A 54-year old-woman with a history of myelodysplastic disease presents after radiation therapy for follicular lymphoma. She is awaiting stem cell transplant and is bothered by palpitations and weak spells. Her echocardiogram shows normal ventricular function. An electrocardiogram (ECG) is performed (Figure 1).
The ECG shows which of the following?
The correct answer is: D. Blocked premature atrial contraction (PAC).
The ECG shows sinus rhythm with normal PR interval. The premature atrial contraction (PAC) beats (4, 7 and 10) are full and early complexes. The blocked PACs would appear on the T wave after (beats 5, 8 and 11), so conducted and blocked PACs are present. The 10th beat is a PAC with ventricular aberration with partial block of the left anterior fascicle.
Mobitz I AV block can be ruled out as the PR interval before and after the blocked PACs are the same.
Mobitz II AV block is incorrect as the P waves are early and do not march.
Sino-atrial block can be ruled out since the morphology of the blocked P wave looks like the conducted PACs; however, the sinus beats and the P waves do not march. Therefore, the correct answer is D.
Akdeniz C, Tanidir IC, Tuzcu V. CeBlocked atrial bigeminy presenting with bradycardia. Congenit Heart Dis 2012;7:E82-4.