comparison of prehospital monomorphic and polymorphic ventricular tachycardia: prevalence, response...

EMS/ORIGINAL CONTRIBUTION

Comparison of Prehospital Monomorphic and Polymorphic Ventricular Tachycardia: Prevalence, Response to Therapy, and Outcome

From the Department of Emergency Medicine, Medical College of Wisconsin, Milwaukee.

Received for publication March 11, 1994. Revision received July 25, 1994. Accepted for publication August 4, I994.

This worl~ was presented in part at the Annual Meeting of the 5ociety for Academic Emergency Medicine, San Francisco, California, May 1993.

Copyright © by the American College of Emergency Physicians.

William Brady, MB Stephen Meldon, MD Daniel DeBehnke, MD

Objective: Monomorphic ventricular tachycardia (MVT) is the most common form of prehospital ventricular tachycardia (VT). Recent literature suggests that polymorphic ventricular tachycardia (PVT) is more common during cardiopulmonary arrest than previously thought but responds poorly to advanced cardiac life support (ACLS) therapy. We undertook this study to determine the prevalence, response to therapy, and outcome of both MVT and PVT in the prehospital sudden cardiac death victim.

Design: Retrospective prehospital chart review from 1987 to 1991.

Setting: Municipal, fire department-based, multitiered emergency medical system serving a population of approximately one million.

Participants: Adult patients older than 18 years experiencing prehospital, nontraumatic cardiopulmonary arrest with VT occurring at any time during the resuscitation. VT was defined as PVT if the QRS-complex configuration was not stable when viewed in a single electrocardiographic lead (ie, episodic changing of the QRS-complex electrical axis, amplitude, or both or the presence of more than two QRS-complex morphologies). Outcome was defined in terms of both the presence or absence of spontaneous circulation at the end of the prehospital phase of care and ultimate outcome (survival to hospital discharge or death). Four hundred seventy-six patients met entry criteria; 37 patients were excluded because of incomplete medical records, and 439 patients were used for data analysis.

Interventions: ACLS therapy based on the 1987 American Heart Association guidelines.

Results: MVT occurred in 323 patients (73.6%), with 119 (36.8%) showing return of spontaneous circulation (ROSC) in the prehospital setting; 35 MVT patients (10.8%) survived to hospital discharge. PVT occurred in 116 patients (26.4%), with 48 (41.4%) showing ROSC in the prehospital setting; 15 PVT patients (12.9%) survived to hospital discharge. The use of ACLS therapy (defibrillation, endotracheal intubation, medication usage) between the two rhythm groups was not statistically different.

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TACHYCARDIA Brady, Meldon & DeBehnke

The Pvalues for ROSC, ultimate outcome, and use of ACLS therapy were all not significant.

Conclusion: We conclude that PVT is a common rhythm occurring in prehospital cardiopulmonary arrest that responds as well as MVT to ACLS therapy. Until prospective data are available, standard ACLS therapy should be used in all forms of prehospital VT occurring during cardiopulmonary arrest.

[Brady W, Meldon S, DeBehnke D: Comparison of prehospital monomorphic and polymorphic ventricular tachycardia: Prevalence, response to therapy, and outcome. Ann Emerg MedJanuary 1995; 25:64-70.]

INTRODUCTION

Sudden cardiac death remains a significant public health problem in the United States. Sudden death, most frequently caused by a ventricular tachyrhythmia, E-4 accounts for a significant majority of the 600,000 annual deaths due to coronary heart disease. Ventricular fibrillation (VF) is often preceded by ventricular tachycardia (VT), either monomorphic or polymorphic.>4 Monomorphic VT (MVT) is common, easily recognized, and most often managed without difficulty in the prehospital setting. Polymorphic VT (PVT), however, is less well characterized in the out-of-hospital arena. In a pilot study, 5 we showed that PVT is a relatively common arrhythmia in the prehospital sudden death victim. Further, PVT appeared to respond well to American Heart Association Advanced Cardiac Life Support (ACLS) therapy as MVT. To our knowledge, only one previous report has examined PVT in the prehospital setting. 6 The true prevalence, response to resuscitative

therapy, and outcome of PVT in the out-of-hospital cardiac arrest victim is not known.

MATERIALS AND METHODS

A retrospective prehospital chart review was performed on the records of adult patients who experienced prehospital cardiopulmonary arrest with VT occurring at any time during resuscitation. All patients were treated by paramedic personnel from the Milwaukee County Paramedic System, a municipal, fire department-based, multitiered emergency medicine system (EMS) with on-line medical control serving a population of approximately one million. Medical intervention included resuscitation according to 1987 American Heart Association ACLS guidelines. The study period covered five years: January 1, 1987, to December 31,1991. Adult patients older than 18 years were entered into the study if they experienced nontraumatic prehospital cardiopulmonary arrest with VT occurring at any time during the prehospital phase of care.

Prehospital ECG rhythm strips were reviewed by the investigators; all cases of VT occurring during the study period were identified. VT was diagnosed if the QRS complex was widened beyond 0.12 seconds and the rate was greater than 100 beats per minute. VT was then sub- divided into two categories: MVT and PVT. The VT was considered MVT if the QRS-complex configuration was stable when viewed in a single ECG lead (ie, no beat4o- beat variation in the QRS-complex morphology). The VT was considered PVT if the QRS-complex configuration was not stable when viewed in a single ECG lead (ie, episodic changing of the QRS-complex electrical axis, amplitude, or both or the presence of more than two QRS-complex

Figure 1. Electrocardiographic rhythm recording demonstrating rnonomorphic ventricular tachycardia.

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T A C H Y C A R D I A Brady, MeIdon & DeBehnke

morphologies). See Figures 1 and 2 for representative examples of MVT and PVT, respectively.

Information gathered from the prehospital records included rhythm diagnosis, patient age and gender, downtime (defined as the interval from the time of patient collapse to the first paramedic intervention), time to initial defibrillation (defined as the interval from paramedic arrival at patient to first defibrillation), time to the return of spontaneous circulation (ROSC; defined as the interval from first paramedic intervention to ROSC), total cardiopulmonary resuscitation time (defined as the interval from first paramedic intervention to ROSC or termination of efforts), witnessed vs. nonwitnessed arrest, number of defibrillation attempts, use of endotracheal intubation, ACtS medications usage, resuscitation status at the end of prehospital care (defined as the presence or absence of spontaneous circulation at the end of the prehospital phase of treatment), and final outcome (defined as died, with the location of death; or survived, with discharge location).

Proportions were analyzed with the X 2 or Fisher exact test where appropriate. Adjustment for multiple comparisons was made using Bonferroni's method. A P value less than .05 was considered significant.

RESULTS

Four hundred seventy-six patients met entry criteria; 37 patients were excluded from the study because of incomplete medical records, and 439 patients were used for data analysis.

MVT occurred in 323 patients (73:6%), and PVT occurred in 116 patients (26.4%). MVT was the presenting rhythm in 28 patients, and PVT occurred initially in 12 patients. Rhythm characteristics and demographic data are summarized in Table 1. Among patients with MVT,

119 (36.8%) demonstrated ROSC in the prehospital setting and 35 (10.8%) survived to hospital discharge. Of those with PVT, 48 (41.4%) showed ROSC and 15 (12.9%) survived to discharge. Interval data are also summarized in Table 1, and outcome is summarized in Table 2. When adjustments were made for multiple comparisons, the two rhythm groups did not differ signifi- cantly with respect to the use of ACtS therapy (defibrillation, endotracheal intubation, and medication usage), ROSC, or survival•

DISCUSSION

VT can be classified as monomorphic or polymorphic on the basis of the morphological features of the QRS complex. r,8 MVT is a form of VT with a stable QRS-complex configuration s (a uniform beat-to-beat QRS-complex morphology). It is the most commonly encountered form of VT in acute cardiac care. 9 PVT is defined as a VT with an unstable (continuously varying) QRS-complex morphology {n any single ECG lead. 8 Variations in both the R-R interval and the electrical axis are also noted features of this ventricular arrhythmia. 1°,11 The clinical implications of PVT in the prehospital setting, including the incidence, proper resuscitative therapy, and prognosis, are not well characterized. To our knowledge, only one previous report has examined PVT in the prehospital setting. 6

Multiple terms for PVT are found in the medical literature, causing confusion with regard to rhythm recognition, eti- ology, and proper therapy. Torsades de pointes, 12 cardiac ballet, ~ 3 atypical ventricular tachycardia, ~4 transient recurrent ventricular fibrillation,~ 5 swinging ventricular tachycardia, ~ ~ and pleomorphic VT 6 are such examples and are frequently used interchangeably to describe the category of PVT. We believe that polymorphic ventrtcular

Figure 2. Electrocardiographic rhythm recording demot~strating polymorphic ventncular tachycardia.

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1_:YL:,_R :.-_T. 7..7 : ........ , _!_

":: '.7 : ] .t...l--!-,lZ!:-:i".-7-77::.7:::[7 :- '77 ::::L; . .!/.-::.::.L:.

6 6 ANNALS OF EMERGENCY MEDICINE 25:1 JANUARY 1995

T A C H Y C A R D I A

Brady, Mddon & DeBehnke

tachycardia should be the single term used to describe this subtype of VT; the term torsades de pointes should only be employed when delayed repolarization (prolongation of the QT interval) is noted on the ECG. This confusion in terminology, which may affect patient outcome, is found frequently among physicians (emergency medicine and cardiology). 1 r. 18

Torsades de pointes, first described by Dessertenne in 1966, is identified when PVT occurs in the setting of delayed myocardial repolarization manifested on the ECG by a prolongation of the QT interval. 7,11,1r,19,2° Torsades de pointes is therefore one subtype of PVT and not a syn- onym for the category of PVT. The literal translation of the French term torsades de pointes, "twisted fringe of points," elegantly describes the appearance of the QRS- complex as it varies in amplitude, appearing to rotate about the isoelectric baseline in a semisinusoidal fashion. The distinction has clinical significance in the management of PVT, although prehospital recognition may be difficult. Identifica- tion of prolongation of the QT interval in the prehospital setting by paramedic personnel or by on-line medical control physicians, especially among patients initially found in cardiac arrest, may not be possible in the early stages of resuscitative out-of-hospital therapy.

Many cases of SCD occur in outpatient, unmonitored settings. As such, the initial rhythm--as well as the pre- ceding and subsequent arrhythmic events, in many cases-- remains unknown. The introduction of rapid EMS response units with ECG monitoring capabilities in many commu- nities, the widespread use of both ambulatory ECG monitoring and electrophysiological studies in patients with suspected or known cardiovascular disease, and the presence of CCUs with sophisticated cardiac monitoring have in many cases revealed the course of events in the early stages of sudden cardiac death. Polymorphic ventricular tachycardia has been found in victims of prehospital cardiac arrest, 6 in patients undergoing ambulatory cardiac monitoring, 21,22 in survivors of prehospital sudden death subsequently studied in the electrophysiology labo- ratory, 2L23,24 and in patients admitted to the CCU for treatment of acute cardiac ischemia. 25,26 PVT, when noted in these situations, frequently is the initial rhythm; it degenerates to MVT or VE White et al 6 reported four cases of out-of-hospital cardiac arrest involving PVT either as the presenting rhythm or as a rhythm encountered during the course of prehospital resuscitation. Two of these cases involved PVT followed by VE The incidence, however, of PVT in the prehospital setting among patients with sudden cardiac death remains unknown.

Multiple reports of patients experiencing cardiac arrest while undergoing ambulatory cardiac monitoring suggest that PVT is a relatively common arrhythmia among patients with myocardial disease who experience sudden ventricular arrhythmia. Denes et a122 found five cases of sudden cardiac death (all ventricular fibrillation) in 3307 consecutive patients undergoing ambulatory cardiac monitoring to assess their response to antiarrhythmic therapy. In all five cases, PVT was the initial arrest rhythm; it degenerated into VE Panidis et al 3 reported 15 episodes of sudden cardiac death in 38,500 patients subjected to ambulatory monitoring for a variety of cardiovascular reasons. Among the 15 patients who experienced sudden cardiac death, 80% of cardiac arrests were due to a ventricular arrhythmia, with five cases of PVT; in 1 patient with PVT, VF developed. Kempf et al 2r noted 27 cases of sudden cardiac death in ambulatory monitored patients, with 20 total cases of VT. The VT was considered polymorphic in six of these patients. DiMarco et al, 21 in a review of sudden cardiac death, reported a 43% incidence of PVT or VF as the initiating rhythm (obtained from seven such patient case series) among patients with ambulatory monitoring who died suddenly.

PVT is noted in a significant minority of patients resus- citated from cardiac arrest who survive to electrophysiology

Table 1. General characteristics.

Characteristic MVT 95% CI PVT 95% CI P

Patients (%) 323 (73.6) 116 (26.4) No. of patients 28 (8.7) 5.6-11.8% 12 (10.3)

with VT subtypes as initial rhythm (%)

No. of patients 42(13.0) 9.4-16.6% 12(10.3) with paramedic witnessed VT subtype (%)

Age (yr)* 67.5+13.3 66-69 67.6_+12.8 No. of male 198 (61.3) 56.0-66.6% 86 (74.1)

patients (%) Down time 10.7_+5.3 10.1-11.3 9.7_+6.3 Time to initial 3.7_+4.9 3 .2 -4 .2 3.9_+4.8

defibrillation Timeto ROSC 19.4_+10.1 18.3-20,5 19,2_+9.5 Totalcardiopulmonary 29.3_+13.B 27.8-30.8 29.1_+13.9

resuscitation time *Expressed as mean_+SD. tWhen adjustments made for multiple comparisons. MVT-monomorphic ventricular tachycardia. PW=polymorphic ventricular tachycardia. VT=ventncular tachycardia. ROSg=return of spontaneous circulation.

4.8-15.8% NS

4.8-15.8% NS

65-70 NS 66.1-82.1% NS t

8.6-10.9 NS 3.0-4.8 NS

17.5-21,0 NS 26.6-31.6 NS

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T A C H Y C A R D I A Brady, Mddon & DeBehnke

study. Roy et al 2s reported the results of electrophysiology study in 119 survivors of cardiac arrest (59% VF and 28% VT) of whom 72 had inducible arrhythmia. Among 63 cases of VT, PVT was found in 18 patients. Stevenson et a129 noted four cases of PVT in 21 patients referred for EP study to evaluate SCD; in all cases of PVT, the rhythm degenerated to VE DiMarco et al 21 reported a compilation of seven electrophysiology study series in which PVT was induced in 16% of patients who survived out-of-hospital cardiac arrest.

The association of cardiac ischemia syndromes and PVT has been noted in the past. White et al s reported a series of four patients with acute myocardial ischemia (two patients) or infarction (two patients) who presented to EMS personnel with PVT. Grenadier et a126 reported nine patients with PVT who were admitted to the CCU with acute myocardial infarction. These patients represented a PVT incidence of 1.2% among 771 consecutive patients admitted to the CCU with acute myocardial infarction. Wolfe et a125 found an incidence of 2% for PVT in the first 2 weeks after acute myocardial infarction in patients managed in the CCU over a 2.9-year period; in approximately 80% of these patients, recurrent ischemia developed immediately before the appearance of PVT.

With the exception of the report from White et al, 6 these studies describe PVT in patients with suspected or known myocardial disease managed in specialized, inpa- tient settings. We have found no other report in the medical literature characterizing the incidence of PVT in the setting of prehospital sudden cardiac death. White et al s suggest that PVT is a more common arrhythmia than previously

thought in patients with prehospital sudden cardiac death. The findings in our prehospital SCD population support their suggestion. In our series, we found that PVT accounted for a significant minority (26.4%) of cases involving VT. PVT was the presenting pulseless rhythm in 12 cases (10.3%) and was the initial rhythm in 12 paramedic-witnessed episodes (10.3%) of cardiopulmonary arrest. Furthermore, we may not have recognized all cases involving PVT with the use of single-lead ECG monitoring. The polymorphic nature of PVT may not be obvious when the rhythm is viewed from a single ECG lead7

As demonstrated previously in the patients who have SCD while undergoing ambulatory ECG monitoring, PVT is an early, if not initial, rhythm found in patients with cardiopulmonary arrest. In many of these cases of sudden cardiac death characterized by early PVT, monomorphic VT, VF, or both soon follow. The EMS unit response time and delivery- of advanced life support resuscitation in our system is rapid, averaging approximately 10 minutes. In many of these patients, the EMS personnel undoubtedly found the patient in the early arrhythmic stages of sudden death, perhaps accounting for the relatively high frequency of PVT. In the prehospital population, the ability to identify QT-interval prolongation on the ECG while in supraven- tricular rhythm and consequently make the rhythm diagnosis of torsades de pointes once PVT appears would be difficult. Most patients with PVT were found by paramedics in cardiopulmonary arrest, making any comments on the QT interval impossible until a perfusing cardiac rhythm could be restored. Approximately 10% of our PVT patients

Table 2. Patient outcomes in the resuscitation of prehospital cardiopulmonary arrest.

Outcome MVT 95% CI PVT 95% CI P

ROSC at ED arrival (%) 119 (36.8) 31.5-42.1 % 48 (41.4) 32.4-50.4% NS ROSC at ED arrival if V'I" initial rhythm (%) 14 (4.3) 2.2-6.4% 7 (6.0) 1.7-10.3% NS Survival to hospital discharge (%) 35 (10.8) 7.4-14.2% 15 (12.9} 6.8-19.0% NS

Discharge to home 12 (3.7) 2.1-5.8% 10 (8.6) 3.8-13.7% NS Discharge to chronic care facility 20 (6.2) 3.6-8.8% 3 (2.6) 0-5.5% NS* Discharge to unknown location 3 (I .0) 0~2% 2 (I 2) 0-4.1% NS

Death (%) 288 (89,2) 85.8-92.6% 101 (87.1) 81,0-93.2% NS Prehospita] 115 (35,6) 30.4-40.8% 29 (25) 17.1-32.9% NS Dead on arrival to ED 4 (1.2) 0-2.4% 6 (5.1) 1.1-9.1% NS* ED 76 (23.5) 18.9-28.1 27 (23.3) 15.6-31,0% NS Hospital 93 (28.8) 23.9-33.7% 39 (33.6) 25.0-42.2% NS

*With adjustments made for multiple comparison. MVT-monomorphic ventricular tachycardia. PV]-=polymorphic ventricular tachycardia. ROSO=return of spontaneous circulation.


TACHYCARDIA Brady, Meldon & DeBehnke

had an EMS-witnessed cardiac arrest. This small subset of patients would have furnished information to paramedics and on-line medical control physicians about the QT interval on the basis of the rhythm noted before cardiac arrest. Only in this small group could the prehospital diagnosis of torsades de pomtes be reliably made and therapy potentially altered.

A discussion of the resuscitative treatment of polymorphic ventricular tachycardia is plagued by consider- able controversy, similar to the confusion surrounding the proper terminology of PVT. Many reports are found in the literature in which standard ACLS therapy for ventricular tachycardia in patients with PVT is partially effective, ineffective, or potentially dangerous (proar- rhythmic). <1°,a5,26,3° Wolfe et al, 25 in their series of 11 patients with PVT related to acute ischemic heart disease, reported a patient population in which traditional antiarrhythmic therapy produced a variable response. The QT interval in all cases was normal. Lidocaine was used in 10 patients and proved to be effective in only 1 case. Procainamide, administered in six patients, was successful in only one instance. Bretylium (five cases) and magnesium (three cases) showed no benefit in any of the patients in which these agents were used. Grenadier et a126 had even less success in their series of nine patients with PVT occurring in the setting of acute myocardial infarction. The QT interval was prolonged in only one patient. Lidocaine, procainamide, and bretyfium were uniformly ineffective in the treatment of PVT. White et al 6 noted a variable response to ACLS antiarrhythmic medication in the prehospital management of four patients with PVT; one patient in this case series demonstrated evidence of abnormal repolarization on the ECG. Nguyen et al 3° described the clinical characteristics of 45 patients with PVT; approximately 50% of this series of patients had a normal QT interval on the ECG immediately before or during episodes of recurrent PVT. Lidocaine appeared to be effective in only half of the patients in which it was administered (24 patients), whereas bretytium, used only in three cases, was associated with increased frequency of PVT. Sclarovsky et al ~° reported 34 patients with PVT (most with QT prolongation) and characterized their response to treatment. Lidocaine, used in all cases, was successful in only seven patients.

Certain patients experiencing PVT have responded to medical measures aimed at increasing the heart rate, particu- larly in cases where the QT interval is prolonged. Intravenous isoproterenol, "chemical" cardiac pacing, was used successfully by Sclarovsky et aP ° in 10 patients to treat PVT.

i

Nguyen et al 3° reported successful overdrive pacing in 13 patients with PVT, regardless of the QT-interval length.

The existing medical literature suggests that PVT has at best a variable response to the standard antiarrhythmic medications for VT commonly used in the prehospital arena. In our series of prehospital sudden cardiac death victims, patients with both MVT and PVT received statistically similar dosages (both frequency and total amount) of the medications lidocaine and bretyfium. Patients in the two rhythm groups responded equally well to the medications in terms of ROSC in the prehospital setting and eventual survival to hospital discharge. No patient in our series received isoproterenol infusion or underwent overdrive cardiac pacing in the prehospital setting. We are therefore not able to comment on the effectiveness of these two therapies in the management of PVT in the prehospital setting. Epinephrine, however, was used to a statistically similar extent in the two rhythm groups, potentially providing chemical cardiac pacing similar to the effect of isoproterenol.

Transthoracic electrical cardioversion or defibrillation is generally believed to be less effective in the treatment of PVT. Grenadier et a126 reported a 66% response rate to electrical transthoracic cardioversion for patients in PVT. Sclarovsky et al 1° described seven successful cases in which electrical cardioversion terminated the PVT among a total of 34 patients. Kerber et a131 demonstrated that PVT behaves more like VF than like MVT in its response to transthoracic electrical cardioversion. Using increas- ingly higher energy shocks for the three arrhythmias, they found that MVT is successfully converted to a stable rhythm at lower electrical currents than PVT or VE They also noted that the response to electrical therapy of PVT was similar to that of VF and not to that of MVT. In our study of patients with prehospital VT, patients in the two rhythm groups received similar numbers of defibrillation attempts at similar energy levels. Again, similar to the response to the ACLS medications, patients showed statistically similar ROSC and survival rates in the MVT and PVT groups. We did not find resistance to electrical cardioversion or a need for higher energy levels in the PVT group compared with the MVT patients.

Potential limitations to our study include its retrospective nature, as well as the 37 patients who were excluded because of incomplete records. These two limitations, however, do not detract from the primary purpose of the study: to report the relative frequencies of MVT and PVT and the response of these arrhythmias to resuscitative therapy. Additionally, further work is required in the subset of VT patients with QT-interval prolongation and PVT.

J A N U A R Y 1995 25:1 ANNALS OF EMERGENCY MEDICINE 6 9

T A C H Y C A R D I A Brady, Meldon & DeBehn~ee

Such an evaluation would make the diagnosis of torsades de pointes possible with comments about its frequency and response to therapy

C O N C L U S I O N

PVT is a common arrhythmia encountered in patients with prehospital sudden cardiac death. We found PVT in 26.4% of all cases of prehospital VT cardiopulmonary arrest. This relatively high prevalence of PVT may be explained in part by the rapid response time of our EMS personnel. Many of these patients with PVT were found early in the setting of sudden cardiac death. Our study demonstrates that patients with MVT and PVT have similar outcomes without specific adjustments in therapy. W e conclude that until prospective data are available, standard ACLS therapy should be used in all forms of prehospital VT occurring during cardiopulmonary arrest.

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] 8. O'Dea D J, Kay RH, Blake JW, et ah Polymorphic ventricular tachycardia. Ann Emerg Mad 1989;18:100-102.

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The authors wish to thank Laura Zirzow for her assistance with manuscript prepara- tion, as well as Lauryl Pukansky, Rosemarie Ferster, and Elizabeth Manchester for their help with data acquisition and analysis. The authors also wish to thank the members of the Milwaukee County Paramedic System for their excellent care of critically itl or injured prehospital patients.

Reprint no. 47/1/61217

Address for reprints:

Daniel DeBehnke, MD

Department of Emergency Medicine

Medical College of Wisconsin

8700 West Wisconsin Avenue, DH-204

Milwaukee, Wisconsin 53226


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