Does an irregular cardiovascular (CV) reading imply both an irregular rate and rhythm?

Irregular CV Reading Indicates Irregular Rhythm but Not Necessarily Irregular Rate

When a cardiovascular (CV) reading is described as "irregular," this specifically refers to an irregular rhythm, not necessarily an irregular rate. 1

Understanding Irregular Rhythm

• An irregular rhythm is characterized by "absolutely" irregular RR intervals (sometimes called arrhythmia absoluta), meaning the RR intervals do not follow a repetitive pattern 1
• The most common cause of an irregular rhythm is atrial fibrillation (AF), which is defined by uncoordinated atrial electrical activation resulting in ineffective atrial contraction 1
• When evaluating a tachycardia on ECG, the first classification should be whether the ventricular rate is regular or irregular 1

Distinguishing Rate from Rhythm

• Rate refers to the frequency of heartbeats (expressed as beats per minute), while rhythm refers to the pattern of intervals between beats 1
• A patient can have:
  • Regular rhythm with normal rate (normal sinus rhythm)
  • Regular rhythm with fast rate (regular tachycardia)
  • Regular rhythm with slow rate (bradycardia)
  • Irregular rhythm with normal average rate
  • Irregular rhythm with fast average rate (irregular tachycardia)
  • Irregular rhythm with slow average rate 1

Common Irregular Rhythms

• Atrial fibrillation (AF) - characterized by irregularly irregular RR intervals, absence of distinct P waves, and irregular atrial activations 1
• Multifocal atrial tachycardia (MAT) - irregular rhythm with variable P wave morphology 1
• Atrial flutter with variable AV conduction - can present with irregular ventricular response 1
• Frequent premature ventricular contractions (PVCs) - can create an irregular rhythm pattern 1

Clinical Significance of Irregular Rhythm

• An irregular sequence of RR intervals produces adverse hemodynamic consequences independent of heart rate, including:
  • Decreased cardiac output compared to regular rhythm at the same average rate 2
  • Increased pulmonary capillary wedge pressure 2
  • Increased right atrial pressure 2
• Irregular rhythms are associated with increased sympathetic nerve activity, which may contribute to adverse cardiovascular effects 3, 4
• Greater degrees of irregularity cause greater sympathoexcitation, independent of hemodynamic changes 4

Diagnostic Considerations

• When encountering an irregular rhythm on ECG, further evaluation should determine if it's a supraventricular or ventricular arrhythmia 1
• An irregular narrow-complex tachycardia is most likely atrial fibrillation with uncontrolled ventricular response 1
• An irregular wide-complex tachycardia may represent atrial fibrillation with aberrancy, pre-excited atrial fibrillation, or polymorphic ventricular tachycardia 1
• Short irregular supraventricular tachycardias without P waves may represent early stages of atrial fibrillation and are associated with increased risk of stroke 5

In conclusion, when a CV reading is described as "irregular," this primarily refers to the rhythm (pattern of intervals between beats) being irregular, while the rate (frequency of beats per minute) may be normal, elevated, or reduced.