Dr.S.Venkatesan MD

Holter monitoring is the Initial test for all those with documented  syncope (or Pre syncope ) with suspected cardiac arrhythmia .It is a 24 hour ambulatory  ECG monitoring , expected to pick up any electrical abnormality and its correlation with the resultant symptom if any. Though the test looks  attractive , the diagnostic yield is far less. (About 10%) .The reason being the episodes can be rare  to be  missed by 24hr sample time. We have extended Holter (48hr) , Event monitors , Loop recorders and implantable devices that can record ECG for extended periods.(18 Months ,Reveal Plus Medtronic)  that improve the yield  up to 45%.

One common issue that often confuse us  while reporting  Holter is, the  pauses that occur during day / night .

What is the significance of these pauses * ?  Nocturnal vs Daytime

Pauses are obviously significant when the patient is awake . It is generally accepted pauses more than 3 seconds during day time  (ie Heart rate of < 20/mt ) is significant . This is logical , as pauses more than that,  is expected to cause syncope ( or atleast pre-syncope ).The problem comes when you document pauses more than 3 seconds without any symptoms . Then this  difficult  question comes up ,At what degree of pause syncope occurs ? How is that some persons mange  even prolonged pauses with just giddiness.(Good overall vascular integrity and tone ! )

We know such pauses are  especially  common during sleep. How does the brain react when pauses occur  during sleep ? as there is no question of fall as such and loss of muscle tone is non existing.

*Please note ,when we say pause we mean only Sinus pause , Pauses due to AV blocks are very significant

Source : Brodsky M, Wu D, Denes P,et al.Am J Cardiol 1977; .

Dramatic  pauses during sleep do occur

There has been prolonged pauses reported  during sleep without fatality . A 35 second nocturnal pause resulting in seizures has been documented by implantable  recorders.(Mairesse 2003)

Causes for prolonged pauses

• Sinus node dysfunction
• Obstructive sleep apnea
• High dose beta blockers therapy

Final message

 Most bradycardic episodes during sleep are benign.This is due to depressed autonomic control during sleep. Holter interpretation is primarily done with  awake rhythm data in most individuals .So, empirically shall we fix a  5 second pause as significant during sleep ? We don’t know.While this may seem applicable even with structural heart disease , one may be vigilant while interpreting the nocturnal pauses in this population .

Caution

** Please note,  all these rhythm monitoring extravaganza is meant for people  with equivocal symptoms .Patients  with well documented syncope with ECG features suggestive of  cardiac rhythm disorders would never require these tests and go for pacemaker straightaway.

Reference

3.Clinical relevance of arrhythmias during sleep: guidance for clinicians L J Gula, A D Krahn, A C Skanes, Heart. 2004 Mar; 90(3): 347–352

4.Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease. Brodsky M, Wu D, Denes P,et al.Am J Cardiol 1977;39:390–5.

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