Mechanism:

• Slow diastolic depolarization of the sinus node

ECG characteristics:

• Sinus rhythm with a frequency of less than 60 per minute

Etiology:

• Sinus node syndrome, medication that may cause bradycardia, raised intracranial pressure, icterus, aortic stenosis, hypothyroidosis, acute myocardial infarction (posterior wall)
  
• Physiological in nature in cases of marked vagotonia

Treatment:

• If the patient is symptomatic, medications that increase cardiac frequency (e.g., atropine) or insertion of pacemaker
  
• Cessation of medication that may cause bradycardia (if possible)

Differential diagnosis:

• Sinus arrhythmia
  
• 2nd degree AV block (Mobitz/Wenckebach)
  
• Bradycardic atrial fibrillation with fibrillation waves (f) of low amplitude

Differential diagnosis:

• Sinus arrhythmia
  
• 2nd degree AV block with 2:1 block (Mobitz/Wenckebach)
  
• Bradycardic atrial fibrillation with fibrillation waves (f) of low amplitude

Mechanism:

• Physiological and respiration-dependent fluctuation of the frequency of the sinus node

ECG characteristics:

• Continuous transition between decrease and increase of the time interval between P waves; no pauses

Etiology:

• Physiological in nature

Treatment:

• none

Mechanism:

• The basic rhythm is influenced by extrasystole; following an SVES, diastolic depolarization of the sinus node is extinguished (reset) and begins anew

ECG characteristics:

• Noncompensatory pause; sum of the PP intervals of two normal beats > sum of PP intervals before and after the pause

Etiology:

• Often physiological in nature, otherwise in degenerative and inflammatory heart disease; heart defects

Treatment:

• none

Mechanism:

• In sinus bradycardia the “too slow” sinus node can be “overtaken” by a faster focus

ECG characteristics:

• From “wandering” of the P wave into the QRS complex to complete amalgamation of the P wave and the QRS complex

Etiology:

• Sinus node syndrome
  
• Medication that may cause bradycardia
  
• In marked vagotonia

Treatment:

• As a rule not necessary
  
• Cessation of medicines that may cause bradycardia

Differential diagnosis:

• Sinus bradycardia (P wave present)
  
• Bradycardic atrial fibrillation with fibrillation waves (f) of low amplitude
  
• Higher-grade AV block (P wave present)

• Intermittent sinus bradycardia with occurrence of escape rhythm, the atria are charged by the sinus node, the ventricles by the escape focus

ECG characteristics:

• “Pause with no P wave” bridged by narrow QRS complex
  
• Projection of the P wave into the ST segment

Etiology:

• Almost exclusively sinus node syndrome
  
• Medication that may cause bradycardia

Treatment:

• Cessation of medicines that may cause bradycardia
  
• As a rule no indication for pacemaker

Differential diagnosis:

• Sinus bradycardia (P wave present), 2nd degree SA block (no P wave)
  
• Bradycardic atrial fibrillation with fibrillation waves (f) of low amplitude
  
• Higher-grade AV block

Mechanism:

• Single intermittent interruption of impulse formation in the sinus node

ECG characteristics:

• “Pause with no P wave”
  
• Absence of a sinus P wave with shorting of the PP intervals
  
• Length of pause < 2 × PP interval

Etiology:

• Often physiological, otherwise in the context of SSS, CHD, CMP, heart defects, hypertension, medication

Treatment:

• None in asymptomatic patients
  
• Cessation of medicines that may cause bradycardia in symptomatic patients and possibly insertion of a pacemaker in case of “severe” symptoms