2-10. HEART BLOCKS
a. General Information. Heart blocks are arrhythmias caused by conduction
disturbances at the AV node.
b. First-Degree (Incomplete) Heart Block.
(1) Analysis. The first-degree heart block takes place where there is an
incomplete block. The regularity and rate depend on the underlying rhythm of the heart.
The P waves are upright and uniform and followed by the QRS complex. The PR
interval is constant and greater than 0.20 seconds. The QRS complex is less than 0.12
Treatment. There is no treatment.
Figure 2-22. First degree (incomplete) heart block.
c. Wenckebach (Second-Degree Heart Block/Mobitz Type 1).
(1) Analysis. The rhythm is irregular, and the R-R interval gets
progressively shorter as the P-R intervals get longer. Grouped beating is characteristic.
The heartbeat rate is usually slightly slower than normal. P waves are upright and
uniform, but some P waves are not followed by QRS complexes. The P-R interval
progressively lengthens until one P wave is not conducted. The QRS complex lasts
less than 0.12 of a second. This condition is a less serious type of second-degree heart
block. It is, however, still quite common in patients with acute myocardial infarction.
The condition may be produced by digitalis.
(2) Treatment. The casualty should be transported to a medical treatment
facility and monitored. If the heart rate is very slow, give atropine in the dosage 0.5 mg
every five minutes to a total dose of 2.0 mg intravenously or until the heartbeat rate is
up to 60 beats per minute.