Pacemaker Wenckebach secondary to variable latency

Volume Number

114 1. Part 1

Brief

Communication-s

189

Fig. 4. Electron micrograph of a hypertrophied cardiac musclefiber. Note the abundanceof mitochondria in perinuclear and intermyofibrillar spaces.The transverse tubules (arrows) are prominent.

Our present study indicates that sinusor paranodal and not ventricular tachycardia was inducible, presumably facilitated by intrinsic cellular derangements, which in this child were most expressedin the sinus region. The fact that ventricular tachycardia was not inducible at EP study suggeststhat the mechanismis an automatic focus (or foci) in the ventricle(s). Sinus entrance block aswell as the inconsistent rate responseto decremental atria1pacing make a definite distinction between triggered and reentrant sinus tachycardia difficult. Although seeminglyparadoxical, stabilization of the bidirectional tachycardia to a bigeminal rhythm following metaproterenol administration indicates a potential treatment regimen that incorporates improvement both of the muscle paralysis and ventricular dysrhythmias associatedwith this disorder.

8. BendheimP, RealeE, Berg B. @-adrenergic treatment of hyperkalemic periodic paralysis. Neurology 1983;35:746. 9. Rosen M, Reder R. Does triggered activity have a role in the genesis of cardiac arrhythmias. Ann Intern Med 1981;94: 194. 10. Gault J, Cantwell J, Lev M, Braunwald E. Fatal familial cardiac arrhythmias: Histologic observations on the cardiac conduction system. Am J Cardiol 1972;29:548.

We wish to thank John Stone, M.D., for his assistance, and Linda Richardson and Marsha Kwicinski for manuscript preparation.

New York, N.Y.

REFERENCES

1. Kastor J, Goldreyer B. Ventricular origin of bidirectional tachycardia: Case report of a patient not toxic from digitalis. Circulation 1973;48:897. 2. Klein R, Gamelin R, Marks J, Usher P, Richards C. Periodic paralysis with cardiac arrhythmia. J Pediatr 1963;62:371. 3. Levitt, L, Rose L, Dawson D. Hypokalemic periodic paralysis with arrhythmia. N Engl J Med 1972;286:353. 4. Lisak R, Leveau J, Tucker S, Rowland L. Hyperkalemic periodic paralysis and cardiac arrhythmia. Neurology 1972; 22:810. 5. Gould R, Steeg C, Eastwood A, Penn A, Rowland L, DiVivo D. Potentially fatal cardiac dysrhythmia and hyperkalemic periodic paralysis. Neurology 1985;35:1208. 6. Buruma 0, Schipperheyn J, Bots G. Heart muscle disease in familial hypokalemic periodic paralysis. Acta Neurol Stand 1981;64:12. 7. Wang P, Clawsen T. Treatment of attacks in hyperkalemic familial periodic paralysis by inhalation of salbutamol. Lancet 1976;1:221.

Pacemaker Wenckebach secondary to variable latency: An unusual form of hyperkalemic pacemaker exit block Philip Varriale, M.D., and Antonis Manolis, M.D.

Impaired myocardial responsivenessto pacing stimulation, or exit block, may be responsiblefor intermittent or total failure of pacemaker capture. An electrophysiologic derangement of the heart is usually recognized as the causeof exit block in the setting of an intact pacing system and myocardial-electrode interface. Perielectrode fibrosis or ischemic injury is frequently present as an anatomic counterpart and may raise the excitability threshold above the maximal energy provided by the pulse stimulus of the pacemaker. Pacemaker Wenckebach phenomenon, displayed asa variable latency of responseand incomplete capture, is an unusual manifestation of pacer exit block.

From Cab&i Cardiology. Reprint 10003.

requests:

Medical Philip

Center, Varriale,

Department M.D.,

of

Medicine,

222 E. 19th

St., New

Division York,

of NY

190

Brief Communications

American

July IQ87 Heart Journal

Fig. 1. Lead II of ECG. A, Pacemaker ventricular cycles showprogressiveincreasein latency, defined as pacer stimulus to QRS response(SR interval), and noncapture of fourth stimulus consistent with a 4:3 pacemaker Wenckebach phenomenon.B, At a slightly slower pacing rate, an incremental increasein the latent interval, characteristic of pacemakerWenckebach, is again noted but with an improved conduction ratio of 6:5. More evident is the decreasein QRS amplitude, progressiveprolongation in QRS duration, and eventual noncapture.

The electrophysiologic mechanism of this most uncommon mode of pacemaker failure is presented and the clinical implications of hyperkalemia and depressedmyocardium as a cause of this phenomenon will be discussed. In June 1985,a 59-year-old woman wasadmitted to the hospital because of crescendo angina and progressively increasing shortnessof breath over a 2-month period. On admission,clinical and chest x-ray examinations supported a diagnosisof mild congestiveheart failure. Myocardial infarction was excluded by serial ECG and enzyme studies. Digoxin was begun and verapamil was added for an episodeof atrial flutter. Progressive clinical improvement was then manifested over the next week and the patient’s treatment continued without incident. On the twelfth hospital day, the patient had sudden cardiac arrest (asystole). Rescuscitation with conventional measures,including a temporary transvenous pacemaker, was employed but the patient remained hypotensive. The ECG at this point showedan acute anterolateral myocardial infarction and hemodynamic study (Swan-Ganz catheter) wasconsistent with cardiogenic shock (cardiac index was 1.6 L/min/m*; pulmonary wedgepressurewas 24 mm Hg). Intra-aortic balloon counterpulsation wasthen initiated. Acute renal failure with anuria ensuedand a progressive but modest hyperkalemia developed (K+ = 7.1 mEq/L). Other measurementsincluded a serumsodiumof 111 mEq/L, a blood urea nitrogen of 64 mg/dl, and a creatinine of 6.3 mg/dl. Pacemaker dependency was then evident and was characterized by a variable latency of responseand by incomplete capture, compatible with a Wenckebach phenomenon of pacemaker origin (Fig. 1). Chest x-ray examination showed a satisfactory electrode position within the right ventricular apex. The effects of pacing rate and current strength on the latency response

and the conduction ratio of this unusualform of exit block are shown in Figs. 2 and 3. On the sixteenth hospital day, the patient developed electromechanical dissociation despite vigorous medical therapy and circulatory support and efforts to reduce the hyperkalemia. The patient died that day. Consent for autopsy was not obtained. Electrophysiologic alterations of the myocardial excitatory process related to drugs, extracellular electrolyte composition, or underlying musclecell diseasemay lead to failure of pacemaker capture.le5 This form of pacing failure, termed exit block, may occur either incompletely or on a persistent basis.An unusual variety of pacer exit block occurswhen a discrete delay or latency separatesthe pacemaker spike from the onset of the QRS complex (SR interval). A Wenckebach periodicity is manifest when this latency of responseprogressively increasesuntil a stimulus fails to excite the myocardium (Fig. 1). Pacemaker Wenckebach due to variable but progressivelatency has been reported infrequently and is usually associatedwith high-dose type I antiarrhythmic therapy and underlying cardiac disease.3,6r7 Hyperkalemia as a significant contributory factor is only supported by one definite previous casereport8 The pacemaker rate and the current strength of the stimulus will influence the interval of latency response (SR) and consequent conduction ratio. A stimulus of increased magnitude decreasesdelay due to latency and increasesthe conduction ratio; contrariwise, a heightened pacemakerrate will accomplishan opposite electrophysiologic effect (Figs. 2 and 3). Latency, as the time delay between pacemakerstimulus and QRS response,includes: (1) the time required for a local responseor the most immediate perielectrode tissueexcitation and (2) the time required for propagated excitation to recruit sufficient muscletissue to initiate the recorded QRS complex. The

Volume

114

Number

1, Part 1

former interval, referred to as true latency, is usually very short in time and the latter, termed conduction time, is commonly of much longer duration.g In experimental canine heart preparations, the latency responseis approximately 50 msecwhen a stimulus at threshold strength (1 to 2 mA) is applied in late diastole; a progressiveincrease in latency is then noted when the impulse is placed gradually earlier in the relative refractory period (RRP)? The observed shortening of the latent interval when pacing stimuli of increasingamplitude are applied may be attributed to a proportionately greater perielectrode tissue excitation as compared to threshold stimuli. Alterations in the latent period incurred by stimuli of variable current strength or those that fall within the relative refractory period primarily affect the first time constituent or true latency. In our patient, reasonableevidence supports the role of hyperkalemia in associationwith underlying heart disease (ischemiccardiomyopathy) asthe the causeof pacemaker Wenckebach phenomenon. Increased extracellular potassium concentration engendersslower conduction due to the reduction of both the resting membrane potential (RMP) and the rate of rise of phase 0 of the action potential. l”,ll Depressedintraventricular conduction due to hyperkalemia is associatedwith prolongation of the HV interval and progressive increase of the QRS duration.12 The effect of modest elevation of potassium on excitability has been inconstant, but elevations above 7.0 mEq/L in man have been associatedwith an increasein excitability threshold and may be responsiblefor complete unresponsivenessand failure to pace.lr2Underlying the progressive increasein pacemaker latency, reflective of Wenckebach periodicity, is a marked decreasein conduction veloicty generated by the combined effects of hyperkalemia and depressedmyocardium. This not only slowsthe processof propagated excitation during the total latent period, but is also responsible for the progressive increase of QRS duration after the initial ventricular capture of each Wenckebach cycle (Fig. 1, B). An abnormally prolonged ventricular refractory period may also contribute to the phenomenon of latency between stimulus and QRS response. In this setting, progressive increasesof latency due to the conduction delay of partially refractory tissuemay be evoked as each successivepacer stimulus encroachesearlier in the RRP of the preceding ventricular response.Failure of a propagated responseis then noted where the stimulus encounters inexcitable tissue or the absolute refractory period. Although the hyperkalemia in our patient was only moderately high, its disproportionate effect on conduction delay may be attributed to the concomitant presenceof muscle diseaseand hyponatremia (Na = 111 mEq/L). A decreased upstroke velocity is a consequent change of hyponatremia, and this associatedelectrolyte abnormality may aid and abet the conduction delay produced by hyperkalemia.13,I4 Six previous caseshave been described as a Wenckebath phenomenonbetween the pacemakerand the ventri-

Brief

Communications

191

Fig. 2. ECG lead II in panels A, C, and D, and lead I in panel B. The influence of an increasingpacing rate (50 to 110 pulsesper minute [PPM]) on the latent interval and conduction ratio; a pacing rate changefrom 50 PPM to 70 PPM increaseslatency from 100msec(A) to 180msec(B), with maintained 1: 1 conduction. 3 : 2 pacemakerWenckebath cycle is establishedat 90 PPM (C) due to a latent responseincrement between first and secondpaced beat, and 2: 1 conduction responseis present when the pacing rate increasesto 110 PPM (0).

cle, manifested as a progressive increase in the latency response.In four instances the causewas attributed to type I antiarrhythmic drugs;3,6T7 in one patient it was ascribed to severemyocardial depression,and in another to hyperkalemia.* In an additional report,15a 2:l pacemaker exit block with an increased and constant latency is described, but a typical Wenckebach periodicity was not evident. The pacemaker Wenckebach phenomenon portends a grim prognosis.All seven patients, including our own, were critically ill with advanced cardiovascular diseaseand only one survived. Despite this extremely poor prognosis, measuresto reverse hyperkalemia should be instituted; these include infusion of sodium bicarbonate, glucosewith insulin, and calcium solution.

192

Brief

Communications

American

July 1987 Hear1 Journal

3. Lead I of ECG. Increasing the current strength of the pacing stimulus from 2 mA to 8 mA changes a 2: 1 exit block (A) to a higher conduction ratio of 4:3 with a Wenckebach pattern (B).

Fig.

REFERENCES

1. SurawiczB, Chlebus H, Reeves JT, Gettes LS. Increase of ventricular excitability threshold by hyperpotassemia. Possible cause of internal pacemaker failure. JAMA 1965; 191:1049-54. 2. Gettes LS, Shabettai R, Downs TA, Surawicz B. Effects of changes in potassium and calcium concentrations on diastolic threshold and strength-interval relationship of the human heart. Ann NY Acad Sci 1969;167:693. 3. Gay RJ, Brown DF. Pacemaker failure due to procainamide toxicity. Am J Cardiol 1974;34:728-32. 4. O’Reilly MV, Murnaghan DP, Williams MB. Transvenous pacemaker failure induced by hyperkalemia. JAMA 1974; 228:336-7. 5. Levick CE, Mizgala HF, Kerr CR. Failure to pace following high dose antiarrhythmic therapy-reversal with isoproterenol. PACE 1984;7:252-6. 6. Mehta J, Khan AH. Pacemaker Wenckebach phenomenon due to antiarrhythmic drug toxicity. Cardiology 1976;61:18994. 7. Moss AJ, Goldstein S. Clinical and pharmacological factors associated with pacemaker latency and incomplete pacemaker capture. Br Heart J 1969;31:112-17. a. Klein HO, DiSegni E, Kaplinsky E, Schamroth L. The Wenckebach phenomennon between electric pacemaker and ventricle. Br Heart J 1976;38:961-5. 9. Brooks C McC, HoffmanBF, SucklingEE, Orias 0. Excitability of the heart. New York: Grune & Stratton, Inc., 1955:75-81. 10. Gettes LS, Surawicz B, Shiue JC. Effect of high K, low K, and quinidine on QRS duration and ventricular action potential. Am J Physiol 1962;203:1135. 11. Surawicz B, Chlebus H, Mazzoleni A. Hemodynamic and electrocardiographic effects of hyperpotassemia. Differences in response to slow and rapid increases in concentration of plasma K. AM HEART J 1967;73:647. 12. Ettinger PO, Regan TJ, Oldewurtel HA. Hyperkalemia, cardiac conduction and the electrocardiogram: A review. AM HEARTJ 1974;88:360. 13. Gettes LS. Possible role of ionic changes in the appearance of arrhythmias. Pharmacol Ther 1976;2:787-810. 14. Ewy GA, Karliner J, Bedynek JL. Electrocardiographic QRS axis shift as a manifestation of hyperkalemia. JAMA 1971;215:429.

15. Bashour TT. Spectrum of ventricular pacemaker exit block owing to hyperkalemia. Am J Cardiol 1986;57:337-8.

Observations on incraased wscaptkHty to coronary artery vasojspasm Wing beta blockade Henrik Nielsen, M.D.,* Henrik Egeblad, M.D.,* Svend Aage Mortensen, M.D.,** and Erik Sand@e,M.D., Ph.D.** Copenhagen, Denmark The present report indicates that beta-blocking agents may reduce the threshold of vasospastic angina pectoris (VAP). VAP wasdiagnosedin the presenceof (1) repeated attacks of angina pectoris at rest during more than 2 months, (2) ST segment elevation of at least 0.15 mV in more than two ECG leads during angina, (3) normalization of the ECG and relief of symptoms after administration of nitroglycerin, and (4) no subsequent evidence of myocardial necrosis.VAP wassuspectedin three consecutive patients (Table I). Their ECGs at rest and during exercise were normal. After obtaining informed consent from the patients, all drugs were discontinued for at least 3 days. Prolonged hyperventilation test (PHT) was carried out as previously described.l Repeated examinations were performed at the samehour of the day, accounting for the known circadian variation of the attacks in VAP.’

From Medical Department 2, Kommunehospit&t* and Medical Department B, Rigshospitalet.** Reprint requests: Henrik Nielsen, M.D., Medical Department 2, Kommunehospitalet, DK-1399 Copenhagen K, Denmark.