WHAT IS IT?
WPW is a specific derangement of nerve conduction tissue in the heart. First and always there is an accessory bypass tract, a redundant pathway named, when present, the bundle of Kent, that runs from the atria to the ventricles, bypassing the atrioventricular (AV) node (the normal pathway for conduction of sinus rhythm). This, in and of itself, would probably cause few or no significant problems, but it is very often accompanied by a “looped” additional reentrant pathway nervous tissue which can – and usually will – cause intermittent reentrant tachycardia (supraventricular tachycardia) and less frequently, atrial fibrillation (AF). It is these arrhythmias, and especially the latter, which are the major concern.HOW IS IT RECOGNIZED?
WPW is a “cooperative” disorder, since it usually produces some degree of delta wave caused by a shortened P-R interval, so that the ascending R wave appears stretched back toward the P wave and is usually a very distinctively asymmetric delta shape, thus the name. This is peculiar to WPW, and is not seen in the rare Lown-Ganong-Levine (LGL) syndrome, which is in other respects similar, but with more subtle EKG abnormalities.SYMPTOMS
When symptoms are present and recognized they are usually in the form of palpitations, rapid, pounding pulse, fluttering in the chest, vague chest discomfort, lightheadedness, fainting, and in relatively rare instances, sudden death. Very often the condition is discovered without there being any reported symptoms, in the course of a routine office exam.SUDDEN CARDIAC DEATH
WPW is significant for decreased quality of life in the form of the above symptoms, which obviously range from the fairly trivial to the catastrophic. The problem arises first in recognizing the condition or syndrome, and second in choice of management. While many practices feel aggressive therapy is wasteful unless there are symptoms, and because dangerous manifestations tend, statistically, to diminish to zero occurrence beyond the age of 34-40 (a dubious and strictly anecdotal assumption not often referenced anymore), there is a school – which includes some of the more prestigious medical centers, that believes the risk of sudden cardiac death (SCD), at 0.6 percent, is sufficient to treat or eliminate the problem at the earliest age practical.WPW can show up at any age but is usually discovered between adolescence and early adulthood, when the patient is inordinately at risk for SCD because of a much more active lifestyle, involvement in sports and vigorous play, all with consequent rapid sinus rates and increased oxygen debt. These two factors make young people particularly vulnerable to an unexpected episode of reentrant tachycardia or, most seriously, AF. While exercise does not seem to be a specific trigger, the random appearance of AF is always dangerous when seen in the setting of WPW, and especially so during exertion, because that accessory bypass tract allows the atrial rhythm, whatever it may be, to conduct directly to the ventricles without passing through the “braking system” provided by the AV node. AF may occur at rates of 150-300 beats per minute and be extremely chaotic. If such a rhythm is conducted directly to the ventricles, it is, in effect, arriving as ventricular fibrillation (VF) and that rhythm may, in fact, result in very short order. Even without a rapid exercising pulse and oxygen debt, then, such an occurrence may overwhelm the larger, slower ventricles and throw them into a lethal rhythm.
CONSIDERATIONS
If medicine is to be strictly statistics-driven, then a 0.6 percent chance of anyone dying from a sudden, lethal arrhythmia, becomes academic. Will a parent be willing to accept this level of risk for his/her child? Will a reasonable adult be able to understand the relevance of this statistic added to the baseline potential of a random life-threatening arrhythmia? And most importantly, will a physician not specializing in cardiology be appreciative of the concentration of this admittedly small risk in the young and vigorous? Is any such additional risk, if easily eliminated, worth being allowed to run its course till the anecdotal “safe” age cutoff? Many major medical centers in the United States feel the answer is no. This cardiology technician also says no, with experience both in the clinical and field settings to back up this contention. The Mayo Clinic says no. The University of Birmingham, Alabama, Medical Center says no. Many individual practitioners are not willing to take this chance either, especially now that the concentration of risk is understood and because of the relative ease with which the condition can be managed or obliterated.Still, there are those practitioners who hew to the school of thought that patient and family should not “get too excited” about what is, statistically, a fairly benign condition.
REFERAL AND MANAGEMENT
It is the writer’s conviction that any patient of any age who exhibits what may be delta waves on resting EKG should be referred to cardiology for a definitive diagnosis and decision as to management or treatment. The risk of having one patient die unnecessarily is simply too great and the cost-effectiveness of risk stratification too petty to ignore this finding, especially since the problem can well run in families and is often found in siblings and first cousins once it is uncovered in a given patient.Management of the possible adverse or terminal event is usually accomplished, at least temporarily, by use of beta blocker drugs. Properly chosen, these can effectively slow the rate of tachyarrhythmias enough to prevent sudden death, while not slowing the overall cardiovascular response to exercise, though this can sometimes be a tradeoff, in which case the life of the patient must be weighed against medical therapy.
Fortunately there is another approach which is highly successful in obliterating the problem entirely: radiofrequency (RF) ablation of the accessory bypass tract.
Just as with other atrial and some ventricular arrhythmias, RF ablation can be used to test, reproduce, and in the case of WPW usually very simply sever the bypass tract permanently so there is no longer any risk of transmission of rapid, irregular heartbeats to the ventricles. The reentry loop or loops may also be found and ablated via this method, so that the patient will be relieved of even the risk of disruption of activity by these then less-dangerous tachyarrythmias.
Cost is not prohibitive relative to the risk removed. A 0.6 percent chance of a bomb going off in a major metropolitan center would likely not be considered tolerable and vast monies and resources would be expended to prevent it. We should be no less concerned for the safety of any given individual with a known risk that can be removed with surgical precision.
The decision ought to be left to cardiology in every case.
CITE THIS ARTICLE:
John Kenyon, CNA. Wolff-Parkinson-White Syndrome and the Risk of Sudden Cardiac Death. Doctors Lounge Website. Available at: http://www.doctorslounge.com/index.php/blogs/page/14613. Accessed December 29 2010.
