ECHOCARDIOGRAPHY

This procedure make use of ultrasound and the doppler effect to image the moving heart, valves and the blood flow inside the heart and vessels. A transducer containing a piezoelectric crystal transmits and then receives the reflected ultrasound signals thus creating the image.
After processing by the computer, a 2-D image can be seen real-time on the screen.

It provides excellent spatial resolution and is particularly useful in the diagnosis and grading of the severity of valular lesions and congenital heart diseases, heart chamber size, presence of heart muscle damage, pericardial effusion and cardiac tumours.

If an oesophageal probe is used (transoesophageal echocardiography, TOE), a much better image of the heart can be obtained.

The major use of TOE is to identify clot (thrombus) in the left atrium (LA) which may be the cause of strokes.

An exercise ECG test allows doctors to learn how well your heart functions when it is made to work harder. This test can help detect heart problems that may not be apparent at rest.

The exercise ECG test is done while you walk on a treadmill or pedal a stationary bicycle. During the test, an electrocardiogram (ECG) records the electrical activity of your heart.

What Does It Show?
Doctors can see how well your heart functions during exertion by studying what happens during the exercise test.

• How long were you able to exercise? Generally, people with a healthy heart and in good physical condition are able to exercise longer.
• Did you have significant symptoms? It is normal to feel tired and short of breath during strenuous exercise. However, if you develop chest pain or become extremely short of breath, this may indicate a heart problem.
• What happened to your heart rate and blood pressure? The heart rate and blood pressure normally rise during exercise. An abnormal heart rate (too fast, too slow) or a fall in blood pressure may indicate heart disease.
• What did the ECG show? Certain changes in the ECG tracing may indicate that the heart muscle is not getting enough oxygen­rich blood. Sometimes, the ECG during exercise shows arrhythmias (abnormal heart rhythms).

The exercise test is especially useful in diagnosing blockages in the coronary arteries (the vessels that carry blood to the heart). When the coronary arteries are blocked or narrowed, the heart muscle may not be getting enough oxygen during exercise. This often results in symptoms of angina (chest pain) and abnormal changes on the ECG.

Holter Monitoring (or Ambulatory ECG)allows your physician to review your heart's activity for 24 hours. It allows the physician to look at each individual heartbeat.

Your physician may recommend this type of testing whenever you experience symptoms like dizziness,fainting, palpitations, skipped beats or other sensations which may occur during normal day to day activities but not necessarily while you're in the physician's office.

• The monitor itself is the size of a large portable cassette recorder. Your heartbeat is actually recorded on a cassette inside.
• ECG electrodes and wires will be applied to your chest, and secured with tape by the technician.
• You will wear this monitor for a 24 hour period. We want you to continue your normal daily activities.

TILT TESTING

A cardiovascular cause of syncope can be identified in most patients by the use of electrophysiologic studies or the head-up tilt test. Tilt testing with or without isoprenaline can provoke hypotension and bradycardia in patients with neurocardiogenic mechanisms of syncope, also known as vasovagal, vasodepressor, or neurally mediated syncope. Vasovagal is the most common cause of syncope in otherwise healthy young persons.
PROCEDURE: No hospital admission is required for tilt tests - they may be done as an outpatient. Bookings are made with the procedure room RN. The pt is assessed in the flat position for 5 minutes before being tilted at 60 degrees for 45 minutes or the onset of syncope. If syncope occurs, stat BP is recorded and the pt returned to the horizontal position. If no syncope occurs after 45 minutes, commence isoprenaline infusion at 1ug/min and increase until heart rate is 120% of baseline. Continue for 15 minutes or until syncopal.

Signal-averaged ECG

This is a computerized ECG which is capable of recording tiny electrical signals from the heart (late potentials).

What is a late potential?

Late potentials (LPs) are microvolt signals that are part of the terminal portion of the QRS complex. These signals persist into the ST-T segment. They represent areas of delayed ventricular activation which are manifestations of slowed conduction velocity. Slowed conduction results with ischemia or deposition of collagens after an acute myocardial infarction. This causes the preserved myofibrils to separate from their neighbors causing the activation wave to seek other or slower routes. LPs may be detected more readily when they occur in the areas of the heart that normally activate late in ventricular activation such as the posterobasal, posterolateral and inferiolateral segments of the myocardium. This explains why LPs are often detected in patients with right coronary artery/inferior wall MI versus those with left anterior descending artery/anterior MI. But sometimes there is just no difference between these groups.
Ventricular late potentials can show up as early as 3 hours post-MI or as late as 8 weeks post MI. The first 24-48 hours following an acute myocardial infarction are the most unstable. This causes VLP incidences to increase throughout this early period. LPs have been found to be most prevalent in the 6-30 day interval post MI. Approximately 93% of SAECGs are able to be recorded in the 6-14 day post MI period. Obtaining the SAECG during this time period avoids the instability of the immediate post infarction period. At least one week should separate the event from the SAECG acquisition. In the absence of MI the appearance of a new LP is rare. Transient LPs associated with MI are uncommon with 58-70% of positive SAECGs obtained 7-40 days post MI remaining positive even 2 to 6 months later. A variety of reasons have been proposed as explanations for the SAECG becoming normal again. These include: development of collateral circulation decreasing ischemia and recovery of the "stunned" myocardium. However, none of these have been proven.

A signal-averaged ECG showing late potentials in a patient with prior myocardial infarction and recent syncope.

Email: eps@stvincents.com.au