Which of the following is a relative contraindication for symptom-limited maximal exercise testing?

Cardiopulm Phys Ther J. 2012 Sep; 23(3): 16–22.

Abstract

Purpose

Performing exercise tests in patients with an implantable cardioverter defibrillator (ICD) presents specific challenges because of susceptibility to ventricular arrhythmias during maximal levels of exertion. The purpose of this paper is to outline the exercise testing protocol from the Anti-Arrhythmic Effects of Exercise after an ICD trial and to report baseline test results and safety outcomes using the protocol.

Methods and Results

Maximal cardiopulmonary exercise testing was performed to assess levels of physical fitness as part of a randomized trial of walking exercise in patients with ICDs. Subjects were randomized after baseline testing to aerobic exercise plus usual care or usual care alone. A modified Balke treadmill exercise test was used and specific ICD programming procedures were implemented to avoid unnecessary shocks, which included programming off ventricular tachycardia (VT) therapies during testing. To date, 161 baseline tests have been performed. One ventricular fibrillation (VF) cardiac arrest occurred following completion of an exercise test and three tests were stopped by the investigators due to nonsustained ventricular tachycardia. Eleven subjects were not able to achieve maximum exercise, defined as reaching an anaerobic threshold (AT) at baseline testing. There have been no deaths as a result of exercise testing.

Conclusions

Symptom-limited maximal exercise testing can be performed safely and effectively in patients with ICDs for both primary and secondary prevention indications. Specific strategies for ICD programming and preparation for treating ventricular arrhythmias needs to be in place before exercise testing is performed.

Key Words: implanted cardioverter defibrillator, exercise testing, treadmill protocol

INTRODUCTION

Cardiopulmonary exercise testing was originally developed as a tool to assist in the diagnosis and evaluation of coronary artery disease. The technique was based on the discovery that exercise induced ST segment depression on the 12 lead EKG could be used to identify cardiac ischemia.1 The Bruce, Ellestad, Balke, and Naughton protocols were developed early in the process of refining this diagnostic technique.1 There are not standardized, established protocols that assist providers in performing exercise tests in patients who have an implantable cardioverter defibrillator (ICD). Exercise testing has expanded since the 1950s to assist in achieving a variety of clinical and research objectives (See Table ​1).

Table 1

Stress Test Indications

• Evaluation of chest pain in those with or without previous coronary disease.2

• Assessment of risk for perioperative myocardial infarction in patients with known coronary disease or who are at high risk.3

• Determination of timing for correction of congenital heart defects.1

• Determination of safety of engaging in a new exercise program for sedentary individuals.

• Evaluation for presence and significance of exercise-induced arrhythmias.1

• Evaluation of effectiveness of pharmacologic and nonpharmacologic therapies for ischemia, arrhythmias, or hypertension.1, 5

• Quantification of effects of interventions on functional capacity.4, 6

Increasingly, patients with indications for exercise testing will have implanted cardiac defibrillators. According to the National ICD Registry, the number of ICD implants reported in the United States has grown from 92,897 in 2006 to 141,374 in 2009; with the total number of implants in excess of 486,025.7 There are no standardized, established protocols that assist providers in performing exercise tests in patients who have an ICD. Complications of exercise testing (ventricular fibrillation, ventricular tachycardia, bradycardia) in those with known ventricular arrhythmias has been reported as high as 9% with no reported deaths.8 Prior to development of the testing protocol for this study, there were very few reports of exercise testing in people with ICDs. One small trial of exercise training (n= 8) reported two episodes of ventricular tachycardia associated with exercise,9 occurring either at peak exercise testing or during exercise training that required ICD shock therapy.

Several considerations need to be taken into account when doing exercise testing in patients with an ICD. These include being aware of the lowest heart rate cut-off where ICD therapies are programmed on, avoiding unnecessary ICD shocks for sinus tachycardia, and being aware of pacemaker parameters during testing. Tachyarrhythmia therapy programming information including heart-rate cut-offs when a shock or anti-tachycardia pacing (ATP) will be initiated and the sequence of therapies programmed for arrhythmias should be reviewed prior to the test. The testing protocol should include steps to avoid unnecessary ICD shocks for sinus tachycardia while allowing rapid appropriate treatment.10 Inappropriate therapy for exercise induced sinus tachycardia is not only traumatic for the patient, but may be pro-arrhythmic, thereby causing unnecessary hemodynamic instability.11 Awareness of the upper tracking rate of dual chamber pacing before exercise testing will help the clinician to be mindful of the heart rate at which Wenckebach may occur if the upper tracking heart rate is reached during the test and to differentiate ventricular arrhythmia from a paced rhythm. A clinician with specialized training in the care of patients with an ICD should be present at the test to adjust the ICD programming to avoid unnecessary shocks and re-program therapies after the completion of the test.10

There are no standardized exercise test protocols that are adopted for routine use in clinical practice, and none exist for obtaining repeated VO2max measurements in research studies involving persons with an ICD. Performing a maximal exercise test in persons with an ICD requires careful planning and Specific safety measures in order to avoid unnecessary shocks and to obtain a maximum test. If clinicians had a standardized and safe exercise testing protocol that could be used for individuals with an ICD, this modality could be used more effectively in future studies and tests of effects of exercise interventions.

The purpose of this paper is to report on the preliminary safety and baseline results of an exercise testing protocol for the measurement of VO2max in persons with an ICD in the Anti-Arrhythmic Effects of Exercise after an ICD trial (NHLBI 5R01 HL 084550).12 Special considerations for performing an exercise test in persons with an ICD will be outlined.

METHODS

The Anti-Arrhythmic Effects of Exercise after an ICD study is a randomized clinical trial that aims to test the effects of an 8 week walking exercise program on changes in maximum oxygen consumption VO2max when compared to usual care. Measurement of VO2max is considered to be the gold standard for determining functional capacity and fitness,6, 13, 14 and requires performing maximal exercise testing. The primary outcome of the trial is cardiopulmonary fitness as measured by VO2max. Secondary outcomes are ventricular arrhythmias and ICD shocks when compared with usual care. The exercise testing protocol described here was specifically designed to meet the objectives of the trial, while also providing clinicians with an algorithm to perform a safe and efficient exercise test for this population.

Exercise Test Protocol

The exercise testing protocol used was a modified-Balke protocol.15, 16 The major modification made was the addition of slower initial stages so that those with poor functional capability were able to complete an adequate test and those not familiar with treadmill walking were able to acclimate to the testing equipment. Prior to starting exercise, resting cardiopulmonary data were collected for two minutes. Treadmill walking started on 0% grade at 0.5 mph, with increases to 1.0, 1.7, 2.2, 2.7, and 3.3 mph. Stage duration was one minute. Starting at 6 minutes the grade increased in 1% per minute increments with the speed maintained at 3.3 mph until the patient indicated achievement of maximum effort. After this, subjects completed a cool down stage with 5 minutes of walking at 1.5 mph and 0% grade. Specific steps in the protocol are summarized in Table ​2, including ICD programming parameters.

Table 2

Exercise Testing Procedure using Modified Balke Protocol

Cardiopulmonary Exercise Testing Protocol

• 1.

  Spirometry and FEV1 calculations

• 2.

  Place on cardiac monitor before any ICD programming changes

• 3.

  Place A/P defibrillation patches in anyone with previous ICD therapies or hx of VT

• 4.

  Interrogation of ICD. Determine programming and past therapies.

• 5.

  Leave on VF detections and therapies

• 6.

  Turn off VT detections, but leave VT therapies on programmer if already programmed

• 7.

  CPET to maximum test, gas analysis, while walking on treadmill without holding onto front or side bars

• 8.

  Stop exercise test for:

  • Suspicion of acute MI

  • Onset of moderate to severe angina

  • Drop in SBP with increasing workload

  • Onset new arrhythmia (2nd−3rd degree AV block, sustained VT, new onset atrial fib, SVT)

  • Signs of poor perfusion (pallor, cyanosis)

  • Unusual severe SOB

  • CNS symptoms (ataxia, vertigo, visual problems, confusion)

  • SBP > 250 mm Hg or DBP > 120 mm Hg

  • Patient asks to stop

  • Patient cannot balance on treadmill without holding on to side bars

• 9.

  Remain on cardiac monitoring until returning to HR < 100 bpm, resting HR, and/or no arrhythmias.

• 10.

  Turn VT detections back on after test, if previously on.

• 11.

  Leave exercise area after returning to resting HR with no arrhythmias.

Exercise testing for all participants was completed at an academic medical center in the Pacific Northwestern United States. Gas exchange analyzers were calibrated according to American Thoracic Society (ATS) standards17 prior to each test in addition to departmental routine calibration. External defibrillation pads were applied (Quik Combo RTS Pads, Medtronic Inc, Redmond, WA) to the chest wall to facilitate rapid defibrillation or cardioversion should sustained symptomatic ventricular arrhythmias develop during the exercise test or cool-down phase. The ICD was interrogated before testing to assure normal function of the device and determine if the subject had any recent significant dysrhythmias. A clinical specialist from the device manufacturer was present to assist with device interrogation and programming. Ventricular tachycardia therapies were programmed off to avoid unnecessary shocks due to sinus tachycardia; VF therapies were left on and unchanged from pretest settings.

Gas exchange measurements were collected and analyzed using V-Max metabolic system (Viasys Respiratory Care Inc., Yorba Linda, CA). Breath by breath sampling was recorded and tabular data were summarized in 20 second intervals. A 12 lead ECG was continuously monitored using the Cardiosoft program (SensorMedics Corp. Yorba Linda, CA) integrated with the metabolic system. Pulse oximetry was monitored using a Nonin 8600 pulse oximeter (Minneapolis, MN) and blood pressures (BP) were measured every two minutes with a Sun Tech Tango automated BP cuff (Sun Tech Medical, Morrisville, NC). These data were continuously recorded and displayed throughout the duration of the exercise test.

Subjects were continuously monitored for indications of stopping exercise before a maximal effort. See the protocol in Table ​2 for identified indications to stop treadmill testing. In addition it was anticipated that testing would be stopped by the investigators for evidence of ataxia putting the subject at risk for falling, chest pain with ST segment changes, sustained ventricular tachycardia, achievement of maximum predicted heart rate for age, or equipment malfunction that prevented adequate monitoring.18

Procedures

Study participants were recruited from 10 clinical sites in the Pacific Northwest. All study procedures were reviewed and approved by Institutional Review Boards. All study participants provided written informed consent prior to baseline exercise testing. A data safety and monitoring board (DSMB) monitored recruitment procedures, safety, and adverse events. Inclusion criteria were: (1) ICD (without resynchronization pacing) implanted at least 3 months prior to study entry, (2) ability to read and speak English, (3) taking beta blocker medication, and (4) willing to complete the exercise program and all follow-up testing. Exclusion criteria were: (1) clinical co-morbidities that severely impair cognitive and/or physical function; (2) short BLESSED score ≥ 6;19 (3) age less than 21 years; (4) AUDIT-C score > 4 for alcohol use;20 (5) unstable angina, myocardial infarction (MI), or heart surgery within the previous 3 months; 6) concurrent participation in a regular exercise program of 60 minutes 5 days a week; or (7) presenting cardiac rhythm other than normal sinus rhythm. Patients who were interested in the study but were found to have characteristics representing an absolute or relative contraindication for exercise testing as recommended by the American College of Cardiology/American Heart Association (ACC/AHA)18 exercise testing guidelines were not included in the study. The most common contraindications encountered in screening subjects included hemodynamically significant valvular heart disease, severe pulmonary hypertension, or hypertrophic cardiomyopathy with obstructive physiology.

Testing procedures and subject instructions were reviewed by phone several days prior to baseline testing. Subjects were advised to take a routine dose of beta blocker approximately two hours before the test,21, 22 have a light meal and a moderate amount of fluids 4 hours before testing, and avoid caffeine and tobacco the morning of the test. Exercise tests for study subjects were performed to the level of maximal effort to determine VO2max and AT. Participants were determined to be eligible for randomization into the trial if they were able to achieve a maximal test at baseline testing, defined as the ability to reach an AT with a respiratory exchange ratio (RER) of at least 1.0. The anaerobic threshold was determined by computerized algorithms using the V-slope method (separation of VCO2-VO2Lmn slopes) and confirmed by two reviewers.17 Subjects were then randomized to receive the exercise intervention plus usual care or usual care alone. Included in this paper are the results of baseline exercise testing for all subjects randomized at this point in the trial.

RESULTS

Demographics

One hundred sixty-one subjects have completed baseline exercise tests, and 16 subjects were not randomized into the trial. Of these, 11 were not able to achieve a maximal test, 3 were not randomized due to exercise induced arrhythmias, and two declined to be randomized. Of those randomized, 77% were male and 84% were Caucasian. The mean (SD) ejection fraction (EF) was 40.7 (15.9%). Average age was 55 (12.6) years. The study sample includes those who received an ICD for either primary or secondary prevention indications. Fifty-seven (39.3%) had received an ICD for primary prevention due to severe left ventricle (LV) systolic dysfunction or other markers of increased risk. The remaining 88 had secondary prevention indications such as VF/VT arrest or sustained VT associated with coronary artery disease and a past history of myocardial infarction.23 See Table ​3. All subjects were on beta blocker therapy. Sixty three (43%) had a prior history of MI. Twelve subjects had hypertrophic cardiomyopathy, 26 had a history of coronary artery bypass, and 49 had a diagnosis of nonischemic cardiomyopathy.

Table 3

Participant Demographics (N = 145)

Baseline Test Results

The mean VO2max for the 145 subjects randomized was 23.8 (6.0) ml/kg/min. with a range of 10.9 to 42.5ml/kg/min. The average exercise time on the modified Balke protocol was 13:42 (4:57) min. (range 3:49 to 33:44 minutes). The mean VO2 at AT was 19.87 (5.28) ml/kg/min. (range 10.6 to 37.5 ml/kg/min). The mean oxygen pulse was 16.9 (5.3) ml/beat. Average respiratory exchange ratio (RER) was 1.10 (0.84). See Table ​4.

Table 4

Baseline Exercise Test Results (N = 145)

Safety and Adverse Events during Exercise Testing

The incidence of adverse events and cardiac arrhythmias using the current protocol has been very low, with one VF event and 2 episodes of nonsustained wide complex tachycardia during exercise testing (3/161, 1.86%, 95% CI: 0.39% − 5.58%.). There have been no deaths and no inappropriate ICD shocks during exercise testing. One subject, with a history of ischemic cardiomyopathy and prior coronary artery bypass, experienced a VF arrest at 2:40 seconds into the 5 minute recovery period. This subject was successfully cardioverted to sinus rhythm with two ICD shocks. He lost consciousness for less than 15 seconds and was ultimately discharged to outpatient follow-up the same day as the test. Myocardial perfusion scanning performed by his usual cardiology providers suggested new ischemia. Angiography was performed but no new targets for revascularization were identified. Therefore, this subject was not enrolled into the study.

Exercise tests were stopped before maximal effort by the investigators in 3 subjects due to wide complex tachycardia. One person had a past history of accessory pathway-mediated tachycardia and was not enrolled due to the need for further evaluation of his arrhythmia. The second person experienced several brief salvos of ventricular tachycardia. He had a history of coronary artery disease and was evaluated after the exercise test by his cardiology providers. The subject had an ischemic work-up that revealed no new areas of ischemia or infarction, and he was retested after an increase in beta blocker dose. He was subsequently enrolled in the study, and completed all follow-up exercise tests with no further exercise induced arrhythmias. Finally, a third subject developed sustained VT during exercise. He was asymptomatic and reverted to SR immediately at the start of recovery. He was also not enrolled and was referred back to his cardiology providers for follow-up care.

With respect to device programming, there were two subjects who exercised to a higher heart rate than their lowest ICD treatment zone, thus two shocks were avoided with programming VT therapies off during the test. In addition to the two subjects who exercised to a higher rate than their VT treatment zone, there were 26 tests in which the subject exercised to within 20 bpm of the preprogrammed VT zone; and of these 26, there were 7 occasions when the peak heart rate was within 10 bpm of the preprogrammed VT zone.

DISCUSSION

One hundred sixty-one symptom-limited maximal exercise tests were performed in persons who had an ICD as part of a randomized trial of exercise. There was one VF cardiac arrest in the recovery phase of exercise testing, but no deaths, refractory arrhythmias, or inappropriate ICD shocks. Prior studies have also shown maximal exercise testing can be completed safely in individuals with known cardiac disease and ventricular arrhythmias.8 A longitudinal observation study by Chinnaiyan et al24 described 44 exercise tests performed over 4 years. The ICDs were not inactivated for these tests. There were 4 patients who had nonsustained VT at peak exercise that self-terminated. A small trial of cardiac rehabilitation by Vanhees et al9 included 8 subjects with an ICD. One patient had nonsustained VT at follow-up exercise testing and one subject had sustained VT while doing the exercise intervention, which was successfully treated by an ICD shock. Keteyian et al25 published a report of exercise test safety in the HF-ACTION trial. Forty percent (932) of the subjects in this trial had an ICD and there were no ICD discharges as a result of the exercise testing. There was no description of whether the ICD programming was adjusted prior to exercise testing. They reported only one episode of VF and one episode of sustained VT. However the HF-ACTION investigators reported only adverse events that occurred at follow-up testing and not initial baseline testing. None of these papers reported incidence of ICD shock for sinus tachycardia.

The adverse event rate in this study is comparable to adverse event rates reported in similar populations of persons at high risk for cardiac arrhythmias during exercise testing. Complications (ventricular fibrillation, ventricular tachycardia, bradycardia) in exercise testing in subjects with known ventricular arrhythmias has been as high as 9% in 263 subjects undergoing 1377 exercise tests, with no reported deaths.8 However these tests were performed before the use of beta blocker therapy in this population.

Several exercise testing protocols have been developed and tested for inducing and detecting myocardial ischemia.6 Ultimately, the Bruce26 protocol became the most common protocol used in clinical practice.27 This protocol was first formalized in the mid 1950s by Robert Bruce in Seattle, WA. The Bruce protocol uses 2 − 3 MET increments of increased treadmill speed and grade every 3 minutes, is symptom-limited, starting at a 10% grade and 1.7 mph. The Bruce,26 Naughton,28 and Ellestad1 protocols are not ideal for impaired or obese individuals as they cannot sustain the relatively high power output required early in the protocols. For purposes of identifying an anaerobic threshold, a progressive test lasting at least 6 or 7 minutes and preferably longer is required, making these exercise test protocols impractical for testing sedentary or obese populations or those with impaired LV function and therefore reduced functional capacity.

The Balke-Ware protocol, which has equivalent increases in workload between stages, was originally designed to test functional capacity in healthy military personnel.15 The primary difference between the modified Balke protocol being used in this study and the classic Balke design is the addition of slow increments of speed at 0% grade in the first 5 minutes at the start of the test. Additional stages of 0.5, 1.0, 1.7, 2.2, 2.7, and 3.0 mph were added in order to achieve an exercise test of adequate duration to consistently measure anaerobic thresholds and maximal VO2. Exercise protocols, such as the modified Balke protocol, that have a more linear or ramp pattern of increasing workload than the Bruce, Ellestad, or Naughton protocols have been found to produce a more continuous increase in cardiorespiratory responses and ultimately more accurate measurement of VO2max.1 A modified Balke protocol was selected for this trial to maximize patient safety and allow for sufficient accuracy and reproducibility of VO2max measurements for purposes of data collection and analysis. See Table ​5 for a side by side comparison of protocols. The ramp protocol with gradual increments accommodates subjects with limited treadmill experience and/or mild balance difficulties, provides optimal reproducibility of VO2max measurements, and sufficient treadmill time to increase the likelihood of achieving an AT.4 The modified Balke protocol used was found to be very suitable for this population as the majority of subjects were able to exercise to the point of achieving an anaerobic threshold.

Table 5

Exercise Test Protocols

One key safety feature of the protocol described here is the 5 minute cool-down phase. A carefully monitored cool-down phase may be important for prevention of recovery phase arrhythmias.2 Catecholamines rise significantly at peak exercise and continue to rise into recovery. The early recovery period may be the time when patients are most at risk for exercise-related ventricular arrhythmias. 29 One patient who experienced VF cardiac arrest with this protocol did so in the early phase of recovery.

A second key safety feature of our testing protocol was the management of the ICD before, during, and after the exercise test. The subjects’ heart rate was carefully monitored during the exercise test in order to stop exercise should it approach the set rate for ICD therapies. Persons who are familiar with ICD programming are present at the test so that rapid changes to ICD programming can be made if necessary. In this protocol, the ICD was reprogrammed before the exercise test in order to avoid ICD shocks if the predicted exercise heart rate was likely to exceed the lower ICD cut-off rate during the exercise test. This was accomplished by programming VT therapies off during the test. In the event of a sustained ventricular arrhythmia the device can be easily programmed back on to provide the appropriate therapy or emergency equipment for defibrillation can be used that is available in the lab. For added safety, VF therapies were left on because the heart rate threshold for VF therapies is much higher than can be typically achieved with exercise. By programming VT therapies off and leaving on VF therapies, a balance can be achieved between allowing subjects to exercise to their symptom limited maximum heart rate while still providing rapid protection against the most lethal of ventricular arrhythmias. In this study it was beneficial to program VT therapies off during testing thereby avoiding inappropriate shocks in two subjects and the need for reprogramming in 7 others during the test.

The limitations of applying of these findings to the general ICD population include the relatively small sample size, the careful prescreening that occurred before subjects were enrolled in the study, and the requirement for the baseline cardiac rhythm to be normal sinus rhythm. These screening measures may render the adverse event rate lower than would be encountered in general practice.

CONCLUSIONS

The modified Balke exercise testing protocol described here can be applied in general practice for exercise testing, both with and without cardiopulmonary testing, in patients with a history of arrhythmias, those with an ICD, or patients with limited functional capacity in whom exercise testing would be helpful clinically. The preliminary data presented demonstrate that maximal exercise testing can be performed safely with few adverse events in patients with ICDs who are at high risk for sudden cardiac death or ventricular arrhythmias. The modified Balke protocol described has been shown to be effective for measuring exercise capacity in impaired and/or obese persons with the majority able to achieve a maximum test. Clinicians performing the test need to be aware of the ICD settings and make adjustments as needed to allow the subject to exercise to full capacity without fear of receiving an unnecessary ICD shock. We have incorporated management of the ICD into the exercise testing protocol. These techniques can be easily applied in other clinical or research settings provided personnel are available to interrogate and program the ICD, the contraindications for exercise testing are considered and clinicians are present who possess the training to identify indications for stopping the test when manifested.

DEFINITIONS

Anaerobic threshold (AT): Theoretical physiologic point at which muscles add in anaerobic metabolism as an energy source.30

Exercise time: Total number of minutes: seconds spent in treadmill exercise not including the 5 minute cool-down stage.

Maximal oxygen consumption (VO2max): Represents the largest amount of oxygen used during dynamic exercise involving large amount of muscle mass.30 Value is the average observed over the last 10 seconds of exercise.

Oxygen pulse (VO2/HR): Volume of oxygen taken up by pulmonary blood during an individual heart beat. If oxygen delivery and extraction are normal, O2 pulse can be used to estimate stroke volume.6

Oxygen consumption at the AT (VO2 at AT): Oxygen consumption measured at the time AT is estimated. This value usually occurs at about 40% to 60% of VO2max.30

Respiratory exchange ratio (RER): Ratio of VCO2/VO2.: An RER > 1 may be related to both lactic acidosis and hyperventilation. The ratio is determined by fuels used for metabolic processes.17

ACKNOWLEDGMENT

Funding: National Institutes of Health, National Heart, Lung, and Blood Institute, 5R01 HL084550.

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