His bundle recordings in paroxysmal atrioventricular block produced by carotid sinus massage

Inhaled ambient-level traffic-derived particulates decrease cardiac vagal influence and baroreflexes and increase arrhythmia in a rat model of metabolic syndrome

Background

Epidemiological studies have linked exposures to ambient fine particulate matter (PM_2.5) and traffic with autonomic nervous system imbalance (ANS) and cardiac pathophysiology, especially in individuals with preexisting disease. It is unclear whether metabolic syndrome (MetS) increases susceptibility to the effects of PM_2.5. We hypothesized that exposure to traffic-derived primary and secondary organic aerosols (P + SOA) at ambient levels would cause autonomic and cardiovascular dysfunction in rats exhibiting features of MetS. Male Sprague Dawley (SD) rats were fed a high-fructose diet (HFrD) to induce MetS, and exposed to P + SOA (20.4 ± 0.9 μg/m³) for 12 days with time-matched comparison to filtered-air (FA) exposed MetS rats; normal diet (ND) SD rats were separately exposed to FA or P + SOA (56.3 ± 1.2 μg/m³).

Results

In MetS rats, P + SOA exposure decreased HRV, QTc, PR, and expiratory time overall (mean effect across the entirety of exposure), increased breathing rate overall, decreased baroreflex sensitivity (BRS) on three exposure days, and increased spontaneous atrioventricular (AV) block Mobitz Type II arrhythmia on exposure day 4 relative to FA-exposed animals receiving the same diet. Among ND rats, P + SOA decreased HRV only on day 1 and did not significantly alter BRS despite overall hypertensive responses relative to FA. Correlations between HRV, ECG, BRS, and breathing parameters suggested a role for autonomic imbalance in the pathophysiologic effects of P + SOA among MetS rats. Autonomic cardiovascular responses to P + SOA at ambient PM_2.5 levels were pronounced among MetS rats and indicated blunted vagal influence over cardiovascular physiology.

Conclusions

Results support epidemiologic findings that MetS increases susceptibility to the adverse cardiac effects of ambient-level PM_2.5, potentially through ANS imbalance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-017-0196-2) contains supplementary material, which is available to authorized users.

Diesel exhaust inhalation increases cardiac output, bradyarrhythmias, and parasympathetic tone in aged heart failure-prone rats

Acute air pollutant inhalation is linked to adverse cardiac events and death, and hospitalizations for heart failure. Diesel engine exhaust (DE) is a major air pollutant suspected to exacerbate preexisting cardiac conditions, in part, through autonomic and electrophysiologic disturbance of normal cardiac function. To explore this putative mechanism, we examined cardiophysiologic responses to DE inhalation in a model of aged heart failure-prone rats without signs or symptoms of overt heart failure. We hypothesized that acute DE exposure would alter heart rhythm, cardiac electrophysiology, and ventricular performance and dimensions consistent with autonomic imbalance while increasing biochemical markers of toxicity. Spontaneously hypertensive heart failure rats (16 months) were exposed once to whole DE (4h, target PM(2.5) concentration: 500 µg/m(3)) or filtered air. DE increased multiple heart rate variability (HRV) parameters during exposure. In the 4h after exposure, DE increased cardiac output, left ventricular volume (end diastolic and systolic), stroke volume, HRV, and atrioventricular block arrhythmias while increasing electrocardiographic measures of ventricular repolarization (i.e., ST and T amplitudes, ST area, T-peak to T-end duration). DE did not affect heart rate relative to air. Changes in HRV positively correlated with postexposure changes in bradyarrhythmia frequency, repolarization, and echocardiographic parameters. At 24h postexposure, DE-exposed rats had increased serum C-reactive protein and pulmonary eosinophils. This study demonstrates that cardiac effects of DE inhalation are likely to occur through changes in autonomic balance associated with modulation of cardiac electrophysiology and mechanical function and may offer insights into the adverse health effects of traffic-related air pollutants.

Whole and particle-free diesel exhausts differentially affect cardiac electrophysiology, blood pressure, and autonomic balance in heart failure-prone rats

Epidemiological studies strongly link short-term exposures to vehicular traffic and particulate matter (PM) air pollution with adverse cardiovascular (CV) events, especially in those with preexisting CV disease. Diesel engine exhaust is a key contributor to urban ambient PM and gaseous pollutants. To determine the role of gaseous and particulate components in diesel exhaust (DE) cardiotoxicity, we examined the effects of a 4-h inhalation of whole DE (wDE) (target PM concentration: 500 µg/m(3)) or particle-free filtered DE (fDE) on CV physiology and a range of markers of cardiopulmonary injury in hypertensive heart failure-prone rats. Arterial blood pressure (BP), electrocardiography, and heart rate variability (HRV), an index of autonomic balance, were monitored. Both fDE and wDE decreased BP and prolonged PR interval during exposure, with more effects from fDE, which additionally increased HRV triangular index and decreased T-wave amplitude. fDE increased QTc interval immediately after exposure, increased atrioventricular (AV) block Mobitz II arrhythmias shortly thereafter, and increased serum high-density lipoprotein 1 day later. wDE increased BP and decreased HRV root mean square of successive differences immediately postexposure. fDE and wDE decreased heart rate during the 4th hour of postexposure. Thus, DE gases slowed AV conduction and ventricular repolarization, decreased BP, increased HRV, and subsequently provoked arrhythmias, collectively suggesting parasympathetic activation; conversely, brief BP and HRV changes after exposure to particle-containing DE indicated a transient sympathetic excitation. Our findings suggest that whole- and particle-free DE differentially alter CV and autonomic physiology and may potentially increase risk through divergent pathways.

Paroxysmal atrioventricular block: clinical experience with 20 patients

BACKGROUND

Paroxysmal atrioventricular (AV) block is an ill-defined entity, previously described in sporadic cases in association with vasovagal reaction, coronary angiography and distal conduction disease.

METHODS

We describe 20 patients (10 women) aged 26 to 80 years with symptomatic paroxysmal AV block.

RESULTS

Eight patients had ischemic heart disease-three with dilated cardiomyopathy, and two with co-existing carotid sinus hypersensitivity. Eight were taking chronic AV blockers. In five patients, the paroxysmal AV block occurred during a vagal reaction, in one during migranotic headaches, in one following aortic valve replacement and in one while recovering from acute myocardial infarction. The events lasted between 2.2 and 36 s. In 10 patients, the QRS configuration on the electrocardiogram was wide. Immediate treatment consisted of intravenous atropine and fluid supplements in two patients, discontinuation of the AV blocking agents in four, and the insertion of a temporary pacemaker in eight. Seventeen patients required a permanent pacemaker.

CONCLUSIONS

Paroxysmal AV block is an underestimated clinical entity related to vagal reaction, AV blocking drugs and distal conduction disease. Most of our patients eventually required implantation of a permanent pacemaker.

Carotid sinus massage. Its diagnostic and therapeutic value in arrhythmias

Carotid sinus massage is a simple bedside maneuver that helps to clarify the type and sometimes also the mechanism of different rhythm disturbances. The major indication for carotid sinus massage is the diagnosis of tachyarrhythmias in which the atrial activity is either absent or intermittently present. Carotid sinus massage is also useful in some patients with normal heart rates; increased vagal tone may normalize a bundle branch block or localize the site of type I second-degree atrioventricular block and can be used for evaluation of the sensing function of permanent pacemakers. Carotid sinus massage is also an important diagnostic procedure in patients with suspected hypersensitivity of the carotid sinus. Massage of the carotid sinus is contraindicated in patients with diseased carotid arteries because of the risk of cerebrovascular accident. In rare instances, carotid sinus massage may initiate ventricular tachycardia.

Multiple electrophysiologic manifestations and clinical implications of vagally mediated AV block

Clinical, surface ECG, and intracardiac findings were analyzed in 20 patients with spontaneous conduction disturbances in whom vagally mediated AV block could be induced by carotid sinus pressure during electrophysiologic evaluation. The latter demonstrated that the surface ECG pattern attributed to bradycardia-dependent (phase 4), and paroxysmal block within the His bundle and bundle branches could reflect vagally mediated, bradycardia-associated (rather than bradycardia-dependent), and paroxysmal AV nodal (AH) block. The decision regarding the use of pacemakers was not based on QRS duration or on patterns (or site) of block but on the underlying clinical settings and the correlation of symptoms with maximal ventricular (R-R) pauses. However, more studies are required to extend our findings, especially to other subgroups of patients (or normal individuals) in whom vagally mediated block occurs.

Symptomatic spontaneous paroxysmal AV nodal block due to localized hyperresponsiveness of the AV node to vagotonic reflexes

Two apparently healthy patients had recurrent syncope with documented paroxysmal AV block. In both patients the site of AV block was demonstrated to be in the AV node. Coronary angiography (in both patients) and sustained deep inspiration (one patient) reproducibly initiated episodes of paroxysmal AV nodal block (identical to spontaneous episodes). Atropine abolished further attempts of AV block induction. Vagal hyperresponsiveness was limited to the AV node, since the interventions provoking paroxysmal AV nodal block produced only appropriate sinus slowing. This syndrome reflects hyperresponsiveness of the AV node to vagotonic reflexes, and exists as a clinically significant entity producing recurrent syncope.

Prolongation of atrioventricular conduction time by electrical stimulation of the carotid sinus nerves in man

Electrical stimulation of the carotid sinus nerves was applied during diagnostic catheterization of two patients who had coronary artery disease. The immediate reflex prolongation of the atrioventricular (AV) interval was due to prolongation of the AH interval only and was roughly parallel to the reflex RR interval prolongation evoked without atrial pacing. After cholinergic block, the reduced prolongation of both the RR interval and the AV interval caused by reflex inhibition of sympathetic tone followed a time course similar to the arterial pressure decrease. This is the first demonstration in man of the parallel baroreflex effects on the sinoatrial node and the AV node.

Baroreceptor control of atrioventricular conduction in man

Although human baroreflexes are known to exert a powerful physiological control on heart rate, little information exists on the physiological control they exert on the atrioventricular conduction system. In 11 normotensive subjects with normal atrioventricular conduction, we altered baroreceptor activity by injection of pressor and depressor drugs (phenylephrine and trinitroglycerin) and recorded mean arterial pressure (MAP, catheter measurements), R-R interval, and pre-His and post-His intervals (A-H and H-V, His bundle recording). With the subjects in sinus rhythm, increasing MAP by 21+/- 1 mm Hg caused a marked lengthening (250 +/- 28 msec), and decreasing MAP by 17 +/- 2 mm Hg a marked shortening (142 +/- 16 msec) of the R-R interval. There was little change in the A-H interval and no change at all in the H-V interval. However, when the R-R interval was kept constant in these subjects by atrial pacing, a similar increase and decrease in MAP caused, respectively, a marked lengthening (49 +/- 6 msec) and shortening (19 +/- 3 msec) of the A-H interval, although the H-V interval remained unaffected. Thus physiological ranges of baroreceptor activation have a marked influence on the atrioventricular node but apparently not on the ventricular portion of the atrioventricular conduction system. This influence is unmasked when pacing prevents the baroreceptor influence on the sinoatrial node.

Electrophysiologic observations in a patient with bradycardia-dependent atrioventricular block

In a patient with atrioventricular (A-V) block distal to the His bundle (H), 1:1 A-V conduction with right bundle branch block and H-V interval of 70 msec was established with atrial pacing at rates of 120 to 150/min, suggesting that the A-V block was bradycardia-dependent. Advanced second degree A-V block distal to the H deflection occurred with atrial pacing at 160/min after completion of A-V nodal Wenckebach periodicity proximal to the H deflection because of the long H-H encompassing the blocked P wave. Atrial extrastimulus testing coupled with sinus rhythm (with A-V block) demonstrated that critical H1-H2 intervals of less than 545 msec allowed conduction to the ventricles. The H2-V2 interval shortened progressively from 290 to 70 msec with shortening of these critical H1-H2 intervals. Atrial extrastimulus testing coupled with an atrial driven cycle lenght of 500 mesc (with intact A-V conduction) revealed block of the H2 deflection with an H1-H2 interval longer than 540 msec. In conclusion, at critical diastolic intervals, impulses were blocked, creating a state of decreased responsiveness. If a cycle length of subsequent impulses was shorter than the critical diastolic blocking interval, membrane responsiveness gradually improved and conduction resumed. If a cycle length of subsequent impulses was longer than the critical blocking diastolic interval, A-V block was sustained. Blocked impulses continually penetrated to the site of block and reset the state of membrane responsiveness.

Atrioventricular block after reciprocating atrioventricular junctional tachycardia

Short runs of symptomatic atrioventricular (A-V) block occurred after spontaneous cessation of reciprocating A-V junctional tachycardia in a patient with right bundle branch block, normal H-V interval and sinus nodal dysfunction. These episodes were characterized by long (more than 1 sec) P-P intervals during which the A deflections were not followed by His bundle electrograms. Three possible explanations are: (1) a posttachycardia-induced period of abnormally prolonged A-V nodal refractoriness; (2) pseudo-A-V block produced by concealed A-V junctional tachycardia, or (3) bradycardia-dependent (phase 4) A-V block at the "upper" His bundle, above the site from which the H deflection was recorded.

His bundle recordings in bradycardia-dependent AV block induced by premature beats

Symptomatic bradycardia-independent atrioventricular block occurred in a patient with right bundle-branch block, left anterior hemiblock, and prolonged HV interval. The arrhythmia, triggered by a spontaneous or induced premature beats, appeared when the post-extrasystolic PP and HH intervals increased to a critical value. Reinitiation of atrioventricular conduction required the presence of ventricular escapes. Bradycardia-dependent atrioventricular block was related to either an enhanced or slightly rising slope of diastolic depolarization, or to a decrease in membrane responsiveness. The patient also, most probably, had tachycardia-dependent atrioventricular block. Both types of conduction disturbance occurred in the same part of the intraventricular conducting system, either in the low His bundle or left bundle-branch or its posteroinferior division. It is suggested that the electrophysiological study of cases with prolonged HV intervals should include procedures which can expose bradycardia-dependent atrioventricular block.