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Monitoring Ventricular Repolarization With QTc Interval During Antipsychotic Therapy in Patients With Ventricular Conduction Abnormalities

TO THE EDITOR: Ventricular conduction delays and repolarization abnormalities have characteristic electrocardiogram changes, including a lengthened QT interval.¹ Antipsychotics are known to lengthen the QT interval on electrocardiogram, likely by delaying repolarization.^2,3 The QT interval (if corrected for heart rate, the QTc interval), is composed of the QRS complex and the JT interval. The QRS complex largely represents ventricular depolarization; repolarization is demonstrated by the JT interval.⁴

Ventricular conduction abnormalities (also referred to as left and right bundle-branch blocks) are common, particularly in patients with coronary artery disease, congestive heart failure, or history of myocardial infarction.⁵ Patients with conduction abnormalities often have widened (>0.12 sec) QRS complexes on electrocardiogram. Because the QRS complex is included in the QTc measurement, a widened QRS complex lengthens the QTc. Patients with conduction abnormalities may have baseline QTc intervals that are borderline (0.42 sec–0.45 sec) or prolonged (>0.45 sec), complicating risk assessment and clinical judgment.^2,6 Repolarization measurement is important because delayed repolarization increases the risk of developing arrhythmias.²

Several formulas precisely define repolarization time; however a clinically useful formula:

JTc=QTc – QRS closely approximates ventricular repolarization time.⁵ Data from Piotrowicz et al.⁵ show that, in patients with conduction abnormalities, a JTc interval >360 msec is a practical cutoff in identifying prolonged repolarization, a value helpful in risk stratification. This study evaluated prognostic significance of repolarization abnormalities in post-myocardial infarction patients and did not specifically assess drug-induced repolarization abnormalities. However, this tool for measuring repolarization may prove useful in future research relating to antipsychotic-induced interval prolongation in patients with ventricular conduction abnormalities.

REFERENCES

1. Marriot HJL: Practical Electrocardiography, 7th Edition. Baltimore, MD, Williams & Wilkins, 1983
2. Zareba W, Lin DA: Antipsychotic drugs and QT interval prolongation. Psychiatr Q 2003; 74:291–306[CrossRef][Medline]
3. Glassman AH, Bigger JT Jr: Antipsychotic drugs: prolonged QTc interval, torsades de pointes, and sudden death. Am J Psychiatry 2001; 158:1774–1782[Abstract/Free Full Text]
4. Zhou SH, Wong S, Rautahatju PM, et al: Should the JT rather than the QT interval be used to detect prolongation of ventricular repolarization? J Electrocardiol 1992; 25 (suppl):131-136
5. Piotrowicz K, Zareba W, Mcnitt S, et al: Repolarization duration in patients with conduction disturbances after myocardial infarction. Am J Cardiol 2007; 99:163–168[CrossRef][Medline]
6. Das G: QT interval and repolarization time in patients with intraventricular conduction delay. J Electrocardiol 1990; 23:49–52[CrossRef][Medline]

Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Email this article to a Colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to My Articles & Searches Download to citation manager Articles by Cerimele, J. PubMed Citation Articles by Cerimele, J. Syndromes Secondary to General Medical Disorders

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