How will you identify Long QT Syndrome ?

Following notes will give you an idea how to calculate QT interval 

LQTS: Calculating the corrected  QTc

QTc= QT/square root of the RR interval

This will correct QT for the heart rate-  there is normally an inverse relation between heart rate and QTinterval,as one goes up/the other goes down and vice versa

Long QT  by definition  QTc in - males >470 ms 

                                                    - females of > 480 ms

Borderline prolonged QTc is present if the corrected QTc is 450-470 ms

Average QTc for someone with the LQTS is 490 ms

Diagnostic Criteria for LQTS

Certain points are given to each criteria

ECG findings

QTc

>480                                    3

460-470                               2

450 (male)                           1

Torsdade De Pointes            2

T-wave alternans                  1

Notched T wave in 3 leads   1

Low heart rate for age         0.5

Clinical History

Syncope with stress              2

              without stress          1

Congenital deafness             0.5

Family history

Definite LQTS                       1

Unexplained SCD in immediate family member that is less than 30 years of age     0.5

<1 points low probability of QT prolongation

2-3 points intermediate probability

 >4 points high probability

ST Segment abnormalities in ECG

The ST segment represents period between ventricular depolarisation and repolarisation.
The ventricles are unable to receive any further stimulation.
The ST segment normally lies on the isoelectric line.

ST Segment Elevation

The ST segment lies above the isoelectric line.

Represents myocardial injury.

It is the hallmark of Myocardial Infarction.

The injured myocardium is slow to repolarise and remains more positively charged than the surrounding areas.

Other causes to be ruled out include pericarditis and ventricular aneurysm.

Myocardial Infarction

A medical emergency.

ST segment curves upwards in the leads looking at the threatened myocardium.

Presents within a few hours of the infarct.

Reciprocal ST depression may be present.

ST Segment Depression

Can be characterised as.

Downsloping.

Upsloping.

Horizontal.

Horizontal ST Segment Depression

Myocardial Ischaemia:

Stable angina - occurs on exertion, resolves with rest and/or GTN.

Unstable angina - can develop during rest.

Non ST elevation MI - usually quite deep, can be associated with deep T wave inversion.

Reciprocal horizontal depression can occur during AMI.

Downsloping ST segment depression can be caused by digoxin.

Upward sloping ST segment depression normal during exercise.

ECG abnormalities associated with ischaemia

Ischaemic Changes in ECG

S-T segment elevation

S-T segment depression

Hyper-acute T-waves

T-wave inversion

Pathological Q-waves

Left bundle branch block

Basic electrocardiography

Heart beat originates in the SA node.

Impulse spreads to all parts of the atria via internodal pathways .

ATRIAL contraction occurs.

Impulse reaches the AV node where it is delayed by 0.1second.

Impulse is conducted rapidly down the Bundle of His and Purkinje Fibres.

VENTRICULAR contraction occurs.

ECG Waveforms

Normal cardiac axis is downward and to the left.

ie the wave of depolarisation travels from the right atria towards the left ventricle.

When an electrical impulse travels towards a positive electrode, there will be a positive deflection on the ECG.

if the impulse travels away from the positive electrode, a negative deflection will be seen.

The P wave represents atrial depolarisation.

The PR interval is the time from onset of atrial activation to onset of ventricular activation.

The QRS complex represents ventricular depolarisation.

The S-T segment should be iso-electric, representing the ventricles before repolarisation.

The T-wave represents ventricular repolarisation.

The QT interval is the duration of ventricular activation and recovery.