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Tests What They Are
1. Treadmill Test
What It Is : A stress test reflects the flow of blood through the heart during exercise, which is a form of physical stress. It is therefore more effective than a simple, resting ECG. Rather, when compared with a resting ECG, a stress test reflects imbalances in blood flow to the heart, especially the left ventricular muscle tissue. Of the four chambers of the heart the left ventricle works hardest while pumping blood.

Why It’s Done :A treadmill test is a reliable indicator of coronary artery disease, especially blockages in the heart. It also provides a picture of an individual’s general physical fitness.

Since the patient is connected to an ECG machine, readings indicate whether the heart muscles are receiving sufficient blood supply during exercise. It is thus possible to see whether and which arteries receive normal supply vis-à-vis those that don’t.

This differential blood supply is reflected on the ECG recorded while the patient works the treadmill and is usually not reflected by a resting ECG. Heart blockages are therefore unmasked by exposing the organ to the stress of exercise.

A Stress Test is performed to diagnose and evaluate the following:
* Coronary artery diseases or CAD which manifest themselves as chest discomfort and shortness of breath.
* Exercise tolerance when patients have unexplained fatigue and shortness of breath.
* Blood pressure response to exercise in patients with borderline hypertension
* Exercise-induced irregular heartbeats.
* Angina pectoris. If this test is positive, other investigations may be required.

Did you know that patients who cannot walk on a treadmill (due to orthopaedic conditions or abnormal resting ECGs) can be ‘exercised’ pharmacologically and thus undergo a stress test? These patients are administered drugs that are vasodilators or dobutamine (which stimulates heart rate and pumping force) while an ECG and blood pressure recording is taken.

2. Electrocardiogram (ECG)
Natural Pacemaker : Did you know that the heart has its own natural pacemaker? This natural pacemaker is called the ‘sinoatrial node’, which is a group of cells embedded in the wall of the right atrium, one of the four chambers of the heart. It is the sinoatrial node that triggers cardiac contractions, which in turn, determines your heartbeat.

What It Is : An ECG is recorded by attaching electrodes to the surface of the skin on the chest. These electrodes detect and amplify tiny electrical changes on the skin that are caused by your heartbeat. The electrical activity of your heart and its rhythm are picked up by these electrodes, which are connected to a monitor.

Why It’s Done: An ECG is most effective in the diagnosis of abnormal heart rhythms although a Holter Monitor test is preferred in some cases. In case of a heart attack (myocardial infarction), this test can identify if and where the heart muscle has been damaged.

3. Ambulatory Blood Pressure Monitoring (ABPM)
What is BP : Blood pressure is the force of blood inside an artery. As the heart beats, blood flows rhythmically through the arteries, exerting force, then releasing it, alternately. Blood pressure readings consist of an upper and lower number (such as 120 over 90 or 120/90).

The upper reading is the systolic reading and it indicates the pressure of blood against the walls of the arteries, that is, when the heart has just finished contracting or pumping. The lower reading is the diastolic reading and it indicates the pressure of blood against the walls of the arteries between heartbeats, that is, when the heart is relaxed and filling with blood.

Hypertension : This is a state where blood pressure readings are consistently high. Hypertension could be caused by cardio-vascular damage or consistently raised stress levels, factors which are often correlated. Blood pressure often increases with age and is linked to a variety of medical conditions.

Why It’s Done : Ambulatory Blood Pressure Monitoring (ABPM) provides a continuous recording of an individual’s blood pressure. It indicates how your blood pressure responds to normal activities which includes typical day-time stress and is therefore a reliable diagnostic tool for hypertension.

This test is preferred over a one-time BP test in a doctor’s office for many reasons. One, it eliminates the ‘white coat effect hypertension’. The term refers to a sudden increase in BP due to heightened anxiety when recorded by a doctor (in a white coat). Ever heard of a patient who is ‘relaxed’ in a doctor’s clinic or hospital? (The opposite effect – yes, it exists! – is called ‘masked hypertension’)

Constant monitoring of BP provides a series of readings or a pattern that gives clinicians a chance to correlate BP readings with possible triggers or to eliminate them. It also provides a picture of an individual’s daily stress as opposed to self-administered, night-time self-readings, when stress levels are usually lower.

ABPM is a reliable indicator of end-organ damage but not when BP is measured in a clinical setting. End organ damage is damage that occurs in major organs fed by the circulatory system, that is, the heart, kidneys, brain and eyes. A condition commonly diagnosed in hypertensive patients is Left Ventricular Hypertrophy (LVH) or the narrowing of the retinal arteries, which is strongly correlated with ABPM than with clinical BP recordings.
ABP also helps to make an accurate prognosis than a one-time clinical recording. For instance, individuals with hypertension whose nocturnal (sleep) blood pressure remains high may have a worse prognosis.

4. Holter Monitoring
What It Is : A Holter Monitoring test indicates how the heart responds to normal activity. Also called a portable ECG, it provides a continuous reading of the heart’s response to daily activities under typical stress. Since it records heart rate and rhythm for 24 hours or 48 hours, it correlates symptoms of dizziness, palpitations, arrhythmia (irregular heart rhythms) or blackouts with the readings.

Why It’s Done : A Holter Monitor Test is preferred over an ECG because it provides a pattern of continuous recordings via-a-vis a one-time resting ECG, which reveals much less. It is performed to diagnose and evaluate various irregular heart rhythms such as:
* Atrial fibrillation / flutter
* Multi-focal Atrial Tachycardia
* Paroxysmal supraventricular tachycardia
* Bradycardia