Asymptomatic myocardial ischemia following cold provocation

Raynaud phenomenon and microvasculopathy in systemic sclerosis: multi-modality imaging for diagnosis and evaluation

PURPOSE OF REVIEW

To describe the clinical significance of and the diagnostic approach to Raynaud phenomenon (RP) in the peripheral extremities and the heart.

RECENT FINDINGS

Nailfold capillaroscopy has recently been standardized in an expert consensus paper. Abnormal capillaroscopy in combination with specific autoantibody profiles and clinical signs are highly predictive of progression of RP to systemic sclerosis (SSc). Magnetic resonance imaging (MRI) can also perform tissue characterization of both the extremities and the heart. Microvascular wall abnormalities detected using nailfold capillaroscopy in patients with SSc may lead to deposition of erythrocyte-derived iron, due to microhemorrhages, which may predispose to fibrosis. MRI can assess the presence of iron using T2∗ measurements.

SUMMARY

RP is a hallmark of the microvasculopathy in SSc and can affect both the peripheral extremities and the heart. Nailfold capillaroscopy is the current gold standard for the evaluation of the peripheral microvasculature. Other imaging modalities include thermography, laser Doppler-derived methods, 99m Tc-pertechnetate hand perfusion scintigraphy, power Doppler ultrasonography, dynamic optical coherence tomography, MRI, and photoacoustic imaging, but these are currently not widely used. Cardiac RP can be investigated with positron emission tomography or cardiovascular magnetic resonance, with the latter offering the additional possibility of tissue characterization and iron content quantification secondary to microhemorrhages.

Exercise in cold: Friend than foe to cardiovascular health

Exercise has been proven to benefit human health comprehensively regardless of the intensity, time, or environment. Recent studies have found that combined exercise with a cold environment displays a synergistical beneficial effect on cardiovascular system compared to exercise in thermoneutral environment. Cold environment leads to an increase in body heat loss, and has been considered a notorious factor for cardiovascular system. Exercise in cold increases the stress of cardiovascular system and risks of cardiovascular diseases, but increases the body tolerance to detrimental insults and benefits cardiovascular health. The biological effects and its underlying mechanisms of exercise in cold are complex and not well studied. Evidence has shown that exercise in cold exerts more noticeable effects on sympathetic nervous activation, bioenergetics, anti-oxidative capacity, and immune response compared to exercise in thermoneutral environment. It also increases the secretion of a series of exerkines, including irisin and fibroblast growth factor 21, which may contribute to the cardiovascular benefits induced by exercise in cold. Further well-designed studies are needed to advance the biological effects of exercise in cold. Understanding the mechanisms underlying the benefits of exercise in cold will help prescribe cold exercise to those who can benefit from it.

Cardiovascular diseases, cold exposure and exercise

Both acute and prolonged cold exposure affect cardiovascular responses, which may be modified by an underlying cardiovascular disease. In addition, exercise in a cold environment increases cardiovascular strain further, but its effects among persons with cardiovascular diseases are not well known. Controlled studies employing whole-body or local cold exposure demonstrate comparable or augmented increase in cardiac workload, but aggravated cutaneous vasoconstriction in persons with mild hypertension. A strong sympathetic stimulation of a cold pressor test, increases cardiac workload in persons with coronary artery disease (CAD), but does not markedly differ from those with less severe disease or healthy. However, cold exposure reduces myocardial oxygen supply in CAD, which may lead to ischemia. Exercise in cold often augments cardiac workload in persons with CAD more than when performed in thermoneutral conditions. At the same time, reduced myocardial perfusion may lead to earlier ischemia, angina and impaired performance. Also having a heart failure deteriorates submaximal and maximal performance in the cold. Antianginal medication is beneficial in the cold in lowering blood pressure, but does not affect the magnitude of cold-related cardiovascular responses in hypertension. Similarly, the use of blood pressure lowering medication improves exercise performance in cold both among persons with CAD and heart failure. Both the acute and seasonal effects of cold and added with exercise may contribute to the higher morbidity and mortality of those with cardiovascular diseases. Yet, more controlled studies for understanding the pathophysiological mechanisms behind the adverse cold-related health effects are warranted.

Cardiac overexpression of metallothionein rescues cold exposure-induced myocardial contractile dysfunction through attenuation of cardiac fibrosis despite cardiomyocyte mechanical anomalies

Cold exposure is associated with an increased prevalence of cardiovascular disease although the mechanism is unknown. Metallothionein, a heavy-metal-scavenging antioxidant, protects against cardiac anomalies. This study was designed to examine the impact of metallothionein on cold exposure-induced myocardial dysfunction, intracellular Ca(2+) derangement, fibrosis, endoplasmic reticulum (ER) stress, and apoptosis. Echocardiography, cardiomyocyte function, and Masson trichrome staining were evaluated in Friend virus B (FVB) and cardiac-specific metallothionein transgenic mice after cold exposure (3 months, 4 °C). Cold exposure increased plasma levels of norepinephrine, endothelin-1, and TGF-β; reduced plasma NO levels and cardiac antioxidant capacity; enlarged ventricular end-systolic diameter; compromised fractional shortening; promoted reactive oxygen species (ROS) production and apoptosis; and suppressed the ER stress markers Bip, calregulin, and phospho-eIF2α, accompanied by cardiac fibrosis and elevated levels of matrix metalloproteinases and Smad-2/3 in FVB mice. Cold exposure-induced echocardiographic, histological, ER stress, ROS, apoptotic, and fibrotic signaling changes (but not plasma markers) were greatly improved by metallothionein. In vitro metallothionein induction by zinc chloride ablated H(2)O(2)- but not TGF-β-induced cell proliferation in fibroblasts. In summary, our data suggest that metallothionein protects against cold exposure-induced cardiac anomalies possibly through attenuation of myocardial fibrosis.

Exposure to extreme cold lowers the ischemic threshold in coronary artery disease patients

BACKGROUND

Cold temperature is known to commonly precipitate angina pectoris in patients with symptomatic coronary artery disease (CAD). It was previously shown that the ischemic threshold was lower during exercise testing at -8 degrees C than at +20 degrees C in patients with a history of cold-induced angina, whereas it was unchanged in patients without cold-induced angina. Few data exist on the impact of more severe cold exposure on myocardial ischemia.

OBJECTIVE

To determine the effect of extreme cold exposure (-20 degrees C) on the ischemic threshold among CAD patients.

METHODS

Thirteen men with CAD and documented exercise-induced ischemia performed two treadmill exercise tests, one at +20 degrees C and one at -20 degrees C, in random order. Electrocardiograms were recorded every 30 s and analyzed separately in random order by two experienced readers blinded to temperature.

RESULTS

The mean (+/- SD) time to ischemic electrical threshold was 53+/-60 s lower at -20 degrees C than at +20 degrees C (P=0.008), corresponding to a relative change of -8.0+/-10.5%. All other exercise parameters, including total exercise time and rate-pressure product, were unchanged during exposure to extreme cold.

CONCLUSION

Exposure to extreme cold (-20 degrees C) lowers the ischemic threshold during exercise testing in patients with CAD, even if asymptomatic or without a history of cold-induced angina. Patients with CAD and evidence of exertional angina or myocardial ischemia wishing to perform exercise at extremely low temperatures should discuss this matter with their physicians.

The physiology behind exercise testing

Despite significant advances in related technologies, the exercise test remains a useful clinical tool. It can define the limits of performance in an athlete or the functional capabilities of the patient with heart disease. Although virtually all of the body's physiologic and metabolic systems interact in a coordinated fashion to perform a single bout of exhaustive exercise, a major burden falls on the cardiopulmonary system. A good understanding of the basic physiologic responses to acute exercise can assist the clinician in applying the information gained from the test. These responses are influenced by state of health and fitness, age, gender, type of exercise, exercise position, and the environment. This article provides an overview of the physiologic responses to acute exercise, and discusses the many factors that influence these responses.

Cold stress alters characteristics of sympathetic nerve discharge bursts

Frequency-domain analyses were used to determine the effect of cold stress on the relationships between the discharge bursts of sympathetic nerve pairs, sympathetic and aortic depressor nerve pairs, and sympathetic and phrenic nerve pairs in chloralose-anesthetized, baroreceptor-innervated rats. Sympathetic nerve discharge (SND) was recorded from the renal, lumbar, splanchnic, and adrenal nerves during decreases in core body temperature from 38 to 30 degrees C. The following observations were made. 1) Hypothermia produced nonuniform changes in the level of activity in regionally selective sympathetic nerves. Specifically, cold stress increased lumbar and decreased renal SND but did not significantly change the level of activity in splanchnic and adrenal nerves. 2) The cardiac-related pattern of renal, lumbar, and splanchnic SND bursts was transformed to a low-frequency (0-2 Hz) pattern during cooling, despite the presence of pulse-synchronous activity in arterial baroreceptor afferents. 3) Peak coherence values relating the discharges between sympathetic nerve pairs decreased at the cardiac frequency but were unchanged at low frequencies (0-2 Hz), indicating that the sources of low-frequency SND bursts remain prominently coupled during progressive reductions in core body temperature. 4) Coherence of discharge bursts in phrenic and renal sympathetic nerve pairs in the 0- to 2-Hz frequency band increased during mild hypothermia (36 degrees C) but decreased during deep hypothermia (30 degrees C). We conclude that hypothermia profoundly alters the organization of neural circuits involved in regulation of sympathetic nerve outflow to selected regional circulations.

Estrogen acutely abolishes abnormal cold-induced coronary constriction in men

BACKGROUND AND STUDY OBJECTIVE

Ambient cold exposure may induce myocardial ischemia by precipitating coronary artery constriction and a decrease in coronary blood flow. Estrogen has vasoactive properties that may prevent abnormal coronary constriction in a sex-independent manner. The purpose of this study is to determine whether estrogen acutely abolishes abnormal coronary responses to cold exposure in men.

DESIGN

Randomized, double-blinded placebo-controlled clinical trial.

SETTING

Cardiac catheterization laboratory.

PATIENTS

Men referred for routine diagnostic coronary angiography who exhibit abnormal coronary artery constriction in response to a 90-s cold pressor test (CPT).

INTERVENTION

Intravenous conjugated estrogens (1.25 mg) vs. placebo.

MEASUREMENTS AND RESULTS

Rate-pressure product, coronary cross-sectional area (CSA), and coronary blood flow responses to the CPT were measured before and 15 min after intervention. In 12 men with CPT-induced coronary constriction who were assigned to estrogen, CPT induced a mean 21.8% decrease in coronary CSA (p < 0.01) and a nonsignificant change in coronary flow. After estrogen, the repeated CPT induced a 16.3% increase in CSA (p < 0.01) and a 54.9% increase in flow (p < 0.01). CSA and coronary flow responses to CPT were significantly different before and after estrogen (p < 0.01). In contrast, placebo was not associated with changes in CSA or coronary flow responses to CPT in eight men.

CONCLUSIONS

In men, conjugated estrogens acutely abolish abnormal coronary constriction and improve coronary blood flow responses to an exogenous cold stimulus. These results suggest that estrogen favorably alters coronary vasoreactivity in men.

Effect of amlodipine, atenolol and their combination on myocardial ischemia during treadmill exercise and ambulatory monitoring. Canadian Amlodipine/Atenolol in Silent Ischemia Study (CASIS) Investigators

OBJECTIVES

This study compared the effects of amlodipine, atenolol and their combination on ischemia during treadmill testing and 48-h ambulatory monitoring.

BACKGROUND

It is not known whether anti-ischemic drugs exert similar effects on ischemia during ambulatory monitoring and exercise treadmill testing.

METHODS

Patients with stable coronary artery disease and ischemia during treadmill testing and ambulatory monitoring were randomized to receive amlodipine (n = 51) or atenolol (n = 49). Each group underwent a counterbalanced, crossover evaluation of single drug and placebo, followed by evaluation of the combination.

RESULTS

Amlodipine and the combination prolonged exercise time to 0.1-mV ST segment depression by 29% and 34%, respectively (p < 0.001) versus 3% for atenolol (p = NS). During ambulatory monitoring, the frequency of ischemic episodes decreased by 28% with amlodipine (p = 0.083 [NS]), by 57% with atenolol (p < 0.001) and by 72% with the combination (p < 0.05 vs. both single drugs; p < 0.001 vs. placebo). Suppression of ischemia during exercise testing and ambulatory monitoring was similar in patients with and without exercise-induced angina. Exercise time to angina improved by 29% with amlodipine (p < 0.01), by 16% with atenolol (p < 0.05) and by 39% with the combination (p < 0.005 vs. placebo, atenolol and amlodipine). In patients with angina, total exercise time improved by 16% with amlodipine (p < 0.001), by 4% with atenolol (p = NS) and by 19% with the combination (p < 0.05 vs. placebo and either single drug). In those patients without angina, no therapy significantly improved total exercise time.

CONCLUSIONS

Ischemia during treadmill testing was more effectively suppressed by amlodipine, whereas ischemia during ambulatory monitoring was more effectively suppressed by atenolol. The combination was more effective than either single drug in both settings.

Pathophysiologic factors governing the variability of ischemic responses to treadmill and bicycle exercise

Ischemic responses may vary considerably when patients with coronary artery disease (CAD) are tested serially, but the pathophysiologic mechanisms that govern this variability have not been well evaluated. We thus evaluated whether clinical, hemodynamic, physiologic, and anatomic factors influenced the variability in ischemic responses among 140 patients (mean age 54 +/- 11 years) subjected to both bicycle and treadmill exercise electrocardiography. Radionuclide ventriculography was obtained during bicycle exercise in each patient. The population included 77 patients with CAD, 21 patients with normal coronary arteriograms, and 42 patients with < 5% likelihood of CAD. Bicycle exercise evoked higher systolic blood pressure (p < 0.001) and double-product (p < 0.001) responses compared with treadmill exercise in the patients with CAD and in the normal subjects, and it evoked a lower frequency of chest pain (12% vs 41%, p < 0.001) in the 34 patients with CAD who had ST-segment depression during both exercise tests. There was a high frequency of variability in ischemic responses during treadmill versus bicycle exercise: 22 (39%) of the 56 CAD patients who had exercise-induced ST-segment depression manifested this response during one stress test only. This variability was strongly related to the functional and anatomic magnitude of disease. Ischemic variability decreased progressively as the response of left ventricular ejection fraction (LVEF) to exercise worsened progressively (p = 0.003 by analysis of variance), from 83% in those with an LVEF increase of > 10% with exercise to only 13% in those with an LVEF fall of > or = 5% with exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex cutaneous vasoconstriction during cold pressor test is mediated through alpha-adrenoceptors

The effects of the cold pressor test on the coronary circulation have been clearly defined but the effects on the peripheral vasculature are less well understood. To measure the peripheral vasomotor response during cold pressor test perfusion in the upper extremity contralateral to the cold immersion was assessed by laser Doppler flowmetry and skin-surface temperature gradients. To identify the mechanism of vasoconstriction, cold pressor test was performed before and after the administration of phentolamine, an alpha-adrenoceptor antagonist. Vasoconstriction during cold pressor test was demonstrated by both skin-surface temperature gradients and by laser Doppler flowmetry. This vasoconstrictor response was significantly attenuated by the administration of phentolamine. The results demonstrate that the cold pressor test induces an alpha-adrenoceptor mediated vasoconstriction in the peripheral vasculature.

Endothelin release and enhanced regional myocardial ischemia induced by cold-air inhalation in patients with stable angina

This study was designed to determine the influence of cold-air inhalation on regional myocardial perfusion in patients with ischemic heart disease. A selected group of vasoactive hormones was measured to investigate their possible roles as ischemic agents. Ten men who had recently had a myocardial infarction and anginal symptoms and with verified pathologic ST deviations during a preceding exercise test volunteered to participate in this randomized cross-over study. Two identical exercise tests were performed on different days; one with inhalation of cold (-22 degrees C) air and the other one with inhalation of thermoneutral air (22 degrees C). Scintigraphic imaging (single-photon emission computed tomography) of regional myocardial blood flow was performed with technetium 99m isonitrile flowtracer and a Bull's eye visual display with calculation of the scintigraphic ischemic severity score. The score was significantly higher during exercise with inhalation of cold air as compared to exercise with inhalation of thermoneutral air. Furthermore, only with cold-air inhalation did arterial plasma endothelin concentration increase significantly from rest to exercise and correlate with the change of ischemic severity score. In contrast, no change was observed under thermoneutral conditions. There was no significant difference between peak values of heart rate, systolic blood pressure, adrenaline, and noradrenaline concentrations in the two situations. We conclude that inhalation of cold air during exercise increases the degree of regional myocardial ischemia and that this is not caused by an increased myocardial oxygen demand. We suggest that cold air directly influences the vasomotor tone of the myocardial resistance vessels and that endothelin may be involved in the ischemic response.

Role of behavioral and psychological factors in mental stress-induced silent left ventricular dysfunction in coronary artery disease

OBJECTIVES

We examined the relationship of the psychological profile to left ventricular dysfunction induced during mental stress.

BACKGROUND

The contribution of psychological factors to mental stress-provoked silent myocardial ischemia has not been explored.

METHODS

Thirty patients with chronic stable coronary artery disease and a reversible defect on stress thallium-201 imaging completed a psychological assessment by questionnaire and Structured Interview, serially administered mental stress and brief walking exercise. Blood pressure, electrocardiogram (ECG) and left ventricular indexes were obtained by ambulatory serial radionuclide ventriculography. Silent ventricular dysfunction was defined by a decrease > or = 0.05 in ejection fraction or > or = 1 mm in ST segment on the ECG in the absence of symptoms.

RESULTS

Of the 30 patients, 15 (Group I) had evidence of silent left ventricular dysfunction during mental arithmetic. The other 15 (Group II) showed no change. In addition, 18 of 30 patients had this dysfunction during the Structured Interview. Both ischemic and nonischemic groups developed comparable and significant increases in heart rate and blood pressure. Group I patients were distinguished by higher scores on measures of aggressive responding (p < 0.001), trait anger (p < 0.0001), hostile affect (p < 0.003) and an index of behavioral reactivity (p < 0.003) and a lower score on anger control (p < 0.001). No other variables, including historical and clinical indexes, discriminated between the two groups.

CONCLUSIONS

Patients with coronary artery disease and mental stress-provoked silent ventricular dysfunction were distinguished by a psychological profile consistent with emotional reactivity to social interaction and mental provocation, with anger as the predominant affective state. Patients with such a profile may be at risk of frequent silent left ventricular dysfunction.

Defective coronary prostaglandin modulation in anginal patients

In order to investigate whether coronary vasodilating prostaglandins (PGI2 and PGE2) have a role in the pathophysiology of myocardial ischemia, 26 patients with angina pectoris and 23 control subjects (nonischemic patients) were studied by assessing coronary hemodynamics and prostaglandin formation in relation to sympathetic stimulation. Following a cold pressor test (CPT), coronary prostaglandin output markedly increased (p less than 0.001) and coronary vascular resistance (CVR) decreased (p less than 0.001) in all control subjects. In contrast, in anginal patients prostaglandins in the coronary sinus were undetectable and after CPT prostaglandin output did not increase, whereas CVR paradoxically increased (p less than 0.001). In control subjects the inhibition of coronary prostaglandin formation (by ketoprofen [1 mg/kg intravenously] or by aspirin [15 mg/kg intravenously]) caused a paradoxical increase of CVR following CPT (p less than 0.001). In anginal patients the inhibition of prostaglandins further exaggerated the increase of CVR after CPT (p less than 0.001). These results indicate that coronary vasodilating prostaglandin PGI2 and PGE2 play a role in modulating coronary vascular response to sympathetic stimulation induced by CPT. Their defective production in anginal patients may be responsible for the paradoxical increase in CVR following sympathetic stimulation.

Exercise-induced myocardial ischemia in a cold environment. Effect of antianginal medications

The influence of cold on the threshold for myocardial ischemia and the efficacy of antianginal drugs in a cold environment were assessed in 24 patients with stable angina and exercise-induced ST depression. Treadmill exercise tests were done according to a randomized double-blind protocol 90 minutes after administration of placebo, 80 mg propranolol, or 120 mg diltiazem, each at both -8 degrees and 20 degrees C. Eight of the patients were classified by history as cold-sensitive before the study. For the entire group, none of the exercise end points differed significantly between cold and normal temperatures with placebo. However, cold-sensitive patients developed 1 mm ST depression 30% sooner (169 +/- 41 versus 244 +/- 38 seconds, p less than 0.01) at -8 degrees C compared with 20 degrees C. At the onset of ischemia, rate-pressure product was lower in the cold (19.8 +/- 1.0 versus 22.0 +/- 1.6 x 10(-3), p less than 0.05). Both propranolol and diltiazem prolonged time to onset of 1 mm ST depression at both temperatures. The magnitude of improvement at -8 degrees C was equal to that at 20 degrees C, and differences between the two drugs were not statistically significant. Only diltiazem prolonged total exercise duration. Thus, as assessed by exercise testing, cold does not worsen ischemic threshold in most stable angina patients. However, in a subgroup identifiable by history, ischemic threshold is lower in the cold. Propranolol and diltiazem are as effective for exercise-induced ischemia in a cold environment as at normal temperatures.

Ambulatory (Holter) electrocardiography and myocardial ischemia

Ambulatory (Holter) electrocardiography has evolved over the past two decades to allow accurate assessment of the cardiac rhythm, and more recently, accurate detection and measurement of ST segment changes. These ambulatory ECG ST segment changes that occur with and without symptoms, although thought to be of questionable clinical value for many years, have recently been clearly documented in coronary artery disease patients to represent true myocardial ischemia. Concurrent with these technologic developments has been an evolution of the pathophysiologic understanding of myocardial ischemia, and the relative role and sequential nature that ECG ST segment changes have in its development. This review examines from a clinical perspective the current understanding of the pathophysiologic sequence of development of myocardial ischemia, emphasizes the ECG diagnostic methods that detect this sequential change, examines the criteria that define ambulatory ECG myocardial ischemia, and discusses those nonischemic factors that affect the ECG ST segment and its interpretation. Moreover, an ever increasing number of ambulatory ECG studies of coronary artery disease and normal patients have defined unique characteristics of the ambulatory ECG ST segment changes observed with regard to its diagnostic, prognostic, and therapeutic assessment value in the study of myocardial ischemia.