Figure 2-23. Wenckebach (second-degree heart block/Mobitz Type I).
d. Classical Second-Degree Heart Block (Mobitz Type II).
(1) Analysis. The rhythm is regular if the conduction ratio is constant;
however, the rhythm is irregular if the conduction ratio varies. The rate for atrial is
usually normal, and the ventricular rate is usually bradycardia. P waves are upright and
uniform with more P waves than QRS complexes (usually a ratio of 2:1, 3:1, and so
forth.). The P-R interval is constant on conducted beats, but it may be longer than
(2) Treatment. If the cardiac output is adequate, there is no treatment. If
there are signs of an inadequate cardiac output, treat with 0.5 mg atropine sulfate IV
bolus. This dose may be repeated until the pulse reaches 60 or more beats per minute
or until a maximum dose of 2.0 mg has been given. If atropine sulfate is ineffective,
administer 2 mg of isoproteronal in 500 cc D5W IV piggyback until the blood pressure is
80 or the heart rate is greater than 60. Radio the medical treatment facility to have a
Figure 2-24. Classical second-degree heart block (Mobitz Type II).