber of the heart knows when and how fast to beat so that the heart can pump efficiently.
The electrical system of the heart is significantly affected by the brain and certain hormones and body chemicals called electrolytes. How these elements work with the rhythm generators of the heart determines the heart rate and sequence of the heartbeat. The Sino-atrial (SA) node is the body’s primary natural cardiac pacemaker. The heartbeat starts here and spreads like the ripples in a pond throughout the network of conduction fibers in the two atria (the two upper chambers), causing them to contract. Typically, the heartbeat can only reach the ventricles (the two lower chambers) after it has passed through the atrioventricular (AV) node. The AV node slows down the electrical signal so that the atrial contractions can finish and fill the ventricles more completely. The AV node also prevents the lower chambers from beating too fast if the atria develop a fast rhythm (tachyarrhythmia). The electrical signal finally passes to the ventricles, the leading workhorses of the heart, through the bundle of His, bundle branches, and the Purkinje system (a specialized network of nerves that coordinates contraction of the ventricles). Each heartbeat is then completed, and a new one is initiated in the SA node.
NON-INVASIVE CARDIOLOGY TESTING
Being able to assess and measure how the heart is functioning without entering the body is called noninvasive cardiology. Non-invasive cardiology uses ultrasound waves to examine the heart (an echocardiogram). An echocardiogram can provide information on contractility, valve function, blood flow through the heart and other vessels, and evaluation of any clots that may have formed in the chambers of the heart. The findings from this test can answer some questions or tell us if further tests are indicated.
Before a cardiac catheterization (angiogram) is ordered, you may have a form of stress test ordered. Exercise or stress testing is used to determine exercise capacity and to monitor cardiac arrhythmias. A stress test can also determine if myocardial ischemia (lack of oxygen to the heart muscle) is the cause of chest pain for the patient.
Several tests in this field may be used:
Treadmill test– Patient walks on a treadmill while an electrocardiogram is being recorded. This allows doctors to study how the heart functions when made to work harder. Arrhythmias and other subtle changes may occur, making more tests necessary. Click here for instructions
Echocardiogram – For an “echo,” ultrasound waves are used on a resting heart to look at blood flow through the heart, contractility, valve function, any clot formation, and cardiac wall motion abnormalities. Click here for instructions
Stress Echocardiogram – A “stress echo” involves getting a resting echo before exercise, an echo during the last minute of exercise at target heart rate, and then immediately after terminating exercise. In order to achieve the target heart rate, the patient exercises on a treadmill or supine bicycle. Significant ECG changes with cardiac wall motion abnormalities indicate myocardial ischemia. At this point, an angiogram is often recommended. Click here for instructions
Dobutamine Echocardiogram – This test is for those patients who are unable to perform enough exercise to achieve a target heart rate. Dobutamine is given through an intravenous catheter placed in the patient’s arm. An echo is taken at rest, at target heart rate after Dobutamine is given and immediately after it is given. This test gives us the same information as the stress echo. A small percentage of patients will experience shaking or tremors associated with the use of dobutamine.
Nuclear Stress Testing – Nuclear perfusion imaging uses a radioactive isotope injected into the bloodstream to detect areas of abnormal blood flow to the heart muscle during exercise treadmill stress or with a drug used to vasodilate the coronary arteries (in place of the exercise treadmill).
Peripheral Vascular Studies – Noninvasive vascular studies are also done on the carotid arteries in the neck and other vessels in the arms and legs. These are done to study blood flow, check for narrowing (atherosclerosis), clots, and possible dissection of the vessel.
Hospital-based procedure in which a device implanted to treat symptomatic slow heart rhythms/rates.
Patients with very slow heart rhythms, bradycardias, may need to have a permanent pacemaker inserted. The main reasons a pacemaker would be required are:
1. Blocked or injured areas in the conduction system caused by normal aging or following an ablation.
2. A combination of fast and slow heart rates requiring medications to control the fast rhythms and a pacemaker to prevent the slow rhythms.
If you have any questions regarding your pacemaker checks, you can reach us at 410-761-8007.
ELECTIVE EXTERNAL ELECTRICAL CARDIOVERSION
Procedure performed in the hospital setting, typically for symptomatic atrial arrhythmias, such as atrial fibrillation. Sometimes a (TEE) transesophageal echo (unique echo involving the passing of a small thin ultrasound tipped probe down the esophagus) is used to exclude any blood clots in the heart before the procedure. The patient is completely sedated, and a shock is delivered through electrode pads (placed on the front and back of the chest) which help in the restoration of a normal rhythm. In some instances, the patient may need to be admitted for a few days on a cardiac telemetry floor (in order to be monitored for side effects), in order to be started on heart rhythm medication used to help sustain a normal rhythm.
IMPLANTABLE CARDIOVERTER DEFIBRILLATOR (ICD)
An ICD is an implantable device (somewhat similar to a pacemaker) that not only has pacemaking function, but also has the ability to treat potentially harmful rapid arrhythmias that arise from the ventricles (bottom of the heart) using rapid ventricular pacing and/or internal shocks from a wire placed in the heart such as from a Transvenous Implantable Cardioverter Defibrillator (TV-ICD) or a Subcutaneous Implantable Cardioverter Defibrillator (S-ICD) that uses shocks from a wire placed subcutaneously in the chest, outside of the heart.
CARDIAC RESYNCHRONIZATION THERAPY (CRT)
CRT is the ability to pace the left ventricle, thereby restoring more physiologic contraction of the heart in patients with chronic systolic congestive heart failure and marked left bundle branch block. The particular additional lead may be placed with an ICD creating a Biventricular Implantable Cardioverter Defibrillator (BIVICD or CRT-D) system or a PPM creating a Biventricular Permanent Pacemaker (CRT-P) system.
IMPLANTABLE LOOP RECORDER (ILR)
ILR is a tiny device placed under the chest wall skin that may stay for up to a few years (removed subsequently) that is used to help record/diagnose arrhythmias over a long period.
COMPREHENSIVE ELECTROPHYSIOLOGICAL STUDY (EPS) AND ABLATION THERAPY
An EPS is a diagnostic procedure using electrode-tipped catheters, placed in the heart, to help assess the electrical status/function of the heart, diagnose arrhythmias (abnormal heart rhythms) and possibly treat rapid arrhythmias using ablation therapy.
CLEFT ATRIAL APPENDAGE (LAA) OCCLUSION DEVICE
LAA occlusion device, such as the WATCHMAN, is an implantable device placed in the heart using a catheter, that is used to reduce the risk of stroke in patients with a history of atrial fibrillation. It is primarily used in patients having an appropriate reason to seek a non-drug alternative to warfarin.