Thread by @ToxTalks, Use of hydroxychloroquine for #COVID19 has made QT prolongation topicalso how do [...]

Use of hydroxychloroquine for #COVID19 has made QT prolongation topical

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">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-wave

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">time taken for myocardial tissue to repolarise

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">phase 3 of the action potential

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">due to outward flow of K+ blockage of K+ channels by drugs/toxins can

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">

https://abs.twimg.com/emoji/v2/... draggable="false" alt="⬇️" title="Downwards arrow" aria-label="Emoji: Downwards arrow">K+ flow

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">prolongs phase 3

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">QT prolongation

2.QT interval=beginning of q-wave to end of t-wavehttps://abs.twimg.com/emoji/v2/... draggable=

3.Upward rises in voltage can -early after depolarisations-can occur during phase 3 if prolonged

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">potentially triggers ectopic beat

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">ventricular arrhythmia if sustained classically TdP more here https://pubmed.ncbi.nlm.nih.gov/14999113/ ">https://pubmed.ncbi.nlm.nih.gov/14999113/...

3.Upward rises in voltage can -early after depolarisations-can occur during phase 3 if prolongedhttps://abs.twimg.com/emoji/v2/... draggable=

potentially triggers ectopic beathttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">ventricular arrhythmia if sustained classically TdP more here https://pubmed.ncbi.nlm.nih.gov/14999113/..." title="3.Upward rises in voltage can -early after depolarisations-can occur during phase 3 if prolongedhttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">potentially triggers ectopic beathttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">ventricular arrhythmia if sustained classically TdP more here https://pubmed.ncbi.nlm.nih.gov/14999113/..." class="img-responsive" style="max-width:100%;"/>

4. QT varies with heart rate

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">to standardise to 60 bpm machine calculates QTc,most common formula used is Bazzett’s BUT

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow"> only accurate over HRs of 50-80 bpm

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">underestimates QT at low heart rates AND

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">overestimates at higher heart rates

5.quetiapine is a common poisoning which rarely/never causes TdP but is known to prolong QTc in overdose

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">this is spurious and secondary to tachycardia from anticholinergic effects of quetiapine https://pubmed.ncbi.nlm.nih.gov/14634598 ">https://pubmed.ncbi.nlm.nih.gov/14634598&...

Quetiapine Poisoning: A Case Series - PubMed

Quetiapine overdose causes central nervous system depression and sinus tachycardia. In large overdoses, patients may require intubation and ventilation for associated respiratory depression. Although...

https://pubmed.ncbi.nlm.nih.gov/14634598

6.automatically calculated QT measures can also be inaccurate when t-wave flat

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">may not pick return to baseline accurately

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">underestimates QT interval, critical difference illustrated below

6.automatically calculated QT measures can also be inaccurate when t-wave flathttps://abs.twimg.com/emoji/v2/... draggable=

may not pick return to baseline accuratelyhttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">underestimates QT interval, critical difference illustrated below" title="6.automatically calculated QT measures can also be inaccurate when t-wave flathttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">may not pick return to baseline accuratelyhttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">underestimates 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 ">https://pubmed.ncbi.nlm.nih.gov/17881416&...

8.This #FOAMTox review covers the topic well,image shows nomogram findings with specific drugs/poisonings

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">no/minimal risk for droperidol/quetiapine

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">much higher risk with amisulpride

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">known to be torsadogenic in overdose https://pubmed.ncbi.nlm.nih.gov/23167578 ">https://pubmed.ncbi.nlm.nih.gov/23167578&...

8.This #FOAMTox review covers the topic well,image shows nomogram findings with specific drugs/poisoningshttps://abs.twimg.com/emoji/v2/... draggable=

no/minimal risk for droperidol/quetiapinehttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">much higher risk with amisulpridehttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">known to be torsadogenic in overdose https://pubmed.ncbi.nlm.nih.gov/23167578&..." title="8.This #FOAMTox review covers the topic well,image shows nomogram findings with specific drugs/poisoningshttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">no/minimal risk for droperidol/quetiapinehttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">much higher risk with amisulpridehttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">known to be torsadogenic in overdose https://pubmed.ncbi.nlm.nih.gov/23167578&..." class="img-responsive" style="max-width:100%;"/>

9. You may have heard of the half R-R rule…not recommended as a risk assessment tool

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">false +ve’s and false -ve’s

https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">worst of both worlds, nicely illustrated in this study https://pubmed.ncbi.nlm.nih.gov/26375169 ">https://pubmed.ncbi.nlm.nih.gov/26375169&...

9. You may have heard of the half R-R rule…not recommended as a risk assessment toolhttps://abs.twimg.com/emoji/v2/... draggable=

false +ve’s and false -ve’shttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">worst of both worlds, nicely illustrated in this study https://pubmed.ncbi.nlm.nih.gov/26375169&..." title="9. You may have heard of the half R-R rule…not recommended as a risk assessment toolhttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">false +ve’s and false -ve’shttps://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Rightwards arrow" aria-label="Emoji: Rightwards arrow">worst 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

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