Table 2.

Risk mechanisms and genotype-specific therapy based on clinical and experim ental data in LQT1, LQT2, and LQT3 forms of long QT syndrome

	LQT1	LQT2	LQT3
Sensitivity to sympathetic stimulation	Yes	To some degree	No
Torsade de pointes	Exercise related	Startle	Sleep/rest
Specific triggers/Occurrence	Swimming	Telephone, alarm clock, postpartum	Inactivity
Risk by mutation	Dominant neg., transmembrane location, A341V	Pore location, K28E	ΔKPQ
Exercise restriction	+++	++	?
Beta-blockers	+++	++	?
Potassium supplement	+	++	+
Mexiletine	+	+	++
Flecainide	No data	No data	+++ (ΔKPQ, D1790G)
Ranolazine	No data	No data	++ (ΔKPQ)
LCSD in high -risk patients	++	++	++
ICD in high-risk patients	+++	+++	+++

ICD = implantable cardioverter-defibrillator; LCSD = left cervicothoracic sympathetic denervation. The number of plussigns indicates the relative benefit of therapy in minimal (+), moderate (++), and marked (+++) effectiveness categories; ? = uncertain. (Reproduced and modified with permission. Table 1 from Shimizu W, et al. The long QT syndrome: therapeutic implications of a genetic diagnosis. Cardiovasc Res. 2005;67:347-356).²⁹