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Intermittent palpitations noticed during a night shift

The case

36-year-old woman. Intermittent palpitations noticed during a night shift

No structural heart disease. She drinks several energy drinks during night shifts and takes no regular medication.

On arrival

HR
78
GCS
15
SpO₂ (%)
98
Respiratory rate
16
Temperature (°C)
36.7
Systolic BP (mmHg)
126
Diastolic BP (mmHg)
74

Stage 1 of 1

She is comfortable and the pulse feels irregular in a repeating pattern. The twelve-lead is recorded during the palpitations.

The tracing for the quiz “Intermittent palpitations noticed during a night shift”.
Twelve-lead recorded on arrival, 25 mm/s, 10 mm/mV. Open this tracing in the studio

Observations

HR
78
SpO₂ (%)
98
Respiratory rate
16
Temperature (°C)
36.7
Systolic BP (mmHg)
126
Diastolic BP (mmHg)
74
How should the rhythm regularity be described?

The tracing shows narrow sinus complexes interrupted at regular intervals by broad ectopic beats, creating a grouped pattern. This is distinct from the irregularly irregular rhythm of atrial fibrillation and from the progressive cycle-length shortening of a Wenckebach sequence. The tracing is clearly not regular throughout, since the ectopic beats fall early and are followed by a compensatory pause.

What causes the irregularity on this tracing?

The premature beats are broad, have no preceding P wave and show discordant ST-T changes, all consistent with a ventricular origin. Atrial fibrillation would produce an irregularly irregular baseline without discrete P waves, which is not what this tracing shows. Mobitz I block would show progressive PR prolongation before a dropped QRS, not interpolated broad complexes. Sinus arrest would produce pauses, not extra beats.

Which feature most strongly argues against atrial fibrillation?

Atrial fibrillation is defined by the absence of organised atrial activity and an irregularly irregular ventricular response. On this tracing, upright P waves of consistent morphology precede each narrow QRS complex at a fixed PR interval, proving that the atria are being depolarised in an organised fashion by the sinus node. A rate below 100 or haemodynamic stability may be seen in atrial fibrillation and do not exclude it. Broad complexes in AF would suggest aberrant conduction, not rule it out.

Diagnosis

Sinus rhythm with frequent ventricular ectopy causing a regularly recurrent irregularity

The tracing shows sinus rhythm interrupted by frequent premature ventricular complexes arising from a right ventricular focus. The irregularity is grouped and repeating rather than random, which is what produces the patterned sensation the patient describes. The key distinction from atrial fibrillation is the presence of consistent P waves before every narrow sinus complex, proving organised atrial activity.

In a young patient with no structural heart disease and a clear precipitant such as caffeine, frequent ventricular ectopy is usually benign. The practical lesson is that a regularly recurring irregularity with broad complexes is ectopy until proven otherwise, and proving otherwise means looking for the P waves.

References

  1. Latchamsetty R, Bogun F. Premature ventricular complexes and premature ventricular complex induced cardiomyopathy. Curr Probl Cardiol 2015;40(9):379-422.
  2. Marcus GM. Evaluation and management of premature ventricular complexes. Circulation 2020;141(17):1404-1418.
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This tracing was generated, not recorded. It opens in the studio with every dial live.

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Discussion

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