This rhythm strip is most consistent with second-degree AV block with 2:1 conduction:

The textbook description notes that 2:1 AV block cannot reliably be typed as Mobitz I versus II solely from the pattern; a narrow QRS supports a more proximal block mechanism. The Washington Manual of Medical Therapeutics, p. 265. The American Heart Association overview explains that second-degree block involves intermittent failure of atrial impulses to reach the ventricles.

If this is from a real patient, obtain a 12-lead ECG, review medications and electrolytes, and assess symptoms. Urgent evaluation is needed for syncope, dizziness, chest pain, breathlessness, low blood pressure, or worsening bradycardia.

Sinus bradycardia with a regular rhythm, rate about 55-60 beats/min.

Each QRS complex appears preceded by a P wave with no dropped beats. This strip does not show 2:1 AV block.

Sinus bradycardia - regular sinus rhythm with a rate of approximately 40 beats/min. Each QRS is preceded by a normal P wave with a consistent PR interval.

Torsades de pointes - a polymorphic ventricular tachycardia with waxing and waning QRS amplitude, appearing to “twist” around the baseline.

Second-degree AV block, Mobitz type II - regular P waves with intermittent non-conducted P waves (dropped QRS complexes) and a constant PR interval in conducted beats.

Atrial fibrillation - an irregularly irregular ventricular rhythm with no distinct P waves and a fibrillatory baseline.

Ventricular fibrillation (VF) - chaotic, irregular electrical activity with no identifiable P waves, QRS complexes, or organized rhythm.

Pulseless electrical activity (PEA) - an organized, sinus-like electrical rhythm is present on the monitor, but the patient has no palpable pulse.

Monomorphic ventricular tachycardia (VT) - a regular, broad-complex tachycardia at approximately 180-200 beats/min.

Monomorphic ventricular tachycardia (VT) - regular wide-complex tachycardia, approximately 180-200 beats/min.

Atrial flutter with sawtooth flutter waves, likely variable AV block.

Fine ventricular fibrillation (VF) - chaotic, disorganized low-amplitude electrical activity with no identifiable P waves or QRS complexes.

Third-degree (complete) AV block - P waves and QRS complexes occur independently, with a slow ventricular escape rhythm.

Atrial flutter with 2:1 AV conduction - regular narrow-complex tachycardia at approximately 150 beats/min, with characteristic flutter (“sawtooth”) waves between QRS complexes.

Ventricular paced rhythm - pacing spikes immediately precede broad QRS complexes, indicating ventricular capture.

Sinus tachycardia - regular narrow-complex rhythm at approximately 150 beats/min, with a P wave before each QRS complex.

Asystole - essentially no organized cardiac electrical activity, apart from minimal baseline artifact.

Asystole - no organized electrical cardiac activity.

Supraventricular tachycardia (SVT) - a regular, narrow-complex tachycardia at approximately 220-250 beats/min. P waves are not clearly visible or may be buried within the QRS/T complexes.

Normal sinus rhythm - regular narrow-complex rhythm at approximately 70 beats/min, with a P wave before every QRS complex.

Fine ventricular fibrillation (VF) - low-amplitude, chaotic electrical activity with no identifiable P waves or QRS complexes.