Differential Diagnosis
- Atrial fibrillation
- Ventricular paced rhythm
- Atrial paced rhythm
- Sinus bradycardia
Diagnosis
The diagnosis in this case is atrial paced rhythm, left bundle branch block. This ECG shows an atrial paced rhythm with a rate of 60 beats per minute. There is a left bundle branch block without signs of ischemia. For more information regarding left bundle branch blocks, see the ECG case in the May 2023 issue of JUCM.1
Pacer spikes are visualized preceding the atrial complexes (Figure 2), indicating that the pacemaker initiated the impulse. Implantable pacemakers are indicated for a range of electrophysiologic issues including (but not limited to) sinus node dysfunction, high-grade atrioventricular block, syncope and bundle branch block, and cardiac resynchronization therapy for severe systolic heart failure.2,3 They are programmed with 5 variables, 3 of which are relevant for urgent care providers. The 3 variable code indicates: 1) the chamber paced; 2) the chamber sensed; and 3) the response to sensing (Figure 3).4
| I | II | III |
| Chamber paced | Chamber sensed | Response to sensing |
| O = none A = atrium V = ventricle D = dual (atrium and ventricle) | O = none A = atrium V = ventricle D = dual (atrium and ventricle) | O = none T = triggered I = inhibited D = dual (trigger and inhibition) |
Figure 3. Pacemaker code
The presence of atrial pacer spikes indicates that an atrial lead is present. A ventricular lead is likely present (ie, dual chamber pacemaker), although ventricular spikes are not seen. The most common pacemaker mode is DDD, which indicates that both chambers (ie, right ventricle and right atrium) have the potential to be paced and sensed, and the response to sensing can be either inhibitory or triggering. When the intrinsic rate drops below a certain threshold (eg, 60 beats per minute), the pacemaker triggers a signal. In this case, an atrial signal is triggered, and the ventricular contraction is allowed to occur naturally provided that the atrioventricular delay does not exceed a predefined threshold. If the atrioventricular delay were to exceed the predefined threshold, the ventricular lead would also trigger a signal resulting in a pacer spike preceding the ventricular (ie, QRS) complex. Atrial pacing does not interfere with recognition of ischemic patterns.
Another common pacemaker mode is VVI. In this mode, the ventricle is sensed and paced via a single right ventricular lead, and the response to sensing is inhibition. If intrinsic activity is sensed and the rate is above the threshold, then the pacemaker will inhibit the response; otherwise, the pacer will initiate a signal resulting in a pacer spike preceding the ventricular (ie, QRS) complex (Figure 4).
The presence of an implantable pacemaker itself is not an indication for emergency department (ED) referral; however, it is an indicator of electrophysiologic pathology, and the urgent care provider should maintain a low threshold to refer someone to the ED with cardiopulmonary complaints and a known pacemaker to a cardiac capable ED.
What to Look For
- Pacer spikes preceding the atrial (eg, P waves) or ventricular (eg, QRS complexes) indicate the presence of a pacemaker.
- Pacemaker modes are indicated by a 3-code system which refers to: 1) the chamber paced; 2) the chamber sensed; and 3) the response to sensing.
- Atrial pacing does not interfere with recognition of ischemic patterns.
Pearls for Management, Considerations for Transfer
- Maintain a low threshold to refer patients with pacemakers that present with cardiopulmonary complaints (eg, chest pain, dyspnea, syncope) to a cardiac capable ED.
References
- Cooper BL. A 69-Year-Old Male with Left-Sided Chest Pain and Dyspnea for 3 Days. Journal of Urgent Care Medicine. 2023;17(8):49-50.
- Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhyth. Circulation. 2019;140(8):e382-e482. doi:10.1161/CIR.0000000000000628
- Dalia T, Amr BS. Pacemaker Indications. StatPearls Publishing; 2020. Accessed January 11, 2021. http://www.ncbi.nlm.nih.gov/pubmed/29939600
- Cooper BL, Giordano JA, Fadial TT, Reynolds CE. ECG Stampede: A Case-Based Curriculum in Electrocardiography Triage. 1st ed. (Cooper BL, ed.). Null Publishing Group; 2021.
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