ECG Case #1 Scott E. Ewing, DO

Question 1 86-yr-old man with slow pulse and fatigue What is the atrial mechanism? What is the AV relationship? What is pacing the ventricles?

Answer Atrial fibrillation with complete heart block and junctional escape mechanism Intraventricular conduction delay with left axis and left ventricular hypertrophy and there is Q-T(U) prolongation Etiologic differential diagnosis includes intrinsic conduction disease, rule out drug toxicity or metabolic factors Ischemic heart disease, hypokalemia, antiarrhythmic drug effects (i.e. sotalol, amiodarone) should be excluded Treatment: If no reversible causes, patient will likely require an implanted ventricular pacemaker, as well as anticoagulation for afib

Question 2 23-year-old female with palpitations What is the ECG diagnosis?

Other ECG Waves Delta wave – ventricular pre-excitation Osborn wave – hypothermia, hypercalcemia, certain CNS lesions, etc. Epsilon wave – arrhythmogenic right ventricular dysplasia

Classic Wolff-Parkinson-White Classic Wolff-Parkinson-White (WPW) Wide QRS Short PR Delta waves Distinctive pattern due to electrical activation of ventricles during sinus rhythm via AV bypass tract (accessory conduction pathway) which allows an impulse to short-circuit the slowly conducting AV node WPW pre-excitation is clinically important because it is a substrate for the development of tachycardias, especially atrio-ventricular reentrant tachycardia (AVRT) Therapy of choice for patients with WPW and AVRT or atrial fibrillation is radiofrequency ablation

Classic Wolff-Parkinson-White Classic triad of Wolff-Parkinson-White pre-excitation Wide QRS complex Short RR interval Delta waves Delta waves with notching or slurring of the initial portion of the QRS complex Predominantly negative here in leads VI and III, and positive in other leads (I, aVL, and the lateral chest leads) Distinctive pattern is due to electrical activation of the ventricles during sinus rhythm via an atrio-ventricular bypass tract, an accessory conduction pathway, which allows an impulse to short-circuit the slowly conducting AV node Pre-exciting the ventricles in this abnormal way during sinus rhythm causes the PR interval to be shortened The QRS is widened, not because of a bundle branch block or related delay in activation, but because the pre-excitation actually starts the QRS off earlier than normal Of note, the bypass tract activates the myocardium, rather than the faster specialized (His-Purkinje) conducting system in the ventricles This early myocardial conduction imparts the distinctive notching or slurring (delta wave) to the initial part of the QRS. The polarity of the delta wave on the 12-lead ECG provides a major clue to the location of the bypass tract For example, when the bypass tract pre-excites the lateral wall of the left ventricle, the initial QRS vector will point from left to right Thus, the delta wave with a lateral bypass tract will be negative in lead I and positive in lead VI. In the present ECG, what does the vector of the delta wave indicate about the likely location of the bypass tract? Ans: the fact that the delta waves are predominantly negative in VI and positive in the lateral leads is consistent with a bypass tract inserting into the free wall of the right ventricle. WPW pre-excitation is clinically important because it is a substrate for the development of tachycardias, especially atrio-ventricular reentrant tachycardia (AVRT). Some patients may have multiple bypass tracts. The therapy of choice for patients with WPW syndrome with AVRT or atrial fibrillation is radiofrequency ablation of the bypass tract(s). For an excellent tutorial presentation and animation of these and related supraventricular arrhythmias, see: http://blaufuss.org. The patterns of WPW may be mistaken for bundle branch blocks, hypertrophy and infarction due to the anomalous pattern of ventricular activation which can lead to tall R waves and Q waves in selected leads, along with the wide QRS. Bypass tract is postero-septal, consistent with the positive delta waves V2-V5, I and aVL; and negative delta wave in III Left posterior free wall bypass tracts have a similar pattern, but usually with prominent positive delta waves in all the precordial leads, including V1, as well as negative delta waves in the inferior leads Left lateral bypass tracts usually produce positive delta waves inferiorly and in all the precordial leads, with negative delta waves in I and aVL