Acute changes in blood pressure as a cause of cardiac arrhythmias

The role of desmin alterations in mechanical electrical feedback in heart failure

AIM

Mechanoelectric feedback (MEF) was related to malignant arrhythmias in heart failure (HF). Desmin is a cytoskeleton protein and could be involved in MEF as a mechanoelectrical transducer. In this study, we will discuss the role of desmin alterations in mechanical electrical feedback in heart failure and its mechanisms.

METHODS

We used both an in vivo rat model and an in vitro cardiomyocyte model to address this issue. For the in vivo experiments, we establish a sham group, an HF group, streptomycin (SM) group, and an MDL-28170 group. The occurrence of ventricular arrhythmias (VA) was recorded in each group. For the in vitro cardiomyocyte model, we established an NC group, a si-desmin group, and a si-desmin + NBD IKK group. The expression of desmin, IKKβ, p-IKKβ, IKBα, p-NF-κB, and SERCA2 were detected in both in vivo and in vitro experiments. The content of Ca²⁺ in cytoplasm and sarcoplasmic were detected by confocal imaging in vitro experiments.

RESULTS

An increased number of VAs were found in the HF group. SM and MDL-28170 can reduce desmin breakdown and the number of VAs in heart failure. The knockdown of desmin in the cardiomyocyte can activate the NF-κB pathway, decrease the level of SERCA2, and result in abnormal distribution of Ca²⁺. While treatment with NF-κB inhibitor can elevate the level of SERCA2 and alleviate the abnormal distribution of Ca²⁺.

SIGNIFICANCE

Overall, desmin may participate in MEF through the NF-κB pathway. This study provides a potential therapeutic target for VA in HF.

Labile hypertension: a new disease or a variability phenomenon?

Blood pressure (BP) is a physiological parameter with short- and long-term variability caused by complex interactions between intrinsic cardiovascular (CV) mechanisms and extrinsic environmental and behavioral factors. Available evidence suggests that not only mean BP values are important, but also BP variability (BPV) might contribute to CV events. Labile hypertension (HTN) is referred to sudden rises in BP and it seems to be linked with unfavorable outcomes. The aim of this article was to review and summarize recent evidence on BPV phenomenon, unraveling the labile HTN concept along with the prognostic value of these conditions.

Effects of artemisinin on ventricular arrhythmias in response to left ventricular afterload increase and microRNA expression profiles in Wistar rats

Background

Patients with dilated cardiomyopathy, increased ventricular volume, pressure overload or dysynergistic ventricular contraction and relaxation are susceptible to develop serious ventricular arrhythmias (VA). These phenomena are primarily based on a theory of mechanoelectric feedback, which reflects mechanical changes that produce alterations in electrical activity. However, very few systematic studies have provided evidence of the preventive effects of artemisinin (ART) on VA in response to left ventricle (LV) afterload increases. MicroRNAs (miRNAs) are endogenous small non-coding RNAs that regulate expression of multiple genes by suppressing mRNAs post-transcriptionally.

Aims

The aims of this study were to investigate preventive effects of ART on mechanical VA and the underling molecular mechanisms of differentially expressed miRNAs (DEMs).

Methods

For the study, 70 male Wistar rats were randomly divided into seven groups: group 1 was a control group (sham surgery); group 2 was a model group that underwent transverse aortic constriction (TAC) surgery; groups 3, 4, 5 and 6 were administered ART 75, 150, 300 and 600 mg/kg before TAC surgery, respectively; and group 7 was administered verapamil (VER) 1 mg/kg before TAC surgery. A ventricular arrhythmia score (VAS) was calculated to evaluate preventive effects of ART and VER on mechanical VA. The high throughput sequencing-based approach provided DEMs that were altered by ART pretreatment between group 2 and group 4. All predicted mRNAs of DEMs were enriched by gene ontology (GO) and Kyoto Encyclopedia annotation of Genes and Genomes (KEGG) databases. These DEMs were validated by a real time quantitative polymerase chain reaction (RT-qPCR).

Results

The average VASs of groups 3, 4, 5, 6 and 7 were significantly reduced compared with those of group 2 (2.70 ± 0.48, 1.70 ± 0.95, 2.80 ± 0.79, 2.60 ± 0.97, 1.40 ± 0.52, vs 3.70 ± 0.67, p < 0.01, respectively). The three top GO terms were neuron projection, organ morphogenesis and protein domain specific binding. KEGG enrichment of the 16 DEMs revealed that MAPK, Wnt and Hippo signaling pathways were likely to play a substantial role in the preventive effects of ART on mechanical VA in response to LV afterload increases. All candidate DEMs with the exception of rno-miR-370-3p, rno-miR-6319, rno-miR-21-3p and rno-miR-204-5p showed high expression levels validated by RT-qPCR.

Conclusions

Artemisinin could prevent mechanical VA in response to LV afterload increases. Validated DEMs could be biomarkers and therapeutic targets of ART regarding its prevention of VA induced by pressure overload. The KEGG pathway and GO annotation analyses of the target mRNAs could indicate the potential functions of candidate DEMs. These results will help to elucidate the functional and regulatory roles of candidate DEMs associated with antiarrhythmic effects of ART.

Sex Differences in Susceptibility to Epinephrine-Induced Arrhythmias

Gender differences in incidence of cardiac arrhythmias have been documented. It is generally believed that cardiac pathology provides an arrhythmogenic substrate but that a trigger such as sympathetic nervous system activation is required to initiate arrhythmias. This study was done to determine whether there is a sex difference in susceptibility to epinephrine-induced arrhythmias in healthy rats without preexisting pathology and to determine whether gonadal hormones play a role in development of arrhythmias. Untreated, sham-operated, and gonadectomized male and female rats were anesthetized and given IV boluses of epinephrine. ECG, heart rate, and blood pressure were measured continuously for 1 minute and intermittently over a period of 30 minutes. Male rat hearts have a higher occurrence and frequency of epinephrine-induced premature ventricular contractions, missed beats, and blocks than female rat hearts. Ovariectomy increases arrhythmias, thereby abolishing the female advantage. Castration has no effect on occurrence and frequency of premature ventricular contractions but attenuates missed beats and blocks. Sex differences and effect of gonadectomy on epinephrine-induced alterations in heart rate and blood pressure implicate baroreceptor reflex in the dimorphic arrhythmogenic response. Male rat hearts are more susceptible than female hearts to epinephrine-induced arrhythmias, and gonadal hormones play a role in this disparity.

Arterial hypertension and cardiac arrhythmias

PURPOSE AND DATA IDENTIFICATION: One of the main clinical problems of patients with arterial hypertension is the presence of arrhythmias, especially if left ventricular hypertrophy exists. Recent results from our group and all data available via Med-Line-search have been analysed. The analysis was focused on atrial and ventricular arrhythmias and arrhythmic risk prediction, using non-invasive markers. RESULTS OF ANALYSIS AND CONCLUSION: Arterial hypertension is a major cause of non-rheumatic atrial fibrillation and other supraventricular arrhythmias. The prevalence of ventricular arrhythmias is increased in hypertensive patients without left ventricular hypertrophy, compared to normotensives. If left ventricular hypertrophy is present, the risk for ventricular tachycardias is quadrupled. The presence of left ventricular hypertrophy is associated with an increase in all-cause mortality by a factor of seven in men and nine in women. In particular, patients with hypertrophy, increased rate of ventricular extrasystoles up to non-sustained ventricular tachycardia and ST-depression in long-term ECG are threatened by sudden cardiac death. At present, it is not possible to safely identify patients with increased risk. Regression of hypertrophy exists along with a decreased rate of ventricular extrasystoles. We hypothesize that by the regression of hypertrophy, the prevalence of sustained ventricular tachycardia decreases and therefore the prognosis of those patients can be improved, although controlled studies are not yet available.

Wall stress-induced dysrhythmias in the isolated working rat heart perfused through a cannula placed in the left ventricle via aorta

The purpose of the present study was to determine if our recently introduced novel working rat heart preparation could be used to study wall stress-induced dysrhythmias. A double cannula, which consisted of an outer cannula that, was inserted in the aorta and an inner cannula that was advanced into the left ventricle was used. The perfusion flowed through the inner cannula into the left ventricle and was ejected from there into the aorta. Afterload was changed suddenly from 60 to 160 Hg of pressure by turning a valve so that the fluid was diverted to a column set at a different height. A sudden increase of aortic pressure that lasted for 10 sec caused cardiac ectopic beats. Wall stress-induced dysrhythmias were more sustained during perfusion with low potassium and low magnesium Krebs-Henseleit solution. Bradykinin (1 microg) or epinephrine (10 microg) was injected as a bolus via an in-line injection port placed at the inner cannula. Bradykinin significantly reduced the incidence of ectopic beats and epinephrine increased the incidence of nonsustained runs of VT. This "working" heart preparation is a convenient tool to study wall stress-induced dysrhythmias.

Mechanosensitivity as an integrative system in heart: an audit

This review examines a manifold of apparently loosely linked observations and mechanisms, from membrane to man, and assembles them to support the notion that mechanoelectric transduction is an integrative regulatory system in the heart. For this, the assemblage has to satisfy, at least to some extent, criteria that apply to other integrative regulatory systems such as the endocrine and nervous systems. The integrative effectors in the endocrine system are chemical linkages, circulating hormones: in the nervous system the linkage is a network of cables, nerve conduction and neurotransmitters. Mechanical integration is would be effected through mechanical machinery, cardiac contractile and hydraulic function with attendant stress and strain transmitted via "tensegrity". This can, through the cytoskeleton, begin with membrane integrins and transmit intracellularly for example via F actins to reach the rest of the membranous integrins. Further transmission to the organ is via cell-to-cell adhesion complexes and the extracellular matrix. This tensegrity facilitates integration of force and strain changes from area to area. In consequence, and analogous to the neurendocrine system, mechanoelectric transduction should, and does (1) operate at the molecular or membrane level--this would be via mechanotransducers affecting transmembrane ionic flow; (2) operate in the cell--to influence electrophysiology; (3) have a multicellular expression--e.g. mechanical distortion of one cell can raise intracellular calcium of an adjacent cell; (4) express in the intact organ--e.g. an increase in venous return hydraulically distends the sinoatrial node, steepening its pacemaker potential, thus increasing heart rate. It should also (5) demonstrate elements of a feedback system--"mechanoelectric feedback", and (6) interact with other systems--the cytoskeleton incorporates cell signalling complexes intersecting with other signal cascades. Finally, (7) it can malfunction to produce clinical abnormality--it contributes electrophysiologically to lethal cardiac arrhythmia. This anatomical and functional behaviour of mechanoelectric transduction could sanction the prospect of viewing it as analogous to the other integrative physiological systems.

Segmental wall motion abnormalities alter vulnerability to ventricular ectopic beats associated with acute increases in aortic pressure in patients with underlying coronary artery disease

OBJECTIVE

To evaluate whether patients with coronary artery disease are susceptible to pressure related ventricular arrhythmias, and if so to identify possible risk factors.

DESIGN

Interventional study.

METHODS

Metaraminol was given to 43 patients undergoing coronary arteriography for ischaemic heart disease to increase their aortic pressure, provided their systolic blood pressure was < 160 mm Hg and they were in sinus rhythm, without any ventricular ectopic activity (or with fewer than six ventricular ectopic beats a minute) during a five minute control period.

RESULTS

During the metaraminol infusion, systolic aortic pressure rose from 131 (15) to 199 (12) mm Hg (mean (SD)). Ventricular ectopy appeared (or ventricular ectopic beats increased by > 100%) in 13/43 patients. Ventricular ectopy was not related to age, sex, presence of hypertension, history of myocardial infarction, use of beta blockers, positive exercise test, number of vessels diseased, or heart rate change during metaraminol infusion. There was a strong relation between the appearance of ventricular arrhythmia and segmental wall motion abnormalities: 1/19 (5.3%, 95% confidence interval 0.1% to 26.0%) without abnormality; 2/12 (16.7%, 2.1% to 48.4%) with hypokinesia; and 10/12 (83.3%, 51.6% to 97.1%) with akinesia or dyskinesia, chi 2 = 22.7, p < 0.001). Ejection fraction was also a significant but not independent risk factor.

CONCLUSIONS

Patients with segmental wall motion abnormalities are predisposed to ventricular ectopic beats during an increase in systolic aortic pressure. This could be explained by associated electrophysiological inhomogeneity. The presence of mechanical inhomogeneity, as may occur in postinfarction akinesia or dyskinesia, may affect the aortic pressure above which ventricular arrhythmias appear.

Ventricular arrhythmias in normotensive subjects and in mild hypertensive patients

Twenty-five normotensive subjects (14 men, 11 women) aged from 25 to 60 years (mean 36) and 30 untreated patients with mild hypertension (stages 1 and 2, JNC V) without target organ damage (16 men, 14 women), aged 26-59 years (mean 35.8) underwent continuous 24-hour ECG Holter monitoring with a Fukuda Denshi SM-40 ambulatory recorder and SCM-400 ECG analyzer. During 24-hour ambulatory ECG recording, mean heart rate was slightly but not significantly higher in hypertensive patients (73.3 +/- 10 beats per minute [bpm]) in comparison with normotensive subjects (71.2 +/- 12 bpm). The prevalence of premature atrial contractions was similar in the two groups. Total ventricular arrhythmias were more prevalent in the group of mild hypertensive patients (P < 0.05), who also had a higher prevalence in complex forms of ectopy (r = 0.81 for bigeminy; r = 0.83 for trigeminy; r = 0.83 for couplets). Holter recordings did not show abnormalities of ST-T wave or episodes of silent ischemia.

Ventricular tachyarrhythmias, myocardial ischemia, and sudden cardiac death in patients with hypertensive heart disease

Hypertensive heart disease is increasingly considered to be a strong and independent risk factor for sudden cardiac death. Ventricular tachyarrhythmias in these patients are common and mainly the result of electrophysiologic abnormalities and increased electrical vulnerability of the hypertrophic myocardium. However, proarrhythmia in the hypertrophic heart often is facilitated and aggravated by electrolyte disturbances, the sympathoadrenergic tone, transient blood pressure crisis, and especially by the occurrence of myocardial ischemia. Myocardial ischemia in the setting of hypertensive heart disease may result from stenotic lesions in large and/or small coronary artery vessels and, in the absence of both, will result from the altered cellular oxygen supply and consumption in the hypertrophic myocardium. Recent studies have shown that acute and transient myocardial ischemia are common in many hypertensives, often fail to be symptomatic, and that the dynamic interaction of left ventricular hypertrophy, transient myocardial ischemia, and ventricular tachyarrhythmias may provide a crucial link for the high incidence of sudden cardiac death in patients with hypertensive heart disease.

Effect of preload and afterload on ventricular arrhythmogenesis

To examine whether it is an increase in preload or afterload that may cause ventricular arrhythmias, the ventricles of 13 anesthetized open-chest dogs were bandaged. Next, metaraminol, an almost pure alpha stimulator, was given, followed by removal of the bandage. The ventricles were then sucked in a plastic cup, which was finally removed. The systolic and diastolic ventricular pressures were measured, and the presence of arrhythmias (ventricular ectopic beats or ventricular tachycardia) was observed. Banding the ventricles caused a significant diminution of systolic pressure (-42 +/- 38.0 mmHg; mean +/- SD) and a rise in diastolic pressure (+3.5 +/- 3.7), starting from control values of 126 +/- 36/6.5 +/- 3.0, but no arrhythmia. Metaraminol raised both pressures (+122 +/- 58 and +9.0 +/- 10.3) and caused ventricular arrhythmias in 6 of 13 experiments. Removing the bandage further increased the systolic pressure (+45 +/- 42) and reduced the diastolic pressure (-7.2 +/- 10.3), but made the arrhythmia worse in 10 of 13 experiments. Suction reduced both pressures (-166 +/- 96 and -5.4 +/- 14) and stopped all arrhythmias. Removing the cup increased both pressures (+133 +/- 68 and +15.5 +/- 15.3, respectively) and worsened the arrhythmia in seven of eight experiments. In general, deterioration of ventricular arrhythmias was observed in 23 of 25 maneuvers with either an increase or no change in systolic pressure, but in none of the maneuvers was there a decrease (P < .0001) in systolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Is ventricular wall stress rather than left ventricular hypertrophy an important contributory factor to sudden cardiac death?

Sudden cardiac death comprises a significant proportion of cardiac mortality in Western society. Left ventricular hypertrophy has been identified by many authors as a possible risk factor for sudden cardiac death, however, left ventricular hypertrophy develops in response to external stimuli on the heart as a means of normalizing wall stress. It is possible that the fundamental abnormalities in wall stress, rather than the left ventricular hypertrophy itself, pose the increased risk of sudden death. Left ventricular hypertrophy, the consequence of raised wall stress, is easy to measure and easy to study and it is understandable why this parameter should have received more attention. Wall stress by contrast is difficult to measure, and worse, is variable throughout the ventricle so that it cannot be measured in a single quantifiable figure. As a consequence, only a limited amount of attention has been paid to wall stress as a possible trigger mechanism for cardiac arrhythmia. However, there is evidence from both basic and clinical research to suggest that raised wall stress may be a risk factor for sudden cardiac death and cardiac arrhythmia. This review discusses the evidence for and against left ventricular hypertrophy and wall stress as risk factors for sudden cardiac death, and also presents recent evidence that left ventricular hypertrophy in isolation can protect the heart against the arrhythmogenic effects of raised wall stress.

Ventricular dysrhythmias, left ventricular hypertrophy, and sudden death

Left ventricular hypertrophy has been documented to be a powerful risk factor for sudden death, acute myocardial infarction, and other cardiovascular morbidity and mortality. The major determinant of left ventricular mass is the hemodynamic burden. However, the hypertrophic process is modified by demographic parameters (age, sex, race), nutritional parameters (salt intake, alcohol, obesity), and neuroendocrine factors (angiotensin, catecholamines, growth hormones, etc.). Ventricular ectopy and more serious arrhythmias are commonly seen in patients with left ventricular hypertrophy. Specific antihypertensive therapy will reduce left ventricular hypertrophy, although not all antihypertensive drugs are equipotent in this regard. A reduction in left ventricular hypertrophy has been shown to diminish left-ventricular-hypertrophy-associated arrhythmias. However, it remains to be shown that patients with left ventricular hypertrophy and ventricular ectopy are at a higher risk of sudden death than those without ventricular ectopy and that the reduction of left-ventricular-hypertrophy-associated ventricular ectopy indeed confers a clinical benefit that exceeds the one from the reduction in arterial pressure alone.

Effect of acute ventricular pressure changes on QRS duration

The effect of acute changes in ventricular pressure is examined on the QRS duration to clarify the mechanism of ventricular pressure-related arrhythmogenesis. Ventricular pressure was changed acutely by arterial transfusion-bleeding into an open-air ventricular pressure reservoir that was either off or on a metaraminol intravenous drip. While maintaining ventricular pressure at several levels, the QRS duration was measured at 200 mm/s paper speed. The QRS duration correlated significantly with the left ventricular pressure in all 14 dogs examined. An average change in ventricular by 100 mmHg was associated with a change of about 18% in the QRS duration. An acute ventricular pressure elevation impairs the ventricular conduction, which may contribute to ventricular pressure-related arrhythmogenicity.

Effects on ventricular arrhythmias of oral captopril and of oral mononitrate started early in acute myocardial infarction: results of a randomised placebo controlled trial

OBJECTIVE

To assess the effects of oral vasodilator treatment on ventricular arrhythmias in acute myocardial infarction.

SETTING

Coronary care units at the John Radcliffe Hospital, Oxford, and the Royal Infirmary, Edinburgh.

PATIENTS

100 patients with suspected acute myocardial infarction entered the study at a mean of 13 hours from symptom onset. DESIGN OF INTERVENTION: Double blind randomisation to 4 weeks treatment with captopril (12.5 mg three times a day after a 6.25 mg test dose (n = 32)) or isosorbide mononitrate (20 mg three times a day (n = 31)) or placebo control (n = 37).

OUTCOME MEASURES

Ventricular arrhythmic events assessed by 48 hours of Holter monitoring starting at the time of randomisation.

RESULTS

The number of ventricular extrasystoles/hour for captopril, mononitrate, and placebo was respectively (median and range) 6 (0-162), 4 (0-38), and 10 (0-932) (2p < 0.02 mononitrate v placebo). The number of episodes of multiple extrasystoles/hour was 0.2 (0-22), 0.3 (0-4), and 0.5 (0-19); (2p < 0.02 mononitrate v placebo). Episodes of ventricular tachycardia showed a non-significant decrease in the captopril and mononitrate groups (mean (SEM) 3.2 (0.8), 2.4 (0.7), and 4.7 (1.3) for the 48 hour period). The incidence of idioventricular rhythm was also reduced in both active treatment groups (28%, 19%, and 46% (2p < 0.05 mononitrate v placebo)).

CONCLUSIONS

Oral mononitrate (and perhaps also captopril) seems to reduce the incidence of ventricular arrhythmias in the early phase of acute myocardial infarction. The effects on life-threatening arrhythmias, such as ventricular fibrillation, and on death can only be assessed in a much larger trial.

Anatomical origin of pressure-related ventricular ectopic rhythms

In order to determine the origin of pressure-related ectopic rhythms, the main arteries were clamped in 11 anesthetized dogs, or the arteries or veins were transfused, while on or off metaraminol. The epicardial right atrial electrogram, the intracavity electrograms and the pressure of the two ventricles were recorded. Sinus rhythm was associated with 64/64 (100%) of the control periods off metaraminol, but only 19/50 (38%) of the clamping of the main arteries (P << 0.0005). In 14/27 aortic clampings ectopic beats appeared from the left ventricle and in 13/27 from the right one. In 4/23 clampings of the pulmonary artery ectopic beats appeared from the left ventricle and in 15/23 from the right one (P < 0.05). Sinus rhythm was associated with significantly lower left ventricular systolic pressure than any ventricular arrhythmia. The left ventricular systolic pressure associated with ectopic rhythms from the left ventricle was significantly (P < 0.005) higher than that associated with those from the right ventricle. The right ventricular systolic pressure during sinus rhythm was significantly (P < 0.005) lower than that during ectopic rhythm from any ventricle. It is concluded that a rise in the pressure of one ventricle tends to cause ventricular ectopic rhythms originating predominantly, but not exclusively, from this ventricle. The origin of ventricular ectopic rhythms from the right ventricle does not preclude that the arrhythmia may respond favorably to lowering of the systemic pressure.

Hypertension, left ventricular hypertrophy, ventricular ectopy, and sudden death

Left ventricular hypertrophy (LVH) is a common sequela of sustained arterial hypertension, although the correlation between spot blood pressure measurements and LV mass is not a close one. LVH has been shown to be a powerful blood pressure-independent risk factor for cardiovascular morbidity and mortality. LVH has been shown to trigger or to accelerate ventricular dysrhythmias, although the connection between ventricular dysrhythmias and sudden death is poorly documented. LVH can be reduced by specific antihypertensive therapy; however, not all drugs are equipotent in this regard. A reduction of LVH has been shown to be associated with a suppression of ventricular dysrythmias. Preliminary studies also indicate that the reduction of LVH may reduce its inherent excessive morbidity and mortality.

Ambulatory blood pressure monitoring and circadian variation of cardiovascular disease; clinical and research applications

Ambulatory blood pressure monitoring is an evolving technology. It has an established role in the diagnosis of hypertension, the clinical management of selected patients, and in the evaluation of new medication. From continuous recording much has been learned about the circadian nature of blood pressure and heart rate. Future research holds promise for a greater understanding of the mechanisms and treatment of cardiovascular disease. The purpose of this short review is to describe the development of ambulatory blood pressure monitoring, and outline some of its important contributions to date; and also to explore the research potential and clinical utility of advanced intravascular monitoring techniques, such as the continuous recording of pulmonary artery pressure in ambulant patients.

The circadian profile of extrasystolic arrhythmia: its relationship to heart rate and blood pressure

This paper aims at examining whether there is an association between the circadian patterns of systolic blood pressure, heart rate and the incidence of ventricular ectopic beats, as well as to confirm that reducing the blood pressure by a diuretic may also reduce the ectopic frequency. Thirty-four ambulatory patients with ventricular ectopic beats and a systolic blood pressure of 131.33 +/- 17.46 mmHg had a 24-hour Holter electrocardiographic and blood pressure monitoring following 1 week off any antiarrhythmic and antihypertensive treatment. Then they received for one week a standard diuretic combination (amiloride 5 mg + hydrochlorothiazide 50 mg) at a dose depending on their systolic pressure value and their monitoring was repeated. The mean hourly values of systolic blood pressure, heart rate and ventricular ectopic beats were "normalized", i.e. expressed as (x-x)/SD, taking each patient's 24-hour average as zero and his own standard deviation as the unit of measurement. As a group, there was an independent positive correlation between blood pressure and ectopic beats, while the heart rate was a nonsignificant negative factor for ectopic beats. On an individual level, however, an independent positive significant correlation between blood pressure and ectopic beats was found in only 8 cases, with a negative one in 4 cases. While the blood pressure of the group ranged symmetrically around its daily average value, the corresponding ectopic beat curve was highly asymmetric, with a very high incidence (up to 2.56 +/- 0.52 SD) for a rather short time (only 9.41 +/- 3.56 hours above average) and a low incidence (up to 1.26 +/- 0.49 SD) for the remaining 14.59 hours below average. Sudden rises in ectopic beat (greater than 1 SD/hour) occurred 1 to 6 times per day in each individual, significantly (P less than 0.01) more often (20.31%) with a high (greater than 1 SD) blood pressure than with a low (less than -1 SD) one (8.99%) with intermediate frequencies at intermediate pressures. After treatment with the diuretic, the systolic blood pressure was reduced, the heart rate increased and the ventricular ectopic beat incidence reduced (significant changes). The mean change in systolic pressure in 25 patients with a reduction in ectopy was a significant (P less than 0.01) decrease (-5.21 +/- 8.70 mmHg) while in the remaining 9 cases there was a non significant increase (+1.68 +/- 7.63 mmHg). The heart rate was higher in both subgroups.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional changes in ventricular excitability during load manipulation of the in situ pig heart

1. The effect of load manipulation on myocardial excitability was studied in the anaesthetized, in situ pig heart. 2. A 33% increase in systolic left ventricular pressure achieved by aortic clamping reduced the mean effective refractory period by 11 ms (7.6%, P less than 0.01); whereas a 15% reduction in ventricular pressure achieved by intravenous infusion of sodium nitroprusside increased the mean effective refractory period by 4 ms (3.2%, P less than 0.05). 3. Changes in action potential duration, measured to 70% repolarization, roughly paralleled those of the effective refractory period. 4. The changes in effective refractory period were inhomogeneous, with a greater change occurring at the apex compared to the base in response to an increase in load, i.e. there was an increase in regional dispersion of refractoriness across the left ventricle. 5. Since inhomogeneity of repolarization and refractoriness is known to be potentially arrhythmogenic, these findings suggest that mechanical factors may contribute directly to the arrhythmias commonly seen clinically in high load states such as congestive cardiac failure and may also have consequences for the treatment of such arrhythmias.

Pressure-related ventricular tachycardia

A case with syncope on exertion and paced heart block is presented. Non-sustained ventricular tachycardia was seen on Holter monitoring and reproduced repeatedly by either exercise or an injection of an alpha agonist, but not with provocative electrophysiology. Antihypertensive treatment using a beta-blocker with endogenous sympathomimetic activity prevented recurrences. It is suggested that this is a case of pressure-related tachycardia.

Echocardiographic study of U wave inversion in the electrocardiograms of hypertensive patients

The prevalence of U wave inversion was evaluated in 58 adult patients with hypertension, and a possible mechanism for it was examined using M-mode echocardiographic indices. U wave inversion was the most common electrocardiographic abnormality, occurring in 34% of patients; voltage criteria for left ventricular hypertrophy were present in only 14% of patients, and ventricular strain pattern was not detected in any patient. Nonetheless, on echocardiography left ventricular posterior wall thickness was increased in 58% of patients. However, neither U wave inversion nor conventional voltage criteria for left ventricular hypertrophy was strongly predictive for this finding. The authors conclude that U wave inversion is a frequent finding in patients with hypertension, often occurring alone. Although it does not appear to be closely linked to the presence of left ventricular hypertrophy, it may relate to other, perhaps subtle, abnormalities of diastolic ventricular relaxation.

Psychological distress as a predictor of ventricular arrhythmias in a post-myocardial infarction population

A prospective study examining the relationship between psychological distress and ventricular ectopy was conducted with 125 post-myocardial infarction patients equipped with a transtelephonic ECG monitor. Subjects were subsequently grouped according to the occurrence (n = 59) or nonoccurrence (n = 65) of ventricular arrhythmias over a 1-year period. Results indicated a direct relationship between self-reported distress levels and occurrence of ectopic beats. This relationship was unaltered by adjusting simultaneously for known predictors of arrhythmias, including cardiac risk, age, and the prescription of beta-blocker agents. Thus this study represents an initial demonstration in a post-myocardial infarction population that psychosocial factors have prognostic significance for arrhythmias and, presumably, sudden death.

Effect of acute hypertension on the cardiac rhythm. Experimental observations

An acute increase in blood pressure (BP) may be associated with the genesis of ventricular ectopy. Fourteen anesthetized dogs were examined to find out whether the critical pressure that causes an arrhythmia may be an index of the tendency of the myocardium to generate ectopic rhythms. An acute change in BP was produced 321 times using an arterial pressure reservoir or aortic obstruction or a metaraminol infusion or, inversely, arterial bleeding. Each time the BP was increased, cardiac arrhythmias appeared and each time the BP was decreased the cardiac arrhythmias disappeared. The most common type of arrhythmia was ventricular ectopy (123/167 acute BP increases), usually in a form of bigeminy. The next most common rhythm disturbance was atrioventricular block (32/167 acute BP increases), especially when a constant rate was achieved by atrial pacing. The BP above which an arrhythmia appeared varied greatly among different animals (189.0 +/- 55.1 mmHg, means +/- SD). It was significantly (p less than 0.01) reduced (-29.0 +/- 17.1 mmHg) following coronary ligation and significantly (p less than 0.05) raised (+/- 41.6 +/- 38.7 mmHg) following lidocaine administration. The incidence of ventricular ectopy on increasing the BP was significantly higher at low heart rates in ten experiments, lower in two and not significantly different in 14. The incidence of premature ventricular complexes, the degree of atrioventricular block and the PR interval in first-degree atrioventricular block, whenever these rhythm disorders appeared, were a function of the BP level. It is concluded that an acute increase in BP may cause rhythm disturbances, usually in the form of ventricular ectopy and/or atrioventricular block.(ABSTRACT TRUNCATED AT 250 WORDS)