A 65-year-old woman comes in for her Welcome to Medicare examination. She has a history of hypertension and diabetes mellitus type 2. On questioning, she says she has had 2 syncopal episodes in the past week. On physical examination, her blood pressure is 138/78 mm Hg, her pulse is 80 bpm, and her respiratory rate is 14/min. Lungs are clear to auscultation. Cardiovascular examination reveals a regular rate and rhythm with no murmurs, gallops, or rubs. Her extremities have no edema.
Her EKG is shown in Figure 15-1.
1. What is your diagnosis?
First-degree AV block usually results from a conduction delay within the AV node in which the PR interval is lengthened beyond 200 milliseconds. The most common causes include increased vagal tone (athletes), drug effect, electrolyte abnormalities, ischemia, and conduction system disease.
Asymptomatic patients require no therapy. Stop or decrease the dose of AV node blocking medications such as beta-blockers or calcium channel blockers if these are being used (Figure 15-2).
There are 2 types of second-degree AV blocks. These are recognized based on their pattern of impulse conduction, and the distinction between type I and type II is important, as the 2 types carry different prognostic implications.
Mobitz Type I (Wenckebach) Block
Mobitz type I heart block is characterized by the progressive prolongation of the PR interval on consecutive beats followed by a blocked p-wave (Figure 15-3). This is recognized as a dropped QRS complex. After the dropped QRS complex, the PR interval resets and the cycle repeats. The RR interval progressively shortens before a blocked p-wave.
Prior to initiating treatment for Mobitz type I AV block, reversible causes of slowed conduction such as myocardial ischemia, increased vagal tone, and medications should be excluded. If no reversible causes are present, and the patient is asymptomatic, no specific therapy is required. Atropine can be used emergently, and for persistent symptomatic bradycardia a permanently implanted pacemaker is indicated.
Mobitz type II block is characterized by an abrupt AV ...