• ECG and Electrical Impulse
• ECG and Cardiac Cycle
• Asystole
• ECG and Asystole

ECG and Electrical Impulse

• The ECG curve illustrates the propagation of the impulse through the heart
• The impulse propagates
• Quickly through the conduction system
• Slowly through the working myocardium
• which then contracts - systole occurs
  
  
• The ECG curve mainly shows:
• The slow propagation of the impulse in the working myocardium
• The impulse creates a cardiac vector in the working myocardium
  
  
• Electrical activity in the atrial myocardium creates:
• P wave (atrial depolarization)
• Ta wave (atrial repolarization)
• which is hidden in the QRS complex
  
  
• Electrical activity in the ventricular myocardium creates:
• QRS complex (ventricular depolarization)
• T wave (ventricular repolarization)

Asystole

• Pulseless Electrical Activity
• The heart is electrically active, but does not function as a pump (no effective systole and diastole)
• The patient has no palpable pulse
• Common causes include:
• Hypovolemia and hypoxia
• The patient may have sinus tachycardia
• but with hypovolemia, the ventricles are not filled (the patient does not have a peripheral pulse)
• Asystole
• It is an absolute absence of electrical and mechanical activity of the heart
• On the ECG, there is a flat line (no action potential)
• The heart is electrically "turned off"
• Causes are the same as in pulseless electrical activity
• Pulse is often not present even in ventricular tachycardia and ventricular fibrillation
• However, these 2 malignant arrhythmias do not fall under pulseless electrical activity
• Because they can be defibrillated (by electrical shock)
• Pulseless Electrical Activity and Asystole cannot be defibrillated
  
  
• Sudden Cardiac Arrest
• It is an abrupt cessation of heart function primarily due to malignant ventricular arrhythmia
• The heart is electrically active
• Common causes
• Ventricular tachycardia (ventricles have a high rate, ineffective diastole)
• Ventricular fibrillation (ventricles are quivering)
• The patient can be defibrillated
• Sudden Cardiac Death
• The patient dies from cardiac arrest within 1 hour of symptom onset

Asystole

• On the ECG there is a flat line
• Asystole cannot be defibrillated

Ventricular Fibrillation

• In the ventricles there are multiple foci
• The mechanism is most often micro re-entry
• Frequency is 300-450/min.
• The width and amplitude of QRS complexes vary
• QRS complexes are low, and their amplitude is not precisely defined
• The heart does not function as a pump (cardiac arrest is present)
• At such a high frequency, diastole is ineffective
• QRS complexes decrease in amplitude and after about 2 minutes asystole occurs
• Ventricular fibrillation can still be defibrillated, but asystole cannot be defibrillated

Ventricular Fibrillation and Asystole

• Ventricular fibrillation can occur during a myocardial infarction
• With unsuccessful treatment - defibrillation, it progresses to asystole in about 2 minutes