ECG characteristics of various heart blocks:

• First degree heart block: PR interval is prolonged but there are no dropped beats.
• Second-degree AV block
  •  Mobitz type I (Wenckebach)
  •  Mobitz type II.
• Mobitz type I block - Progressively lengthening PR interval, shortening of the RR interval, followed by a pause (skipped) that is less than two times the immediately preceding RR interval
• Mobitz type II block -  Sudden skipped beat, without progressive prolongation of the PR interval.
• Third degree heart block: The atrial rate is more than ventricular rate with broad QRS complexes. The two rates are independent.

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