Periods Of Sinus Rhythm Research Articles

PO-01-106 ATRIAL ISOCHRONAL LATE ACTIVATION MAPPING KEEPS THE DIAPHRAGM ALIVE

Isochronal late activation mapping (ILAM) is a well-established mapping method for ventricular arrhythmias. However, the role of ILAM mapping during atrial arrhythmias is less clear. This case provides an example of ILAM use during right atrial flutter ablation using the high-density Optrell (Biosense Webster, CARTO) catheter in a patient with congenital heart disease. N/A N/A A 27-year-old female with D-transposition of the great arteries status post Nikaidoh (arterial switch operation with ventricular septal defect repair, pulmonary valve replacement, and typical atrial flutter status post ablation presented with SVT and was referred for catheter ablation. During EPS, conventional activation mapping of fleeting atrial flutter was attempted utilizing the Optrell catheter, which localized the region of interest to a large section of the inferior posterolateral RA, which also had diffuse phrenic nerve capture (figure 1, panel A). However, during periods of sinus rhythm, ILAM and voltage mapping was conducted that demonstrated a distinct, confined, region of isochronal crowding along the mid-posterolateral right atrium, distant from the phrenic nerve (figure 1, panel B). The ILAM site was addressed with catheter ablation rendering the atrial flutter non-inducible with preservation of phrenic nerve function. The patient has remained free of atrial arrhythmias in the 6 months period since the ablation. The application of ILAM is well-established for ventricular tachycardia, however, its role in atrial arrhythmias is less clear. ILAM may be especially useful in adults with congenital heart disease given the complexity of atrial arrhythmia and the benefit of ablation in this unique population. Novel high-density mapping catheters, such as Optrell, allow for rapid and granular voltage data and translate well to ILAM regions within the atrium. Application of ILAM within atrial substrate, particularly for congenital heart disease which predisposes to higher recurrence rates, may improve both recurrence rates and safety, like in this case where the use of this method allowed avoiding ablation on the phrenic nerve.

"Pill-in-Pocket" Anticoagulation for Atrial Fibrillation: Fiction, Fact, or Foolish?

"Pill-in-Pocket" Anticoagulation for Atrial Fibrillation: Fiction, Fact, or Foolish?

Abstract 16058: Abnormal P Wave Morphology is Associated With Decreased Left Atrial Appendage Ejection Velocity

Introduction: P-wave abnormalities measured during periods of sinus rhythm have been associated stroke in people with atrial fibrillation (AF). The majority of AF-related strokes occur from left atrial appendage (LAA) thromboembolism. Electrical and mechanical dysfunction of the left atrium (LA) and left atrial appendage (LAA) can lower the threshold for thromboembolism and stroke. Hypothesis: We aimed to determine whether P-wave abnormalities are associated with decreased LAA ejection velocity (LAAV) on transesophageal echocardiography (TEE). Methods: We conducted a retrospective cross-sectional study. We reviewed patients at a tertiary care medical center who had underwent TEE in sinus rhythm and had an interpretable sinus rhythm ECG within 12 months of TEE. Participants were excluded for history of complex congenital heart disease, age<18, cardiac transplantation, and atrial pacing. Logistic regression analysis was used to estimate the odds ratios of LAAV<40 cm/s for P-wave abnormalities—advanced interatrial block (aIAB), abnormal P-wave terminal force in V1 (aPTFV1), prolonged P-wave duration (PPWD), and abnormal P-wave axis (aPWA). Results: In our final cohort of 169 patients, the odds ratios of aIAB and aPTFV1 for LAAV<40 cm/s after adjustment for CHA 2 DS 2 VASc variables, heart rate during TEE, history of atrial arrhythmias, and left atrial volume index were 2.81 (1.07-7.53) and 2.48 (1.13-5.60), respectively. Conclusions: P-wave abnormalities are independently associated with low LAAV, which may explain their association with AF-related stroke. Further research is needed to determine if incorporation of P-wave analysis will aid AF-related stroke prediction algorithms.

Tailored Anticoagulation for Thromboembolic Risk Reduction in Paroxysmal Atrial Fibrillation.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, affecting up to six million people in the United States and more than 35 million individuals worldwide. Thromboembolism, including stroke, represents the most common AF-related morbidity and mortality and data indicate that anticoagulation can mitigate this risk by 65%. Our understanding of thromboembolism in AF, however, remains incomplete, and the mechanisms by which AF increases thromboembolic risk are areas of ongoing investigation and debate. Current guidelines do not differentiate between the frequency and duration of AF episodes (AF burden) when selecting which patients with AF should be treated with anticoagulation for thromboembolic risk reduction. Recent data, primarily using cardiac implantable electronic devices (CIEDs) such as pacemakers, implantable cardioverter-defibrillators, and implantable loop recorders, however, have challenged this longstanding notion that AF burden does not influence thromboembolic risk. Continuous and automated cardiac rhythm monitoring via CIEDs with accurate and rapid acquisition and transmission of rhythm data also affords the opportunity to study the relationship between AF burden and thromboembolism and novel ways to reduce thromboembolic risk while minimizing the risk associated with chronic anticoagulation use. This manuscript will review the associations between subclinical, CIED-detected atrial arrhythmias and thromboembolic events. It will also discuss the emergence of “tailored anticoagulation,” an anticoagulation strategy wherein CIEDs and remote AF monitoring are employed to allow dynamic administration of oral anticoagulation only around episodes of AF, and the holding of anticoagulation during prolonged periods of sinus rhythm when the thromboembolic risk associated with AF is presumably very low.

Effectiveness of Extracorporeal Life Support for Patients With Cardiogenic Shock Due To Intractable Arrhythmic Storm.

Extracorporeal life support is used for patients with severe heart failure as a bridge to heart transplantation or recovery. We aimed at analyzing the efficacy and safety of extracorporeal life support to treat refractory arrhythmic storm responsible for cardiogenic shock in patients resistant to antiarrhythmic drugs. Retrospective study. University Hospital of Rennes, France. Patients with refractory arrhythmic storm admitted between January 2005 and March 2015. Patients with intractable refractory arrhythmic storm and cardiogenic shock despite optimal medical therapy were implanted with an extracorporeal life support. Patients' characteristics and outcomes after extracorporeal life support implantation were analyzed. Twenty-six patients (23 men, 52.4 ± 9.2 yr old) were included, most of them having ischemic cardiomyopathy (65.4%). Stable sinus rhythm restoration was immediate in 61.5% of patients and occurred after a median time of 3 hours after extracorporeal life support implantation for the remaining ones. Thirteen patients (50%) eventually died, none of them due to extracorporeal life support-related complications, but mostly due to the occurrence of multiple organ failure, and occurred after a median time of 4 days. The remaining 13 patients (50%) had extracorporeal life support withdrawn after 6.7 ± 3.6 days and were discharged after 34.7 ± 14.7 days after admission. Patients with repetitive ventricular tachycardia/ventricular fibrillation episodes alternating with periods of sinus rhythm at the time of implantation had a better survival than those in refractory ventricular fibrillation (p = 0.017). This is the largest database of patients temporary implanted with extracorporeal life support for refractory arrhythmic storm responsible for cardiogenic shock resistant to antiarrhythmic drugs. It provides efficient hemodynamic support and survival rate after the implantation is 50%.

Intermittent bundle branch block: a clinical model for the study of electrophysiological phenomena

Disorders of intraventricular conduction (bundle branch block and hemiblock) are usually stable and remain unchanged irrespective of heart rate. Not infrequently, however, their appearance is related to the duration of the cardiac cycle, so that they appear and disappear with changes in heart rate. This may not even represent a pathological phenomenon, since sudden and consistent changes in cardiac cycle can result, even physiologically, in aberrant conduction. However, when a bundle branch block appears intermittently for simple and progressive increments, or even deceleration, of the sinus rate, this is related to a true bundle branch pathology, i.e. tachycardia-dependent (or phase 3) block or bradycardia-dependent (or phase 4) block, respectively. Phase 3 block is believed to express a pathological increase in the duration of the recovery period of the bundle branch. Phase 4 block was best explained on the basis of enhanced phase 4 depolarization of the bundle branch system, with inability of excitation if the cardiac cycle is particularly prolonged. The two types of block, phase 3 and phase 4, often coexist. An intraventricular conduction disturbance that appears during increasing heart rate for a phase 3 block is maintained, if frequency slows down, even for cycles greater than those that brought about its appearance. This is due to retrograde activation of the bundle branch blocked in the antegrade direction, with delay of its action potential inscription. Sometimes, in the presence of phase 3 bundle branch block, very early atrial ectopic beats are paradoxically conducted in the normal way (supernormal conduction). Perhaps, this phenomenon is related to a possible "climb over" of the injured zone of the bundle branch by the blocked impulses that arise beyond the injured area as subliminal impulses, exciting the healthy tissues if catches them during their phase of supernormal excitability. In the presence of intermittent bundle branch block, it is not uncommon to observe long periods of sinus rhythm with regular PP interval, conducted with alternating (2:1) bundle branch block. Intermittent left bundle branch block is a clinical model of cardiac memory: in these cases, negative T waves in the antero-septal leads during normal conduction are often evident. This negativity is an expression of cardiac memory, and not of ischemia as initially interpreted. Intermittent bundle branch block is an excellent model to study in vivo the effects of antiarrhythmic drugs on the pathological bundle branches. Narrowing of the QRS complex in the presence of bundle branch block is not always an expression of intermittent aberrancy: beware of late ectopic beats originating from the ipsilateral ventricle to the blocked branch, that merging with the antegrade beat conducted with bundle branch block, restrict the QRS, simulating intermittent aberrancy.

Persistent atrial fibrillation presenting in sinus rhythm: Pulmonary vein isolation versus pulmonary vein isolation plus electrogram-guided ablation

The classification of atrial fibrillation as paroxysmal or persistent (PsAF) is clinically useful, but does not accurately reflect the underlying pathophysiology and is therefore a suboptimal guide to selection of ablation strategy. To determine if additional substrate ablation is beneficial for a subset of patients with PsAF, in whom long periods of sinus rhythm (SR) can be maintained. We included patients presenting with PsAF in whom continuous periods of SR>3months were documented. All patients were in SR on the day of the procedure. Electrical pulmonary vein isolation (PVI) was performed in all patients. Additional electrogram (EGM)-guided ablation was left to the discretion of the operator. Patient characteristics and follow-up were analysed with respect to presence or absence of additional EGM-guided ablation. Sixty-five patients (mean age 60.1±8.9years; 81.5% men) met the inclusion criteria. EGM-guided ablation was performed in 32 (49%) patients. Patients with and without EGM-guided ablation had similar baseline characteristics. Absence of EGM-guided ablation was one of the independent predictors for arrhythmia recurrences after the index procedure (hazard ratio 0.24; confidence interval 0.12-0.47). After a median follow-up of 18±10months, the number of procedures required was significantly higher in the 'PVI-only' group (2.24±0.75 vs. 1.84±0.81; P=0.04) to achieve a similar success rate (84% vs. 81%; P=0.833). The addition of EGM-guided ablation requires fewer procedures to achieve similar clinical efficacy in mid-term follow-up compared with a PVI-only strategy in patients with PsAF presenting for ablation in SR.

Permanent junctional reciprocating tachycardia in a dog

A 5-year-old male English Bulldog was presented with a 1-year history of paroxysmal supraventricular tachycardia (SVT) partially responsive to amiodarone. At admission the surface ECG showed sustained runs of a narrow QRS complex tachycardia, with a ventricular cycle length (R–R interval) of 260 ms, alternating with periods of sinus rhythm. Endocardial mapping identified the electrogenic mechanism of the SVT as a circus movement tachycardia with retrograde and decremental conduction along a concealed postero-septal atrioventricular pathway (AP) and anterograde conduction along the atrioventricular node. These characteristics were indicative of a permanent junctional reciprocating tachycardia (PJRT). Radiofrequency catheter ablation of the AP successfully terminated the PJRT, with no recurrence of tachycardia on Holter monitoring at 12 months follow-up.

Congenital Fetal Heart Block

Congenital heart block affects 2% of all mothers with anti-Ro/La antibodies, can cause heart failure in utero, and has a 20% mortality rate in the first 3 years of life. Maternal fluorinated steroids to prevent or reverse congenital heart block can cause pregnancy complications. Intravenous immunoglobulin (IVIG) has been given with maternal steroids to prevent the recurrence of congenital heart block, although its efficacy is unproven. We report the use of IVIG to prevent progression of 2:1 congenital heart block with intermittent complete heart block. After two maternal infusions of IVIG (0.4 g/kg) at 31 weeks of gestation, the fetal heart rate reverted to long periods of sinus rhythm, which was sustained until postnatal life. Our case supports investigating IVIG in the prevention or treatment of this life-threatening condition.

Triggering of Nocturnal Arrhythmias by Sleep-Disordered Breathing Events

This study sought to evaluate respiratory disturbances as potential triggers for arrhythmia in patients with sleep-disordered breathing (SDB). SDB is associated with an increased risk of atrial fibrillation and nonsustained ventricular tachycardia (NSVT) as well as a predilection for sudden cardiac death during nocturnal sleeping hours. However, prior research has not established whether respiratory disturbances operate as triggers for nocturnal arrhythmias. Overnight polysomnograms from the Sleep Heart Health Study (n = 2,816) were screened for paroxysmal atrial fibrillation and NSVT. We used the case-crossover design to determine whether apneas and/or hypopneas are temporally associated with episodes of paroxysmal atrial fibrillation or NSVT. For each arrhythmia, 3 periods of sinus rhythm were identified as control intervals. Polysomnograms were examined for the presence of respiratory disturbances, oxygen desaturations, and cortical arousals within a 90-s hazard period preceding each arrhythmia or control period. Fifty-seven participants with a wide range of SDB contributed 62 arrhythmias (76% NSVT). The odds of an arrhythmia after a respiratory disturbance were nearly 18 times (odds ratio: 17.5; 95% confidence interval: 5.3 to 58.4) the odds of an arrhythmia occurring after normal breathing. The absolute rate of arrhythmia associated with respiratory disturbances was low (1 excess arrhythmia per 40,000 respiratory disturbances). Neither hypoxia nor electroencephalogram-defined arousals alone increased arrhythmia risk. Although the absolute arrhythmia rate is low, the relative risk of paroxysmal atrial fibrillation and NSVT during sleep is markedly increased shortly after a respiratory disturbance. These results support a direct temporal link between SDB events and the development of these arrhythmias.

Clinical predictors and prognostic significance of electrical storm in patients with implantable cardioverter defibrillators

Insufficient data exists regarding predictors of electrical storms (ES) and clinical outcome in patients treated with an implantable cardioverter defibrillator (ICD). The purpose of this study was to delineate a subgroup of patients likely to experience ES and to determine the impact of ES on mortality in ICD recipients. Baseline characteristics of 307 ICD-treated patients were retrospectively analysed. ES was defined as two or more ventricular tachyarrhythmias within 24 h leading to an immediate electrical therapy (antitachycardia pacing and/or shock), separated by a period of sinus rhythm. Clinical characteristics and survival of 123 patients experiencing a total of 294 episodes of ES (median 2 ES/patient, range 1-9), were compared with those of 184 ES-free patients during a median follow-up of 826 days (inter-quartile 1141 days). Median actuarial duration for the first ES occurrence after ICD implant was 1417 days [95% confidence interval (CI) 1061-2363] with a median follow-up of 816 days (7-4642 days) in ES-free patients. Univariate analysis identified older age, depressed left ventricular ejection fraction (LVEF), ventricular tachycardia (VT) as index arrhythmia, chronic renal failure and absence of lipid-lowering drugs as variables significantly associated with an increased risk of ES. Multivariable Cox analysis confirmed an independent predictive value for chronic renal failure [hazard ratio (HR) 1.54, 95% CI 0.95-2.51, P=0.052], VT (HR 2.20, 95% CI 1.44-3.37, P=0.0003), and LVEF (HR 0.98, 95% CI 0.97-0.99, P=0.027). In contrast, diabetics (HR 0.49, 95% CI 0.27-0.90, P=0.022) were less affected by ES. There was no difference in survival between both groups. ES is frequent but does not increase mortality in ICD's recipients. Patients with severe systolic dysfunction, chronic renal failure and VT as initial arrhythmia are likely to experience ES. Diabetics are less affected by ES.

Role of dispersion of atrial refractoriness in the recurrence of clinical atrial fibrillation; a manifestation of atrial electrical remodelling in humans?

The mechanism of atrial fibrillation recurrence following cardioversion is unknown, although experimental studies have indicated that changes in dispersion of atrial refractoriness may play a role. The aims of this study were to assess (1) if dispersion of atrial refractoriness is relevant to atrial fibrillation recurrence and (2) if dispersion of refractoriness is part of the atrial electrical remodelling process in humans. Thirty-seven consecutive patients underwent internal cardioversion (CV1) of persistent atrial fibrillation. Patients were monitored by daily transtelephonic recordings following discharge and if there was spontaneous atrial fibrillation recurrence they were rapidly admitted for repeat cardioversion (CV2). We used the 5th percentile of 100 consecutive atrial fibrillation cycle lengths (AFCL(P5)) and the atrial effective refractory period (AERP) as measures of atrial refractoriness at four different atrial sites. Dispersion of AFCL(P5)at CV1 was significantly higher in those who had subsequent recurrence of atrial fibrillation than in those who remained in sinus rhythm for at least 1 month after cardioversion (35+/-17 ms vs 9+/-13 ms;P<0.02). Dispersion of AFCL(P5)measured at CV2 was significantly lower than that measured in the same patients at CV1 (19+/-8 ms vs 35+/-11 ms;P=0.02). i.e. dispersion of AFCL(P5)had reduced following a period of sinus rhythm. In contrast, there was no difference in dispersion of AERP between the recurrers and non-recurrers. Dispersion of AERP between CV1 and CV2 did not change following a period of sinus rhythm. Dispersion of AFCL is relevant to atrial fibrillation recurrence and may represent a manifestation of atrial electrical remodelling in humans. Treatment directed at AFCL dispersion may be useful in the suppression of atrial fibrillation recurrence following cardioversion.

Effects of MgSO 4 and Glucose, Insulin and Potassium (GIK) on Atrial Conduction during the First 12 Hours after DCconversion of Chronic Atrial Fibrillation

Objective - To investigate changes in atrial conduction induced by MgSO 4 and glucose, insulin and potassium (GIK) during the first 12-h period of sinus rhythm after successful DC-conversion of chronic atrial fibrillation (CAF). Methods - Signal-averaged P-wave duration, QRS-duration and PQ-time were recorded in 20 patients who were randomly assigned to control or intervention. Ten patients received no infusates (control group) and 10 patients received MgSO 4 and GIK infusions (intervention group). P-wave duration was determined from the X-, Y- and Zleads, which were further combined to obtain a spatial magnitude. P-wave morphology was studied by analysing global activation patterns and discrete components from the calculated spatial magnitude signal. Results - No changes in the measured parameters were seen in the control group. The P-wave duration, QRSduration and PQ-time increased from 139(13) [mean(SD)] to 149(15) ( p < 0.01), 90(7) to 94(9) ( p < 0.05) and 188(10) to 207(13) ms ( p < 0.01), respectively, after bolus infusion of MgSO 4 . The time from the start of the P-wave to its 1st and 2nd max. locations increased by 6 ms ( p < 0.01) in both cases after bolus infusion of MgSO 4 and had reversed after 10 h of MgSO 4 and GIK infusion. P-wave duration and PQ-time decreased after 10 h of MgSO 4 and GIK infusion, from 149(34) (bolus) to 138(12) and from 207(13) to 195(27) ms ( p < 0.05), respectively, in spite of an even higher serum Mg concentration at the end of this period. Conclusion - Bolus infusion of MgSO 4 2 h after DC-conversion of CAF produced an intra-atrial conduction delay that could be reversed by adding a GIK infusion, in spite of a concomitant increase in serum Mg concentration. No recovery of the intra-atrial conduction delay, seen after DC-conversion of CAF, was observed in either of the two groups during the 12-h study period.

Are electrophysiological changes induced by longer lasting atrial fibrillation reversible? :observations using the atrial defibrillator.

Studies in animal hearts have shown shortening of the atrial effective refractory period (AERP) and loss of the relation between the AERP and heart rate after prolonged periods of atrial fibrillation (AF). The purposes of this study were (1) to evaluate atrial electrophysiology after a long period of sinus rhythm in patients who had longer lasting recurrent AF that was successfully treated with the Metrix Atrioverter and (2) to analyze the effect of prompt cardioversion on subsequent AF episodes and the duration of sinus rhythm. Four patients with recurrent AF (duration, 3 to 21 years; mean+/-SD, 13+/-7.6 years) were studied after the implantation of an Atrioverter. The Atrioverter stores and analyzes 3 minutes of cardiac rhythm every hour. Before implantation, AERP was measured. During a mean follow-up of 14 months, 52 spontaneous (39 treated and 18 nontreated) AF episodes occurred while the patients were on antiarrhythmic drugs. All patients were electrophysiologically studied after they had been in sinus rhythm for at least 1000 hours (range, 1052 to 2675 hours). Before Atrioverter implantation, AF was induced by 1 atrial premature beat in 3 patients and not induced in the remaining patient. After a long period in sinus rhythm (>1000 hours), AF could be induced in the same 3 patients in the same way as before implantation. In the patient in whom no AF was induced, right AERP values measured using the single extrastimulus technique at 3 pacing cycle lengths (600, 500, and 430 ms) were similar to those before implantation. AF was still inducible by a single atrial premature beat after long episodes of sinus rhythm in 3 of 4 patients with previously longer lasting AF. In the patient in whom no AF was induced, AERP behaved like it did before implantation. In these patients with longer lasting recurrent AF, no return to "normal" atrial electrophysiology could be demonstrated.

Use of an advanced mode switching algorithm in Inos 2 CLS and Logus dual chamber pacemakers

Background: According to literature, 30–60 % of pacemaker patients suffer from paroxysmal atrial fibrillation (PAF). As rapid tracking of PAF may cause severe symptoms in patients with dual chamber pacemakers, refined algorithms providing AV synchronous pacing during periods of sinus rhythm and preventing high ventricular rates during PAF are highly desirable. Aim and method: This comprehensive paper introduces a new mode switching (MS) algorithm which uses either a fixed (Inos2CLS) or programmable (Logos) number of short intervals out of 8 consecutive atrial intervals to detect PAF. If the MS criterion is fulfilled, a switch from AV synchronous pacing to nontracking mode is automatically performed. The algorithm is described together with a discussion on optimization of the programming of parameters which may indirectly influence the MS sensitivity and specificity. Results: This MS concept maintains the high sensitivity and fast reactivity towards PAF of the “mode conversion” in Actros and Kairos pacemaker systems, preventing a long time delay between onset of PAF, detection of the arrhythmia, and switch to nontracking mode. In addition, adequeate sensing and short blanking periods in the new MS concept enable reliable MS. The occurrence of atrial oversensing should be tested, as it may lead to inappropriate MS. Programmability of the MS algorithm may be advantageous for individual programming with respect to the patients' arrhythmia rate and atrial sensing performance, but the use of very restrictive or very liberal criteria should be avoided as both may lead to mode oscillations. Finally, examples of stored diagnostic data are presented to assess MS reliability, identify possible problems, and optimize MS function during follow-up.

Magnesium sulfate prophylaxis after cardiac operations

One hundred patients undergoing elective cardiac operations were randomized into placebo (n = 54) and magnesium (n = 46) groups. The magnesium group received six doses of 2.4 g (19.2 mEq) magnesium sulfate intravenously in the first 24 hours after the cardiac operation. The magnesium group had higher serum magnesium concentrations postoperatively (1.09 +/- 0.20 versus 0.75 +/- 0.13 mmol/L; p < 0.0001), postoperative day 1 (1.49 +/- 0.34 versus 0.70 +/- 0.12 mmol/L; p < 0.0001) and postoperative day 2 (0.96 +/- 0.19 versus 0.76 +/- 0.07 mmol/L; p < 0.0001). Patients in the magnesium group had a lower incidence of ventricular tachyarrythmias (VTs) (17.3% versus 51.9%; p = 0.0006), less need for treatment (6.5% versus 20.3%; p < 0.0001), fewer VT episodes/patient (0.3 +/- 0.8 versus 1.39 +/- 1.9; p < 0.0001), and a reduction in the severity of VTs as measured by the modified Lown grade (p = 0.0002). No differences were demonstrated with respect to supraventricular tachyarrythmias. The magnesium group had reduced absolute creatine kinase-MB levels (5.3 +/- 4.2 versus 28.4 +/- 28 IU/L; p = 0.001) as well as creatine kinase-MB fraction (0.01 +/- 0.02 versus 0.05 +/- 0.04; p = 0.001) on postoperative day 1. Serum magnesium concentrations were lower during VTs than during periods of sinus rhythm (0.75 +/- 0.75 versus 1.02 +/- 0.35 mmol/L; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The Plasma Catecholamine Responses to Ventricular Pacing: Implications for Rate Responsive Pacing

Many patients with VVI and VVIR pacemakers will alternate between periods of sinus rhythm and ventricular pacing. These rhythm shifts may be poorly tolerated by some patients. Changes in plasma catecholamine levels during these rhythm shifts may contribute to these patients' symptoms. We measured blood pressure, ejection fraction and plasma norepinephrine, epinephrine, and dopamine serially in nine patients with normal left ventricular ejection fractions and VVI pacemakers during sinus rhythm and at paced rates of 10 beats per minute (bpm) above sinus rates (10 + NSR), 100 bpm, and 130 bpm. The mean norepinephrine level at baseline was 143 +/- 16 pg/mL and increased to 166 +/- 36 pg/mL at 10 + NSR, 204 +/- 47 pg/mL at 100 bpm, and 182 +/- 34 pg/mL at 130 bpm. These increases corresponded to mean percent changes from baseline of 17% (P = 0.02), 33% (P = 0.002), and 24% (P = 0.07), respectively. The magnitude of the norepinephrine response was not correlated with the pacing rate. The mean plasma epinephrine level at baseline was 57 +/- 6 pg/mL and peaked at 51 +/- 12 pg/mL at 10 + NSR, 89 +/- 31 pg/mL at 100 bpm and 101 +/- 28 pg/mL at 130 bpm. These increases corresponded to mean percent changes from baseline of -10% (P = NS), 30% (P = 0.07), and 89% (P = 0.02), respectively. No trends in the dopamine response to pacing were noted. During ventricular pacing there were no significant changes in mean blood pressure and only slight changes in ejection fraction. The individual percent changes in plasma norepinephrine and epinephrine at 100 bpm were inversely correlated to the changes in systolic blood pressure (R = -0.68, P = 0.06, and R = -0.81, P = 0.03, respectively). These results suggest that plasma norepinephrine and epinephrine increase acutely in response to ventricular pacing at rates commonly seen during rate responsive ventricular pacing.

Prenatal measurement of cardiothoracic ratio in evaluation of heart disease.

The cardiothoracic ratio was measured in 410 normal fetuses and in a group of 73 fetuses with functional or structural heart disease. In normal fetuses it was fairly constant throughout pregnancy, but of those with congenital heart disease it was raised in cases of Ebstein's anomaly, tricuspid dysplasia, atrioventricular septal defect, and complete heart block. In some forms of congenital heart disease, however, it was within the normal range. There was a significant positive correlation between the cardiothoracic ratio and fetal hydrops in the group of 15 fetuses with supraventricular tachycardias. In these fetuses the cardiac size decreased significantly once the fetus reverted to sinus rhythm after the mother had been treated. Measurement of the cardiothoracic ratio is essential in the evaluation of fetal hydrops, as an increased value may point to the diagnosis of an intermittent fetal tachycardia if the fetus is assessed during a period of sinus rhythm. The measurement of this index forms a part of the complete prenatal evaluation of structural heart disease. The degree of cardiomegaly may provide useful information about secondary lung compression or cardiac failure and therefore assist in giving an accurate prognosis for postnatal survival.

Circadian Variations of Heart Rate and STIMT Interval: Adaptation for Nighttime Pacing

In order to determine the optimal pacing rate for pacemaker patients at night, 150 normal subjects with regular sinus rhythm and free of manifest heart disease, were studied using 24-hour Holter monitoring. Minimum and average heart rates were analyzed on an hourly basis. The study group was divided into six age groups, 25 subjects each, ranging from 20-29 years to 60-69 years. The minimum heart rate during the night was found to be lower than 65 ppm for all groups. The youngest subjects showed the largest variation in the minimum heart rate. The results suggest that an automatic lowering of the pacing rate during the night would allow for longer periods of sinus rhythm, thereby improving hemodynamic performance and reducing pacemaker power consumption. Suitable sensors for automatic lowering of the pacing rate include inbuilt 24-hour clock systems and the QT interval that lengthens during sleep.

Sinus bradycardia and atrial fibrillation associated with the Wolff-Parkinson-White syndrome

Thirty-three patients with atrial fibrillation associated with the Wolff-Parkinson-White (WPW) syndrome were studied to determine the relation of sinus bradycardia and atrial fibrillation. In seven patients the sinus rate was less than 40 beats/min and sinus nodal disease was considered a cause of the periods of bradycardia. Ventricular fibrillation or functional cardiac arrest was documented in four instances. Twenty-six patients demonstrated a type A and seven a type B WPW pattern during periods of sinus rhythm. Male patients predominated. The average age was 38.5 years among patients with a type A pattern compared with 25.3 years among those with a type B pattern. The shortest R-R cycle length in this group was 130 msec during a period of atrial fibrillation. Five thousand serial microscopic sections were studied in one patient who demonstrated ventricular fibrillation. Three anomalous pathways were located in this patient with the widest tract, 380 μ, containing about 400 muscle cells. Most of the sinoatrial node was replaced by collagen elastic fibers, and there was widespread destruction of the atria with a marked increase in fibrous connective tissue. Ventricular fibrillation or functional cardiac arrest is not a rare arrhythmia in patients with atrial fibrillation associated with the WPW syndrome and may be responsible for sudden death in patients with these arrhythmias. Hence, precise electrophysiologic studies and pharmacologic or surgical management, or both, are suggested to prevent sudden death in patients with short refractory periods associated with atrial fibrillation and the WPW syndrome.