Wide Complex Irregular Rhythm in a Paced Patient: A Clinical Approach

Figures

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  Figure 1. 12-lead ECG of our patient at admission: There is an irregular rhythm with wide complex QRS and a left bundle branch morphology. The average heart rate is 75 bpm.

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  Figure 2. Patient chest X-ray at admission: a cardiac pacemaker is present in the right pectoral region with a ventricular stimulation lead placed on the free wall of the right ventricle and an abandoned atrial lead. There is no apparent lead displacement or fracture. The inferior segment of the left border of the heart is elongated and bulging. An aortic prosthetic valve is present. There are no pleural or pulmonary lesions.

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  Figure 3. Echocardiography exam images at admission: A transthoracic echocardiography (TTE) exam was performed in the apical 4-chamber view (a,b) and subcostal view (c,d), revealing the insertion of the pacing probe into the myocardium of the right ventricle free wall, without any visible fractures or ruptures of the lead.

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  Figure 4. Holter ECG monitoring summary, presenting the general data of the patient and heart rhythm parameters.

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  Figure 5. Holter ECG strip: Wide QRS beats alternate with narrow complexes in an irregular sequence. Wide QRS beats have approximately the same morphology, but only one is preceded by a stimulation spike. Between the QRS complexes, the atrial activity can be observed, replacing the isoelectric line.

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  Figure 6. Holter ECG strip: Atrial activity seems disorganized, suggestive of coarse wave atrial fibrillation (see Figure 11A). This pattern is frequent in patients under Amiodarone. The intrinsic rhythm exhibits a narrow complex QRS, reflecting the fast activation through the specialized conduction system (see Figure 13A).

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  Figure 7. Holter ECG strip: The ventricular stimulated rhythm has a rate of 70 bpm. The pacemaker-generated spike is followed by a wide QRS complex. The lead is placed at the apex of the right ventricle (see Figure 3 and Figure 13C), depolarizing the right ventricle before the left ventricle. The lead is in contact with the myocardium, and the conduction is slow, cell-to-cell, thus generating a broad QRS, reflecting the interventricular and intraventricular dyssynchrony.

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  Figure 8. Holter ECG strip: Hysteresis: The paced rhythm is set at 70 bpm, but pacing is triggered at a lower heart rate, of 55 bpm. This demonstrates that the hysteresis option is activated, to favor the intrinsic rhythm rather than the right ventricle pacing that induces dyssynchrony.

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  Figure 9. Holter ECG strip: Paced beat morphologies: Fusion (beat 3), pseudofusion (beat 4), intrinsic beat (beat 5), and stimulated complexes (beats 1, 2, and 6). The fusion beat has an intermediary pattern between the stimulated and intrinsic beat, due to the electrical activation through both the conduction system and the pacemaker lead (see Figure 13D). The pseudofusion has the same pattern of an intrinsic beat with a spike overlayed; the spike is delivered in the absolute refractory period and does not depolarize the myocardium (see Figure 13E).

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  Figure 10. Holter ECG strip: Intermittent bundle branch block: At frequencies above 75 bpm, the QRS becomes wide and there are ST-T changes. It should be noted that the rhythm is irregular, the heart rate is above the pacing rate, and there is no spike, meaning that the beats are not stimulated but conducted with a frequency-dependent bundle branch block.

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  Figure 11. Lewis Leads: (A). ECG strip showing the atrial waves, which are slightly polymorphic and with different frequencies. The ventricular rate is variable, suggesting that the atrial rhythm is indeed atrial fibrillation with coarse waves. (B). Lead placement in standard and (C). Lewis configurations. (Figure 11B,C are adapted from a public domain image).

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  Figure 12. 2D-TTE speckle-tracking strain imaging shows enlargement of the left atrium with an increase in the left atrial volume index (LAVi = 101 mL), demonstrating a loss of contractile phase (−2%) and atrial stunning due to atrial fibrillation.