PCL 1 INVESTIGATIONS

Initial Investigations

• Urea and electrolytes

• Thyroid Stimulating Hormone

• Electrocardiogram

• Chest X-Ray

• Transthoracic echocardiogram

Urea and electrolytes

• Chronic Disturbance of Electrolytes.

• Hypokalaemia [potassium level less than 3.5 mEq/L.]

• Repolarisation of SA node action potential is due to the inward K+ movement.

• With this said, the contraction of the atrium is affected as there is limited repolarisation of the SA node.

• Dependence on the nodes after the SA node is needed. (AV node etc.)

• Predisposal to atrial fibrilation

• Implications for therapy

• Predisposes to digoxin toxicity [ in which the PR interval is prolonged]

• Collection of Urine sample.

TSH

• Useful to screen for thyrotoxicosis

– A thyroid crisis, severe hyperthyroidism

– TSHà Production of triiodothyronine (T3) and thyroxine (T4), helping with metabolism

– Increased production of TSH can affect the heart by racing pulse rate.

• Should be performed on patients with first episodes of AF

• Done by having a blood test

ECG

• Standard 12 Leads

-aVR,aVL,aVF= augmented limb leads

-3 Unipolar Limb leads

• VR:Right arm

• VL:Left arm

• VF:left foot

-Unipolar Chest leads

• Precordial

• V1-V6

• Electrical current generated by heart and analysed in 2 planes.

Groupings of leads of ECG

V1-V4: Anterior Group

I,V5,V6= Left Lateral Group

II,III,aVF= Inferior

• P wave: Atrial depolarisation

- Short p wave= accessory pathway to the ventricle, bypassing the normal conduction.

- Absence of p wave= atrial fibrilation

(contributes to sawtooth baseline ECG)

• QRS complex: depolarisation of ventricles.

- AV nodeà conducting system à bundle of Hisà divides to left and right bundle branchesà Purkinje Fibres

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- Left Axis Deviation: Left ventricular hypertrophy[QRS of -30° or more]

- Right Axis Deviation: Right ventricular dilatation

(less common)

• ST Segment: Time for ventricular depolarisation to repolarisation.

- Height is affected by ischaemia and infarction

- Configuration can be associated with infarction and troponin release.

• T Wave and QT Interval

-T Wave: Due to repolarisation of ventricles.

Peaked T waves: Hyperkalaemia

QT Interval: Start of depolarisation to end repolarisation of ventricles.

Characteristics of ECG of Atrial Fibrillation

• absence of p waves

• Irregular sawtooth baseline

• Irregular ventricular rate

• Underlying features of other diseases:

- Left ventricular hypertrophy (left deviation)

- Myocardial infarction (abnormal Q waves)

Chest X-Ray

• Cardiomegaly=the heart enlarges in a cardiothoracic ratio of more than 0.50 (Low cardiac output, in this case like AF)

• Indication of underlying heart disease or congestive heart failure.

Transthoracic Echocardiogram

• Measure atrial size and screen for thrombus (although sensitivity is low) and valvular heart disease.

Plus, ventricular size and function can be quantified

Furthur Investigations

• Holter Monitoring

• Transoesophageal echocardiography

• Electrophysiological Studies

Holter Monitoring

• 24 hour ECG monitoring

• Diagnose paroxysmal atrial fibrillation (irregular heart rhythm occurs periodically)

• Ideal for patients who are suspected of atrial fibrillation but who remain in sinus rhythm on initial investigations

Transesophageal echocardiography

• Suggestion of left atrial thrombus on transthoracic imaging

• Steps to performing TEE:

- Transducer passed into the esophagus (the swallowing tube) and is positioned directly behind the heart.

- Patient sedated, local anest. To suppress gag reflex.

- Once in position directly behind the heart, the transducer bounces sound waves off the heart (just as in the standard echocardiogram), and images of the cardiac structures are produced

Electrophysiological studies

• To define the mechanism for atrial fibrillation in patients in whom curative catheter ablation is being considered

• Not diagnosis oriented

• Invasive

• Detecting arrhythmias.

• wire electrodes in the heart to measure electrical activity along the heart's conduction system and in heart muscle cells themselves.

• The doctor uses moving x-ray images to carefully guide the catheter up into the heart and place the electrodes into the proper areas.

• The electrodes detect the heart's electrical activity

• Mapping out any abnormal heartbeats.

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Intervals

Intervals