Hyperventilation facilitates induction of supraventricular tachycardia: a novel method and the possible mechanism

Atrioventricular Conduction: Physiology and Autonomic Influences

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Atrioventricular Conduction: Physiology and Autonomic Influences

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Cardiac Stromal Cell Patch Integrated with Engineered Microvessels Improves Recovery from Myocardial Infarction in Rats and Pigs

The vascularized cardiac patch strategy is promising for ischemic heart repair after myocardial infarction (MI), but current fabrication processes are quite complicated. Vascularized cardiac patches that can promote concurrent restoration of both the myocardium and vasculature at the injured site in a large animal model remain elusive. The safety and therapeutic benefits of a cardiac stromal cell patch integrated with engineered biomimetic microvessels (BMVs) were determined for treating MI. By leveraging a microfluidic method employing hydrodynamic focusing, we constructed the endothelialized microvessels and then encapsulated them together with therapeutic cardiosphere-derived stromal cells (CSCs) in a fibrin gel to generate a prevascularized cardiac stromal cell patch (BMV-CSC patch). We showed that BMV-CSC patch transplantation significantly promoted cardiac function, reduced scar size, increased viable myocardial tissue, promoted neovascularization, and suppressed inflammation in rat and porcine MI models, demonstrating enhanced therapeutic efficacy compared to conventional cardiac stromal cell patches. BMV-CSC patches did not increase renal and hepatic toxicity or exhibit immunogenicity. We noted a significant increase in endogenous progenitor cell recruitment to the peri-infarct region of the porcine hearts treated with BMV-CSC patch as compared to those that received control treatments. These findings establish the BMV-CSC patch as a novel engineered-tissue therapeutic for ischemic tissue repair.

Neuro-autonomic changes induced by remote ischemic preconditioning (RIPC) in healthy young adults: Implications for stress

The mechanisms underlying the protective effects of remote ischemic preconditioning (RIPC) are not presently clear. Recent studies in experimental models suggest the involvement of the autonomic nervous system (ANS) in cardioprotection. The aim of this study was to investigate the changes in ANS in healthy young volunteers divided into RIPC (n = 22) or SHAM (n = 18) groups. RIPC was induced by 1 cycle of 4 min inflation/5 min deflation followed by 2 cycles of 5 min inflation/5 min deflation of a cuff placed on the upper left limb. The study included analysis of heart rate (HR), blood pressure (BP), heart rate variability (HRV), measurements of microcirculation and porphyrin fluorescence in the limb before and after the RIPC. RIPC caused reactive hyperemia in the limb and reduced blood porphyrin level. A mental load (serial sevens test) and mild motor stress (hyperventilation) were performed on all subjects before and after RIPC or corresponding rest in the SHAM group. Reduction of HR occurred during the experiments in both RIPC and SHAM groups reflecting RIPC-independent adaptation of the subjects to the experimental procedure. However, in contrast to the SHAM group, RIPC altered several of the spectral indices of HRV during the serial sevens test and hyperventilation. This was expressed predominantly as an increase in power of the very low-frequency band of the spectrum, increased values of detrended fluctuation analysis and weakening of correlation between the HRV parameters and HR. In conclusion, RIPC induces changes in the activity of ANS that are linked to stress resistance.

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Brief ischemia/reperfusion episodes of distant organs (RIPC) protect other organs.

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Mechanism of RIPC is not known but it involves neuronal activity.

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RIPC applied to volunteers was interspersed with mild mental and physical stress.

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RIPC was confirmed by hyperemia in the limb and metabolic response to hypoxia.

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Heart rate variability shows that RIPC modulates ANS to increase stress resistance.

Occurrence of intermittent Wolff-Parkinson-White syndrome during intravenous sedation

Patients with intermittent Wolff-Parkinson-White (WPW) syndrome, defined as intermittent loss of the delta waves, can show occasional conduction through the accessory pathway. WPW syndrome often causes paroxysmal supraventricular tachycardia or atrial fibrillation. However, it may be difficult to identify the abnormalities preoperatively because of their only intermittent occurrence. We report a case in which exogenously administered epinephrine and an autonomic imbalance may have precipitated the abrupt occurrence and disappearance of the delta waves.

Decremental Ramp Atrial Extrastimuli Pacing Protocol for the Induction of Atrioventricular Nodal Re-entrant Tachycardia and Other Supraventricular Tachycardias

AIM

The primary aim of this study was to evaluate the utility of decremental ramp atrial extrastimuli pacing protocol (PRTCL) for induction of atrioventricular nodal re-entrant tachycardia (AVNRT), and other supraventricular tachycardias (SVTs), compared to standard (STD) methods.

METHODS

The study cohort of 121 patients (age 57.51 +/- 14.02 years) who presented with documented SVTs and/or symptoms of palpitations and dizziness, and underwent invasive electrophysiological evaluation was divided into Group I (AVNRT, n = 42) and Group II (Control, n = 79). The PRTCL involved a train of six atrial extrastimuli, delivered in a decremental ramp fashion. The STD methods included continuous burst and rapid incremental pacing up to atrioventricular (AV) block cycle length, and single and occasionally double atrial extrastimuli. Prolongation in the Atrio-Hisian (Delta-AH) intervals achieved by both methods were compared, as were induction frequencies.

RESULTS

In Group I, three categories of responses--(1) induction of AVNRT, (2) induction of echo beats only, and (3) none--were observed in 29 (69%), 11 (26%), and 2 (5%) patients with the PRTCL, when compared with 14 (33%), 16 (38%), and 12 (29%) patients with STD methods in the baseline state without the use of pharmacological agents. The Delta-AH intervals for each of these three categories were larger using PRTCL versus STD methods; 293.3 +/- 95.2 ms versus 192.9 +/- 61.4 ms (P < 0.005), 308.6 +/- 68.5 ms versus 189. 9 +/- 64.9 ms (P < 0.0005), and 203.0 +/- 86.3 ms versus 145.8 +/- 58.9 ms (P = NS), respectively. In Group II, in one patient with dual AV nodal physiology but no clinical tachycardia, the PRTCL induced nonsustained (12 beats) AVNRT. Additionally, in this group, both PRTCL and STD methods induced atrial tachycardia in two patients and orthodromic AV re-entrant tachycardia in one patient.

CONCLUSION

Decremental ramp atrial extrastimuli pacing PRTCL demonstrates a superior response for induction of typical AVNRT as compared to STD techniques. Because of easy and reliable induction of AVNRT and echo beats by the PRTCL, we recommend it as a method to increase the likelihood of induction of AVNRT. For induction of other SVTs, the PRTCL and the STD methods are comparable.