Volume 118, Issue 12 , Pages 1381-1386, December 2005
Pacemaker stress echocardiography predicts cardiac events in patients with permanent pacemaker
Article Outline
Abstract
Purpose
Noninvasive pacemaker stress echocardiography is a newly introduced method for the diagnosis of coronary artery disease in patients with a permanent pacemaker. The prognostic value of pacemaker stress echocardiography has not been studied.
Subjects and methods
We studied 136 patients (mean age 64
±12 years) with a permanent pacemaker who underwent pacemaker stress echocardiography for evaluation of coronary artery disease. All patients underwent pacemaker stress echocardiography by external programming (pacing heart rate up to ischemia or target heart rate).
Results
Thirty-one patients (23%) had normal study results. Ischemia was detected in 75 patients (55%). During a mean follow-up of 3.5±2.4 years, 35 deaths (26%) (20 the result of cardiac causes) and 2 nonfatal myocardial infarctions (1%) occurred. The annual cardiac death rate was 1.3% in patients without ischemia and 4.6% in patients with ischemia (P=.01). The annual all-cause mortality rate was 3.1% in patients without ischemia and 7% in patients with ischemia (P=.004). The presence of ischemia during pacemaker stress echocardiography was the strongest independent predictor of cardiac death (hazard ratio 4.1, confidence interval 1.2-14.5) and all-cause mortality (hazard ratio 2.7, confidence interval 1.2-6.0) in a multivariable model.
Conclusion
Myocardial ischemia during pacemaker stress echocardiography is an independent predictor of cardiac death and all-cause mortality in patients with a permanent pacemaker.
Keywords: Stress testing , Echocardiography , Pacemaker , Prognosis
The number of permanent pacemaker implantations has exponentially increased in the last decades and may be related to the increase of the elderly population and the expanding indications for pacing.1 Coronary artery disease may concomitantly exist in patients with a pacemaker or be the underlying cause of conduction defects in some cases.2, 3, 4, 5 Noninvasive evaluation of coronary artery disease is challenging in these patients, because the electrocardiogram is often uninterpretable.6 Myocardial perfusion abnormalities in the septum and apex have been reported in the absence of coronary artery disease in patients with paced rhythm.7 Noninvasive pacemaker stress echocardiography has been recently introduced as a feasible method to increase heart rate and to induce myocardial ischemia in these patients.8, 9 There are currently no data to define the prognostic value of pacemaker stress echocardiography. The aim of this study was to assess the value of pacemaker stress echocardiography for prediction of cardiac death and all-cause mortality in patients with known or suspected coronary artery disease who have a permanent right ventricular pacemaker.
Material and methods
Patients
The study population comprised 140 consecutive patients with a permanent right ventricular pacemaker who were referred to the Thoraxcenter, Rotterdam, The Netherlands, between 1998 and 2004 for evaluation of myocardial ischemia. Follow-up was successful in 138 patients (99%). Two patients underwent coronary revascularization in the first 60 days after pacemaker stress echocardiography. These patients were excluded from the analysis, because referral to myocardial revascularization in the first 60 days after stress testing tends to be based on the results of the test, whereas referral to revascularization more than 60 days after testing tends to be based on worsening of the patient’s clinical status.10 Data on the remaining 136 patients are reported. The protocol was approved by the hospital ethics committee. All patients gave informed consent before the test. A structured interview was performed and a clinical history was taken, and cardiac risk factors were assessed before pacemaker stress echocardiography
Hypertension was defined as a blood pressure of 140/90 mm Hg or more or treatment with antihypertensive medication. Diabetes mellitus was defined as a fasting glucose level of 7.8 mmol/L or more or the need for insulin or oral hypoglycemic agents. Hypercholesterolemia was defined as a total cholesterol level of 6.4 mmol/L or more or treatment with lipid-lowering medication.
Pacemaker stress echocardiography
Echocardiography was performed with standard equipment (Sonos 5500, Andover, Mass) using second harmonic imaging (1.8 MHz/3.6 MHz). Images were obtained with the patient in the left lateral decubitus position and were acquired before the stress test and every 3 minutes throughout the stress test, using the standard parasternal and apical views. Continuous ventricular pacing was started at the rate of 100 beats/min and was increased by 10 beats every 3 minutes until the test endpoint was reached. In patients with a dual-chamber pacemaker, the pacemaker stress test was started with atrial pacing; if target heart rate or other test endpoints were not reached with this approach, the pacemaker was programmed to ventricular pacing. Test endpoints were achievement of target heart rate (85% of maximum age predicted heart rate), pacemaker maximal programmable heart rate, severe angina, systolic blood pressure decrease greater than 40 mm Hg, blood pressure greater than 240/120 mm Hg, or significant cardiac arrhythmia. The echocardiograms were recorded in a quad-screen format. Two experienced observers, unaware of the clinical data, scored the echocardiograms using a standard 16-segment model as suggested by the American Society of Echocardiography.11 In case of disagreement, a consensus decision was achieved by a third observer. Regional wall motion and systolic wall thickening were scored on a 5-point scale (1 = normal, 2 = mild hypokinesia, 3 = severe hypokinesia, 4 = akinesia, 5 = dyskinesia). Ischemia was defined as new or worsened wall motion abnormalities during stress indicated by an increase of wall motion score ≥1 grade in ≥1 segment. Ischemia was not considered to be present when akinetic segments at rest became dyskinetic during stress. Myocardial septal and apical function were evaluated on the basis of systolic thickening because wall motion could be influenced by ventricular pacing.
Follow-up
Follow-up data collection was performed by contacting the patient’s general practitioner and by review of hospital records. The date of the last review or consultation was used to calculate follow-up time. Follow-up events noted were cardiac and all-cause mortality. Cardiac death was defined as a death caused by acute myocardial infarction, significant cardiac arrhythmias, or refractory congestive heart failure. Sudden death occurring without another explanation was considered as cardiac death. Myocardial revascularization procedures were registered.
Statistical analysis
Values were expressed as means (± standard deviation) or number, and compared using the Student t test or chi-square test. Univariate and multivariate Cox proportional hazard models (BMDP Statistical Software Inc., Los Angeles, Calif) were used to identify variables that were independently predictive of cardiac death and all-cause mortality.12 Variables were selected in a stepwise forward selection manner with entry and retention set at a significance level of 0.05. The risk of a variable was expressed as hazard ratios with corresponding 95% confidence intervals. Clinical data, stress test variables, and noninvasive imaging data were incorporated into the analysis. The incremental value of dobutamine stress echocardiography over the clinical value in the prediction of cardiac death and all-cause mortality was performed according to two models. In Model 1, only clinical data were entered; in Model 2 dobutamine echocardiographic variables including resting wall motion abnormalities and myocardial ischemia were added to the clinical variables. The probability of survival was calculated using the Kaplan-Meier method, and survival curves were compared using the log-rank test. P values less than .05 were considered statistically significant.
Results
Clinical data are presented in Table 1. Ninety-eight patients (72%) had a dual-chamber pacemaker, and 38 patients (28%) had a single-lead right ventricular pacemaker. In patients with a dual-chamber pacemaker, pacemaker stress echocardiography using atrial pacing was performed in 82 patients (84%) and ventricular pacemaker stress testing was performed in 16 patients (16%).
Table 1. Baseline characteristics (136 patients)
| Number (%) | |
|---|---|
| Age (y) | 64±12 |
| Men | 94(69%) |
| Systemic hypertension | 28(20%) |
| Hypercholesterolemia | 87(64%) |
| Smoker | 10(7%) |
| Diabetes mellitus | 27(20%) |
| Prior myocardial infarction | 44(32%) |
| Prior heart failure | 48(35%) |
| Beta blockers | 57(42%) |
| Diuretics | 34(25%) |
| Angiotensin-converting enzyme inhibitors | 43(32%) |
| Nitrates | 49(36%) |
| Calcium channel blockers | 28(20%) |
| Indications for pacemaker implantation | |
| Atrioventricular block | 53(39%) |
| Sick sinus syndrome | 43(32%) |
| Bradycardia | 40(29%) |
Hemodynamic data are presented in Table 2. During the pacing there was a mild increase of systolic blood pressure (119 ± 24 mm Hg to 123 ± 26 mm Hg, P <.05). No major adverse effects were observed during the test. Thirty-one patients (23%) had angina during pacemaker stress echocardiography. Angina was the reason for the test termination in 3 of these patients. Other causes of test termination were achievement of the target heart rate in 126 patients (93%) and achievement of pacemaker maximal programmable heart rate in 5 patients (4%). Two patients (1%) experienced nausea during pacemaker stress echocardiography.
Table 2. Pacemaker stress echocardiographic data
| Heart rate at rest (beats/min) | 73±18 |
| Heart rate at peak (beats/min) | 124±17 |
| Rest systolic blood pressure (mm Hg) | 119±24 |
| Peak systolic blood pressure (mm Hg) | 123±26 |
| Rest rate pressure product | 9456±2863 |
| Peak rate pressure product | 15423±4627 |
| Angina during stress | 31(23%) |
| Resting wall motion score index | 2.1±0.7 |
| Ischemia (patients) | 75(55%) |
| Number of ischemic segments | 6.4±5.7 |
Pacemaker stress echocardiography and outcome
Thirty patients (22%) had a normal pacing stress echocardiogram. Fixed wall motion abnormalities were detected in 31 patients (23%), and ischemia was induced in 75 patients (55%). Eighteen patients (13%) showed ischemia only in the septum and/or apex. During a mean follow-up of 3.5 ± 2.4 years, there were 35 deaths (26%), of which 20 (15%) were attributable to cardiac causes. Nonfatal myocardial infarction occurred in 2 patients (1%). Forty-one patients (30%) underwent coronary angiography within 6 months from the stress test. Late revascularization was performed in 36 patients (26%); of these, 17 (12%) underwent percutaneous interventions and 19 (14%) underwent coronary bypass surgery.
Predictors of events
Predictors of cardiac death and all-cause mortality in univariable and multivariable models are presented in Table 3. Ischemia was the strongest independent predictor of cardiac and all-cause mortality, with incremental value to the clinical variables (log-likelihood, −75 to −72, P ≤.05 for cardiac death, and −140 to −136, P ≤.05 for all-cause mortality). Kaplan-Meier survival curves for the endpoints cardiac death and all-cause mortality are presented in Figure 1, Figure 2. Event-free survival was significantly better for patients without ischemia compared with patients with ischemia. The annual cardiac death rate was 1.3% in patients without ischemia and 4.6% in patients with ischemia (P=.01). The annual all-cause mortality rate was 3.1% in patients without ischemia and 7% in patients with ischemia (P=.004). Patients with ischemia involving only the septum and/or the apex had a comparable prognosis as patients with ischemia in other regions (Figure 3).
Table 3. Predictors of events by Cox models
| Parameter | Univariate RR (CI) | Multivariate model 1 RR (CI) | Multivariate model 2 RR (CI) |
|---|---|---|---|
| Cardiac death | |||
| Age | 1.03(1.01-1.06) | ||
| Previous myocardial infarction | 1.5(1.0-2.1) | ||
| Diabetes mellitus | 4.6(1.2-18.0) | 3.0(1.1-9.2) | 3.1(1.1-9.6) |
| Smoking | 3.4(1.2-9.4) | 2.9(1.1-7.3) | 2.9(1.2-7.4) |
| Resting wall motion abnormalities | 2.4(0.7-8.9) | ||
| Ischemia | 3.9(1.2-12.2) | 4.1(1.2-14.9) | |
| All cause mortality | |||
| Age | 1.03(1.01-1.06) | ||
| Male gender | 2.1(0.8-5.3) | 2.1(1.1-6.2) | 2.1(1.1-5.2) |
| Previous myocardial infarction | 1.4(1.0-2.1) | ||
| Diabetes mellitus | 5.0(1.3-19.0) | 2.4(1.1-6.0) | 2.4(1.1-5.8) |
| Resting wall motion abnormalities | 1.6(0.6-4.3) | ||
| Ischemia | 3.1(1.3-7.2) | 2.7(1.2-6.0) |
Figure 1.
Kaplan-Meier survival curves (endpoint cardiac death) in patients without ischemia during pacing stress echocardiography versus patients with ischemia.
Figure 2.
Kaplan-Meier survival curves (endpoint all-cause mortality) in patients without ischemia during pacing stress echocardiography versus patients with ischemia.
Figure 3.
Kaplan-Meier survival curves for endpoint cardiac death (A) and all-cause mortality (B) in patients with ischemia involving only the septum and/or the apex versus patients with ischemia in the other regions.
The annual cardiac death rate was 5.4% in patients with ischemia involving only the septum and/or the apex and 7.6% in patients with ischemia in other regions (P=.9). The annual all-cause mortality rate was 6.4% in patients with ischemia involving only the septum and/or the apex and 9.5% in patients with ischemia in other regions (P=.9).
Discussion
In the present study, the prognostic value of pacemaker stress echocardiography was evaluated in 136 patients with a permanent pacemaker and known or suspected coronary artery disease. During a follow-up period of 3.5 ± 2.4 years, 35 deaths (36%) occurred of which 20 (15%) were attributable to cardiac causes. The presence of ischemia during pacemaker stress echocardiography was associated with a significantly increased risk of cardiac and all-cause mortality, incremental to the clinical variables. Patients without ischemia during pacemaker stress echocardiography had an annual cardiac death rate of 1.3%, identifying a lower-risk group of patients who do not need further invasive evaluation. Conversely, in patients with ischemia the annual cardiac death rate was 4.6%, identifying a high-risk group of patients who can potentially benefit from invasive evaluation. Pacemaker stress echocardiography provided independent prognostic information for the prediction of cardiac death and all-cause mortality. Patients with ischemia involving the septum or the apex had a worse outcome compared with patients without ischemia and a similar prognosis compared with patients with ischemia in other regions.
There were no significant differences in mortality between patients with myocardial ischemia only located in the septum and/or apex compared with those with ischemia in other myocardial regions. This finding suggests that interpretation of (changes in) function in these regions is reliable for the detection of myocardial ischemia. The presence of resting wall motion abnormalities was not associated with cardiac death or all-cause mortality. This could be explained by the fact that the abnormal function at rest of the interventricular septum can be present in patients with permanent pacemaker and is not related to the presence of coronary artery disease.
The high number of abnormal tests in this study (77%) is probably related to the prevalence of comorbidity in the population. Table 1 shows that a large number of patients had diabetes mellitus, prior myocardial infarction, prior heart failure, and, obviously, conduction abnormalities.
Previous studies showed that pharmacologic stress echocardiography is a feasible and accurate alternative for the detection of coronary artery disease in pacemaker-dependent patients.13 However, this examination can be time-consuming and may be associated with varying side effects and a hemodynamic response.14, 15, 16 Pooled data have shown that approximately 10% of patients fail to achieve the target heart rate during dobutamine stress echocardiography.14 Transesophageal atrial pacing has been proposed as an effective alternative technique for the detection of coronary artery disease in the general population.17, 18, 19, 20, 21, 22 A controlled increase of heart rate can be used to assess impaired regional wall thickening independently from regional myocardial dysfunction caused by abnormal electrical activation. Nevertheless, transesophageal pacing is an invasive procedure and its efficacy has been limited by patient intolerance. Moreover, intact atrioventricular conduction and absence of esophageal diseases are preliminary conditions to perform the test.
In patients with permanent pacemakers, pacemaker stress echocardiography has been reported as a safe, rapid, and effective noninvasive tool to detect coronary artery disease.8, 9 Picano et al8 evaluated the feasibility, safety, and diagnostic accuracy of pacemaker stress echocardiography in 46 consecutive patients with a permanent pacemaker with suspected or known coronary artery disease. Sensitivity for detection of significant coronary artery disease was 70%, specificity was 90%, and accuracy was 78%. Forty-two of 46 patients (91%) achieved the target heart rate or positive test endpoint. Four patients (9%) had a submaximal test. In the present study, 93% of patients with a permanent pacemaker reached the target heart rate, which is comparable to previous studies performed by dobutamine stress echocardiography.23
Pacemaker echocardiography is a simple, rapid, safe test for the assessment of prognosis in patients with a permanent pacemaker and suspected or known coronary artery disease. Although no study directly has compared pacemaker and dobutamine stress echocardiography, pacemaker stress seems less time-consuming and is associated with fewer side effects. Therefore, when information on myocardial ischemia and/or prognosis is required, pacemaker stress echocardiography is a reasonable choice. One limitation of pacemaker stress echocardiography is to assess myocardial viability. Therefore, when information on myocardial viability is needed, dobutamine stress echocardiography should be preferred.
Clinical implications and conclusions
Pacemaker stress echocardiography is a safe and feasible method for the risk stratification of patients with permanent pacemakers. The presence of ischemia during pacemaker stress echocardiography is independently associated with an increased risk of cardiac death and all-cause mortality. Pacemaker stress echocardiography identifies high-risk patients in whom aggressive evaluation or therapy is required.
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PII: S0002-9343(05)00498-5
doi:10.1016/j.amjmed.2005.04.040
© 2005 Elsevier Inc. All rights reserved.
Volume 118, Issue 12 , Pages 1381-1386, December 2005
