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Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from Postgraduate Medical Journal (1985) 61, 379-386

Review Article

The prolonged QT interval - a frequently unrecognized abnormality

R.A. Kenny and R. Sutton Department ofCardiology, Westminster Hospital, Horseferry Road, London SW] 2AP, UK.

Introduction The clinical importance of the long QT interval slowing rate (Browne et al., 1983a; Lown et al., syndrome lies in its association with malignant ven- 1973). tricular dysrhythmias which are usually amenable to The physiological control of the QT interval has treatment with either drugs or cardiac pacing. been used to construct a which The QT interval extends from the beginning of the senses the interval between the delivered stimulus and QRS complex (whether the initial component is a Q or the evoked and uses this interval to set the an R wave) to the end of the T wave. It therefore subsequent pacemaker escape interval (Rickards & represents the algebraic sum of the individual action Norman, 1981; Donaldson et al., 1983). potentials of the ventricular myocytes, including both (the QRS complex or QJ interval) and

(the T wave or JT interval). The rapid Measurement of the QT interval copyright. process of depolarization is rarely sufficiently prolon- ged to make any clinically significant difference to the Measurement of the QT interval on the surface QT interval duration and the term effectively refers to electrocardiogram (ECG) can present technical changes in the duration ofrepolarization, that is the JT problems because the end of the T wave may be interval. difficult to define. The point at which the line of maximal downslope ofthe T wave crosses the baseline is therefore often used to identify the end of the T

Physiological variations in the QT interval wave. The surface ECG leads chosen for QT interval http://pmj.bmj.com/ measurement are those which show the greatest T It is well known that the QT interval alters with heart wave amplitude and duration. The QT interval should rate (Bazett, 1920). However, is only one of be measured in at least three consecutive cardiac cycles the determinants of the QT interval duration (Rick- and the time values averaged. Although tables that list ards & Norman, 1981) and other factors, particularly normal values for a specific cardiac rate, age and sex changes in autonomic activity, also contribute to QT are available, Bazett's formula (1920) for calculating interval shortening during exercise (Browne et al., the QT interval corrected for heart rate is commonly 1983b). By comparing QT interval changes during used: on September 24, 2021 by guest. Protected atrial synchronized and asynchronous ventricular pacing, Fanazapazir et al. (1983) determined that the QT calculated (QT,) = QT (measured) contribution of the intrinsic effect of the heart rate to k QT interval shortening during exercise varied from 26 /RR interval (s) to 75%. where k is 0.37 for men and 0.40 for women. The upper Sleep represents a naturally occurring period of limit is 0.39 s for men and 0.44 s for women (Braun- increased parasympathetic tone or sympathetic tone wald, 1984). Because ofvariations in the measured QT withdrawal (Kleinman, 1963; Baust & Bohnert, 1969) interval as a result of influences other than heart rate, and prolongs the QT interval independently of the such as sympathetic and parasympathetic activity, drugs, electrolyte changes, ventricular , Correspondence: R.A. Kenny, MB., M.R.C.P.I. Depart- ischaemia, and acid-base disturbances, different ran- ment of , Westminster Hospital, Horseferry ges of normality are accepted by different inves- Road, London SWI 2AP tigators. For practical purposes therefore, minor Accepted: 9 October 1984 deviations from the expected QT, interval should be © The Fellowship of Postgraduate Medicine, 1985 380 R.A. KENNY & R. SUTTON Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from disregarded as being of questionable clinical sig- sion of repolarization which involves premature re- nificance. polarization will not be reflected by prolongation of The use of QT, is at times misleading when interval the QT interval and, unless the mass of cells is large, changes are examined in association with rapid chan- may not even cause an alteration of T wave mor- ges in heart rate (Camm et al., 1984). The biophysical phology. Such patients are, however, just as likely to effect of heart rate on QT interval develops slowly be at risk from ventricular dysrhythmias as those in (Arnold et al., 1982) and therefore the use of formulae whom temporal dispersion of ventricular repolariza- such as that described by Bazett may result in gross tion is the result of abnormally delayed repolarization overcorrection (Milne et al., 1980). (Han & Moe, 1964; Han & Goel, 1972; El-Sherifet al., 1977). These concepts can explain the apparently paradoxical effects of different drugs. Thus, anti-arr- Repolarization, the vulnerable period and the long QT hythmic agents which prolong repolarization may act interval by normalizing premature depolarization in abnormal myocardium, while in other situations, such as tor- Myocardial repolarization is complex, poorly under- sades de pointes in the acquired LQTS, drugs which stood and even more difficult to study than de- shorten abnormally prolonged depolarization, such as polarization. It is also, possibly because of its slower , are effective when many standard agents time course, more obviously affected by , are not or may even exacerbate the dysrhythmia drugs, and biochemical abnormalities. It is normally a (Bennett, 1982; Soffer et al., 1982). well coordinated but non-uniform process, as is Long term treatment ofrabbits with beta adrenergic evident from the consistent asymmetry of the normal antagonists induces several adaptive changes in the T wave. myocardium which persist long after the drugs have The vulnerable period is that part of the cardiac been eliminated from the body (Vaughan Williams, cycle during which ventricular or fibrilla- 1977). This 'adaptive syndrome' includes prolonga- tion can be most easily provoked and this is always the tion of the duration and the QT relative refractory period of the ventricular myocar- interval and both these effects have been shown to dium, corresponding to the declining limb of the T occur in man although the full clinical implication of wave from peak to iso-electric line. Increased vul- the findings are unclear (Edvaardssonn & Olsson,copyright. nerability to the provocation ofventricular 1981; Vaughan Williams et al., 1980; Milne et al., can be induced by many means which have in common 1980). the effects ofcausing temporal dispersal ofrepolariza- tion often combined with increased excitability. Tem- poral dispersal of the repolarization process may occur as a result of premature repolarization of some myocardial cells or as abnormally delayed repolariza- Torsades de pointes is virtually always associated with http://pmj.bmj.com/ tion of other cells. The latter may be reflected in the prolongation of the QTc interval (Smith & Gallagher, surface electrocardiogram as prolongation of T wave 1980) and is the most important and singular arrhyth- with corresponding lengthening of the QT interval. mia complicating both acquired and congenital long Marked lengthening of the QT interval of the order QT interval syndromes (Bonatti et al., 1983; Montro, which can be measured on the surface ECG is almost 1981). Torsades de pointes is characterized by short inevitably associated with increased temporal disper- intervals of which consist of sion of repolarization and thus increases the duration bursts of ventricular waves occurring at a high rate of the vulnerable period as well as decreasing the (from 150 to 250 beats/min) and showing progressive- on September 24, 2021 by guest. Protected threshold for . ly varying amplitude and polarity (Figure 1). Attacks The severe prolongation of repolarization found in may be brief or prolonged, when may occur. the long QT syndrome (LQTS) decreases the degree of Attacks most often stop spontaneously but on some prematurity required for an to occur occasions they progress to ventricular fibrillation and within the vulnerable period and therefore enhances (Krikler, 1976; Krikler et al., 1976). The distinc- the likelihood of ventricular (Lipman et tion between torsades de pointes and those polymor- al., 1979; Montro, 1981). These hypotheses account phous ventricular occurring in patients for the frequent association of arrhythmias and the with a normal QT interval has important therapeutic prolonged QT syndrome. They may also explain why implications. The former requires strict avoidance of some patients with abnormally prolonged QT in- all drugs that may potentially further delay repolariza- tervals run a trouble free course. tion, including class I antiarrhythmic agents such as Conventional only reflects the , disopyramide and lignocaine. Immediately, net resultant of the repolarization of all ventricular the initiation of cardiac pacing is often necessary for myocardial cells. Thus any abnormal temporal disper- control and, on a long term basis, sym- Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from THE PROLONGED QT INTERVAL 381

Figure 1 Torsades de pointes illustrating bursts of ventricular waves at a high rate with varying amplitude and polarity. pathetic nervous blockade is beneficial. In contrast, nomonic electrocardiographic finding is an abnormal polymorphous ventricular tachyarrhythmias with a lengthening of the QT interval with asymmetric or normal QT interval respond to conventional therapy notched T waves. The syncopal episodes are almost (Soffer et al., 1982). always induced by one or more of the following: (a) psychological or physical stress, (b) induction of

anaesthesia (Callaghan et al., 1977; Forbes & Morton, copyright. Congenital long QT syndrome 1979; Medak & Bennmof, 1983) and (c) medications which prolong the QT interval or change the sympath- A prolonged QT interval may be due to congenital etic tonal control of the heart (Reynolds & Van- (idiopathic long QT syndrome) or acquired disease derArk, 1976; Puritz et al., 1977; Siklos et al., 1978; states. In 1957, Jervell and Lange-Neilson reported the Laasko, 1981; Ludomirsky et al., 1982). Patients may congenital association of QT prolongation, syncope, also develop brief episodes of deep, severe T wave sudden death and deafness. Six years later Romano et inversion following the same stimuli which trigger al. (1963) and Ward (1964) independently reported a syncopal attacks (Schwartz et al., 1975). http://pmj.bmj.com/ similar syndrome in children with normal hearing. These conditions are collectively known as the long Pathophysiology QT syndrome (LQTS) and are both familial; the variety reported by Jervell and Lange-Nielson is The pathogenesis ofcongenital prolonged QT interval transmitted as an autosomal recessive while the is still unclear, but the most popular hypothesis centres Romano-Ward syndrome is inherited as an around the adrenergic nervous system - unbalanced autosomal dominant (Fraser et al., 1964; Ward, 1964). activity of the cardiac sympathetic nerves which is To date no positive association has been demonstrated either exaggerated on the left or depressed on the right on September 24, 2021 by guest. Protected with any particular HLA antigen and there is no (Schwartz et al., 1975; Browne et al., 1983a). This evidence of viral aetiology (James et al., 1978). asymmetry of sympathetic stimulation results in In the British Isles, the incidence of congenital severe prolongation (and temporal dispersal) of re- LQTS is not less than one per 300,000 births and may polarization ofthe ventricular myocardium leading to be greater (Fraser et al., 1964). A world wide prospec- increased susceptibility to fibrillation (Vaughan tive register was established in 1979. The average age Williams, 1982). of the population was 24 y with almost twice as many Further evidence for involvement of the sympath- women as men. Congenital deafness was present in 6% etic nervous system lies in: (a) syncopal attacks which ofpatients and all had one or more syncopal episodes may be reproducibly precipitated by events or before age 1Oy (Schwartz et al., 1983). activities that increase sympathetic stimulation, such The LQTS is an idiopathic disorder in which the as emotion or physical exercise; (b) the production of affected individuals have an unusual ventricular re- characteristic electrocardiographic signs - QT interval polarization abnormality and a propensity to syncope prolongation and episodes ofaltered T wave activity - and fatal ventricular tachyarrhythmias. The pathog- by asymmetric alterations in sympathetic tone (Sch- 382 R.A. KENNY & R. SUTTON Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from wartz & Malliani, 1974); (c) satisfactory therapeutic usually require both long term beta blockade and results obtained by antagonizing the effects of sym- permanent pacing. pathetic activity on the heart with beta adrenoceptor In patients undergoing surgery and general anaesth- antagonists. Ablation of the left stellate ganglion and esia adequate premedication should be given in addi- first thoracic ganglion ablation may also be successful tion to these measures to minimize the release of (Schwartz et al., 1975). catecholamines and reduce sympathetic nervous sys- The results of animal studies also support the tem activation resulting from fear and anxiety. importance of unbalanced sympathetic stimulation in Halothane lowers the ventricular arrhythmia thre- the genesis of the congenital LQTS (Schwartz & shold produced by exogenously administered Malliani, 1974; Schwartz et al., 1975). noradrenaline and is a particularly poor choice of anaesthetic agent (Wig et al., 1979; Medak & Benn- Anaesthesia mof, 1983) but isofluorane, which raises the ven- tricular arrhythmia threshold is preferable (Joas & The detection and management of long QT interval Stevens, 1971; Medak & Benumof, 1983). syndrome in patients undergoing surgery is of par- ticular importance. Patients who have not been treated appropriately prior to general anaesthesia have all had Acquired long QT syndrome severe ventricular arrhythmias or a or both at some time in the perioperative period Apart from congenital syndromes, there are a number (Callaghan et al., 1977; Forbes & Morton, 1979; ofdrugs and clinical disorders associated with prolon- Medak & Benumof, 1983; Owitz et al., 1979; Wig et al., gation ofthe QT interval. In the present issue, Duncan 1979; Brown et al., 1981; Ponte & Lund, 1981). This is & Ramsey (1985) have reported a case of ventricular hardly surprising in view of the intense sympathetic tachycardia precipitated by the administration of stimulation which occurs during induction ofanaesth- iothalamate (Conray 420) in a patient already esia and intubation, perioperative haemodynamic taking phenylamine, both of which drugs prolong the stresses and the variations in autonomic tone occur- QT interval. Antiarrhythmic agents, beta blockers, ring during recovery from anaesthesia. tricyclic antidepressants and phenothiazines may all be associated with a prolonged QT interval. In patientscopyright. Prognosis and treatment ofcongenital LQTS treated with , a class III , lengthening of the QT interval may be used In a retrospective series of233 patients with LQTS, the clinically to estimate myocardial drug concentrations, 15 y survival after the first syncope was 45% in serum levels reflecting drug activity poorly (Debbas et untreated patients and 90% in patients treated with al., 1984). propranolol or left stellate ganglionectomy (Schwartz Tricyclic antidepressants prolong the QT interval. et al., 1983). In normal subjects this increase is usually insignificant http://pmj.bmj.com/ The evidence to date strongly suggests that any (Burkhardt et al., 1978). However, in patients in whom patient with prolonged QT interval syndrome should the QT interval is already prolonged, administration have a trial of long term beta adrenoceptor blockade. may be calamitous, increasing the risk of ventricular Propranolol, by antagonizing excessive sympathetic arrhythmias (Motte et al., 1970). discharge, causes homogeneity of repolarization and Ischaemic heart disease, , congen- shifts the rate adjusted QT interval closer to the ital and electrolyte changes are all normal range thereby reducing the frequency of associated with QT prolongation. Altered myocardial arrhythmias and the death rate (Krikler, 1976). A repolarization also occurs in a wide variety ofdiseases on September 24, 2021 by guest. Protected linear dose reponse relationship may exist - the greater affecting the central nervous system, particularly acute serum propranolol concentration being associated events such as subarachnoid haemorrhage or skull with a shorter QT interval (Medak & Bennmoff, fracture (Harries, 1981). 1983). Percutaneous left stellate ganglion blockade , either occurring accidentally or in- also suppresses symptoms perioperatively (Moss & duced experimentally, is characterized by delay of MacDonald, 1971; Callaghan et al., 1977). both the upstroke and downstroke of membrane In patients in whom medical treatment achieves action potential (Marshall, 1959). As a consequence only a reduction in syncopal attacks, left sympathec- there is prolongation of the QT interval. tomy suppresses attacks and shortens the QT interval The electrocardiographic changes, other than (Schwartz et al., 1975). Ventricular pacing may also be , observed in patients with hypoth- effective by 'normalizing' depolarization and sub- yroidism include prolongation of the QT interval, but sequent repolarization (Keren et al., 1981). Those since the T wave amplitude is low, precise patients who suffer from both paroxysmal ventricular measurement of this interval is often impossible fibrillation and paroxysmal complete heart block (Surawicz & Mangiardi, 1977). THE PROLONGED QT INTERVAL 383 Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from

Repolarization changes of hypokalaemia are 1973). A predisposing state of vulnerability is accompanied on the surface electrocardiogram by ST therefore necessary for ventricular ectopics to initiate segment depression, diminished T wave amplitude and ventricular fibrillation. When compared with post increased prominence of the with resultant myocardial patients, the electrocar- prolongation ofthe QT (QU) interval. Hypocalcaemia diograms of ventricular fibrillation survivors clearly is characterized by a long, flat ST segment resulting in show repolarization abnormalities including ven- QT prolongation. The other case report published in tricular ectopy and QTc prolongation (Haynes et al., the current issue (O'Keefe et al., 1984) concerning the 1978; Schwartz & Wolf, 1978). LQTS emphasizes the vulnerability to cardiac arrhyth- mias associated with biochemical abnormalities. Prognosis and treatment of acquired LQTS 'Giant T wave inversion' As distinct from congenital forms of LQTS, patients with acquired disease are usually seen in the fifth and The slow idioventricular escape rhythm in cases of sixth decades and childhood electrocardiograms, complete is at times associated when available, do not show any QT prolongation. with large, broad, bizarre and inverted T waves with Because of the multitude of factors which may be marked prolongation of the QT interval. This phen- responsible for QT prolongation in acquired disease, omenon is usually best seen in leads V2 to V4 and is one must initially establish the cause of QT prolonga- termed 'giant T wave inversion' (Jacobson & Schrire tion and direct attention to its specific management 1965, 1966). Giant T wave inversion also occurs such as drug withdrawal, electrolyte balance or treat- particularly after a syncope in both clinical and ment of hypothermia. experimental cerebral disorders (Birke & Stroma, Torsades de pointes in the acquired LQTS must not 1955). A proposed genesis of these 'giant' inverted T be treated with the standard drugs used for the control waves and the associated prolonged QT, is intense of ventricular tachycardia and fibrillation as they sympathetic stimulation resulting from the anoxia ofa invariably exacerbate the disorder, presumably by syncopal attack. Thus, the appearance of these T increasing the temporal dispersion of repolarization

waves in cases ofcomplete atrioventricular block may (Soffer et al., 1982). Instead, treatment which shortens copyright. indicate that the patient has had a recent syncopal repolarization is required, such as intravenous Stokes-Adams attack due to either ventricular stand- isoprenaline or rapid cardiac pacing. still or ventricular fibrillation. In appropriate cases, for the termination of life Others have described a type of 'cardiac memory' threatening sustained ventricular tachycardia, both which may offer an alternative explanation for the T temporary pacing as well as permanently implanted wave changes. The authors demonstrated massive T devices for anti-tachyarrhythmia pacing, cardiover- wave inversion and ST segment depression in associa- sion or may be used (Steinbeck et al., tion with cardiac pacing. The magnitude of T wave 1983; Ludiomorsky et al., 1982; Maloney et al., 1980). http://pmj.bmj.com/ inversion was related to the amount ofelectrical power used for ventricular pacing and the time taken for complete regression after pacing was directly related Conclusion to the duration of pacing (Chatterjee et al., 1969; Rosenbaum et al., 1982). The pathophysiology of the congenital and acquired forms ofthe long QT syndrome is different, and this is Ischaemic heart disease reflected in the differences in their management. General anaesthesia presents special hazards, which on September 24, 2021 by guest. Protected Some survivors ofventricular fibrillation seem to have may be avoided ifthe diagnosis is made pre-operative- a sustained propensity for occurrence of ventricular ly. fibrillation, probably reflecting a continued state of Although relatively uncommon the LQTS carries a myocardial instability (Haynes et al., 1978; Borggrefe high risk for both morbidity and mortality. In spite of et al., 1984). In patients with coronary heart disease, its importance and treatable clinical implications it is ventricular ectopics are associated with an increased often overlooked, or diagnosed retrospectively, be- risk of sudden cardiac death (Vismara et al., 1977; cause measurement of the QT interval tends to be Chiang et al., 1969; Oliver et al., 1974). Yet a majority omitted from routine ECG reporting unless it is of middle aged adults with no apparent heart disease grossly abnormal. Abnormal QT prolongation is have dysrhythmias with little effect on mortality possibly the single most commonly missed marker of (Clarke et al., 1976; Pribble et al., 1975; Desai et al., preventable dysrhythmic death. 384 R.A. KENNY & R. SUTTON Postgrad Med J: first published as 10.1136/pgmj.61.715.379 on 1 May 1985. Downloaded from

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