HeartCalc / QTc

QTc and LQTS Score Experimental

Four QT corrections side by side, pediatric reference context, and the Schwartz 1993–2011 points score

Patient

Age years Sex

Age selects the pediatric reference context (children 6 years or younger in Phan 2015). Sex matters for the 450–459 ms score item. Nothing is saved or sent.

ECG measurement

QT interval ms

Rate entered asNo default: pick one

Heart rate (bpm) RR interval (ms)

Measure QT in lead II or V5, from QRS onset to T-wave end, excluding U waves. In sinus arrhythmia, a single heart rate averages over beats; the RR immediately before the measured QT is more specific.

QTc, Bazett

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Schwartz score

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Low ≤1
Intermediate 1.5–3
High ≥3.5

Model, equations and sources

QT corrections (QT and QTc in ms; RR in seconds = 60 / HR)

Bazett       QTc = QT / RR^(1/2)
Fridericia   QTc = QT / RR^(1/3)
Framingham   QTc = QT + 154 x (1 - RR)      [Sagie 1992: QT + 0.154 (1 - RR), all in seconds]
Hodges       QTc = QT + 1.75 x (HR - 60)    [HR in beats/min]
All four equal QT at RR = 1 s (HR 60).

Framingham: Sagie et al., 5,018 Framingham Heart Study adults aged 28–62 (abstract retrieved). Its constant 0.154 is in seconds; mixing seconds and milliseconds gives a near-zero correction.
Hodges: formula as printed in Phan 2015. The original Hodges 1983 abstract was not retrieved [unverified as to original wording].
Bazett and Fridericia are the standard exponent forms (Phan 2015 describes them as QT/RR^e, e = 0.5 and 0.33). The 1920 originals were not retrieved.

Pediatric reference context

Phan 2015 (702 children ≤6 y, mean age 26 months, mean HR 122 bpm): Bazett gave the most consistent correction across heart rates (QTc-RR slope −0.019). A Bazett QTc >460 ms was 2 SD above the mean; the matching values were 414 ms (Fridericia) and 443 ms (Hodges). The page shows these only for age ≤6 years.
Phan's Framingham value (353 ms) is not shown: its Framingham QTc values (overall low of 217 ms) could not be reconciled with the Sagie formula in seconds.
Saarel 2018 (PHN, 2,400 healthy children, digital ECGs): QTc in lead II differed by sex and race; from age 3 years girls' mean QTc (Bazett) was 5–10 ms longer than boys'; under 3 years the 98th percentile reached 464 ms in one race group. Its age, sex and race tables are not reproduced here (AHA copyright).
Formula choice changes "prolonged": state the formula with any QTc you report.

Schwartz score (Schwartz & Crotti 2011, Table 2: "1993–2011 LQTS Diagnostic Criteria")

Item	Points
QTc (Bazett) ≥480 ms	3
QTc 460–479 ms	2
QTc 450–459 ms (in males)	1
QTc 4th minute of recovery from exercise stress test ≥480 ms	1
Torsade de pointes (mutually exclusive with syncope)	2
T-wave alternans	1
Notched T wave in 3 leads	1
Low heart rate for age (resting HR below the 2nd percentile for age)	0.5
Syncope with stress / without stress (mutually exclusive with TdP)	2 / 1
Congenital deafness	0.5
Family members with definite LQTS	1
Unexplained sudden cardiac death below age 30 among immediate family members	0.5

ECG findings count only "in the absence of medications or disorders known to affect these electrocardiographic features". The same family member cannot be counted in both family items.
Score: ≤1 point low probability; 1.5 to 3 points intermediate; ≥3.5 points high probability of LQTS.
The 4th-minute recovery item was added in 2011; the editorial adopted a 480 ms cut-off (the source study, Sy et al., found an optimal cut-off of 445 ms). The 1993 version (Schwartz, Moss, Vincent, Crampton) did not include it.
When TdP and syncope are both ticked, this page counts the higher-scoring of the two (an interpretation of "mutually exclusive").
"Low heart rate for age" needs an age-specific heart-rate reference that this page does not provide.

References

Phan DQ, Silka MJ, Lan YT, Chang RK. Comparison of formulas for calculation of the corrected QT interval in infants and young children. J Pediatr 2015;166(4):960-964.e2. doi:10.1016/j.jpeds.2014.12.037 (full text, PMC4380641)
Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol 1992;70(7):797-801. doi:10.1016/0002-9149(92)90562-d
Schwartz PJ, Crotti L. QTc behavior during exercise and genetic testing for the long-QT syndrome. Circulation 2011;124(20):2181-2184. doi:10.1161/CIRCULATIONAHA.111.062182 (Table 2)
Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria for the long QT syndrome: an update. Circulation 1993;88(2):782-784. doi:10.1161/01.cir.88.2.782 (not retrieved)
Saarel EV, Granger S, Kaltman JR, et al. Electrocardiograms in healthy North American children in the digital age. Circ Arrhythm Electrophysiol 2018;11(7):e005808. doi:10.1161/CIRCEP.117.005808
Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV. Circulation 2009;119(10):e241-e250. doi:10.1161/CIRCULATIONAHA.108.191096 (not retrieved; cited for context only)

The Schwartz score estimates the probability of LQTS from clinical findings. It does not replace genetic testing, repeated ECGs or specialist review.

Experimental. Check every result against the primary references.