Cardiac
Investigations and Procedures: 
Cardiac Investigations
Electrocardiogram (ECG)
This involves putting multiple electrodes over
the chest
wall and limbs in standard positions. The small electrical signal from
the heart is then recorded.The procedure is totally harmlesss and
painless.
Although the chest electrodes may sometimes impinges some red marks on
the chest wall which will fade away in few days time. The ECG can give
us invaluable information on the electrical rhythm of the heart, its
electrical
conduction, muscle mass, presence of arrhythmia, ischemia or infarction
and even electrical disturbance and drug effects. It is a routine
cardiac
investigation procedure. It is completely harmless.
Chest X-Ray (CXR)
A CXR involves radiation to the body though
the level
is just minimal. A pregnant women will need special precaution and
shielding
of the fetus. The CXR gives us inforamtion about thesize and the
configuration
of the heart and the great vessels and also on the lung fields and
vessels.
It is a routine cardiac investigation procedure with very low radiation
exposure..
Echocardiography
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| This procedure make use of the ultrasound and the doppler effect to image the moving heart, valves movement and blood flow inside the heart and vessels. A transducer (USG probe) containing a piezoelectric crystal transmit and receive the reflected ultrasound thus creating the image. After processing by the computer, a 2-D or even 3-D image can be seen real-time on the screen. It provides excellent spatial resolution and is specially useful in the diagnosis and grading of the severity of valular and congenital heart diseases (mitral and aoritc stenosis or insufficiency), endocarditis, heart chamber movement and hypokinesia, pericardial effusion, cardiac tumours, etc. If an oesophageal probe is used (transoesophageal echocardiography, TEE), a much better image of the heart can be obtained though this will involve a procedure of putting the probe into the oesophagus. This procedure has absolutely no radiation risk or exposure. | ||
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Trans-oesophageal Echocardiography (TEE)
This procedure is similar in theory to that of the transthoracix echocardiography except that it required insertion of a ultrasound probe into the oesophagus down to the stomach. The patient will need to be under light sedation (put to sleep) to facilitate the insertion of the probe. TEE provides a much better image of the heart as the ultrasound beam do not need to pass through the skin, fat and lung before scanning the heart. This method is particularily useful for the imaging of the valves of the heart, the aorta and septal defects. The procedure usually only lasted for few minutes and carries little complications.
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| Treadmill Testing
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| This investigative procedure involves putting multiple electrodes over the chest wall, a pressure monitoring cuff (BP cuff) over the arm and the patient need to run on a treadmill. The speed and slope of the treadmill will increase gradually in stepwise fashion in order to test the function of the heart. We are monitoring the ECG, blood pressure and heart rate of the patient to specifically look for exercise induced ischaemia and arrhythmias. It is also useful to assess the functional status of a patient with specific heart diseases. Information such as the functional class of the patient can also be obtained. It carries a less than 1% risk of sudden arrhythmia or myocardial infarction necessitating resuscitation. The test is specially useful for the diagnosis of coronary artery disease, post myocardial infarction risk stratification and exercise induced arrhythmia. | ||
Tilt Table Test
This a test specially designed to confirm the
neurocardiogenic
syndrome. The test involve placing the patient on a flat table with the
arms and legs straped. Continous blood pressure and ECG monitoring is
made
along with the tilting up of the table to 60 or 75 degree (head up
tilt).
Patient suffering from this syndrome will have eithor or both decrease
in heart rate or blood pressure. Negative patients will be given
Isoprenaline
infusion to provoke the response.
Thallium Radionucleotide Scanning of the Heart
The function and perfusion of the heart can be
assessed
by the scan. It involves the injection of the radioactive thallium 201
into the circulation after the patient's exercising. Its usefulness
lies
on the diagnosis and management of coronary artery disease and
myocardial
infarction. The particular area of infarction (lack of blood supply) or
the area of ischemia can be visualised and located. This test will help
the doctor to choose the particular therapy most suitable for the
patient.
Other newer imaging techniques
Fast CT scanning and Magnetic Resonance Imaging (MRI).
Ultrafast CT (Computer Tomography) and MRI
provdies another
imaging modality to look at the heart, the proximal coronary arteries
as
well as the aorta and mediastinum in more details.
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Cardiac Catherization, Percutanous transluminal coronary angioplasty (PTCA), stenting (PTCS), drug eluting stent and brachytherapy (radiation)
These procedures involve putting the patient in a cardiac catherization laboratory. The laboratory area is shield from leakage of radiation. The patient is usually awake or under a mild sedation. Local anaesthetic will be applied to the groins, elbow or the neck. The catheters will be inserted through sheaths into the arteries and veins of the body and then pass up to the heart. Pressures within the different area of the heart is measured and gradients across the valves calculated. Dyes will be injected into the coronary arteries (LAD- left anterior descending artery, LCX-left circumflex artery and the RCA-right coronary artery) and the left ventricle to look for degrees of narrowing, site of the lesion and the ejection fraction (EF) of the left ventricle. Sometimes, the right side of the heart is also entered to check the pressure and the oxygen content of the blood. This would be of great help in diagnosis and grading of the severity of congenital heart disease (e.g. Atrial septal Defect ASD, ventricular Septal Defect VSD, etc.)
The procedure will be under X-Ray fluoroscopic screening. The narrowed vessels can be treated by angioplasty. PTCA involves putting in a small ballon into the narrowed area of the artery and then by inflating the balloon for a certain fixed period of time, to dilate up the stenosised area to improve the blood flow. Other modalities include directional arthrectomy, stenting (to put in a metallic stent to keep the previously dilated artery patent- PTCS), rotablator and laser therapy. Major advantage of this procedure is its relative safety and the patient can usually be discharged in 1-2 days time. The major disadvantage is that the dilated vessels do get re-stenosis in a significant proportion of cases. The restenosis rate is around 40% for PTCA and around 20-25% for PTCS. Thus repeated PTCA/PTCS or even CABG will be needed.
Newer drug coated stents (sirolimus or paclitaxel) has been shown to lower the rate of restenosis to less than 10% in 6 months follow up period!
In brachytherapy, a radiation source (beta or gamma radiation) is put in close proximity to the stent or stenotic lesion and the radiation is apply for a short period of time (a few minutes). This has been shown to reduce the rate of restenosis inside the stent. Side effect includes: edge effect, aneurysm formation.
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Electrophysiological Study of the Heart (EPS) and Radio-frequency Ablation (RF)
For EPS and RF, The patient is usually awake or sedated in the laboratory. Local anaesthetic is injected into the groins, neck or the clavicle. Arterial and venous sheaths are then thread into the various vessels. Catheters with electrodes on the end will be put into different specific areas of the heart to measure the small electrical impulses inside the heart. The relative timing of the electrical impulse in the heart is then measured and analysed.
The cause of the arrhythmia is then studied. Sites of the abnormal impulse formation, re-entry circuits or accessory pathways are located. Treatment will be given by radiofrequency (RF) energy to burn and coagulate away the accessory pathways, areas of unstable arrhythmogenic tissue or other conduction pathways. Each lesion size is small at around 0.5mm. The application of RF energy is usually not painful and is relatively safe.
This EP and RF procedures has become more and
more popular
and the need for surgical intervention is much reduced. The RF ablation
technique can be used to treat more than 90% of supraventricular
tachycardias
(SVT) like atrioventricular junctional re-entry tachycardia (AVJRT),
bypass
tract associated SVTand some form of atrial flutter. It is also
effective
in AV nodal ablation and treatment of ventricular tachycardias. The
complication
rate is less than 1%, including local bleeding, cardiac arrhythmias
during
procedure, cardiac tamponade and complete heart block which necessitate
a permanent pacemaker
insertion.
| This is the EPS of the heart showing catheters in the right atrium and ventricle, HIS, coronary sinus and the RF catheter. (Photo from Dr. K Lee). | EPS catheters
position under X-Ray  Click for enlarge the photo 43k |
Permanent Pacemaker Implantation
When patient has a very slow heart rate or if
the patient
has occasional pause in the normal heart beat rhythm with symptoms of
syncope
or loss of consciousness, a permanent pacemaker will be needed. The
pacemaker
is an electronic device containing a computer board with a CPU and a
battery.
It is usually implanted under local anaesthesia under the skin below
the
clavicle of the shoulder either on the left or the right side. One or
two
electrode leads will pass through the venous system into the right
atrium
and right ventricle of the heart. Very minute electrical discharge will
be given by the device to "pace" or stimulate the heart to beat if
anything
goes wrong 24 hours a day! Newer device will be able to adjust the
heart
rate according to the patient's activity (rate adaptive pacemaker). The
battery usually last for 7-9 years and after that, a replacement of the
pacemaker will be needed.
Automatic Implantable Cardiovertor-Defibrillator (AICD)
AICD is similar to a pacemaker in that it is
an electronic
device which includes a CPU computer and a large capacity battery. The
main use of this device is to terminate life threatening arrhythmias
(e.g.
fast ventricular tachycardias VT and ventricular fibrillation VF). This
dangerous arrhythmias usually occurs suddenly and unpredictably in
patients
after myocardial infarction (especially with a poor heart function),
with
ischemic heart diseases and dilated cardiomyopathy. In these cases,
studies
have shown that implanting an AICD is better than just drugs (like
sotalol
and amiodarone) in preventing arrhythmic deaths and total mortality.
The
device will monitor the heart rhythm of the patient 24 hours a day to
look
for these dangerous arrhythmias. If it detects the arrhythmias, after
confirmation,
it will usually try pacing the heart in a faster rate to try to
terminate
the tachycardia, if fail, it will charge up and go for cardioversion or
defibrillation by giving a "shock" to rectify the arrhythmia. Some
newer
devices have dual chamber pacing and sensing ability so that the
arrhythmias
can be detected more accurately and bradycardias can be paced
accordingly. Recent studies in 2005 had shown that patient with low
ejection fraction (<30%) post myocardial infarction or in heart
failure would benefit from AICD +/- bi-ventricular pacing.
Automated External Defibrillators (AEDs)
"PADL, or the Public Access Defibrillation
League, is
a non-profit group of cardiologists and other emergency rescue
personnel
working to educate the public about the many sudden cardiac arrest
victims
who could be saved by rapid defibrillation using AEDs. AEDs, or
Automated
External Defibrillators, are devices that weigh from 4-6 pounds and use
an internal computer chip to analyze heart rhythms. These devices take
the "shock" decision away from the rescuer, and advise when to deliver
defibrillation. Because these devices are so easy to use, the American
Heart Association is advising that all persons trained to perform CPR
learn
how to use an AED." AEDs have been installed in International Airports,
airlines and major shopping malls.
Coronary Artery Bypass Graft (CABG) & MIDCAB
This is a surgical procedure where the patient undergone general anaesthesia. The cirulation is supported by a bypass machine. The blood of the body is bypassed to an external machine where it is oxygenated and pump back to the circulation. The heart is stopped by cardioplegic solution. A section of the saphenous vein (a vein in the lower limb) or the internal mammary arteries, IMA (sometimes, the radial artery, gastroepiploic and other arteries) is being used to make the connection between the aorta and the coronary artery distal to the obstructive lesion. The indication for the procedure includes triple vessel disease (where are 3 major arteries supplying the heart is stenosed), left main stem artery disease and impaired myocardial function. The advantage of this procedure is that it can significantly reduce the angina, the risk of re-stenosis is less compared with PTCA. the mortality is less than 4% in experienced hands. Recent development in surgery involve minimally invasive bypass surgery (MIDCAB) in which the wound is much smaller and the operation may even be performed on a beating heart (i.e. no cardiopulmonary bypass is needed).
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Transmyocardial Revascularization (TMR, DMR & PMR)
TMR & DMR procedures involved the use of
the CO2 Laser
to make very tiny holes in the muscle of the heart to promote oxygen
supply
to the region of ischemia. This is reserved for patient who has ischemic
heart disease with narrowed coronary arteries but are not suitable
for both PTCA and CABG. The
theory
behind this method is that this microvascular channels will promote
blood
flow to the heart muscle and reduce the angina symptoms of the patient.
This will require open heart surgery.
For PMR (percutaneous), no open heart surgery is
needed.
The procedure is just like PTCA and a catheter is passed from the leg
up
to the cavity of the heart and laser holes are fired from within the
heart
into the muscle of the heart. Results looks promising for PMR but is
less
certain for DMR & TMR. Recent studies showed that PMR and TMR only
have symptomatic improvement but no effect on long term survival. Newer
studies on direct injection of angiogensis material is underway.
Myocardial Reduction Surgery
For patient with end stage heart failure which
is refractory
to all medical treatment and who are not candidate of heart transplant,
a novel surgery which involves excising (removing) part of the left
ventricular
wall muscle is proven to improve symptoms and ejection fraction
(contractility)
of the heart. This procedure is done in certain highly specialised
cardiac
surgery centres and is still under study.
Bi-Ventricular Pacing for heart failure (Bi-Vent Pacing)
A pacemaker is inserted for patient with drug refractory heart failure and a delay in conduction of the electrical activity in the heart (bundle branch block). 3 wires are inserted into the heart chambers. One in the right atrium, one in the right ventricle and one in the coronary sinus close to the left ventrivle. By pacing the heart, the conduction delay can be abolished and the ejection function of the heart improved. Studies have shown that the device can decrease hospital admissions and improve the functional status of the patient. Many patients with heart failure can benefit from this new device. Newer studies in 2005 showed that Bi-vent Pacing can decrease mortality in patients with symptoms of heart failure who faied medical treatment. In 2007, more and more BiVent pacemakers have been implanted to improve the outcome of patients with Class II - IV heart failure. Devices like AICD+BiVent pacing have been used more frequently. In 2008, it is indicated for patients with symptomatic heart failure and widen QRS complex. Some Bi-vent pacemaker has been implanted in patients with narrow QRS complexs with good clinical response.
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MD-CT
& MR angiogram
Fast CT and MR can
show up the proximal coronary arteries and CT can caluclate the
"Calcium score". A low calcium score can usually rule out significant
coronary artery disease or high risk patients. If the MD-CT or MR
angiogram is
normal, the chance of having coronary artery disease would be very low.
This investigative technique has been used more frequently in 2008.
Author: Dr. Michael Wan
