Arrhythmia Recognition: The Art of Interpretation

A rhythm strip from lead 2 illustrates sinus rhythm with a PAC.

Rate: About 75 BPM	PR intervals: Different in event
Regularity: Regular with an event	QRS width: Normal
P waves: Present Morphology: Normal Axis: Normal	Grouping: None
P waves: Present Morphology: Normal Axis: Normal	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus rhythm with a PAC

Discussion:

ECG 13-1 shows a nice, regular sinus rhythm temporarily broken by one PAC. Notice that the third complex arrives earlier than expected and has a different P-wave morphology and PR interval. This meets all of the criteria for a PAC. If you use your calipers, you will notice that this is one of those instances when a PAC is associated with a full compensatory pause.

ECG 13-2

A rhythm strip from lead 2 illustrates sinus bradycardia with a PAC.

Rate: About 30 BPM	PR intervals: Different in event
Regularity: Regular with an event	QRS width: Normal
P waves: Present Morphology: Normal Axis: Normal	Grouping: None
P waves: Present Morphology: Normal Axis: Normal	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus bradycardia with a PAC

Discussion:

In ECG 13-2 we have a pretty intense sinus bradycardia as the underlying rhythm. The third complex is a PAC. This is easily identifiable by the different P-wave morphology, the different PR interval, the early arrival, and the noncompensatory pause. The cause for the serious bradycardia is probably infarct related. Notice the severe, flat ST depressions present in the complexes. You should get an ECG immediately on this patient and get ready to do some emergency pacing.

ECG 13-3

Rate: About 40 BPM	PR intervals: Different in event
Regularity: Regular with an event	QRS width: Normal
P waves: Present Morphology: Inverted in event Axis: Abnormal in event	Grouping: None
	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus bradycardia with a PAC

Discussion:

ECG 13-3 shows a sinus bradycardia with a single PAC. The PAC is the third complex on the strip. Notice the inverted P wave and the early timing of this complex. This PAC is associated with a full compensatory pause.

ECG 13-4

Rate: About 55 BPM	PR intervals: Different in event
Regularity: Regular with an event	QRS width: Normal
P waves: Present Morphology: Different in event Axis: Normal	Grouping: None
	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus bradycardia with a PAC

Discussion:

ECG 13-4 also shows a sinus bradycardia associated with one PAC; however, the findings are much more subtle. At first glance, it appears to be a regular rhythm, but using your calipers, it soon becomes apparent that the third complex is a PAC. Note the differing morphology and PR interval of this complex. The pause is also a noncompensatory pause, as would be expected. Do not confuse this rhythm with a sinus arrhythmia. A longer strip would be helpful in isolating the abnormality.

ECG 13-5

A rhythm strip from lead 2 illustrates sinus tachycardia with frequent PACs.

Rate: About 120 BPM	PR intervals: Normal, consistent
Regularity: Regular with multiple events	QRS width: Normal
P waves: Present Morphology: Inverted in event Axis: Abnormal in event	Grouping: None
	Dropped beats: None
P:QRS ratio: 1:1	Rhythm: Sinus tachycardia with frequent PACs

Discussion:

ECG 13-5 shows a sinus tachycardia at about 120 BPM associated with frequent PACs. They actually occur every fourth beat, making this a supraventricular quadrigeminy, to be exact. Either terminology is correct with this type of rhythm. Notice the inverted P waves associated with the PACs and the compensatory pauses.

ECG 13-6

Rate: A little over 100 BPM	PR intervals: Different in event
Regularity: Regular with multiple events	QRS width: Normal
P waves: Present Morphology: Different in event Axis: Not applicable	Grouping: None
	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus tachycardia with frequent PACs

Discussion:

This poor patient is having one heck of an acute myocardial infarction (AMI) with that much ST elevation! The underlying rhythm in ECG 13-6 is sinus tachycardia associated with frequent PACs. The PACs are probably due to the myocardial irritability from the AMI, but other possibilities need to be ruled out. For example, drugs, hypoxemia, and congestive heart failure must be ruled out and treated accordingly. Remember, you need to treat the underlying cause of the PACs, not the PACs themselves, in this case.

ECG 13-7

A rhythm strip from lead 2 illustrates sinus rhythm with frequent PACs.

Rate: A bit over 60 BPM	PR intervals: Different in event
Regularity: Regular with multiple events	QRS width: Normal
P waves: Present Morphology: Different in event Axis: Normal	Grouping: None
	Dropped beats: Present
P:QRS ratio: 1:1	Rhythm: Sinus rhythm with frequent PACs

Discussion:

ECG 13-7 shows NSR with frequent PACs. This is, in actuality, supraventricular trigeminy with every third beat being a PAC. Once again, be careful of calling this a sinus arrhythmia or, as we shall study later on, a second-degree AV block.

ECG 13-8

Rate: Slightly over 60 BPM	PR intervals: Different in event
Regularity: Regular with multiple events	QRS width: Normal
P waves: Present Morphology: Different in event Axis: Normal	Grouping: None
	Dropped beats: None
P:QRS ratio: 1:1	Rhythm: Sinus rhythm with frequent PACs

Discussion:

What do you call the rhythm in ECG 13-8? Every other beat is a PAC. You can easily call it sinus rhythm with frequent PACs and be perfectly correct. But, the more appropriate diagnosis is sinus rhythm with supraventricular bigeminy due to PACs. When you are confronted with this type of rhythm, you obtain the rate by multiplying the number of complexes in a 6-second strip by 10.