Source: https://guthlabs.ai/docs/instruments/qtc-interval-calculator-education/mechanism/

instrument mechanism / verified-clean

# QTc Interval Calculator (education) mechanism

The inspectable method record for QTc Interval Calculator (education), kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The mathematical formulas are standard, but the specification needs an explicit input contract for heart rate versus RR, a required unit/conversion rule, valid ranges, and defined QTc reference thresholds. The existing educational/not-medical-advice label is appropriate and should remain prominent; QTc output must not be presented as a clinical interpretation.

- The Bazett and Fridericia formulas are standard when QT and RR are expressed in the same time units, but the specification does not define how a heart-rate input is converted to RR.

- The output claims a prolonged-flag reference, but no threshold definition is provided; thresholds can depend on sex, age, methodology, and clinical convention.

## Units and conventions

- QT and RR must use the same time unit; using milliseconds for both is valid because the ratio is dimensionless, and the resulting QTc is reported in milliseconds.

- If heart rate is supplied in beats per minute, RR must be calculated as RR(ms)=60000/heart_rate or RR(s)=60/heart_rate before applying either formula.

- The square-root and cube-root operations apply to the dimensionless RR ratio after normalizing RR to 1 second: Bazett QTc=QT(s)/sqrt(RR(s)) and Fridericia QTc=QT(s)/RR(s)^(1/3).

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "QT_ms": 400,
    "RR_ms": 1000
  },
  "expected_outputs": {
    "QTc_Bazett_ms": 400,
    "QTc_Fridericia_ms": 400
  },
  "working": "Convert: QT=400 ms=0.400 s; RR=1000 ms=1.000 s. Bazett: 0.400/sqrt(1.000)=0.400/1.000=0.400 s=400 ms. Fridericia: 0.400/(1.000)^(1/3)=0.400/1.000=0.400 s=400 ms."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The zero-RR input produces undefined results and must be rejected. The specification also leaves QT/RR unit conventions and prolonged-reference thresholds insufficiently defined, allowing materially different results or an indeterminate prolonged flag.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/qtc-interval-calculator-education/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/qtc-interval-calculator-education/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/qtc-interval-calculator-education/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`