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Use of hydroxychloroquine for #COVID19 has made QT prolongation topical
so how do we approach assessment of this in ED/acute care environment? #Tweetorial #ToxicTweetTale #QTprolongation
so how do we approach assessment of this in ED/acute care environment? #Tweetorial #ToxicTweetTale #QTprolongation
2.QT interval=beginning of q-wave to end of t-wavetime taken for myocardial tissue to repolarisephase 3 of the action potentialdue to outward flow of K+ blockage of K+ channels by drugs/toxins can
K+ flowprolongs phase 3QT prolongation
time taken for myocardial tissue to repolarisephase 3 of the action potentialdue to outward flow of K+ blockage of K+ channels by drugs/toxins canK+ flowprolongs phase 3QT prolongation
3.Upward rises in voltage can -early after depolarisations-can occur during phase 3 if prolongedpotentially triggers ectopic beatventricular arrhythmia if sustained classically TdP more here https://pubmed.ncbi.nlm.nih.gov/14999113/
potentially triggers ectopic beatventricular arrhythmia if sustained classically TdP more here https://pubmed.ncbi.nlm.nih.gov/14999113/
4. QT varies with heart rateto standardise to 60 bpm machine calculates QTc,most common formula used is Bazzett’s BUT only accurate over HRs of 50-80 bpmunderestimates QT at low heart rates ANDoverestimates at higher heart rates
to standardise to 60 bpm machine calculates QTc,most common formula used is Bazzett’s BUT only accurate over HRs of 50-80 bpmunderestimates QT at low heart rates ANDoverestimates at higher heart rates
5.quetiapine is a common poisoning which rarely/never causes TdP but is known to prolong QTc in overdosethis is spurious and secondary to tachycardia from anticholinergic effects of quetiapine https://pubmed.ncbi.nlm.nih.gov/14634598
this is spurious and secondary to tachycardia from anticholinergic effects of quetiapine https://pubmed.ncbi.nlm.nih.gov/14634598
6.automatically calculated QT measures can also be inaccurate when t-wave flatmay not pick return to baseline accuratelyunderestimates QT interval, critical difference illustrated below
may not pick return to baseline accuratelyunderestimates QT interval, critical difference illustrated below
7.The QT nomogram outperforms QTc as a risk assessment tool and is the method of choice for assessing at risk QT for toxins, images below show nomogram and how to use https://pubmed.ncbi.nlm.nih.gov/17881416
8.This #FOAMTox review covers the topic well,image shows nomogram findings with specific drugs/poisoningsno/minimal risk for droperidol/quetiapinemuch higher risk with amisulprideknown to be torsadogenic in overdose https://pubmed.ncbi.nlm.nih.gov/23167578
no/minimal risk for droperidol/quetiapinemuch higher risk with amisulprideknown to be torsadogenic in overdose https://pubmed.ncbi.nlm.nih.gov/23167578
9. You may have heard of the half R-R rule…not recommended as a risk assessment toolfalse +ve’s and false -ve’sworst of both worlds, nicely illustrated in this study https://pubmed.ncbi.nlm.nih.gov/26375169
false +ve’s and false -ve’sworst of both worlds, nicely illustrated in this study https://pubmed.ncbi.nlm.nih.gov/26375169
10. Management of long QT is another topic but in poisoning centres around correcting reversible causes eg low Mg2+,K+levels, stopping offending agent and cardiac monitoring until 12 lead ECG HR/QT pairs below nomogram risk line
