Functional Invalidation of Putative Sudden Infant Death Syndrome-Associated Variants in the KCNH2-Encoded Kv11.1 Channel

BACKGROUND

Heterologous functional validation studies of putative long-QT syndrome subtype 2-associated variants clarify their pathological potential and identify disease mechanism(s) for most variants studied. The purpose of this study is to clarify the pathological potential for rare nonsynonymous KCNH2 variants seemingly associated with sudden infant death syndrome.

METHODS

Genetic testing of 292 sudden infant death syndrome cases identified 9 KCNH2 variants: E90K, R181Q, A190T, G294V, R791W, P967L, R1005W, R1047L, and Q1068R. Previous studies show R181Q-, P967L-, and R1047L-Kv11.1 channels function similar to wild-type Kv11.1 channels, whereas Q1068R-Kv11.1 channels accelerate inactivation gating. We studied the biochemical and biophysical properties for E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels expressed in human embryonic kidney 293 cells; examined the electronic health records of patients who were genotype positive for the sudden infant death syndrome-linked KCNH2 variants; and simulated their functional impact using computational models of the human ventricular action potential.

RESULTS

Western blot and voltage-clamping analyses of cells expressing E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels demonstrated these variants express and generate peak Kv11.1 current levels similar to cells expressing wild-type-Kv11.1 channels, but R791W- and R1005W-Kv11.1 channels accelerated deactivation and activation gating, respectively. Electronic health records of patients with the sudden infant death syndrome-linked KCNH2 variants showed that the patients had median heart rate-corrected QT intervals <480 ms and none had been diagnosed with long-QT syndrome or experienced cardiac arrest. Simulating the impact of dysfunctional gating variants predicted that they have little impact on ventricular action potential duration.

CONCLUSIONS

We conclude that these rare Kv11.1 missense variants are not long-QT syndrome subtype 2-causative variants and therefore do not represent the pathogenic substrate for sudden infant death syndrome in the variant-positive infants.

Opioid withdrawal suppression efficacy of oral dronabinol in opioid dependent humans

BACKGROUND

The cannabinoid (CB) system is a rational novel target for treating opioid dependence, a significant public health problem around the world. This proof-of-concept study examined the potential efficacy of a CB1 receptor partial agonist, dronabinol, in relieving signs and symptoms of opioid withdrawal.

METHODS

Twelve opioid dependent adults participated in this 5-week, inpatient, double-blind, randomized, placebo-controlled study. Volunteers were maintained on double-blind oxycodone (30mg oral, four times/day) and participated in a training session followed by 7 experimental sessions, each testing a single oral test dose (placebo, oxycodone 30 and 60mg, dronabinol 5, 10, 20, and 30mg [decreased from 40mg]). Placebo was substituted for oxycodone maintenance doses for 21h before each session in order to produce measurable opioid withdrawal. Outcomes included observer- and participant-ratings of opioid agonist, opioid withdrawal and psychomotor/cognitive performance.

RESULTS

Oxycodone produced prototypic opioid agonist effects (i.e. suppressing withdrawal and increasing subjective effects indicative of abuse liability). Dronabinol 5 and 10mg produced effects most similar to placebo, while the 20 and 30mg doses produced modest signals of withdrawal suppression that were accompanied by dose-related increases in high, sedation, bad effects, feelings of heart racing, and tachycardia. Dronabinol was not liked more than placebo, showed some impairment in cognitive performance, and was identified as marijuana with increasing dose.

CONCLUSION

CB1 receptor activation is a reasonable strategy to pursue for the treatment of opioid withdrawal; however, dronabinol is not a likely candidate given its modest withdrawal suppression effects of limited duration and previously reported tachycardia during opioid withdrawal.

Tako-Tsubo syndrome after an exercise echocardiography

The Tako-Tsubo syndrome is a clinical entity recently described that associate a chest pain occurring during a stress, an abnormal ECG and/or an increase in the troponin blood level and a transient left ventricular dysfunction with an akinesis involving generally the midsection and the apex of the heart. It has also been reported that left ventricle (LV) dysfunction may involve only the midventricle, although it seems less common. We report the case of a 66 year old woman that developed a stress-induced cardiomyopathy (Tako-Tsubo syndrome) involving the midventricle when performing an exercise echocardiography. To our knowledge, this is the first case reported in such circumstances.

Extensive Ablation During Pulmonary Vein Antrum Isolation Has No Adverse Impact on Left Atrial Function: An Echocardiography and Cine Computed Tomography Analysis

BACKGROUND

Although pulmonary vein antrum isolation (PVAI) may cure atrial fibrillation (AF) and improve left atrial (LA) function, the effect of extensive LA ablation on LA function is not well known.

OBJECTIVE

To assess the impact of PVAI on LA function remotely postablation.

METHODS

Consecutive patients undergoing PVAI had either transthoracic (TTE) and transesophageal (TEE) echocardiography (n = 41) or cine EBCT (n = 26) performed preablation and 6 months postablation. Only patients with paroxysmal and persistent, but not permanent, AF were included. Imaging was done in sinus rhythm for all patients. LA diameter (LAD), LA systolic and diastolic areas, and left atrial fractional area change (LFAC) were assessed by TTE. Transmitral (TMF), left atrial appendage (LAA), and pulmonary venous (PVF) Doppler flows were measured by TEE. Peak A on TMF, LAA peak emptying velocity (LAAF), and peak A reversal (AR) on PVF were used as surrogates of LA contractile function. Peak S on PV flow was used as a surrogate of reservoir function. LA areas, volumes, and LA ejection fraction (LAEF) were measured from cine EBCT.

RESULTS

Mean radiofrequency ablation time was 45 +/- 21 minutes. All four PVs were isolated for all patients; there were no cases of PV stenosis. Echocardiography revealed a significant reduction in LAD and LA areas post-PVAI. Both peak A and peak AR were also higher post, while other variables showed strong trends toward improvement. In the subset of patients with persistent AF, post-PVAI improvements were seen in LA size, peak A, and even peak S (P = 0.04). Cine EBCT showed a significant decrease in both LA areas and volumes post-PVAI. There was also a significant improvement in LAEF post-PVAI from 17 +/- 6% to 22 +/- 5% (P = 0.01).

CONCLUSION

Extensive ablation during PVAI does not cause deterioration in LA function, and may cause long-term improvement, especially in patients with higher AF burden.