Acupuncture in Angina Pectoris: Do Psycho-Social and Neurophysiological Factors Relate to the Effect?

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ACUPUNCTURE IN ANGINA PECTORIS: DO PSYCHO-SOCIAL AND NEUROPHYSIOLOGICAL FACTORS RELATE TO THE EFFECT?

ABSTRACT

We studied the effect of acupuncture in 49 patients with angina pectoris with focus on its relationship to psycho-social factors and changes in skin tempeature, pain thresholds, and pain tolerance thresholds. No significant influence from patient expectation, social stress (strain) or profiles of the Minnesota Multiphasic Personality Inventory (MMPI) was found (all p > 0.1). Acupuncture slightly increased exercise tolerance (median 7%), the difference in Systolic Blood Pressure - Heart Rate Product between rest and maximal exercise (delta PRP) (median 3%), and the time to onset of pain (median 10%); decreased nitroglycerin consumption (median 58%) and anginal attack rate (median 38%). Improvement in exercise tolerance was significantly correlated to an improvement in delta PRP (correlation coefficient = 0.7; p < 0.0001)but not to time of myocardial ischemia (correlation coefficient = 0.1 ;p = 0.1). Compared with 28 patients with a less pronounced anti-anginal effect, the 21 patients with a pronounced effect had a significant increase in local skin temperature, but had no significant change in distant skin temperature and pain thresholds. It is concluded that acupuncture, due to hemodynamic alterations, might have a specific effect on angina pectoris in addition to drug treatments.

Key words: Acupuncture, Angina pectoris, Skin temperature, Pain threshold, MMPI, Social network.

INTRODUCTION

When treating angina pectoris, the existence of a placebo effect is well known ( 1). However, acupuncture cannot meet the criteria for the conventional double-blinded trial, as neither the acupuncturist nor the patient can be fully blinded. The present trial is the third part of a study to elucidate the effect of acupuncture on angina pectoris, taking these methodological problems into account. While the first studies focused on the elimination of observer bias ( 2), acupuncturist bias and choice of control treatment ( 3), this study investigates the relationship to psycho-social factors and changes in skin temperature and pain thresholds, and summarizes the entire three-part study.

MATERIALS AND METHODS

Methodological considerations

Because of the many questions in the Minnesota Multiphasic Personality Inventory (MMPI) and the psycho-social questionnaire, we carried out an initial retrospective testing of the psycho-social effects in 13 angina pectoris patients, who previously had acupuncture ( 4). It showed that patients with low expectation toward the effect of acupuncture, high degree of social strain, and high scores on the MMPI Hysteria (Hy) and Hypocondriasis (Hs) scales tended to have no effect from the acupuncture treatment. Therefore, in the prospective study, the focus was on these criteria.

Study population

Of 215 patients recruited consecutively, 49 received acupuncture as they met the inclusion criteria: stable and exercise-induced angina pectoris of > 6 months duration, two or more anginal attacks per week, consumption of two or more nitroglycerin tablets per week, a positive exercise test (> 1 mm ST-depression in one or more ECG leads). The exclusion criteria were: previous heart surgery, other known cause of chest pain, intermittens claudication, previous myocardial infarction within the last 6 months, valvular heart disease, severe heart failure, arterial hypertension, treatment with digetalis or anti-arrhytmic drugs, and previous acupuncture treatment for heart disease. Their clinical data are summarized in Table 1. Thirty-four patients completed the psycho-social study. Fourteen patients had received acupuncture before the psycho-social testing was initiated, and one failed to complete the MMPI.

Study design

This prospective study consisted of two parts: a clinical study and an experimental study. The following 3 different tests were performed by 3 separate research teams, each team being blinded for the results of the other teams' tests (Fig. 1).

(I): The patients underwent psychosocial tests in order to evaluate the influence of certain physiological characteristics, social strain, and the expectations of the patient toward the outcome of the treatment for angina pectoris.

Fig. 1. Study design.

I: Psycho-social test. II: Clinical acupuncture trial, during which the patients were randomized to either genuine (IIA) or sham (IIB) acupuncture for their angina pectoris. III: Experimental acupuncture trial, during which the patients received genuine acupunture while skin temperature and skin pain thresholds were recorded.

(II): In the clinical study, the patients were randomized to either genuine or sham acupuncture treatments for their angina pectoris ( 2). This allowed the evaluating physicians to remain blind to the nature of the treatment.

(III): In the experimental study, the patients received genuine acupuncture by a different acupuncturist, while the change in skin temperature, pain threshold (PT) and pain tolerance threshold (PTT) were recorded. By correlating these results with those of the clinical trial (II), bias from acupuncturist expectations and choice of control treatment in the clinical trial could be eliminated. The patients were told that the experimental trial examined the effect of acupuncture on skin temperature, PT and PTT, and had no therapeutical aim. A computerized test program and automatic monitors were used to minimize the communication between the investigators and the patients, and the patients and reseachers were informed not to discuss acupuncture during the procedure.

All patients gave their informed consent before entering the study, which was approved by the local ethics committee.

Psycho-social measurements

The Danish translation of the MMPI ( 5), consisting of 408 true/false questions, was used to evaluate personality function and psychopathology. The scores from the patients were tested for the presence of a "V" - shape between the neurotic triad scales: Hypocondri (Hs), Depression (D), and Hysteria (Hy), which happens when the score on the D-scale is numerically lower than the score on both the Hs- and Hy- scales. Such a "V"- shape, named "Conversion-V", has been found to be related to poor treatment outcome in conservative and surgical treatment of low back pain ( 6, 7, 8, 9), and refers to the Freudian diagnosis of conversion hysteria, in which an unconscious conflict is converted into a symbolic symptom and thus protects the subject from anxiety. The low score on the D-scale is associated with the hysteric "belle indifference", which means that the hysteric subject knows only one problem, namely the symptom, and since it is not possible to avoid the annoying symptom, the hysteric subject accommodates to the symptom more or less with a shrug. Furthermore, he or she gains a secondary profit, as one is often able to manipulate the surroundings by using one's symptoms.

To assess social strain, a protocol of 13 questions ( 10) was used concerning human contact (number of contacts, frequency and degree of closeness), and satisfaction with social life (with spouse, family, friends, acquaintances, colleagues and general practitioner). For each question, a 5-step ordinal scale was used, including the answer "do not know" and "irrelevant question".

For estimating patient expectation concerning the anti-anginal effect, the maximal expectation was indicated by "very high expectations" and submaximal expectations by "somewhat high" -, "neutral" -, "slightly negative" -, "moderately negative expectations" or "do not know". The interpretation of the answers was done blindly to ensure a useful discrimination on each item, controlled for homogeneous contribution to the total score ( 11).

Clinical measurements

The anti-anginal effect was evaluated blindly from pre- and post treatment exercise tests and 3-week diaries ( 2). Systolic-blood-Pressure-Heart-Rate-Product (PRP) was used as a index for myocardial oxygen consymption, and thus cardiac work ( 12). Daily well-being was measured on a 5-step ordinal scale from very good (score 1) to very bad (score 5). After the end of the trial the patients were asked for a global evaluation of the Treatment on a 7-step ordinal scale ranging from much improved (score 1) to much worse (score 7).

Experimental measurements

The effect of acupuncture on the blood circulation of the skin was assessed from changes in skin temperature ( 13, 14, 3), whereas the effect on pain modulation was done from changes in pain thresholds and pain tolerance thresholds ( 15, 16, 17). The experimental set-up is illustrated in Fig. 2.

By correlating the results of this trial (III) with the effect of acupuncture on angina pectoris observed in the clinical study (II), the underlying mechanisms of a possible anti-anginal effect could be elucidated.

The pain threshold for electrical stimuli was defined as the lowest current intensity in mA which elicited a pain sensation ( 18). Pain tolerance threshold was defined as the highest current intensity that the person could tolerate. Electrical stimulation was applied through ring electrodes placed around the index finger and the hallux (big toe) with the anode on the distal part of the distal phalanx and the cathode 20 mm proximal to it. The skin was rubbed with ether to reduce the impedance before placing the electrodes. The stimulus of 0.2 msec duration was applied through a constant current stimulator with a digital display of the current in mA (Neuromatic 2000, Dantec, Copenhagen, Denmark). In order to minimize researcher-patient contact, the stimulator was managed by a computer, and a special software program was designed to apply stimuli randomly and gradually to increase stimulus strength. The thresholds (in mA) were determined as the mean of three measurements. Recordings were after 30 minutes of rest and after 20 minutes of acupuncture.

Skin temperature was measured by a mirror-galvanometer graded in 0.1 degrees (Type Ellab TE 3, Copenhagen, Denmark) using a standard thermocouple (Type Ellab AH 3, Copenhagen, Denmark). Recordings were done after 30 minutes of rest and after 20,35 and 50 minutes of acupuncture.

Acupuncture treatments

In the clinical study (II) genuine acupuncture treatment was given according to traditional Chinese medicine ( 19), each patient receiving 10 treatments in the supine position within 3 weeks. The needles came from China, were made of stainless steel, and were 30 gauge thick and 1.5 inches long. After obtaining the needle sensation (or the arrival of Qi), the needles were left in place for 20 minutes. No electrical or mechanical stimulation was given. In sham acupuncture, needles were inserted superficiallly through the skin, with no attempt to obtain needle sensation, in points within the same spinal segment as the acupuncture points, but outside the Chinese meridian system and not in trigger points. The needles were then left untouched ( 2).

In the experimental study (III) the needles were inserted in point Hegu (Large Intestine 4) bilaterally (fig.2). The needles were stimulated electrically at 2 Hz at an intensity sifficient to produce visible muscle contraction of musculus interosseus dorsalis number 1, but well below pain threshold using an Electro-stimulator (E. Warner Jírgensen Automatic Ltd. Birkeríd, Denmark) ( 3). The anode was connected to the left point Hegu (the measurement site).

Statistics

We used Kendall's exact gamma-test for non-parametric correlation analysis ( 20), and Wilcoxon's non-parametric test for paired data for intrapersonal differences ( 21). The use of non-parametric test was based on the low number of observations and lack of normal distribution between them. According to this test ( 21), the differences between post-treatment and pre-treatment observation values are calculated and ordered by rank. The observation of lowest numeric value gets the lowest rank, the observation of second lowest numeric value gets the second lowest rank, etc. The rank sum for positive and negative values are calculated, and the statistical test gives the probability for the difference between the calculated sums of the ranks being of stochastic origin.

The Pearson's correlation analysis for parametric data was used to evaluate relations among exercise test variables. Correlation coefficients were compared using z-transformation to normal distribution ( 22). The significance level was set at 5%.

RESULTS

Clinical study

In relation to the inclusion criteria, the post-study examination revealed an insufficient number of anginal attacks and nitroglycerin consumption for 2 and 6 patients, respectively. These patients were excluded from this part of the study. For general well-being two patients did not complete the diary.

Patient expectation had no significant influence on the change in angina pectoris effect variables after acupuncture (all p > 0.1) (Table 2). The median difference between the 21 patients with maximal expection and the 11 patients with submaximal expection was 4% (95% confidence limits: -10% - +18%) concerning change in exercise tolerance, -2% concerning delta PRP (95% confidence limits: -14% - +14%), 11% concerning change in nitroglycerin consumption (95% confidence limits: -47% - +54%), and 5% concerning anginal attack rate (95% confidence limits: -38% - +54%).

No single MMPI scale correlated significantly to the effect of acupuncture on angina pectoris. Five patients showed a "Conversion-V" profile, and none of them experienced a pronounced improvement in exercise tolerance (> 15% improvement ( 3)). Compared to 20 patients with "Non-Conversion-V" profile and a similar lack of a pronounced improvement in exercise tolerance, the 5 patients with "Conversion-V" reported a significant improvement after acupuncture, concerning nitroglycerin consumption, anginal attack rate, general well-being, and global evaluation (Table 3). Patients with less social strain experienced a more pronounced improvement in exercise tolerance than patients with more social strain (correlation coefficient = -0.40, p < 0.05), but none of the other angina pectoris effect variables were significantly correlated to the degree of social strain (all p > 0.1). None of the tested psycho-social factors showed significant correlation to age or duration of disease.

Experimental study

No significant correlation was found between, on the one hand expectation, social strain, any MMPI scale or "Conversion-V" profiles, and on the other hand changes in skin temperature, PT or PTT on either index finger or hallux (big toe). On the index finger, acupuncture increased PT (median 10%, range: -45% +177%) and PTT (median 6%, range: -38% - +155%) (both p < 0.05), but acupuncture had no effect on skin temperature. There were no significant changes on the hallux (p > 0.1).

Clinical and experimental study together

Acupuncture had a pronounced effect on 21 of 49 patients (43%) with angina pectoris, demonstrated an increase in exercise tolerance and/or in delta PRP of at least 15% combined with > 30% reduction in anginal attack rate and/or nitroglycerin consumption ( 3). In the 21 patients with this favourable response, there was a significant increase in skin temperature on the index finger when compared to the patients with a less favourable response, (P < 0.001) (median difference between the change in temperature between the two groups: +4%, 95% confidence limits: -2% - +7%). Otherwise there were no differences between these two groups regarding any other psycho-social or experimental variable (p > 0.1)

The effect of acupuncture on angina pectoris is summarized in Table 4. A slight improvement was found concerning exercise tolerance (median increase: 7%), delta PRP (median increase: 3%), time to onset of pain (median delay: 10%), nitroglycerin consumption (median decrease: 53%), anginal attack rate (median reduction: 38%), daily well being (median improvement: +2 arbitrary units) and global evaluation (median improvement: "somewhat improved").

During exercise tests, a significant correlation was found between the effect of acupuncture on exercise tolerance and delta PRP (correlation coefficient: R1 = 0.70; p < 0.0001), but not between exercise tolerance and time with myocardial ischemia expressed as total time with minimum 1 mm ST-depression on ECG (correlation coefficient: R2 = 0.20; p = 0.1) R1 was significantly greater than R2 (Z = 3.16; P < 0.002).

DISCUSSION

The present clinical study was designed to elucidate the effect of patient expectancy and psycho-social factors on the effects of acupuncture for angina pectoris. In addition, the effect of acupuncture on skin temperature and pain thresholds was evaluated in the experimental study. This combination of two separate prospective trials, a clinical one and an experimental one, aimed at eliminating the methodological problems concerning a possible bias from researcher expectancy and choice of control treatment as well as giving a further understanding for the mechanisms underlying the anti-anginal effect of acupuncture.

Clinical study

In the present study, no significant correlation was found between the expectation of the patient and the anti-anginal effect of acupuncture. The expectation is closely related to the placebo effect ( 23, 24), which is pronounced in angina pectoris therapy ( 1). Given this background, the absence of influence from expectation is surprising. It might be related to the long duration of disease (median value 4 years), during which the patient has achieved some acceptance of the condition ( 24). We have expressed the statistical power of the present findings by calculating the 95% confidence limits of the observed differences between patients with maximal and submaximal expectations.

In the present study we found that patients with a "Conversion-V" profile on the MMPI reported a subjective effect of acupuncture in spite of a corresponding improvement in exercise tolerance. This may be related to the large amount of attention and care the patients received during the study, which may decrease the anxiety of the patient and thus decrease the need of a conversion of an unconscious anxiety into a physical symptom. This may be perceived as an improvement of the disease, although this improvement does not show in their response to a physical stress test ( 25). In patients with tension headache treated with acupuncture, no single MMPI scale predicted the response to the treatment, but the mean profile of the non-responders showed the presence of "Conversion-V" ( 26). Similarly, "Conversion-V" has been found to predict poor treatment outcome in patients with low-back pain undergoing surgery ( 7, 8, 9) or pharmacological treatment ( 6). In 382 patients with angina pectoris, a high score on MMPI Hs scale was associated with poor outcome from medical management ( 27), and in 550 patients receiving acupuncture in a smoking cessation program a normal MMPI profile predicted a successful outcome ( 28).

On the other hand some studies showed that the effect of TENS or acupuncture in pain patients cannot be predicted from psychometric measures ( 29, 30). Furthermore, the use of MMPI neurotic triad scale with pain patients has been questioned as it has been found that elevations found on MMPI reflect somatic symptoms related to pain, not neuroticism ( 31). This point of critics is of particular interest in the present study, as all patients have verified coronary artery disease.

We found no significant correlation between the quantity and quality of the social life and the anti-anginal effect of acupuncture. Studies showing influence of social support on treatment have included more than 100 heart patients and follow up periods of more than half a year ( 32, 33, 34), compared to 50 patients with 3 week follow-up periods in the present study.

Against this background, the present study suggests that the influence from patient-expectation or other psycho-social measures is not so pronounced that it is found reliable in the present study. However, it cannot be ruled out that a larger scale study including different psychometric measures would have produced a different result.

Experimental study

In the present study, no significant correlations were found between the psycho-social variables and the change in skin temperature, PT or PTT during acupuncture.

Acupuncture was found not to change skin temperature. However, in patients with angina pectoris, who responded well to the treatment, a local, but not a distant skin temperature increase was found when compared to patients without a similar response. In patients with peripheral ischemia, Transcutaneous Electrical Nerve Stimulation has been found to increase skin temperature, and the effect is mediated by cyproheptadine, a central serotonergic antagonist, leading to sympathetic nerve inhibition and consequently vasodilation ( 35).

Acupuncture was found to elevate PT and PTT locally, but not distantly. Similar findings have been obtained by others ( 36), and the effect has been found not to be influenced by psycho-social factors ( 37).

It has been shown that the experimental pain threshold is lowered by induction of anxiety ( 38, 39), stress ( 40, 41), and depression ( 42). These observations were not confirmed in the present study. It might be because the present study examined the relation between personality traits and experimental pain, while the other studies dealt with an immediate response to an experimentally induced mood.

Clinical and experimental study together

In the present study acupuncture was found to have an anti-anginal effect with no reliable relation to psycho-social factors. However, the effect was associated with a local increase in skin temperature, but not with an increase in PT and PTT.

The present study design was chosen to elimate the various aspects of the placebo effect: the expectations of the patient, the evaluating researcher, and the treating researcher in combination with a classical conditioned Pavlovian response of the patient ( 43, 21, 44, 45). From the questionnaire it was found that patient expectation did not influence the results. Bias from evaluator expectation was eliminated by including a control treatment ( 2). Bias from acupuncturist expectation was eliminated by correlating the results from two separate, but physiologically related acupuncture trials, performed by two different acupuncturists, each being blind to the results of the other trial. As the patients had not previously received acupuncture for their angina pectoris, the development of a conditioning response can be excluded. On this background the present study suggests that acupuncture has a specific anti-anginal effect.

Concerning an overall evaluation of acupuncture in the treatment of angina pectoris, the present study shows that, acupuncture has a positive effect on exercise tolerance and cardiac work capacity, expressed as a difference in Systolic-Blood-Pressure-Heart-Rate-Product between rest and maximal exercise (delta PRP). This was accompanied by an improved daily well-being, fewer anginal attacks and decreased nitroglycerin consumption.

Concerning the underlying mechanism, the exercise tests showed a significant increase in exercise tolerance and cardiac work capacity expressed as delta PRP without a corresponding increase in maximal PRP and duration of myocardial ischemia. The increase in exercise tolerance correlated significantly to the increase in cardiac work capacity, but not to an increase in myocardial ischemia. Furthermore, by correlating the results of the clinical study (II) with the experimental study (III), it was found that a favourable anti-anginal effect was associated with an increase in skin temperature, rather than an increase in pT and PTT, although acupuncture did increase PT and PTT. In contrast, patients who responded to acupuncture for shoulder and/or facial pain had been found to increase PT during acupuncture, when compared to non-responders ( 41).

The results of the present study suggest that the anti-anginal effect of acupuncture cannot be explained exclusively by inhibition of pain transmission or by psycho-social factors. Instead, an adjusted sympathetic nerve activity leading to an increase in the working capacity of the heart, seems to play a central role ( 46). The hemodynamic changes accounting for this increase might include a decrease in afterload ( 47, 48), an adjustment of myocardial perfusion in the ischemic areas ( 49, 50, 51), and/or increased myocardial contractility ( 52). Further studies, using a more advanced technique, are needed to explore these possibilities.

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By Soren Ballegaard; Benny Karpatschoff; Joan Amalie Holck; Christian Niels Meyer and Werner Trojaborg

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