Arrhythmia Recognition: The Art of Interpretation

A rhythm strip from lead V1 shows a sharp dip of the QRS complex, with small and subtle peaks of the P waves on its either side, marked with dots. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: About 240–250 BPM Ventricular: About 120 BPM	PR intervals: Variable
Regularity: Regular	QRS width: Normal
P waves: Present Morphology: Upright in lead V₁ Axis: Unknown	Grouping: None
	Dropped beats: Yes
P:QRS ratio: 2:1	Rhythm: Focal atrial tachycardia with block

Discussion:

ECG 16-1 was taken in lead V₁. Lead II was useless in this patient. This is a focal AT with a 2:1 AV block. The atrial and ventricular cadence is regular throughout the strip. The QRS complexes are normal morphology and there is some slight alteration in amplitude consistent with tachycardia-related electrical alternans. The blue dots represent P waves.

ECG 16-2

A rhythm strip from lead 2 shows a small dip of the P wave, a sharp peak of the QR wave, a small peak of the S wave, a small dip of the P wave, and a wide and curved peak of the T wave. The P waves are marked with dots. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: About 145 BPM Ventricular: About 72 BPM	PR intervals: Regular
Regularity: Regular	QRS width: Normal; 0.11 seconds
P waves: Present Morphology: Inverted Axis: Abnormal	Grouping: None
P waves: Present Morphology: Inverted Axis: Abnormal	Dropped beats: Yes
P:QRS ratio: 2:1	Rhythm: Focal atrial tachycardia with block

Discussion:

At first glance, ECG 16-2 appears to be a sinus rhythm with a very prolonged PR interval. However, notice that the P waves (represented by the blue dots) are inverted. That means that the P waves are ectopic. As mentioned in the Clinical Pearl, when the PR interval is very prolonged you should look for a buried P wave. There definitely is a buried P wave right after the terminal S wave of the QRS complex. Notice that, in this case, lead II was the best lead to see the P waves.

ECG 16-3

A rhythm strip from lead V1 shows small, sharp peaks of P waves marked with dots, on either side of the sharp dip of the QRS complex. There are fluctuations between two P waves occurring at every third cycle. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: Slightly over 200 BPM Ventricular: About 120 BPM	PR intervals: Variable
Regularity: Regularly irregular	QRS width: Normal
P waves: Present Morphology: Upright in lead V₁ Axis: Unknown	Grouping: None
	Dropped beats: Yes
P:QRS ratio: Variable	Rhythm: Focal atrial tachycardia with block

Discussion:

The ECG 16-3 was taken in lead V₁. The P waves occur with a regular cadence, but the ventricular response is irregular due to the variable AV block. There is a return to the baseline in the segments between the P waves, as expected in a focal AT with block. There is some electrical alternans noted, most probably due to the tachycardia itself. Note that the QRS morphology is altered slightly because of the fusion that is occurring with the P waves.

ECG 16-4

A rhythm strip from lead 2 shows sharp peaks corresponding to QRS complex. Between two complexes, there are four to five small and subtle peaks corresponding to P waves, marked with dots. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: About 200 BPM Ventricular: About 45 BPM	PR intervals: Variable
Regularity: Regular	QRS width: Normal
P waves: Present Morphology: Upright Axis: Normal	Grouping: None
P waves: Present Morphology: Upright Axis: Normal	Dropped beats: Yes
P:QRS ratio: Variable	Rhythm: Focal atrial tachycardia with block

Discussion:

ECG 16-4 is the first one we have shown you with a third-degree heart block. Up to now, the strips have shown either Type II second-degree or variable AV block. The way you can tell is that the QRS complexes are regular and narrow but completely dissociated from the P waves. You would describe this strip as follows: This is a focal AT at a rate of about 200 BPM associated with a complete third-degree heart block and a junctional escape rhythm at a rate of about 45 BPM.

ECG 16-5

A rhythm strip from lead 2 shows small dips, each divided into two, corresponding to QRS complex. Between two consecutive dips are three small and subtle dips, corresponding to P waves, marked with dots. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: About 150 BPM Ventricular: About 55 BPM	PR intervals: Variable
Regularity: Regular	QRS width: Normal
P waves: Present Morphology: Upright Axis: Normal	Grouping: None
P waves: Present Morphology: Upright Axis: Normal	Dropped beats: Yes
P:QRS ratio: Variable	Rhythm: Focal atrial tachycardia with block

Discussion:

ECG 16-5 also shows a complete third-degree heart block with a regular ventricular response. The QRS complexes are within acceptable limits for width in lead II, so a junctional escape rhythm is likely. However, to be completely sure that these are not ventricular complexes, you will need to measure the width of the complexes in the other leads. If any exceed 0.12 seconds, then you would have a ventricular escape rhythm.

ECG 16-6

A rhythm strip from lead V1 shows sharp peaks of QRS complex, which fall gradually to the baseline. There are three to four small and wide peaks corresponding to P waves, marked with dots, between the QRS complexes. — From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

Rate: Atrial: About 160 BPM Ventricular: About 45 BPM	PR intervals: Variable
Regularity: Regular	QRS width: Normal
P waves: Present Morphology: Upright Axis: Unknown	Grouping: None
P waves: Present Morphology: Upright Axis: Unknown	Dropped beats: Yes
P:QRS ratio: Variable	Rhythm: Focal atrial tachycardia with block

Discussion:

ECG 16-6 is a focal AT with a third-degree heart block and a junctional escape. Take special notice of the ST segment elevation in lead V₁. This is grossly abnormal. It is not due to the buried P waves, as they are buried in the ST segments only in the first and third QRS complexes. Notice that the second and fourth T waves are pointier and taller than the others due to the fusion with the P waves. The cause of the arrhythmia in this patient is probably an acute myocardial infarction. Get a 12-lead ECG . . . stat!