Normal activation of the left ventricle (LV) proceeds down the left bundle branch, which consist of three fascicles, the left anterior fascicle, the left posterior fascicle, and the septal fascicle. The posterior fascicle supplies the posterior and inferoposterior walls of the LV, the anterior fascicle supplies the upper and anterior parts of the LV and the septal fascicle supplies the septal wall with innervation. LAFB — which is also known as left anterior hemiblock (LAHB) — occurs when a cardiac impulse spreads first through the left posterior fascicle, causing a delay in activation of the anterior and upper parts of the LV. Although there is a delay or block in activation of the left anterior fascicle there is still preservation of initial left to right septal activation as well as preservation of the inferior activation of the LV (preservation, on the EKG, of septal Q waves in I and aVL and predominantly negative QRS complex in leads II, III, and aVF). The delayed and unopposed activation of the remainder of the LV now results in a shift in the QRS axis leftward and superiorly, causing marked left axis deviation. This delayed activation also results in a widening of the QRS complex, although not to the extent of a complete LBBB.[citation needed]
Diagnosisedit
Abnormal left axis deviation[3] (usually between –45° and –60°)[4]
qR pattern (small q, tall R) in the lateral limb leads I and aVL
rS pattern (small r, deep S) in the inferior leads II, III, and aVF
LAFB cannot be diagnosed when a prior inferior wall myocardial infarction (IMI) is evident on the ECG. IMI can also cause extreme left-axis deviation, but will manifest with Q-waves in the inferior leads II, III, and aVF. By contrast, QRS complexes in the inferior leads should begin with r-waves in LAFB.[citation needed]
Effects of LAFB on diagnosing infarctions and left ventricular hypertrophyedit
LAHB may be a cause of poor R wave progression across the precordium causing a pseudoinfarction pattern mimicking an anteroseptal infarction. It also makes the electrocardiographic diagnosis of LVH more complicated, because both may cause a large R wave in lead aVL. Therefore, to call LVH on an EKG in the setting of an LAHB you should see the presence of a "strain pattern" when you are relying on limb lead criteria to diagnose LVH.[citation needed]
Clinical significanceedit
It can be seen in approximately 4% of cases of acute myocardial infarction[citation needed]
It is the most common type of intraventricular conduction defect seen in acute anterior myocardial infarction, and the left anterior descending artery is usually the culprit vessel.
It can be seen with acute inferior wall myocardial infarction.
It is also associated with hypertensive heart disease, aortic valvular disease, cardiomyopathies, and degenerative fibrotic disease of the cardiac skeleton.[citation needed]
^Rebuzzi AG, Loperfido F, Biasucci LM (July 1985). "Transient Q waves followed by left anterior fascicular block during exercise". Br Heart J. 54 (1): 107–9. doi:10.1136/hrt.54.1.107. PMC481860. PMID 4015909.
^Chandrashekhar Y, Kalita HC, Anand IS (January 1991). "Left anterior fascicular block: an ischaemic response during treadmill testing". Br Heart J. 65 (1): 51–2. doi:10.1136/hrt.65.1.51. PMC1024464. PMID 1899584.
^Horwitz S, Lupi E, Hayes J, Frishman W, Cárdenas M, Killip T (September 1975). "Electrocardiographic criteria for the diagnosis of left anterior fascicular block. Left axis deviation and delayed intraventricular conduction". Chest. 68 (3): 317–20. doi:10.1378/chest.68.3.317. PMID 1157535.
left, anterior, fascicular, block, lafb, abnormal, condition, left, ventricle, heart, related, distinguished, from, left, bundle, branch, block, lbbb, specialtycardiology, caused, only, left, anterior, fascicle, half, left, bundle, branch, being, defective, ma. Left anterior fascicular block LAFB is an abnormal condition of the left ventricle of the heart 1 2 related to but distinguished from left bundle branch block LBBB Left anterior fascicular blockSpecialtyCardiology It is caused by only the left anterior fascicle one half of the left bundle branch being defective It is manifested on the ECG by left axis deviation It is much more common than left posterior fascicular block Contents 1 Mechanism 2 Diagnosis 2 1 Effects of LAFB on diagnosing infarctions and left ventricular hypertrophy 3 Clinical significance 4 See also 5 References 6 External linksMechanism editNormal activation of the left ventricle LV proceeds down the left bundle branch which consist of three fascicles the left anterior fascicle the left posterior fascicle and the septal fascicle The posterior fascicle supplies the posterior and inferoposterior walls of the LV the anterior fascicle supplies the upper and anterior parts of the LV and the septal fascicle supplies the septal wall with innervation LAFB which is also known as left anterior hemiblock LAHB occurs when a cardiac impulse spreads first through the left posterior fascicle causing a delay in activation of the anterior and upper parts of the LV Although there is a delay or block in activation of the left anterior fascicle there is still preservation of initial left to right septal activation as well as preservation of the inferior activation of the LV preservation on the EKG of septal Q waves in I and aVL and predominantly negative QRS complex in leads II III and aVF The delayed and unopposed activation of the remainder of the LV now results in a shift in the QRS axis leftward and superiorly causing marked left axis deviation This delayed activation also results in a widening of the QRS complex although not to the extent of a complete LBBB citation needed Diagnosis editAbnormal left axis deviation 3 usually between 45 and 60 4 qR pattern small q tall R in the lateral limb leads I and aVL rS pattern small r deep S in the inferior leads II III and aVF Delayed intrinsicoid deflection in lead aVL gt 0 045 s LAFB cannot be diagnosed when a prior inferior wall myocardial infarction IMI is evident on the ECG IMI can also cause extreme left axis deviation but will manifest with Q waves in the inferior leads II III and aVF By contrast QRS complexes in the inferior leads should begin with r waves in LAFB citation needed Effects of LAFB on diagnosing infarctions and left ventricular hypertrophy edit LAHB may be a cause of poor R wave progression across the precordium causing a pseudoinfarction pattern mimicking an anteroseptal infarction It also makes the electrocardiographic diagnosis of LVH more complicated because both may cause a large R wave in lead aVL Therefore to call LVH on an EKG in the setting of an LAHB you should see the presence of a strain pattern when you are relying on limb lead criteria to diagnose LVH citation needed Clinical significance editIt can be seen in approximately 4 of cases of acute myocardial infarction citation needed It is the most common type of intraventricular conduction defect seen in acute anterior myocardial infarction and the left anterior descending artery is usually the culprit vessel It can be seen with acute inferior wall myocardial infarction It is also associated with hypertensive heart disease aortic valvular disease cardiomyopathies and degenerative fibrotic disease of the cardiac skeleton citation needed See also editBundle branch blockReferences edit Rebuzzi AG Loperfido F Biasucci LM July 1985 Transient Q waves followed by left anterior fascicular block during exercise Br Heart J 54 1 107 9 doi 10 1136 hrt 54 1 107 PMC 481860 PMID 4015909 Chandrashekhar Y Kalita HC Anand IS January 1991 Left anterior fascicular block an ischaemic response during treadmill testing Br Heart J 65 1 51 2 doi 10 1136 hrt 65 1 51 PMC 1024464 PMID 1899584 Horwitz S Lupi E Hayes J Frishman W Cardenas M Killip T September 1975 Electrocardiographic criteria for the diagnosis of left anterior fascicular block Left axis deviation and delayed intraventricular conduction Chest 68 3 317 20 doi 10 1378 chest 68 3 317 PMID 1157535 Conduction Blocks 2006 KCUMB Retrieved 2009 01 20 External links edit Retrieved from https en wikipedia org w index php title Left anterior fascicular block amp oldid 1187272479, wikipedia, wiki, book, books, library,
