The Sudden Unexplained Death Syndrome in Thai Men
ABSTRACT & COMMENTARY
Synopsis: Physicians propose that these patients all share a common, potentially lethal abnormality in an ionic channel.
Source: Nademanee K, et al. Circulation 1997;96: 2595-2600.
Nademanee and associates identified 27 patients in Thailand who were thought to be survivors of unexplained cardiac arrest in the absence of identified structural heart disease. This syndrome, called sudden unexplained death syndrome (SUDS), has been described previously in Asian males and is known locally in Thailand as Lai Tai. The patients were classified as either true SUDS victims (because they had survived a documented cardiac arrest) or probable SUDS victims (if they experienced symptoms suggesting SUDS, including agonal respiration, unresponsiveness, or syncope but had recovered spontaneously). Patients who had identified structural heart disease during a thorough cardiac evaluation, patients with prolonged QT syndromes, drug ingestion, or evidence for myocardial ischemia as potential causes for an arrest were also excluded. As part of their evaluation, they underwent an electrophysiologic study that included a standard programmed ventricular stimulation protocol. Five patients underwent magnetic resonance imaging, and all of these had normal results.
Of the 17 SUDS survivors, 12 had developed ventricular fibrillation (VF) while sleeping between 8 p.m. and 6 a.m. Two patients suffered VF while awake during the night, and, in the remaining three patients, VF occurred in the late afternoon.
The most striking findings in the group were on the routine scalar ECG and at electrophysiologic study. Sixteen of the 27 patients had a right bundle branch block pattern with ST segment elevation in V1 through V3. This configuration was only intermittent in several of the patients. In six patients, the ECG pattern normalized during exercise but reappeared during recovery. The ECG abnormalities were identical to those described previously in several European families with idiopathic VF (Brugada P, Brugada J. J Am Coll Cardiol 1992;20:1391-1396). Four patients did not undergo electrophysiologic study. Of the remaining 23 patients, 14 had inducible sustained VF, while nine patients had no inducible arrhythmia. Signal averaged electrocardiograms performed in 22 of these 23 patients showed abnormal findings in 12 patients. Patients could be divided into two groups based on the presence or absence of the right bundle branch block pattern with ST segment elevation in V1-V3. There were 16 patients in the group with right bundle branch block and ST elevation. Thirteen of the 14 in this group who underwent electrophysiologic study had inducible ventricular fibrillation. Eleven of 13 signal averaged ECGs in this group were positive. The mean HV interval in the group was mildly prolonged at 63 + 11 msec. By contrast, the 11 patients with normal electrocardiograms only rarely had inducible ventricular fibrillation (1 of 9) or a late potential on SAECG (1 of 9). The HV interval in these latter patients were also normal at 49 + 6 msec. Treatment was at the discretion of the patients’ physicians. It included both drug therapy and ICD therapy. Ten of the 16 patients with the abnormal resting ECG developed either recurrent sudden death or had ventricular fibrillation documented by an implantable defibrillator. Only one patient among the 11 patients with normal electrocardiograms suffered a recurrent episode. In the patients who had recurrent episodes and had an ICD, the ICD electrogram showed episodes of rapid polymorphic ventricular tachycardia degenerating to ventricular fibrillation triggering the ICD discharges.
Nademanee and associates go on to discuss the similarities between the ECG findings in their patients and other groups of patients with right bundle branch block and ST segment elevation in V1 through V3. They propose that these patients all share a common, potentially lethal abnormality in an ionic channel.
COMMENT BY JOHN P. DiMARCO, MD, PhD
In the early 1980s, there were a number of clinical reports about sudden unexplained nocturnal deaths in young male Southeast Asian refugees who had come to the United States after the war in Vietnam. Similar clinical patterns had previously been described in other countries including Thailand, the Philippines, and Japan. Since most of these patients were identified only after their death, the mechanism responsible for these sudden deaths was unknown. In this paper, Nademanee et al have identified characteristic electrocardiographic and electrophysiologic abnormalities in a significant subgroup of a reasonably sized series of patients with this syndrome. The electrocardiographic changes are remarkably similar to those described in other groups in Europe and North America. These patterns have been known to occur in a familial distribution and are almost certainly related to one or more specific genetic defects. Thus, the problem previously thought to occur exclusively in Asians no longer seems to be a purely regional phenomenon but one that can be found in many population groups.
Unfortunately, we do not know the prevalence of right bundle branch block with ST segment elevation in the general population. Without these data concerning the specificity of this finding, it is impossible to know how to react to the asymptomatic patient who presents with this electrocardiographic pattern. Further longitudinal studies are needed in patients who have this finding on an electrocardiogram before specific prophylactic therapy can be recommended. However, in patients with this finding who have a familial history of sudden death, enough data are available about the syndrome’s ominous prognosis to justify prophylactic ICD implantation. Hopefully, if a specific molecular defect or family of defects can be identified, more specific treatment protocols will be devised.
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