AV Blocks – Veterinary ECG Quiz

Dog (Recorded with Beecardia)

Referred for investigation of suspected bradycardia; echocardiogram showed mild (stage B1/2) degenerative mitral valve disease, and blood pressure was normal

Question

This dog was referred for suspected bradycardia. What should you check first before calling this an AV block?

Whether the QRS complexes are narrow or wide

Whether the heart rate is faster or slower than expected

Whether the P wave amplitude changes from beat to beat

Whether every P wave conducts with a constant PR interval

Dog (Recorded with Beecardia)

Male

Question

This tracing shows first-degree AV block. Which feature establishes that diagnosis?

Progressive PR-interval prolongation before a dropped QRS

Intermittently non-conducted P waves with an unchanged PR interval

A prolonged but constant PR interval with every P wave conducted

Cyclical shortening and lengthening of the P-P intervals with breathing

Cat - DMH (Recorded with Beecardia)

14 years • Male • Has not urinated in over 24 hours; an irregular heart rhythm was noted

Question

Is the first-degree AV block on this tracing an incidental finding, or a sign that requires urgent investigation?

It should raise concern for a metabolic disturbance and prompt immediate electrolyte testing.

It is a benign incidental finding and requires no further action.

It reflects primary AV-nodal disease and should prompt pacemaker evaluation.

It reflects lead artifact and should be disregarded until the recording is repeated.

Dog (Recorded with Beecardia)

8 years • Male • Receiving atenolol

Question

Which interpretation best fits this tracing?

Mobitz II second-degree AV block

Third-degree (complete) AV block

Sinus arrhythmia with a blocked atrial premature complex

Mobitz I (Wenckebach) second-degree AV block

Dog - Miniature Dachshund (Recorded with Beecardia)

11 years • Male

Question

Which interpretation best fits the AV conduction pattern shown on this tracing?

Third-degree (complete) AV block

Mobitz II second-degree AV block

Mobitz I (Wenckebach) second-degree AV block

Sinus arrhythmia with a blocked atrial premature complex

Cat - Persian X (Recorded with Beecardia)

13 years • Male • Presented for worsening hindlimb lameness with intermittent leg splaying and facial twitching over the past two days; proBNP was abnormal, prompting concern for neurologic disease versus early feline arterial thromboembolism and referral for neurology and echocardiography evaluation

Question

Which type of AV block best explains the conduction pattern on this tracing?

Mobitz I second-degree AV block

Third-degree AV block

Mobitz II second-degree AV block

First-degree AV block

Dog - Schnauzer (Recorded with Beecardia)

Female

Question

Which finding on this tracing rules out a blocked (non-conducted) P wave?

Narrow QRS complexes throughout the recording

A QRS after every P wave, with a constant PR interval

A heart rate within the normal canine range

P waves of constant morphology and rate

Dog - Pomeranian (Recorded with Beecardia)

13 years

Question

Which finding on this tracing rules out AV block?

Early, abnormally shaped P waves each conduct to their own QRS complex

A P wave arrives on schedule but is not followed by a QRS

Narrow QRS complexes with a normal mean electrical axis

Cyclic variation of the sinus rate with the respiratory cycle

Cat - Domestic Shorthair (Recorded with Beecardia)

13 years • Female • Hyperthyroid, medically managed. An arrhythmia was first noted about 9 months ago, with a heart rate around 120 bpm on auscultation and no murmur. Echocardiogram showed a structurally normal heart

Question

Which rhythm diagnosis best fits this tracing?

Third-degree AV block

High-grade second-degree AV block

Isorhythmic AV dissociation

Atrial tachycardia with 2:1 AV block

Cat - Domestic Shorthair (Recorded with Beecardia)

16 years • Male • Newly diagnosed diabetic with recent diabetic ketoacidosis. A bradyarrhythmia was noted on ECG, with concern for second- or third-degree AV block

Question

This cat has third-degree AV block maintained by an escape rhythm below the block. Which feature of the escape rhythm most influences how well the block is tolerated?

A faster atrial rate driving the P waves ensures adequate ventricular perfusion

An adequate-rate junctional escape rhythm is generally better tolerated than a slower ventricular escape rhythm

A wider QRS duration in the escape complexes indicates a more reliable pacemaker

A constant PR interval preceding the block predicts a favorable outcome

Quiz: AV Blocks

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Quiz: AV Blocks

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