What is considered a prolonged QTc (corrected QT) interval in males?

From the Guidelines

In males, a prolonged QTc interval is generally considered to be greater than 450 milliseconds. This threshold is crucial for clinicians to recognize as QTc prolongation increases the risk of developing dangerous ventricular arrhythmias, particularly Torsades de Pointes, which can be life-threatening 1. The QTc interval represents the time it takes for ventricular depolarization and repolarization, corrected for heart rate. Men typically have shorter QTc intervals than women due to hormonal differences affecting cardiac repolarization.

Key Considerations

• Different correction formulas (such as Bazett's, Fridericia's, or Framingham) may yield slightly different QTc values 1.
• Certain medications (including some antipsychotics, antibiotics, antiarrhythmics, and antihistamines), electrolyte abnormalities (particularly hypokalemia, hypomagnesemia, and hypocalcemia), and congenital conditions can prolong the QTc interval 1.
• If a prolonged QTc is identified, the underlying cause should be addressed, which may involve discontinuing offending medications, correcting electrolyte imbalances, or further cardiac evaluation 1.

Clinical Implications

• QTc values from 440 to 470 ms are considered a ‘grey zone’ due to a considerable overlap between affected and controls in this range 1.
• The normal upper QTc value in men is 450 ms, in women 460 ms, and in children 440 ms, representing the 95th percentile values 1.
• It is essential for physicians to be able to measure the QT interval manually, especially in cases where automated measurements may not be reliable 1.

From the FDA Drug Label

In this clinical trial Sotalol AF treatment was not initiated if the QT interval was greater than 450 msec and during therapy the dose was reduced or discontinued if the QT interval was ≥520 msec Table 7 below relates the incidence of Torsade de Pointes to on-therapy QTc and change in QTc from baseline.

• ( ) Number of patients assessed On-Therapy QTc Interval(msec) Incidence of Torsade dePointes less than 500 500 to 525 525 to 550

  550 The answer to what is considered a prolonged QTc interval in males is:

• A QTc interval of ≥520 msec is considered prolonged, as the dose was reduced or discontinued at this value.
• Additionally, a QTc interval of >550 msec is associated with a higher incidence of Torsade de Pointes. 2

From the Research

Prolonged QTc Interval in Males

A prolonged QTc interval in males is generally considered to be:

• < 450 ms for men, as stated by 3
• However, other studies provide more specific age-related criteria:
  • Age < 40 years: 430 ms 4
  • Age 40 to 69: 440 ms 4
  • Age ≥ 70 years: 455 ms 4

Factors Influencing QTc Interval

Several factors can influence the QTc interval, including:

• Age: QTc shortens in men during adolescence 4
• Sex: Sex difference in QTc originates from shortened QT in adolescent males 4
• Electrolyte disturbances: Hypokalemia and hypocalcemia are associated with prolonged QTc interval 5, 6
• Medications: Certain drugs, such as antiarrhythmic drugs and QTc-prolonging drugs, can increase the risk of QTc prolongation 3, 5, 6, 7
• Comorbidities: Heart disease, thyroid disease, and myocardial infarction are associated with prolonged QTc interval 6
• Illness severity: Severe illness can increase the risk of QTc prolongation and torsade de pointes 7