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Differential effects of beta-blockade on dispersion of repolarization in the absence and presence of sympathetic stimulation between the lqt1 and lqt2 forms of congenital long qt syndrome

Wataru Shimizu, MD, PhD^*,*, Yasuko Tanabe, MD^*, Takeshi Aiba, MD, PhD^*, Masashi Inagaki, MD, PhD, Takashi Kurita, MD, PhD^*, Kazuhiro Suyama, MD, PhD^*, Noritoshi Nagaya, MD, PhD^*, Atsushi Taguchi, MD^*, Naohiko Aihara, MD^*, Kenji Sunagawa, MD, PhD, Kazufumi Nakamura, MD, PhD, Tohru Ohe, MD, PhD, FACC, Jeffrey A. Towbin, MD, Silvia G. Priori, MD, PhD^|| and Shiro Kamakura, MD, PhD^*

^* Division of Cardiology, Department of Internal MedicineSuita, Osaka, Japan
Department of Cardiovascular Dynamics, National Cardiovascular Center, Suita, Japan
Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan
Department of Pediatrics (Cardiology), Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
^|| Molecular Cardiology, Salvatore Maugeri Foundation, Pavia, Italy

View larger version (45K): [in a new window]   Figure 1 Electrocardiographic lead I4 of the body-surface map, which corresponds to lead V6 of the standard 12-lead electrocardiogram, at the baseline condition (A), with oral propranolol (B), during epinephrine infusion at baseline (C) and during epinephrine infusion with oral propranolol (D) in a patient with LQT1 syndrome. Both cQTe and cQTp were prolonged (584 and 461 ms, respectievly) and cTp-e was increased (123 ms) at the baseline condition. Propranolol produced no significant change in cQTe (588 ms), but prolonged cQTp (488 ms), resulting in a decrease in cTp-e (100 ms). Epinephrine produced a remarkable prolongation in cQTe (710 ms), but a mild prolongation in cQTp (532 ms), resulting in an increase in cTp-e (178 ms), and this was completely suppressed by oral propranolol. HR = heart rate.

View larger version (49K): [in a new window]   Figure 2 Electrocardiographic lead I4 of the body-surface map, at the baseline condition (A), with oral propranolol (B), during epinephrine infusion at baseline (C) and during epinephrine infusion with oral propranolol (D) in a patient with LQT2 syndrome. Both cQTe and cQTp were prolonged (545 and 429 ms, respectively) and cTp-e was increased (116 ms) at the baseline condition. Propranolol produced no significant change in cQTe (555 ms), but prolonged cQTp (454 ms), resulting in a decrease in cTp-e (101 ms). Epinephrine produced a prolongation in cQTe (630 ms), but a mild prolongation in cQTp (488 ms), resulting in an increase in cTp-e (142 ms), and this was completely suppressed by oral propranolol. HR = heart rate.

View larger version (23K): [in a new window]   Figure 3 Plots of the mean QTe and mean QTp values against the mean heart rate in 11 patients with LQT1 (open circles and squares) and 11 patients with LQT2 (solid circles and squares). In both groups of patients, the mean Tp-e value (mean QTe – mean QTp) after propranolol administration (P) was smaller than that at the baseline condition (B), even if the mean heart rate was slower after propranolol. The mean Tp-e value after epinephrine administration (E) was much greater than that at the baseline condition, even if the mean heart rate was faster after epinephrine in both groups. Moreover, the mean Tp-e value after epinephrine was larger in the LQT1 group than in the LQT2 group, even if the mean heart rate was faster in the LQT1 group.

View larger version (35K): [in a new window]   Figure 4 Differences before and after epinephrine at the baseline condition and with oral propranolol in the mean cQTe (A), mean cQTp (B), mean cTp-e (C), maximum cQTe (D), minimum cQTe (E) and cQTe-D (F) in 11 LQT1 patients (open circles) and 11 LQT2 patients (solid circles). The differences in the mean cQTe, mean cTp-e, maximum cQTe and cQTe-D values with epinephrine at the baseline condition were significantly greater in the LQT1 group than in the LQT2 group. In both groups, propranolol completely suppressed the influence of epinephrine, and the differences in all variables with epinephrine plus oral propranolol were not significantly different between the two groups.