Typical Behaviours of impulses includes;
- Bradycardia (Slow)
- Usually from dysfunctional automaticity of pacemakers or impulse block resulting in slower impulse
- Tachycardia (Fast)
- Resulted from impulse spreading out from atria (Supraventricular) or ventricle (Ventricular) resulting in rapid/faster impulse.
For treating heart failure and irregular heartbeat like AF – The drug enhances ventricular contractility but lowers heart rate by making more calcium available and increasing vagus nerve activity (cause diminishes SA node automaticity).
- ST depression with curved appearance will occur
- T-wave amplitude diminishes (can appear biphasic) or inverted wave
- U-wave slightly increase in amplitude
- QTc interval shortened at therapeutic doses
For treatment of ventricular tachyarrhythmias or AF
- Prolonged QRS
- ST depressions may develop
- T-wave may diminish in amplitude
- QT & QTc interval may prolong
- May provoke ventricular arrythmias
For treatment of ventricular tachyarrhythmias or symptomatic paroxysmal supraventricular tachyarrhythmias.
- Prolonged QRS
- QT & QTc interval may prolong
Antiarrhythmic drug for serious SVT or VT, and WPW syndrome & AF.
- Prolonged QRS
- Wider T-wave
- Obvious U-wave
- QT & QTc interval may prolong
- Sinus bradycardia &/or torsade de pointes may show
Acute treatment of SVT & VT or controlling AF after return to sinus rhythm.
- PR interval prolonged
- QT & QTc interval may prolong
Role to reduce effect of catecholamines on the heart resulted from low heart rate, &/or decrease conductivity – aim to block the effect of adrenaline.
The SA node decreases in automaticity (sinus rate decrease)
- PR interval prolonged
- QT & QTc may be shortened
- Slower heart rate seen
Prevention of calcium from entering the heart cells and arteries decreasing the muscle action – This therefore, cause muscle relaxation – Less forceful contractions, vasodilation etc.
- PR interval prolonged
- QT & QTc may be shortened
Increased (hypernatremia) or decreased (hyponatremia) sodium levels do not affect the ECG as sodium is more related to fluid volume control.
Caused by hyperthyroidism or malignancies in most causes – other imbalances or diseases can cause this condition;
- Shortened QT interval (longer QRS duration)
- Bradycardia may occur
Potential complications can occur;
- Increased QRS amplitude
- Diminished T-wave amplitude
- STE in V1-V2
- All degrees of AV block
- Osborn-like waves
Caused by issues relating to the pancreas, sepsis, alkalosis or GIT issues.
- Lengthened QT interval (short QRS duration)
- Torsade De Pointes can occur
Potential complications can occur;
- AV block
- Sinus bradycardia
- SA block
- VF
Hypermagnesemia is rare but can cause AV and intraventricular conduction disturbance which can result in asystole or third-degree AV block.
Hypomagnesemia can turn into effects of digoxin and show SVT or VT.
High levels of potassium resulting in decrease impulse transmission to the whole heart – Caused by many medical factors and diseases.
Mild (> 6mmol)
- Pointed T-waves (tall & narrow top)
- LVH patients can show secondary T-wave inversion (V5-V6, aVL & Lead I)
Moderate
- Like mild symptoms but more pronounced
- Wider P-wave (amplitude decrease)
- PR prolonged
- WPW syndrome patient loses delta-wave
- STE in V1-V3
Severe (> 7.5mmol)
- Like mild & moderate but more pronounced
- Wide QRS
- QRS may fuse with T-wave (forms sine wave)
- VF may occur after sine wave is formed
When levels are < 3mmol from fluid loss, malnutrition, medical/injury or alcohol use – Can be caused by medications such as steroids or diuretics & insulin.
- Wider T-wave (lower amplitude)
- ST depression can occur with T-wave inversion
- P-wave amplitude & duration increase (increase PR interval)
- U-wave emerge (Usually V2-V3)
- U-wave can be larger than T-wave in worse case
Page contributors:
 | Thanh Bui, AP60825 Event Medic, Emergency Medical Technician & Volunteer Development Officer
|
 | Andrew Moffat, AP16790 |
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