Ginter, James F.

Loftis, Patrick

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Marquette Universitye-Publications@MarquettePhysician Assistant Studies Faculty Research andPublications Physician Assistant Studies, Department3-18-2011Third Degree Atrioventricular BlockPatrick LoftisMarquette University, patrick.loftis@marquette.eduJames F. GinterAurora Cardiovascular ServicesPublished version. Journal of the American Academy of Physician Assistants, Vol. 24, No. 3 (March2011). Permalink. © 2011, American Academy of Physician Assistants and Haymarket Media Inc.Used with permission.   << Return to Third-degree atrioventricular blockPatrick Loftis, PA-C, MPAS, RN, James F. Ginter, MPAS, PA-CMarch 18 2011Previous discussions have focused on first-degree heart block, which is an abnormal slowing of the impulsethrough the cardiac conduction system, and second-degree heart block, which includes varying degrees of partialblocks. In contrast, third-degree heart block involves a complete blockade of electrical transmission from theatria to the ventricles. The result is atrioventricular (AV) dissociation. This disorder is also commonly known ascomplete heart block or AV dissociation. The location of third-degree atrioventricular block is the AV node itself or lower. In patients with third-degreeheart block, the atria are beating at 60 to 100 beats per minute with normal impulses (unless there is also sinusnode dysfunction or another disorder present). The problem arises when the ventricles do not receive thisimpulse from the atria because of the block. Sensing this lack of impulse, the ventricles begin to generate theirown intrinsic rhythm in order to pump blood to the body. However, the intrinsic ventricular rhythm is only 30 to45 beats per minute, which cannot sustain life for very long. Atria contracting at 60 to 100 beats per minute andventricles contracting at 30 to 45 beats per minute are essentially beating independently of each other, and theresult is incoordination of heart activity. On the ECG, P waves and QRS waves are unrelated.  Symptoms Third-degree heart block may manifest with no symptoms (rare), fatigue, dizziness, exerciseintolerance, generalized weakness, syncope, or sudden death. Symptoms depend on the location of the actualblock (generally, the higher it is located, the less severe the symptoms) and the rate of the intrinsic ventricularrhythm. Etiology Causes of third-degree heart block include congenital defects, antiarrhythmic medications, MI,cardiomyopathy, or severe electrolyte abnormalities. Treatment When treating a patient with third-degree heart block, begin by managing the underlying etiology(eg, remove the offending medication, correct electrolyte abnormalities). Symptomatic patients may be treatedtemporarily with anticholinergic agents, such as atropine or dopamine, and external pacing. Definitive treatmentof persistent third-degree heart block is the placement of a permanent pacemaker.Third-degree atrioventricular block - Print Article - JAAPA http://www.jaapa.com/third-degree-atrioventricular-block/printarticle/19...1 of 2 5/16/2011 11:03 AMAn 87-year-old man complained of weakness and occasional “drop attacks” during the preceding two months.He had a history of diabetes and hypertension but denied any cardiac history. Workup included an ECG (Figure1).1. Is the ECG regular? The QRS complexes march out, but they are independent of the P waves.   2. What is the heart rate?  The ventricular rate on this ECG is about 40 beats per minute (four QRS complexesin 30 large boxes or 6 seconds). The atrial rate is about 100 beats per minute (10 P waves in 30 large boxes or 6seconds).  Note: The pink arrows highlight some of the P waves, while the purple arrows highlight some of theQRS complexes. 3. There is not a P wave for every QRS complex, although all the P waves look the same.4. The PR interval cannot be determined because of the atrioventricular dissociation that is present. 5. The QRS complex spans less than two small boxes, which is normal. 6. The ST segments are normal.7. The T waves appear normal, although some P waves fall on the T waves, giving them an abnormalappearance. 8.  There are no U waves.The dissociation of P waves from QRS complexes indicated the patient had a third-degree heart block. Heunderwent placement of a pacemaker without incident, and his symptoms resolved. JAAPAJim Ginter practices at Aurora Cardiovascular Services in Milwaukee, Wisconsin. Patrick Loftis practicesemergency medicine and is a clinical assistant professor in the Department of Physician Assistant Studies,Marquette University, Milwaukee, Wisconsin. The authors have no relationships to disclose relating to thecontents of this article.Third-degree atrioventricular block - Print Article - JAAPA http://www.jaapa.com/third-degree-atrioventricular-block/printarticle/19...2 of 2 5/16/2011 11:03 AM

Third Degree Atrioventricular Block

Marquette Universitye-Publications@MarquettePhysician Assistant Studies Faculty Research andPublications Physician Assistant Studies, Department1-21-2011First Degree Atrioventricular BlockPatrick LoftisMarquette University, patrick.loftis@marquette.eduJames F. GinterAurora Cardiovascular ServicesPublished version. Journal of the American Academy of Physician Assistants, Vol. 24, No. 1 ( January2011). Permalink. © 2011, American Academy of Physician Assistants and Haymarket Media Inc.Used with permission.   << Return to First-degree atrioventricular blocksPatrick Loftis, PA-C, MPAS, RN, James F. Ginter, MPAS, PA-CJanuary 21 2011An atrioventricular (AV) block is a common cardiac abnormality. It involves a slowing or blockage of theelectrical impulse coming from the sinoatrial (SA) node at or around the AV node (Figure 1). AV blocks arecharacterized by the slowing or partial or complete blocking of the impulse. This discussion will focus on first-degree atrioventricular block, which is the slowing or partial blocking of the impulse; complete blockade will bediscussed in a future segment of this department.Despite the name, no impulse is actually blocked in first-degree AV block. Instead, each impulse is simplyslowed at or near the atrioventricular node. On an ECG, AV block is manifested by a prolonged PR interval,which is measured from the beginning of the P wave to the beginning of the QRS complex. The ECG criterionfor a first-degree atrioventricular block is a PR interval greater than 200 milliseconds.Symptoms First-degree AV block by itself does not result insymptoms. This is because all the impulses get througheventually, and the delay has no ill effect on cardiac function.Etiology While first-degree atrioventricular block may occurin otherwise normal hearts, some patients will have underlyingcauses. These include AV node disease, MI, medications(most commonly beta blockers), or electrolyte abnormalities.A 57-year-old man who had no symptoms presented for apreoperative evaluation. Three years prior to this visit, thepatient had had an MI; he was taking aspirin 325 mg per dayand metoprolol 25 mg twice daily. See Figure 2.First-degree atrioventricular blocks - Print Article - JAAPA http://www.jaapa.com/first-degree-atrioventricular-blocks/printarticle/1...1 of 3 5/16/2011 11:44 AM Stepwise approach to ECG interpretation:1. Is the rhythm of the heartbeat regular? Yes. The QRS complexes march out.2. Estimate the heart rate. Find a QRS complex on or near a dark line.Method A: There are just under 4 large boxes before the next QRS complex. Four boxes would put the heartrate at 75 beats per minute. Because the next QRS complex comes between the lines assigned a rate of 100 beatsper minute and 70 beats per minute, the rate could be estimated at 80 beats per minute.Method B: Approximately eight QRS complexes occur in 6 seconds (30 large boxes), which estimates the rate at80 beats per minute (8 x 10).Method C: Dividing 300 by the number of large boxes (four) gives us an estimated heart rate of 75 beats perminute (300 ÷ 4 = 75).3. There is a P wave for every QRS complex, and all P waves look the same.4. The PR interval is about 5.5 small boxes, which is 220 milliseconds. This exceeds the criterion for a first-degree atrioventricular block.5. The QRS complex spans less than two small boxes, which is normal. There are Q waves in leads II, III, andaVF that have a deflection of greater than 0.1 mm. These are pathologic for MI, age undetermined, and would beconsistent with the patient's known history.6. The ST segments are normal.7. Peaked T waves in leads V3 and V4 are a nonspecific finding. However, they could suggest an electrolyteabnormality, such as hyperkalemia, and should be investigated further.8. There are no U waves.Diagnosis The patient's prolonged PR interval indicates a first-degree AV block, most likely the result of his pastMI. However, the beta blocker he takes or an electrolyte abnormality could also be the culprit and would need toFirst-degree atrioventricular blocks - Print Article - JAAPA http://www.jaapa.com/first-degree-atrioventricular-blocks/printarticle/1...2 of 3 5/16/2011 11:44 AMbe investigated.Treatment There is no specific treatment for first-degree atrioventricular block. Underlying causes should beaddressed, but if none is found, the block requires no further consideration. JAAPAJim Ginter practices at Aurora Cardiovascular Services in Milwaukee, Wisconsin. Patrick Loftis practicesemergency medicine and is clinical assistant professor in the Department of Physician Assistant Studies,Marquette University, Milwaukee, Wisconsin. The authors have no relationships to disclose relating to thecontents of this article.First-degree atrioventricular blocks - Print Article - JAAPA http://www.jaapa.com/first-degree-atrioventricular-blocks/printarticle/1...3 of 3 5/16/2011 11:44 AM

First Degree Atrioventricular Block

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First Degree Atrioventricular Block

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