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Therapeutic issues in STEMI :Persistent sinus tachycardia following thrombolysis

Posted Jun 16 2009 6:10pm

Sinus tachycardia in the early hours of STEMI is  a very common arrhythmia. This seemingly simple problem can be really worrisome to many cardiologists and give sleepless nights(While the patient may sleep comfortably !)

The importance of sinus tachycardia in STEMI  primarily lies in answering the following question

A.  Is it compensatory sinus tachycardia ?,  Where in  , the left ventricle is struggling to maintain the cardiac output and works more  per minute to maintain the vital cardiac index

Or

B. Is it a non compensatory -Inappropriate Sinus tachycardia?  It is a simple  response to heightened adrenergic tone  and   increased neural traffic from the injured ventricular myocardium . (or  high  baseline anxiety levels  )

It should be recalled , tachycardia in any form is  detrimental  following STEMI as it increases the MVo2 ie myocardial oxygen consumption. This is the reason ,  beta blockers are administered in this situation. Compensatory tachycardia  denotes , myocardium is working at it’s reserve capacity  , to prevent an  LVF that is impending .Hence ,  one should recognise , the compensatory tachycardia can not be  tampered  with ,  as we like ! .

How do you clinically differentiate a largely benign inappropriate tachycardia from potentially  harmful compensatory tachycardia ?

It is not an easy task.Heart rate  is typically around 120/mt   in  compensation to impending LVF.  While inappropriate tachycardia has no limits , it can exceed up to 140 or so . Further , tachycardia due to LV dysfunction has reduced variability.( Typically hovers around 120( +/- 5) .In stress or anxiety  heart rate  fluctuates  more .

Accompanying S3 suggest compensatory tachycardia . Even a few basal  crackles would make a diagnosis of  LVF .

The definite way to differentiate  could be   ( Also the dangerous way !  ) looking for  therapeutic worsening to beta blockers .

How to control the sinus tachycardia in STEMI ?

Beta blockers are  the  mainstay. Any of the beta blockers ,  metoprolol, atenolol, carvidilol can be used.Oral metoprolol up to 50 mg can be used. Beta blocker usage is primarily useful in non compensatory tacycardia. It should be  realised , the wide spread routine use of intravenous beta blockade has largely been discontinued as it has adverse outcome.The greatness of carvidilol,  in cardiac failure mainly applies to stable chronic cardiac failures. So ,  it is important to  recognise,  carvidilol can not be used liberally ,  in sinus tachycardia associated with impending or manifest LVF in STEMI.

* The potential source for tachycardia like dopamine,  dobutamine etc should be excluded.

Other options are

Digoxin ( Not withstanding the critics ,  it is still useful in acute MI with persistent sinus tachycardia ,The advantage is ,  it can be used without a need to differentiate whether it is compensatory or non compensatory!)

Ivabradine, a  wonder drug supposed to reduce selcetively  reduce the sinus rate without negative inotropic action could be tried.(Data lacking for this use )

Final message

Sinus tachycardia ,  may be seen as a simple arrhythmia .  but, the circumstances  in which it occurs , it’s mechanism and  the limited therapeutic options , narrow safety margin of beta blockers  , makes it a interesting clinical issue.

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