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About Your Heart


Test Procedures & Diagnosis


About Your Heart

The Structure of Your Heart

In the middle of your chest, tilted slightly to the left, you have an amazing, pumping machine about the size of a clenched fist. It is difivded into two parts by the septum, a thick band of muscle tissue. The right side of your heart receives blood returning from the organs of your body. It then pumps it to your lungs where your blood receives a fresh supply of oxygen and releases carbon dioxide, a waste product. The left side of your heart receives the oxygen rich blood from your lungs and pumps it out to your body through the major artery of your body, your aorta. The left side of your heart is thicker because it has to supply blood to the whole body while the right side’s job is just to send it to your lungs.

There are four chambers within your heart. The upper two are called atria, where your blood is briefly stored when returning to your heart. The atria then send your blood to the lower chambers, the ventricles, the main pumping chambers of your heart.

The blood flows from the upper to the lower chambers of your heart through the valves that work as one-way doors. The blood passes through them in only one direction. Four valves regulate the flow of blood from one part of the heart to another, the mitral, the aortic, the pulmonary, and the tricuspid.

Where does your heart get its own oxygen? From the coronary arteries that surround the heart muscle and pump blood into every portion of it. The right coronary artery supplies blood to the right and left sides of your heart. The left main coronary artery has two main branches – the left anterior descending artery, which feeds the front left side of the heart, and the circumflex artery that feeds the lateral wall and back of your heart. These main coronary arteries have many branches that supply your heart muscle with oxygen-rich blood.


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Heart Attack

The term “heart attack” or myocardial infarction refers to damage to the heart muscle due to complete blockage of a coronary artery. It can be caused by a blood clot plugging the coronary artery (coronary thrombosis) or a severe narrowing or obstruction in the coronary arteries (coronary artery disease CAD also sometimes called coronary heart disease) or a combination of both. We know that clots are more likely to occur in narrowed or blocked arteries. These blockages, which interfere with the blood flow to the heart muscle, decrease the oxygen supply. When there is total blockage of the blood flow, a part of the heart muscle is without oxygen. This can cause damage to the muscle and is called a heart attack. With new treatments and procedures such as, clot reducing medicines and angioplasty or stents, heart damage can be kept to a minimum if the patient comes to the hospital immediately. If the heart is permanently damaged because of a lack of oxygen, a scar forms as the heart heels. Severe damage to the heart leads to a condition known as Congestive Heart Failure.

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Warning Signs of a Heart Attack

It’s easy to deny warning signs and symptoms. Even if you have had a heart attack, it is wise to review the warning signs of a heart attack or angina.

  • Pain or discomfort -a feeling of heavy pressure, squeezing or burning of the chest, back, neck, arms, jaw or shoulders.
  • Unusual shortness of breath.
  • Weakness, dizziness or fainting associated with the pain or discomfort as described above.
  • Excessive sweating or nausea or vomiting associated with above mentioned symptoms.
  • Rapid or irregular heartbeat.
  • A vague feeling of anxiety or doom.

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Angina Pectoris

Angina Pectoris is the Latin for “chest pain.” It is the heart’s way of telling us that it needs more oxygen-rich blood. Patients generally experience chest pain during or shortly after a physical exertion, a stressful event, cold weather, or a large meal. In more advanced cases chest pain may even occur during rest. Angina is not a heart and it does not cause permanent damage to the heart unless it continues for more than approximately 20 minutes, and is not relieved by rest or nitroglycerin. Angina is a symptom of a temporary lack of blood flow to the heart muscle. Some people have occasional chest pain or discomfort and never have a heart attack. Others have silent ischemia (a lack of blood flow but no pain) and can go on to experience a heart attack.

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Coronary Artery Disease (CAD) or Coronary Heart Disease (CHD)

Coronary artery disease or atherosclerosis is a process in which small fatty layers (plaque) are deposited over many years along the inner walls of the artery. The constant deposition of plaque narrows the vessel and can eventually close off the flow of blood through the coronary arteries. CAD can be caused by high blood pressure, smoking, high cholesterol levels, diabetes, or genetic predisposition.


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Test Procedures and Diagnosis

1) What is Percutaneous Transluminal Coronary Angioplasty (PTCA) and Coronary Stent?

Percutaneous transluminal coronary angioplasty (PTCA) is performed to open blocked coronary arterise caused by coronary artery disease (CAD) and to restore arterial blood flow to the heart tissue without open-heart surgery.

A special catheter (long hollow tube) is inserted into the coronary artery to be treated. This catheter has a tiny balloon at its tip. the balloon is infalted once the catheter has been placed into the narrow area of the coronary artery. The inflation of the balloon compresses the fatty tissue in the artery and makes a larger opening inside the artery for improved blood flow.

The use of fluoroscopy (a special type of x-ray, similar to an x-ray “movie”) assists the physician in the location of the blockages in the coronary arteries as the contrast dye moves through the arteries.

A technique called intravascular ultrasound (IVUS) that uses a specialized computer and micro transducer that sends out ultrasonic sound waves to create images of the blood vessels, may be used during PTCA. The use of IVUS provides direct visualization and measurement of the inside of the blood vessels and may assist the physician in selecting the appropriate size of balloons and/or stents, to ensure that a stent, if used, is properly opened, or to evaluate the use of other angioplasty.

The physician may determine that another type of procedure is necessary. This may include the use of atherectomy (removal of plaque) at the site of the narrowing of the artery. In atherectomy, there may be tiny blades on a balloon or a rotating tip at the end of the catheter. When the catheter reaches the narrowed spot in the artery, the plaque is broken up or cut away to open the artery. Atherectomy is used when the plaque is calcified, hardened, or if the vessel is completely closed. Another type of atherectomy procedure uses a laser, which opens the artery by “vaporizing” the plaque.

What is stent placement?

In the past few years, many refinements have been developed in the PTCA procedure. One common procedure used along with PTCA is stent placement. A stent is a tiny, expandable metal coil that is inserted into the newly-opened area of the artery to help keep the artery from narrowing or closing again.

Once the stent has been placed, tissue will begin to form over it within a few weeks to few months after the procedure. In certain types of stents it can take up to a year when stent will be completely covered by tissue. It is necessary to take two medication, typically aspirin and clopidogrel (Plavix), or Effient which decreases the “stickiness” of platelets (a type of blood cells that clump together to form clots), in order to prevent blood clots from forming inside the stent.

Newer stents (drug-eluting stents or DES) are coated with medications to prevent the formation of scar tissue inside the stent. These drug-eluting stents release medication within the blood vessel itself. This medication inhibits the overgrowth of tissue that can occur within the stent. The effect of this medication is to deter the narrowing of the newly stented blood vessel.

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Coronary Artery Bypass

A surgical procedure where the blood vessels from another part of the body, usually a vein from the leg or an artery found in the chest is used to bypass the blocked coronary artery. This procedure allows detour blood to reach the heart muscle beyond the blockage.


Seek immediate medical attention if any of symptoms listed under Warning Signs of Heart Attack, are a new occurrence or are not relived by rest or nitroglycerin. Seek the advice of your physician even if unexpected mild episodes of angina or chest pain occur.

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2) What is Cardiac PET Scan?

Cardiac PET Scan is a non invasive test in which a tiny amount of medically safe, a very short half life radiopharmaceutical is injected through an IV line and pictures of your heart are taken from outside by a very specialized camera, which can help your physician to precisely diagnose Coronary Heart Disease (CHD). This test takes less than an hour to be completed and is considered the gold standard and one of the most reliable non invasive cardiac tests in diagnosing CHD.

The early detection of Coronary Heart Disease is vital as the early treatment of heart disease can prevent heart attacks. Northwest Houston Heart Center is pleased to announce that their center is one of only three centers in Houston area equipped with dedicated cardiac PET scanner for precise diagnosis of Coronary Heart Disease. Clinic studies have shown that Cardiac PET scan is more accurate than other tests such as electrocardiogram (ECG) stress testing, single photon emission computed tomography (SPECT or traditional nuclear stress testing) in diagnosing Coronary Heart Disease. Ask your doctors about Cardiac PET scan if you are having these tests or suspected to have Coronary Heart Disease. For consultation with our physicians call 281-351-4911.

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3) What is an electrocardiogram?

An electrocardiogram (ECG or EKG) is one of the simplest and fastest test used to evaluate the heart. Electrodes (small, plastic patches) are placed at certain locations on the chest, arms and legs. When the electrodes are connected to an ECG machine, the electrical activity of the heart is measured, interpreted, and printed out for the physician’s information and further analysis. This provides your physician valuable information regarding the condition of your heart.

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4) What is an exercise electrocardiogram?

An exercise ECG is performed to assess the heart’s response to stress or exercise. The ECG is monitored while a person is exercising on a treadmill or stationary bike.

An ECG tracing will be taken at certain points during the test in order to compare the effects of increasing stress on the heart.

Periodically, the incline and treadmill speed will be increased. If the person is riding a bicycle, he/she will pedal faster against increased resistance.

In either circumstance, the person will exercise until reaching a target heart rate (determined by the physician based on age and physical status) or until unable to continue due to fatigue, shortness of breath, chest pain, or other symptoms.

ECG is then analyzed by your physician to assess the condition of your heart.


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5) What is a Holter monitor?

The Holter monitor is a type of electrocardiogram (ECG or EKG) used to monitor the ECG tracing continuously for a period of 24 hours or longer. When symptoms such as dizziness, fainting, prolonged fatigue, and palpitations continue to occur without a definitive diagnosis obtained with a resting ECG, an exercise ECG, your physician may request an ECG tracing to be run over a long period of time, using the Holter monitor.

Certain dysrhythmias/arrhythmias (abnormal heart rhythms), which can cause the symptoms noted above, may occur only intermittently, or may occur only under certain conditions, such as stress. Dysrhythmias of this type are difficult to obtain on an ECG tracing that only runs for a few minutes. Thus, the physician will request a Holter monitor to allow a better opportunity to capture any abnormal beats or rhythms that may be causing the symptoms. The Holter monitor records continuously for the entire period of 24 to 48 hours. Some Holter monitors may record continuously but also have an event monitor feature that you activate when symptoms begin to occur.

You will receive instructions regarding how long you will need to wear the recorder (usually 24 to 48 hours), how to keep a diary of your activities and symptoms during the test, and personal care/activity instructions.

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6) What is an event monitor?

Event monitoring is very similar to Holter monitoring, and is often ordered for the same reasons. With an event monitor, you wear ECG electrode patches on your chest, and the electrodes are connected by wire leads to a recording device. Unlike the Holter monitor, however, which records continuously throughout the testing period of 24 to 48 hours, the event monitor does not record until you feel symptoms and trigger the monitor to record your ECG tracing at that time.

When you feel one or more symptoms, such as chest pain, dizziness, or palpitations, you push a button on the event monitor recorder. Some monitors have a feature (memory loop recorder) which captures a short period of time prior to the moment you triggered the recording and afterwards. This feature can help your physician determine more details about the possible change in your ECG at the time the symptoms started, and what was happening with your ECG just before you triggered the recorder. Other monitors, called “post-event recorders,” simply start recording your ECG from the moment you trigger it.

Event recorders are quite small about the size of a pager or cell phone.
After you experience symptoms and record them, you will send the recording of the event to your physician or to a central monitoring center. This transmission is done over the telephone. You will be instructed regarding how to do this on the recorder. You will also keep a diary of your symptoms and corresponding activities (as done during the Holter monitoring procedure).

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7) What is an echocardiogram?

An echocardiogram is a noninvasive and painless (the skins is not pierced) procedure used to assess the heart’s function and structures. During the procedure, a transducer (like a microphone) sends out ultrasonic sound waves at a frequency too high to be heard. When the transducer is placed on the chest at a certain location and angle, the untrasonic sound waves move through the skin and other body tissue to the heart tissues, where the waves echo off of the heart structures. The transducer picks up the reflected waves and sends them to a computer. The computer interprets the echoes into an image of the heart walls and valves.

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8) What is a stress myocardial perfusion scan (Nuclear Stress Test)?

A myocardial perfusion scan is a type of nuclear medicine procedure. This means that a tiny amount of a medically safe radioactive substance, called a radionuclide (radiopharmaceutical or radioactive tracer), is used during the procedure to assist in the examination of the tissue under study. Specifically, the myocardial perfusion scan evaluates the heart’s function and blood flow.

A radionuclide is a radioactive substance used as a “tracer,” which means it travels through the blood stream and is taken up (absorbed) by the healthy heart muscle tissue. On the scan, the areas where the radionuclide has been absorbed will show up differently than the areas that do not absorb it (due to decreased blood flow to the area or possible damage to the tissue from decreased or blocked blood flow).

A stress myocardial perfusion scan is used to assess the blood flow to the heart muscle (myocardium) when it is stressed by exercise or medication and to determine what areas of the myocardium have decreased blood flow. This is done by injecting a radionuclide (thallium or technetium) into a vein in the arm or hand.

There are different types of radionuclides. When one type of radionuclide is used, areas of the myocardium that have blocked or partially blocked arteries will be seen on the scan as “cold spots,” or “defects,” because these areas will be unable to take in the radionuclide into the myocardium. Another type of radionuclide binds to the calcium that is released when a heart attack occurs, so it will accumulate in area(s) of injured heart tissue as a “hot spot” on the scan.

There are two types of stress myocardial perfusion scans, one that is used in conjunction with exercise (myocardial perfusion scan with exercise) and one that is used in conjunction with medication (pharmacologic myocardial perfusion scan).

I) Myocardial perfusion scan with exercise:

A myocardial perfusion scan with exercise is used to determine what areas of the heart muscle (myocardium) have decreased blood flow during exercise. This is done by injecting a radionuclide (thallium or technetium) into a vein in the arm or hand during exercise. After the radionuclide has been injected into a vein and has circulated through the blood stream, a special machine called a gamma camera takes pictures of the heart while the person lies still on a table. This scanning usually lasts about 15 minutes.

Any areas of the myocardium that have blocked or partially blocked arteries during exercise will be seen on the scan as “cold spots,” or “defects,” because these areas will be unable to absorb the radionuclide into the myocardium.

A second set of scans is taken at rest. The resting phase is done in order to compare the results with the exercise phase to see if areas that do not get adequate blood flow while exercising are able to absorb the radionuclide during rest.

II) Myocardial perfusion scan with pharmacologic intervention:

A pharmacologic myocardial perfusion scan is used when the physician has determined that exercise on a treadmill is not an appropriate choice due to the person’s medical condition. In this situation, a medication is given that causes the coronary arteries to dilate. This dilation of the coronary arteries causes an increase in blood flow and is very similar to the response of the arteries during exercise. The medication is injected into a vein in the arm or hand.

After a given period of time, the gamma camera will take pictures of the heart while the person lies still on a table. A resting scan will be performed afterwards, just as with the actual exercise scan. By comparing these two pictures, your doctor can tell if you have blockages in the arteries going to your heart.

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9) What are Vascular Studies?

Vascular studies are a noninvasive and painless (the skin is not pierced) procedure used to assess the blood flow in arteries and veins. A transducer (like a microphone) sends out ultrasonic sound waves at a frequency too high to be heard. When the transducer is placed on the skin at certain locations and angles, the ultrasonic sound waves move through the skin and other body tissues to the blood vessels, where the waves echo off of the blood cells. The transducer picks up the reflected waves and sends them to an amplifier, which makes the ultrasonic sound waves audible.

Vascular studies can utilize one of these special types of ultrasound technology, as listed below:

Doppler Ultrasound

– This Doppler technique is used to measure and assess the flow of blood through the blood vessels. The amount of blood pumped with each beat is an indication of the size of a vessel’s opening. Also, Doppler can detect abnormal blood flow within a vessel, which can indicate a blockage caused by a blood clot, a plaque, or inflammation.

Color Doppler

– Color Doppler is an enhanced form of Doppler ultrasound technology. With color Doppler, different colors are used to designate the direction of blood flow. This simplifies the interpretation of the Doppler technique.

Ankle Brachial Index and PVR

To assess blood flow in the limbs, pulse volume recordings (PVRs) may be performed. Blood pressure cuffs are inflated on the limb and blood pressure in the limb is measured using the Doppler transducer.
To assess the carotid arteries in the neck, a carotid duplex scan may be performed. This type of Doppler examination provides 2-dimensional (2D) image of the arteries so that the structure of the arteries and location of an occlusion can be determined, as well as the degree of blood flow.

A carotid artery duplex scan is a type of vascular ultrasound study done to assess occlusion (blockage) or stenosis (narrowing) of the carotid arteries of the neck and/or the branches of the carotid artery. Plaque (a buildup of fatty materials), a thrombus (blood clot), and other substances in the blood stream may cause a disturbance in the blood flow through the carotid arteries.

Vascular conditions:

The arteries bring oxygen and other nutrients to the cells of the body. The veins take away the blood after the cells have taken in the oxygen and nutrients and given up their waste products, such as carbon dioxide. If blood flow is decreased to any part of the body, that area does not get enough oxygen and nutrients and is unable to get rid of its waste products adequately.

Decreased blood flow can occur in the arteries and veins anywhere in the body, such as the neck and brain. When the neck arteries (carotid arteries) become occluded, symptoms such as dizziness, confusion, drowsiness, headache, and/or a brief loss of ability to speak or move, may be the early warning signs of a possible strong (brain attack).

More severe symptoms, such as sudden sharp headache, loss of vision in one eye, sudden loss of ability to move arms, legs, or one side of the body, sudden forceful vomiting, or sudden decreased level of consciousness may mean that a stroke is imminent.

Some conditions which may affect blood flow include, but are not limited to, the following:

  • Atherosclerosis – a gradual clogging of the arteries over many years by fatty materials and other substances in the blood stream.
  • Aneurysm – a dilation of a part of the heart muscle or the aorta (the large artery that carries oxygenated blood out of the heart to the rest of the body), which may cause weakness of the tissue at the site of the aneurysm.
  • Embolus or thrombus – clots in blood vessels may be either an embolus (a small mass of material such as fat globules, air, clusters of bacteria, or even foreign matter such as a piece of metal from a bullet) or a thrombus (a blood clot).
  • Inflammatory conditions – an inflammation within a blood vessel may occur as a result of trauma (physical trauma, such as from a fall, or chemical trauma, such as from an irritating medication being introduced into the vessel), infection, or an autoimmune disorder (e.g., polyarteritis, Raynaud’s disease, and aortic arch syndrome).
  • Varicose veins – occur when the veins of the circulatory system in the legs are exposed over time to pressure that causes stress on the walls and valves of the veins

Any of these conditions may cause decreased blood flow in arteries and/or veins. Some symptoms that may occur when blood flow decreases to the legs include, but are not limited to, the following:

  • Leg pain and/or weakness during exertion (known as claudication)
  • Swelling
  • Soreness, tenderness, redness, and/or warmth in the leg(s)
  • Pale and cool skin; may even be grayish or blue
  • Numbness or tingling
  • Rest pain

If the physician suspects that a person may have decreased blood flow somewhere in the peripheral (arms, legs, and/or neck) circulation, vascular studies may be performed.

Reasons for the Procedure

Reasons for which vascular studies may be performed include, but are not limited to, the following:

  • Evaluation of signs and symptoms which may suggest decreased blood flow in the arteries and/or veins of the neck, legs, or arms
  • Evaluation of previous procedures that were performed to restore blood flow to an area
  • Evaluation of a vascular dialysis device, such as an A-V fistula in the arm

There may be other reasons for your physician to recommend a vascular study.


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10) What is a pacemaker/implantable cardioverter defibrillator (ICD) insertion?

A pacemaker/implantable cardioverter defribillator (ICD) insertion is a procedure in which a pacemaker and/or an ICD is inserted to assist in regulating problems with the heart rate (pacemaker) or heart rhythm (ICD).


When a problem develops with the heart’s rhythm, such as a slow rhythm, a pacemaker may be selected for treatment. A pacemaker is a small electronic device composed of three parts: a generator, one or more leads, and an electrode on each lead. A pacemaker signals the heart to beat when the heartbeat is too slow.

A generator is the “brain” of the pacemaker device. It is a small metal case that contains electronic circuitry and a battery. The lead (or leads) is an insulated wire that is connected to the generator on one end, with the other end placed inside one of the heart’s chambers. The electrode on the end of the lead touches the heart wall. In most pacemakers, the lead senses the heart’s electrical activity. This information is relayed to the generator by the lead.

If the heart’s rate is slower than the programmed limit, an electrical impulse is sent through the lead to the electrode and the pacemaker’s electrical impulse causes the heart to beat at a faster rate.

When the heart is beating at a rate faster than the programmed limit, the pacemaker will monitor the heart rate, but will not pace. No electrical impulses will be sent to the heart unless the heart’s natural rate falls below the pacemaker’s low limit.

Pacemaker leads may be positioned in the atrium or ventricle or both, depending on the condition requiring the pacemaker to be inserted. An atrial dysrhythmia/arrhythmia (an abnormal heart rhythm caused by a dysfunction of the sinus node or the development of another atrial pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with an atrial pacemaker.

A ventricular dysrhythmia/arrhythmia (an abnormal heart rhythm caused by a dysfunction of the sinus node, an interruption in the condution pathways, or the development of another pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with a ventricular pacemaker whose lead wire is located in the ventricle.

It is possible to have both atrial and ventricular dysrhythmias, and there are pacemakers that have lead wires positioned in both the atrium and the ventricle. There may be one lead wire for each chamber, or one lead wire may be capable of sensing and pacing both chambers.

A new type of pacemaker, called a biventricular pacemaker, is currently used in the treatment of convestive heart failure. Sometimes in heart failure, the two ventricles (lower heart chambers) do not pump together in a normal manner.

When this happens, less blood is pumped by the heart. A bioventricular pacemaker paces both ventricles at the same time, increasing the amount of blood pumped by the heart. This type of treatment is called cardiac resynchronization therapy.

Implantable cardioverter defibrillator (ICD):

An implantable cardioverter defibrillator (ICD) looks very similar to a pacemaker, except that it is slightly larger. It has a generator, one or more leads, and an electrode for each lead. These components work very much like a pacemaker. However, the ICD is designed to deliver an electrical shock to the heart when the heart rate becomes dangerously fast, or “fibrillates.”

An ICD senses when the heart is beating too fast and delivers an electrical shock to convert the fast rhythm to a normal rhythm. Some devices combine a pacemaker and ICD in one unit for persons who need both functions.

The ICD has another type of treatment for certain fast rhythms called anti-tachycardia pacing (ATP). When ATP is used, a fast pacing impulse is sent to correct the rhythm. After the shock is delivered, a “back-up” pacing mode is used if needed for a short while.

The procedure for inserting a pacemaker or an ICD is quite similar. The procedure generally is performed in an electrophysiology (EP) lab or a cardiac catheterization lab.

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11) What is ICG (Impedance Cardiography)?

Every day, clinicians prescribe cardiovascular medications that affect blood flow forces, or hemodynamics. Until recently, obtaining hemodynamic information required invasive monitoring in a hospital setting, leaving clinicians in the office with poor surrogates such as blood pressure and heart rate.

Noninvasive BioZ utilizes Impedance Cardiography (ICG) to quickly provide hemodynamic information and is clinically proven to assist in diagnosis, prognosis, and therapy for patients with shortness of breath, congestive heart failure, and difficult to control blood pressure.

As blood enters and leaves the aorta with each heartbeat, changes in impedance are processed to measure and calculate hemodynamic parameters.

How ICG Works:

  • Disposable sensors transmit a small electrical signal through the thorax
  • Impedance (resistance) to the electrical signal is measured and displayed as the ICG waveform
  • As volume and velocity of blood in the aorta change with each heartbeat, DISQ® (Digital Impedance Signal Quantifier) Technology processes the changes in impedance
  • The changes in impedance are applied to the innovative Z MARC® (Modulating AoRtic Compliance) Algorithm to provide hemodynamic parameters including:
    • Cardiac Output
    • Stroke Volume
    • Systemic Vascular Resistance
    • Contractility
    • Fluid Status

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