EP 101: Case Studies (Part 3)

In a new installment of EP Lab Digest’s EP 101 series, the authors present three brief case overviews, then ask readers to test their knowledge in EP by answering questions about each case. Case #1: Figure 1 shows an intracardiac tracing obtained at the end of an ablation procedure. The patient is a 70-year-old male with a history of coronary artery disease and atrial fibrillation. He was symptomatic during this rhythm. Question: What was the procedure? A. Slow pathway ablation. B. Cavo-tricuspid isthmus ablation. C. Accessory pathway ablation. D. Atrial tachycardia ablation. E. Ventricular tachycardia ablation. The right answer is B. This tracing shows pacing from both distal Halo and proximal CS. During distal Halo pacing, the activation sequence is over the roof of the right atrium such that the proximal CS is activated later than the proximal Halo. This suggests lateral to medial cavo-tricuspid isthmus block. The tracing also shows proximal CS pacing such that distal Halo activation is latest, indicating medial to lateral cavo-tricuspid isthmus block; therefore, it is bidirectional cavo-tricuspid isthmus conduction block. This tracing obtained at the end of a successful cavo-tricuspid isthmus ablation is what would be expected for a typical counterclockwise atrial flutter.1-3 Case #2: The pacing shown in figure 2 was performed during an electrophysiology study for a symptomatic supraventricular tachycardia. Question: Why is there loss of atrial capture after the fourth pacing stimulus? A. The diastolic threshold is high. B. Pacing during atrial refractoriness. C. Retrograde concealed conduction. D. Transient fluctuations in autonomic tone. E. Pacing during relative refractory period. The right answer is B. This is a block due to a premature atrial depolarization causing electrical stimulation during the atrial effective refractory period. Of note is that the third pacing stimulus is also preceded by a premature atrial beat, which resulted in a short coupled paced beat that was associated with AV nodal block. The premature atrial beat had a different atrial activation sequence than the last atrial premature beat, suggesting it originated from a different location. Case #3: The EKG shown in Figure 3 was taken from a 70-year-old asymptomatic female who was referred to the electrophysiology clinic for evaluation of pacemaker implantation. The patient reported living alone and performing activities of daily living with no chest pain, shortness of breath or dizziness. Question: Does this patient have a class I indication for a pacemaker? A. Yes. B. No. The correct answer is B. This EKG shows sinus bradycardia with a junctional escape rhythm that had a right bundle branch block morphology. The patient is asymptomatic, which is the key point. Guidelines for implantation of cardiac pacemakers have been established by a task force formed jointly by the American College of Cardiology, the American Heart Association, and the Heart Rhythm Society (ACC/AHA/HRS).4 The following conditions are considered class I indications for pacemaker placement: • Sinus bradycardia, in which symptoms are clearly related to the bradycardia (usually in patients with a heart rate below 40 beats/min or frequent sinus pauses). • Symptomatic chronotropic incompetence. The following are considered to be class II, or possible indications for pacemaker placement in patients with sinus node dysfunction: • Sinus bradycardia (heart rate